MemOires de P Academic Royale des Sciences et des Lettres de Dauemark, Copenkague,

Section des Sciences, 8me serie t. VII, n° 1.

CONTRIBUTIONS

TO

THE BIOLOGY OF THE DANISH

CULICIM;

BY

C. WESENBERG-LUND

WITH 21 PLATES AND 19 FIGURES IN THE TEXT

D. KGL. DAXSKE VIHEXSK. SKI.SK. SKRIFTER, NATURV. OG MATHEMATISK AFD. 8. R^EKKE, VII, 1.

K0BRNHAVN

HOVEDKOMMISSION^R: ANDR. FRED. H0ST & S0N, KGL. HOF-BOGHANDEL

BIANCO LL'NOS BOGTBYKKEBI
1920—21

CONTRIBUTIONS

TO

THE BIOLOGY OF THE DANISH

CULICID.E

BY

C. NVESENBERG-LUND

WITH 21 PLATES AND 19 FIGURES IN THE TEXT

D. KGL. DANSKE VIDENSK. SELSK. SKRIFTER, NATURV. OG MATHEMATISK AFD. 8. R.EKKE, VII, 1.

K0BENHAVN

HOVEDKOMMISSIO1SLER: ANDR. FRED. HOST & S0N, KGL. HOF-BOGHANDEL

BIANCO LUNOS BOGTRYKKERI

1920—21

Preface.

Jl he history of the work which I hereby take the liberty to offer to the
scientific world has been rather peculiar. More than twenty years ago I saw that
our temporary forest ponds which got water in November — December very often, a
few days later, contained living mosquito larvae; I saw that these larvae hibernated
under the ice and that they could be found again when the ice melted in the
spring. To me it was rather an astonishing fact to find in 1900 air-breathing
insect larvae below the ice, locked out by the ice from the atmospherical air. In the
following years I often visited the temporary ponds in spring and ascertained that
they teemed with mosquito larvae. Even the slightest study with a magnifying glass
showed that these larvae differed very much from the hibernating larvae.

In the admirable chapter in "Histoire des insects" REAUMUR has shown that
Culex pipiens hibernates as imago and lays its eggs in batches, eggboats. In his
work "History of Aquatic Insects" MIALL has had nothing to add; as far as I know,
REAUMUR'S exposition of the biology of C. pipiens has for more than a century been
used as a model of the development of all mosquitoes. In accordance with this
fact year after year I searched for the eggboats in the temporary ponds of our
forests; I never saw a single one.

In the following years I slowly came to understand that there was also upon
another point a striking discrepancy between what we have learned and what I
found out on studying Nature herself. Scientists as well as ordinary people have all
been inclined to suppose that a great number of generations are hatched during
the year. Without any more thorough exploration I felt sure that most of the mos-
quitoes really had only one single generation. In the spring of 1905 I tried to hatch
the above-named two mosquitoes, the one with the hibernating larvae, and the
one with the larvae which only appeared after the ice had melted; the former larva
had very large antennae and a long sipho ; the latter very small antennae and a very
short sipho; of course I got two species of mosquitoes; but the one with the
hibernating larva was unquestionably new to our fauna. Having however taken
material from different forest ponds, to my astonishment I saw that those mosqui-
toes which derived from the hibernating larvae always gave the same species,
whereas those deriving from the larvae in spring, gave specimens which unquestion-
ably belonged to two or three different species.

l*

R368855

I now understood that here was a very wide field for further exploration; as
however a long series of papers: my plancton work, many papers relating to the
biology of freshwater insects, and the bathymetrical explorations of the Fureso-
district first had to be carried out, I could only at rare intervals get time for these
observations during the 10 years from 1905 to 1915. Still the mosquito studies
were not quite laid aside, and in 1916 a more thorough study of the mosquito
larvae and their biology began. In 1912 the first volume of the great work of HOWARD,
DYAR and KNAB relating to the mosquitoes of North and Central-America appeared ;
the volume did not reach me before 1916. I immediately saw that all my above-
named more cursory conjectures were indeed correct, but also, that if published
they could not be regarded with any really new interest.

In the time from 1910 — 1920 a series of shorter papers, dealing with the
biology of the European species, appeared, and the biological facts, mentioned by
the American authors, were generally corroborated by the European ones. In my
opinion this literature very often by no means comes up to the standard which should
be exacted for scientific work.

After brief reflection I resolved that I would carry to an end my own studies
in spite of the whole American and European literature, and moreover that during
the study I would not take the slightest notice of it. My leading scientific views
were the following.

From a purely scientific point of view, I have always regarded the question,
who first made a biological observation as a matter of sublime indifference. It
must never be forgotten, that even with regard to biological observations which
can only rarely be committed to paper with the same convincing exactness as an
anatomical structure, the exact apprehension of a given fact can only be acquired
through repeated observation. It is further of the greatest significance that the
biological observations are tested by different scientists and in different latitudes;
only in that way can our suppositions and hypotheses be registered among real
scientific facts. It must further be remembered that the study of Nature must always
begin with the slightest possible literary ballast. He who has first crammed his
head with all that has been written upon a subject, will at the moment of observa-
tion, when standing face to face with Nature, soon understand that his whole learning
is only felt as a burden and restricts his power of observation. I for my own part
have always been of the opinion that it is exactly the smallest equipment of human
knowledge which gives the greatest peace in my studies, creates the scientific
sovereignty over observations and thoughts and - - as far as possible - - moves the
milestones of time nearer to the borders of eternity.

Having used the neighbourhood round Hillerod for more than twenty-five
years for my studies relating to the freshwater organisms, and often visiting the
hundreds of temporary ponds which were scattered within a radius of about 7 kilom.
over the country, especially in the forest, I had a rather extensive knowledge of
these ponds; having often hatched larva material from many of these ponds, I

knew well which would give the best results, if more thoroughly studied. In accor-
dance with this knowledge twenty-five temporary forest ponds were selected, and
in the time 1916 — 1919 subjected to a regular fortnightly exploration. After the
establishment of the Freshwater Biological Laboratory at Tjustrup lake, near Soro, in
the middle of Seeland, I soon found 15 other ponds, mainly belonging to the open
meadows and large plains which were simultaneously included in the exploration.
The ponds were explored every fortnight, viz. during the winter, when the ponds
were frozen and covered with snow, at longer intervals, but in spring, when the
different larvae appeared, and the imagines arrived, as often as possible, i. e. many
of them almost every day. The ponds were so selected that in the course of a
single excursion I could reach from five to seven. On schemata the results of every
excursion were noted and observations with regard to the freezing and drying
periods taken down. At first I took the temperature of the ponds, but later on I
learned that this was quite useless; on sunny days the temperature might be
about thirty degrees Celsius, the next day, if the weather was cold and rainy, only
about ten. The temperatures could only acquire, scientific significance if I had
been able to indicate the total sum of heat-units which in the course of the year
was conveyed to the ponds. As this was impossible, the temperatures were not
regularly taken.

In 1916 I thought that I should only find very few mosquitoes in the diffe-
rent ponds; in Denmark we had hitherto, viz: STAGGER in his valuable old work:
Systematisk Fortegnelse over de i Danmark hidtil fundne Diptera, only found ten
species of Culicini and of these two were doubtful (C. annulipes Meig. and C. nigripes
Zett.) and one restricted to brackish water; the greatest number that I could ex-
pect to find, in my area of distribution, was therefore only seven. At that time I
had not the slightest idea that the determination would cause troublesome diffi-
culties. I supposed that I could only expect to clear up the biology of the well
known species: C. nemorosus Meig., cantans Meig., ornatus Meig., pipiens Linne and
annulatus Schrank; further I did not know that the larvae of these species practi-
cally speaking were quite unknown, or at all events insufficiently described; the
valuable work of MEINERT: De eucephale Myggelarver 1886, deals only slightly
with the larvae of Culicini. Already in 1916 I understood that this number would
be augmented with several new species, but the determination of these species was
quite impossible to me. A closer examination of the large larva material from the
many ponds, worked out in the winter months, showed that there were especially
some ponds, which must be examined with special care next year. In 1917 these
ponds were examined almost weekly from 15 April to the first part of July. In this
time I then saw from five to seven species appear and disappear after each other.
Some of them were detected in the larva stage, separated in this stage, and then
hatched in special vessels; others appeared from larva material which I first
thought was homogeneous. In 1917 I had demonstrated about 15 different species,
and in 1918 I tried to elucidate the biology of all these species. To my great satis-

6

faction I saw that I almost always might be sure that the different species year
after year were hatched in the same ponds and almost always at the same tempera-
ture. As the larvae appeared in the ponds, they were separated, and about a hun-
dred placed in a special vessel and the vessel set in a hatching cage. The skins
were preserved and where I got a quite homogeneous imago material from a vessel,
I was sure that I had the right connection between larva and imago.

In 1919 many doubtful questions were tried and tried again; and several of
them were now nearer to being solved; especially the group 0. nemorosus, was ex-
tremely troublesome. Again and again I came to the conclusion that there are species
which may easily be distinguished in the imago stage, but which as larvae cannot
be distinguished from each other; further that there are species which as larvae
may be distinguished at a first glance, but as imagines are almost indistinguishable.
At this time the final determination of the species was desirable; most of them at
that time had only numbers. Having myself tried to determine the material, I saw,
that if I used the ordinary works on the European mosquitoes for some of the
most characteristic species, this gave no result. I then reguested my friend Prof.
SIMON BENGTSON of Lund to compare some of my material with ZETTERSTEDT'S speci-
mens in Lund; as I however compared the determinations with my larva material
I saw that somewhere there must be some mistake. I then sent some of the most
troublesome species to Mr. EDWARDS at the British Museum and asked him to look
them over. From him I got the wholly unexpected result that, in my material,
there were no less than three American species: 0. abfichii (Felt), fletcheri (Coquil-
let) and diantceus (H. D. K.), which have hitherto not been found in Europe; in a
following collection Mr. EDWARDS then determined a fourth species 0. prodotes
(Dyar), which also hitherto was only found in America; this species I had over-
looked; having examined the preserved larva material from the pond in which
this species should have been hatched, I really found a very few highly charac-
teristic larvae which most probably belonged to this species. Next year these larvae
were found again in the same pond, separated and, when hatched, really gave 0.
prodotes. Later on it was found out by Mr. EDWARDS that 0. fletcheri was identic
with 0. lutescens (F.) and 0. abfichii with O. excrucians Wlk. Mr. EDWARDS
further came to the same conclusion as I, that the old species C. ornatus Meig. could
not be found in my material; those determined by ST.EGER and now in the collection
of the Royal Museum, Copenhagen, being partly Culicella morsitans, partly C. com-
munis. As these species, apart from 0. prodotes, which was studied in 1920, were
separated as numbers already in 1918 and with regard to all biological data proto-
colled separately, it will be understood that with regard to the biology of the species,
it was not of the slightest significance that they were not finally determined till 1919.

In 1920 two questions had to be solved before the work could be finished.
As the two freshwater laboratories in Hillerod and at Tjustrup were both situated
far from the sea-shore, I had no opportunity to study the sea-shore mosquito
fauna, where the habitat of 0. dorsalis Meig., already found by STAEGER, really is.

It might further be expected, that here also we might find two other species
0. curriei (Coquillet) an American species, already found in England, and 0. detritus
(Haliday). Both species were found. As almost all my studies hitherto had been
restricted to Seeland, with some small trips to the southern islands, it was of in-
terest to become acquainted with the mosquito fauna of Jutland.

My time now being occupied with the preparation of the work for print, I
requested Mr. KRYGER, whom I know as a very skilled observer, to follow the develop-
ment of the mosquito life in the brackish-water pools near Copenhagen, and on a
journey in Jutland to study mosquito life there. Mr. KRYGER was also to gather
information with regard to the occurrence of Anopheles in stables.

STAEGER indicates 15 Culicidae, of which one C. nigripes must unquestionably
be cancelled. Thirteen new species have now been found for our fauna, this
now consisting of twenty-five species. The new species are: Ochlerotatus curriei
(Coquillet), 0. lutescens (F.), 0. excrucians (Wlk.), 0. detritus (Haliday), 0. punctor
(Kirby), 0. prodotes (Dyar), 0. rusticus (Rossi), 0. diantceus (Howard, Dyar and
Knab), 0. sticticus (Meig.), Tceniorynchus Richardii (Ficalbi), Culicella morsitans
(Theobald), Culex ciliaris Linne, C. nigritulus Zetterstedt. Three of the species were
new for Europe. Of these thirteen species I have myself found the twelve; 0. stic-
ticus has been brought me by Mr. KRYGER from the western part of Jutland. Of
the twenty-five species the twenty have been hatched from larvae. Most of these
larvae have hitherto only been very badly described or were wholly unknown.

It will of course be understood that the exploration has taken much more
time than I had thought, when I began. To a much higher degree than I had first
thought the work had to be systematic. Gradually I understood that a redescrip-
tion of the American species was necessary, that all the species of the nemorosus-
communis group should be redescribed, and that all the Iarva3 had to be described
and carefully delineated. It was very much against my wishes that I was forced
into scientific work to which I have always been a stranger. I soon learned that
my descriptions of the imagines would be best if I followed the descriptions by
HOWARD, DYAR and KNAR as closely as possible. Everywhere where it has been
possible I have therefore followed the descriptions of imagines by these authors.
Reference only to the work of HOWARD, DYAR and KNAB was not possible, be-
cause slighter differences could almost always be detected. With regard to the
description of larva? the case is different; these are always wholly original, and it
will be understood that new characters have been used and the older ones esti-
mated in a way differing from that of earlier authors.

As stated above: What I had intended should be the main points of the work:
the statements that almost all our mosquitoes only possess one single generation,
and that the eggs of the Aedini are laid singly and not in eggboats, have now been
made by others. Now one of the main results of the exploration, a result which
was not intended, when the exploration began, is probably, that the North- and Cen-
tral-European mosquitoes should now be recognisable in the larva and imago stage;

. 8

in the pupa stage I do not think that they are so. I first intended in two exten-
sive chapters to give biological sketches of each of the forty ponds, and of the
neighbourhood where some of the more peculiar species are found; further to print
the large schemes of each of the forty ponds, carried on for almost four years ; the
schemes show how each of the species appears and disappears in the course of the
year. Especially these schemes were extremely expensive to print, and I suppose
that their real scientific value is but slight ; they may be regarded as rough draughts,
and will not be printed owing to the great expense. - With regard to the synonyms
I have only given the most necessary information; I refer to the work of LANG
(1920) and to others which I know are under preparation.

As it will be understood from the foregoing pages, this work stands in the
greatest debt to Mr. EDWARDS of the British Museum; I hereby express my most
cordial thanks for all the help he has furnished me with; further to Prof. SIMON
BENGTSON and, last but not least, to Mr. KRYGER who with great skill and warm
interest has solved the tasks, I have given him. A few months before this work
was sent to press, Mr. LANG'S valuable work, relating to the British mosquitoes,
appeared; more than any other it has shown that my paper, now published, issuing
from quite different stand-points, and worked out on other principles, is by no
means superfluous. Also the CARLSBERGFUND I bring my heartiest thanks for two
sums, by means of which I was able to explore the southern islands, mainly with
regard to the Anophilines. For the study of the living larvae the excellent bino-
culary aquarium microscope, also presented to me by the CARLSBERGFUND, has been
of the greatest value. All the tables are drawn by myself and all figures of the same
kind are drawn with the same power and all with camera.

Key to the tables: 1 head (Leitz Ob. 3 Oc. 1) 2 antenna (Leitz Ob. 3 Oc. 6) 3
mandible (Leitz Ob. 3 Oc. 6) 4 maxilla (Leitz Ob. 3 Oc. 6) 5 mentum (Leitz Ob. 6
Oc. 1) 6 the last segments (Leitz Ob. 3 Oc. 1) 7 scales in comb (Zeiss horn. im. Oc. 6)
8 pecten (Zeiss Ob. B Oc. 6) 9 single thorns in pecten (Leitz 6 Oc. 6).

The Freshwater Biological Laboratory.
Hillered. 10/9 1920.

I.

Culicines.

Chapter I.

Morphological Remarks,
a. The Larva.

In the following pages I have tried to elucidate some points in the anatomy
of the Culicin larvae and as far as possible compared the anatomical structures with
the use the larva makes of them. The chapter deals only with our Danish mos-
quito fauna; it would certainly be desirable if the contents could be based upon
larva material gathered in other regions of the world. In the terminology I have
followed the excellent work of HOWARD, DYAR and KNAB.

The Head of a mosquito larva is generally wider than it is long, rarely almost
isodiametric as in Finlaya geniculata; it may be rectangular as in Tceniorynchus; it is
commonly vaulted, but may be flattened (Tceniorynchus) or, as in some of the species
of the genus Ochlerotatus, semiglobular. The anterior margin is formed by a narrow
clypeus furnished with two stout spines, between which the labrum is attached. The
greater part of the upper surface of the head carapace is occupied by the front or
epistome. It bears a number of setse, the number and arrangement of which are of
significance for classification (KNAB 1904 p. 175). Apart from some small tufts, the epi-
stome almost always bears three pairs of tufts, the preantennal tufts, at the root of the
antennae, provided with many and often long hairs; only in Finlaya there are three; the
two other pairs are either arranged in an arch over the epistome or they are arranged
on two lines anterior posteriorly. They are then described as lower and upper frontal
tufts. These tufts are rarely multiple in the Danish species. The number of hairs is
greatest in the genus Culicella (five or six) Calex, Theobaldia and Aedes. In the genus
Ochlerotatus the number is commonly only from four to one. The hair formula : two
strong hairs in lower frontal tuft and four in the upper, is characteristic of the group
O. excrucians, cantans, lutescens, annulipes. In 0. diantceus the arrangement of hair-tufts
and their number of hairs are more in accordance with that of the genus Culicella.
There is always most hairs in the upper frontal tuft ; the highest number I have found,
is six (C. morsitans) in Theobaldia annulata commonly four. The lower frontal tufts
have generally three or two, but these hairs are stronger than those of the upper

D. K. D. Vidensk. Selsk. Skr., naturvidensk. og mathem. Afd. 8. Rsekke, VII, 1. 2

10

frontal tufts. In some species, 0. prodotes and caspius, the number of hairs in both
tufts is restricted to one single long hair; Finlaya geniculata has two in the upper and
one single hair in the lower frontal tuft. In Tceniorhynchus Richardi the upper fron-
tal tuft is lacking; in T. annulata we find an additional lateral, strong, tuft in the
notch between eyes and antenna. Often and especially in Tceniorhynchus we find
small multiple tufts between the above-named larger ones; these tufts are not marked
because they are rather inconstant. The epistome has often drawings, different
among the different species, but remarkably constant in the same. I refer especi-
ally to the tables of T. annulata, 0. rusticus a. o. The colour of the epistome is com-
monly either grey or yellowish red. When in spring the drying ponds in our
woodlands teem with the large, grey larvae of 0. communis, prodotes a. o., ready to
pupate, we almost always find, scattered in the swarms, many, smaller larvae diffe-
ring by their yellowish red heads from these larvae; these larvae with red heads
belong to 0. cantans which will shortly, when the others have disappeared, pre-
dominate in the ponds.

The mosquito larvae have commonly two pairs of compound lateral eyes, ocelli,
like those of other aquatic insect larvae, being absent; in the Tceniorhynchus larvae,
living at the bottom of the ponds, between the roots and almost in total darkness,
we find only a single pair of very small eyes. The outer form of the two pair of
lateral eyes is different in the different stages of the larvae; in the same species
they are often almost separated by a narrow band; the posterior pair has as a
rule not been marked in the figures.

The Antennae consist of a single piece; they are remarkably stiff and possess
only very slight mobility; their length differs greatly, commonly they are half as long
but often as long as the head; in F. geniculata they are extremely short, only one
fourth of the length of the head; in some species, as C. pipiens and C. nigritulus,
they are longer than the head, and in Culicella morsitans and Tceniorhynchus Richardi
more than three times longer. In the short antennated species the antennae are
almost straight, only slightly curved. Where the antennae are very long, they are
especially, as in C. morsitans, elegantly curved, forming together two large, down-
ward directed arches before the head. The antennae always taper at the apex and
in the middle of the shaft or about two-thirds from the base of the shaft, often, in a
constricted part of the antenna, is inserted a fan-shaped tuft of long, commonly
feathered hairs. In Ochlerotatus, Theobaldia and Aedes cinereus they are inserted
directly on the antenna, in Culicella on a conspicuous notch. The development of
the tuft is very various; in Finlaya geniculata it consists of only one single un-
feathered hair; commonly, as in most species of the gen. Ochlerotatus it has only
from five to seven hairs; but in Culex pipiens, C. nigritulus, Culicella morsitans, 0.
diant&us and Tceniorhynchus the number is from twenty to thirty; here too, the
single hairs are very long, forming in these species two large wheels with feathered
spokes. When the larva is hanging from the surface or from a plant, the tuft is
always folded out; a movement of the single rays is rarely observed, but I have

11

often seen the whole wheel suddenly thrown inwards or vice versa. The part of
the antenna from tuft to apex is almost always narrower .than that from tuft to
base; generally it is stiff, but in Tceniorhynchus it is modified into a very long,
extremely flexible flagellum, bearing a single bristle near the tuft, but ending
without any hairs at the apex. - The outer part of the antenna is almost always
(except F. geniculatd) of a much darker colour than the inner part. In C. morsi-
tans the inner part is of an elegant ivory-white shining colour, strongly contrasting
with the almost black outer part. At the apex the antenna carries a different number
of shorter or longer hairs, two of which are as a rule inserted a little from the apex,
the others at the apex itself; the latter further carries one or two digit- shaped soft
organs, undoubtedly of sensory function.

When we remember that all our Culicin larvae are almost of the same size,
and only a few of them half as long as the largest, further, that the larva of F.
geniculata, almost of the same size as C. morsitans, has antennae which are only
about one-forth of the length of those of C. morsitans, it is evident that these organs
must play a very conspicuous role in the economy of the larva. As far as I can
see, they are commonly but slightly developed in those species which live in
extremely small water volumina (tree-holes, water reservoirs of plants etc.); they
are also small in those species which mainly find their food at the bottom of the
ponds or upon plants; with regard to .the large, beautiful, many-rayed tufts, which
occur in those species that find their food in the water layers, where they produce
a circulation in the water by means of the fan-shaped lateral hairtufts of the
labrum, I have got the impression, that these large wheels bound a little water area,
in which the water currents produced by the labrum come in; the large wheels act
as filters, preventing too large particles from entering the area immediately before
the mouth parts. I assume this, because I have seen the wheels, when too large a
particle has struck against them, turn suddenly round and jerk away the particles. It
may be added that the antennae, especially in the lower part, are spinose; antennae
without any spinosity we only find in F. geniculata.

The Thorax, consisting of three fused body segments, is always broad and
flat; the integument is membraneous, often furnished with two deep, longitudinal
furrows. Along the anterior and lateral margin long hairs, single or in tufts, are in-
serted. The arrangement of the hairs, single or in tufts, of the anterior margin, is of
value as a means of classification. In the description of the larvae I have used this
character and by means of figures given the hairs their number and position. The
hair formula of C. morsitans 231124421132 is to be understood in the following way:
In the median line two hairtufts, consisting of four hairs; laterally two double; they
are followed by two single hairs; then follows a tuft with three hairs, and at the
extreme end a tuft with two hairs; twelve hairs or hair- tufts on the frontal margin may
probably be the original number, but now and then one or other of these tufts are
suppressed. The number is almost always largest in the median tuft, commonly three
or four; then follows almost always a series of three or four single or double hairs,

2*

12

and lastly at the anterior corner of the thorax a tuft of from two to five hairs;
these frontal hairs are all long, stiff hairs, directed laterally and protruding beyond
the brushes; in some species of the genus Ochlerotatus the median tuft consists of one
long hair and two or three very short ones; the second tuft often consists either of
one or two very short hairs, which may easily be overlooked. The lateral hairs are
arranged in two large tufts, occupying the middle and hindangles. As HOWARD, DYAR
and KNAB indicate, they are situated on low tubercles and prevented from bending
backward by a smal chitinuous plate. Near both tufts very long stiff single hairs
are often inserted. On the dorsal side of the thorax we often find a number of
small tufts of hair, commonly serially arranged; most probably they very often fall
off after the moult; generally they have not been indicated in the figures.

The Abdomen is long, slender and cylindrical; it consists of nine segments.
The integument is membraneous, except that of the ninth segment; still it is much
thicker on the dorsal than on the ventral side; between the segments the integu-
ment is very thin and delicate; the first segments are always shorter and broader
than the following ones, the seventh is commonly the longest; on the lateral bor-
ders we find tubercles which support the lateral hairs. As it is well known, the
motion of the abdomen is extremely high; the motion of the body is always side-
wise, never dorso-ventral ; when the animal is to rise from the bottom, the position
of the body is vertical and the body is wriggled sidewise upwards; respiratory
movements of the abdomen, as it is well known in the larvae of Chironomidce,
Phryganidce, a. o. have never been observed. The six first segments bear long setae
on lateral tubercles; the number is greatest on the two* first, on the others com-
monly only one or two; on the dorsal side we find the so-called subdorsal hairs,
shorter hairs arranged in two series, and most strongly developed from the third to
the sixth segment. They are often wanting; mostly their number is two; in our Danish
species they are generally rather inconspicuous and are well developed only in one
single species, the one of the tree-holes F. geniculata ; further, fairly well in the Danish
species of genus Culex especially C. nigritulus. In F. geniculata every segment, from
the first to the seventh, bears three pairs of setae, an anterior, a median and a
posterior one; the median pair is best developed and consists of four hairs in
stellate arrangement. Owing to these groups of hairs the whole larva has a very
hairy appearance.

According to drawings and descriptions of tropical larvae it seems that luxuri-
ous development of subdorsal hairs and hairs upon the thorax, mostly in stellate
arrangement, is a very common trait in larvae living in tree-holes and in water
reservoirs in Bromeliaceae and other plants. - - At the base of the lateral hairs,
groups of shorter hairs are often to be found. The development of hairs upon seg-
ment seven is not so luxurious as on the preceding segments.

The eighth segment is short and bears dorsally the sipho or respiratory
tube; it bears three hair-tufts, one dorsally, one ventrally and one posteriorly in the
cleft between the sipho and the anal segment; long stiff single hairs in varying

13

numbers are implanted between these tufts; the posterior tuft is best developed and
always feathered, but all in all the place and the development of these hair-tufts are so
constant that they cannot be used as characters for classification. A peculiar structure
is the lateral groups of spines or scales; these scales are either arranged in a single
line, as is the case with Finlaya geniculata and Tceniorhynchus, often, but not always,
with A. cinereus, or in irregular arched series, covering a triangular spot on the sides
of the eighth segment; the largest number of scales is always in the anterior rows.
The number of scales is very different in the species, but fairly constant in the same.
It is only about from ten to twelwe in F. geniculata, Tazniorhynchus Richardi; com-
monly from twenty to forty in most of the Danish species of the genus Ochlerotatus,
but about one hundred in C. morsitans; it seems as if the number is greatest in
those species which have the longest siphones and the best development of the
flabellae. The base of» the scales is always spatulated ; they are often provided with
one strong spine, two shorter laterally, and many shorter ones bordering the sides
of the spatulated part; they may also as in some of the species of Ochlerotatus be
broad plates, ending in from five to seven thorn-like prolongations of equal length.
They are often laterally covered with a delicate, hyaline membrane, radiated along
the borders. Their number, position and form are of great value as characters for
classification; in the systematical descriptions they are determined as the comb. The
significance of the comb for the animal is in my opinion quite enigmatical. The
median spines of the scales may be rather long and very acute; still it is rather
difficult to understand, how they can be a weapon for the larvae; where there are
many scales, the comb impresses me as a carding apparatus, but I am unable to see,
how the animal should use such an organ.

Dorsally the eighth segment carries one of the most interesting organs of the
Culicin larvae, the sipho; this is always strongly chitinized, of a dark brown or
yellow colour; nearest to the base it has almost always a strong chitinized black
ring. If we compare Tab. XIX of C. morsitans with Tab. II of C. caspius we shall
see the great difference with regard to the dimensions even in a fauna so small as
the Danish one. It is commonly about three times longer than broad but may, as
is the case of C. morsitans, C. pipiens and C. nigritulus, be from five to seven times
longer than broad; it is extremely short, almost inflated, in 0. caspius. At the apex
we find an opening through which the larva takes air into its tracheae. The sipho
is closed by a set of five flaps ; when the larva comes up to the surface, the flaps pierce
the surface of the water; then they are folded out and pressed against it; by means
of the surface film the larvae hang down from the surface and draw the air into
the tracheae. When I have had different species isolated in vessels and have exam-
ined the surface, from which the larvae were hanging, with the binoculary aquarium
microscope I got the impression that the stars which the five flaps formed upon
the surface had quite a different aspect in the different species. The form of
the flaps and their bristles differ from species to species; but this can only be
thoroughly studied when the larvae are killed with the flaps open, the sipho cut

14

off and arranged vertically on the slide, so that it is possible to look directly down-
wards at the apex of the sipho. This is a very difficult process.

The sipho carries hairs and thorns in different arrangement. On the basal third
of the sipho are inserted two ventro-lateral series of spines, commonly determined
as pecten. This organ is of great value for classification. It commonly consists of
from twenty to thirty strongly chitinized spines, arranged on a line and at almost the
same distance from each other; at the base they are dentated, carrying from one
to six teeth; they may be flattened as is the case with F. geniculata, C. morsitans, C.
pipiens and nigritulus, formed here as oblique feathered scales of brighter, almost
yellowish chitin. In Theobaldia annulata we find no thorns, but only a series of
long soft hairs, without any teeth at the base. In some species the last thorns,
those nearest to the apex of the sipho, are at a larger distance from each other than
the following; they are not dentated and often inserted out of line (Aedes cinereus,
0. diantceus, 0. lutescens, excrucians, diversus, prodotes). The position of these spines
varies from species to species. In Tceniorhyncus the pecten is wanting (see remarks
later on). Also the function of this organ is quite enigmatical. It differs from
species to species; that it should have no significance whatever I regard as highly
improbable. It has so great a similarity to a comb that it must be regarded as fairly
probable that it may be used as an organ, by means of which the different hair-tufts
may be cleaned. The hair-tufts of the sipho present some of the best structures
for purposes of classification we have hitherto been able to find in the Culicin larvae.
According to the drawings published by HOWARD, DYAR and KNAB the tufts may be
arranged very differently from what I have seen in the relatively poor Danish fauna;
for a more thorough study I refer the reader to the above-named tables. In the Danish
larvae the most constant tuft is the apical one, very near the apical end of the pecten.
It consists of from five to seven feathered bristles. It may, as in 0. annulipes, lutescens
and excrusians, be highly developed or, as in Aedes, be rather inconspicuous ; it may
be wholly absent, but we then find another, equally well developed, brush at the basal
end of the pecten (Theobaldia annulata, C. morsitans). In Culex pipiens and C. nigri-
tulus we find four or five tufts with two hairs generally arranged serially and
ventrally, but with one or two of the tufts out of line. Only in 0. rusticus four
tufts of double hairs are inserted on the dorsal side of the air tube, opposite to
the pecten. Dorsally near the apex is further inserted a short thorn; two of the
flaps carry two short curved spines which are often used when the larvae rest on
the bottom with the dorsal face downwards, or when they are hanging from or
supported by waterplants. With regard to the modifications of the eighth segment
of Tceniorhynchus I refer to my paper (W.-L. 1918 p. 277).

The ninth segment or Anal Segment is out of plane and inserted upon the
eighth segment. It is short, often almost isodiametrical, in F. geniculata shorter
than broad, in Tceniorhynchus twice as long as broad. It is covered with a chiti-
nous plate, short in the larva of the first stage, but in the fullgrown larva often
rounding the whole segment, but mostly only covering about two-thirds of it. At

15

the apex it bears the anus, surrounded by four anal or tracheal gills, four appen-
dages varying in size individually. In ponds situated only a few rneters from each other
I have found in one of the ponds larvae of 0. communis with the gills only half
as long as the anal segment; in another larvae with gills more than three times as long;
they seem to be most strongly developed in water which is extremely dark and peaty.
In some species, f. i. F. geniculata and C. pipiens, two of them are much smaller
than the two others. In F. geniculata they are remarkably broad, in 0. caspius and
0. detritus extremely short. Some authors regard these organs as having no respira-
tory value, as being only of locomotorical significance, but most suppose that their
main function is really respiratory. (BABAK 1912 p. 81; LIMA 1914 p. 18).
KOCH (1918 p. 105) supposes that the chief function of the branchial leaflets is
probably the absorption of oxygen, while the elimination of carbonic acid from
the blood takes place through the body walls. LIMA maintains that larvae whose
branchial leaflets show numerous tracheal ramifications, remain normally longer
under water than those with only small ones, and that the former can live longer
than the latter when they have no access to atmospherical air.

The anal segment further bears the most important organ of locomotion, the
large swimming brushes; these are divided into two parts, the dorsal and the ven-
tral brush; the dorsal is always the smallest in the Danish larvae; it is inserted on
two chitinous pieces; generally it consists of a coarse multiple tuft with rather long
hairs; below this tuft are inserted two, often very long, stiff hairs to which, as
in T. annulata, a few shorter ones may be added; in F. geniculata, C. pipiens and C.
nigritulus it is replaced by a few long, stiff hairs. The ventral brush is more highly
developed and inserted upon a system of chitin staffs, well described by HOWARD,
DYAR and KNAB. "The tufts of the ventral brush hinge upon slender, transverse strips
of chitin and towards the middle, where the tufts are inserted, these strips are
thickened and perforated. Outwardly these transverse strips are jointed to a pair of
longitudinal strips. The tufts are not inserted exactly upon the median line, but
alternately a little to one side or the other thus showing the bilateral origin of the
structure" (1912 p. 89). The number of the tufts varies from one species to another;
it is only about ten in F. geniculata, C. pipiens and nigritulus but more than twenty
in T. annulata. Each tuft consists of an undivided arched basal part, bearing on
its apex the hairs ; this number is fairly constant for the different species ; it is only
two in F. geniculata, but about twenty in T. annulata; from seven to nine hairs
would probably be the most common number. Before the real ventral swimming
brush a number of much shorter tufts are often inserted; these are not supported
by transversal chitin bands ; among the Danish species these tufts are only wanting
in Finlaya geniculata and C. pipiens; they are but slightly developed in T&niorhyn-
chus. Laterally between the dorsal and ventral brush on the above-named shield a
short tuft consisting only of one or a few hairs is inserted; among the Danish
species it is best developed in F. geniculata.

Mouth-parts: The labrum is divided into three parts: an unpaired median

16

lobe, the palatum, and two large lateral lobes, flabellse; the whole preantennal
region of the head and the relations between the labial folds and the black-pigmented
apodemes which enter the flabellse and to which the muscles are fastened are well
described by THOMPSON (1905 p. 145). Here we shall restrict ourselves to some
remarks with regard to the different development of the hair-coating in the diffe-
rent species.

As far as I can see, we find two quite different types of hair-structures on the
labrum. In 'one group the hairs of the flabellse are all of almost the same kind;
long, soft, yellow hairs. Only the length of these hairs is very different in the different
parts of the flabellse. Sidewards and nearest to the outer margin of the flabellse
they are very long; inwardly and nearest to the palatum they are shorter and
have another direction; those of the outer -margin are held vertically on the
longitudinal axis of the head, those of the inner margin are parallel with it. The
large brushes are therefore divided into two parts, a horizontal and a vertical
brush, which are separated from each other by a curve; this is most conspicuous
in C. morsitans, C. pipiens and nigritulus, Tceniorhynchus Richardi, but it is also to
be observed in O. diantceus and Aedes cinereus. When these species, especially C.
morsitans, are observed with the binoculary aquarium microscope, we see the large
horizontal rami of the flabellse regularly thrust out and in, being expanded and
folded together; in the part held horizontally the hairs are pressed together and act
against the water as a compact mass; in the part held vertically (the inner part) the
hairs are spread out from each other during the stroke outwards, but undulating
motions from without inwards may be observed during the strokes. By means of
these undulating motions particles caught by the outer rami are carried downwards
to the mandibles and then seized by them. We find this type of hair development
on the labrum in all those species which, when undisturbed, always hang down
from the surface and seek their food in the water layers. This food only consists
of all the small particles floating in the water which, by means of the large lateral
hairtufts, are carried with the water-currents down to the mouth.

In all other Danish mosquito larvse we find quite another type of hairs and
hairbrushes; the hairs are almost all equally long, there are no large, horizontally
extended flabellse; seen from above the whole apparatus conveys the impression of
a compact brush with most hairs arranged in a circular row, inserted nearest to
the edges of the brush. Further there is the great difference that the hairs nearest
to the palatum have quite another form; they are elegantly curved, flattened, and
bear upon their inner side from ten to twenty short teeth; the hairs are changed
into combs, and the whole apparatus is a combing apparatus, mainly used in
a way quite different to the corresponding one by the above-named species. Most of
these larvse hang down from the surface, producing water currents by the expand-
ing and unfolding of the hairbrushes. Still they are also able to get their food in
quite another way. Living in ponds, often with extremely small volumina of water,
they go down to the bottom, where they brush and comb off the sedimented par-

17

tides from the decaying leaves, using this material as food. It is a very common
phenomenon to see these larvae sink down to the bottom and, in an oblique posi-
tion, with the hair-brushes expanded and pressed down to the substratum, steadily
move over the leaves or along the sides of the aquaria. It is a remarkable fact
that these two types of hair-brushes and the very different mode of getting food in
the mosquito larvae have hitherto been quite overlooked. It is the last-named form
of the flabellae which we mainly find in Ochlerotatus.

The hairs of the labrum as well as the short hairs on the palatum have prob-
ably also quite another function ; they pay the double debt as organs of nutriment and
of locomotion. Undisturbed most Culex larvae hang down from the surface with the apex
of the sipho supported by the surface film, and with the flabellae whirling water
currents into the mouth-parts. Apart from the flabellse the body is motionless. Sud-
denly we see the larvae, with the apex of the sipho in the surface, move slowly
forward. In quite the same way we see the larvae which seek their food, either on
the sides of the aquaria or at the bottom, suddenly stand still, and suddenly, but
slowly, move forward, the flabellae being pressed down against the substratum.
Many of the species are also able to move slowly forward in a peculiarly sliding
manner in a horizontal direction in the free watermasses, stand still for a moment
and then move onward again. Otherwise the free watermasses are commonly not
the home of the mosquito larvae; they are only traversed when the larvae is to go
from the bottom to the surface or vice versa. The way is traversed either actively
by means of wriggling of the abdomen and of the swimming brushes or passively
(see later) ; the active motion is mainly in a vertical direction with the head turned
away and the tail in the direction of the locomotion; it is generally very rapid.

Now I have often thought that the above-named sliding motions were produced
by the brushes of the last abdominal segment, but studying the organ in living larvae
under the binoculary aquarium microscope I have convinced myself that this
locomotion is not produced by these organs. At all events the tail and its hairs are
held quite motionless. There is therefore no other possibility but that the move-
ments are due to the flabellae. To me there is only this great difficulty that it is quite
impossible to see why the organs, though almost always in constant motion, in some
moments produce a motion of the whole body and in others, though still moved,
produce not even the slightest movement of the body. I have tried with my
best microscopes to study this in living animals, but I have been quite unable
to see what the larva prepares to do, when it suddenly applies the organ to be
used in the service of locomotion. I only feel convinced that it is not the hair-
fringes on the mouth-parts which are used; it is the hairs of the flabellae, which
are suddenly either moved faster, or struck out in another direction. In the first year
while I was always studying C. morsitans, which commonly in the autumn hangs
down from the surface, I thought for a long time that the larva was in some way
glued to the surface by the apex of the sipho and, without altering the use of
the flabellae, only moved when the agglutination ceased. Later on, when studying

D. K. D. Vidensk. Selsk. Skr., naturvidensk. og raathem. Afd. 8. Rsekke, VII, 1. 3

18

the other larvae, I saw that this supposition was probably wrong. - - Most probably
the flabellae have yet a third function; they certainly play a prominent role as organs
which contribute to the renovation of water in in the neighbourhood of the larva.

The structure of the mandibles is rather complicated; they are well described
by some earlier authors, especially HOWARD, DYAR and KNAB, but the use made
of them is not clearly understood. They are almost hidden by the large, very broad
maxillae. The dorsal (inner) margin of the mandibles bears a system of thorns, setae,
and strong chitinised teeth, the arrangement of which is common to all mosquito
larvae. - - Nearest to the outer angle some strong movable spines are inserted; the
number (from two to four) of these spines varies from species to species; the inner
margin is further equipped with a series of tubercles carrying thorns in very different
states of development in the different species; these thorns are badly developed or
almost absent in those species which find their food in the water layers, but strongly
developed in those which mainly brush off the food from a substratum. In T. annulata
the spines are comb-like with very long, curved teeth. On the inner side of the
mandibles, parallel with the inner margin, an elegant fringe of long, soft hairs is
inserted; they take their rise from a crescentic chitinous ridge; every hair in this
fringe is kneed, and all always at the same distance from the crescentic ridge;
therefore the whole fringe is kneed; also in the development of this fringe there is
great difference in the different species; it is always largest in those species which
only live upon suspended material; it may further be added, that the hairs in the
fringe are much stronger, almost thorn-like, in those which live upon sedimented
bottom material. The apices of the mandibles facing each other bear a number of
dark, strongly chitinised teeth, and in front of them commonly a long, movable
often dentated tooth; this part of the mandible varies from species to species; it
is always chitinised, most strongly in the species living upon sedimented bottom
material. Below the teeth we find a peculiarly shaped single or double fork-like lobe,
with two constant hair-brushes Between this lobe and the dark chitin teeth a series
of hairs is inserted; these hairs are thorn-like in the bottom feeders. The three
above-named parts: the strong spines on the outer angle, the fringe, and the chitin
teeth below, play quite a different role in the act of feeding. Under the bino-
culary aquarium microscope it is easy to see, that the mandibles, whenever the
flabellae are folded together, with the above-named two or four spines on the outer
angle are struck into the hair-brushes; when refolded, the hairs pass between the
spines, acting as teeth between which the hairs are combed free from adherent
particles. At the moment when the fiabellae are struck inwards, and the whole
organ folded together, the mandibles meet each other in the middle line, and the
above-named thorns form the combing apparatus; when removed the mandibles
are thrown outwards.

The function of the fringe is most probably partly to bound the space in
which the particles are swept down, partly to brush them downwards into the
masticatory part of the mandible, the short sharp chitinous teeth between which

the particles are to be masticated. The teeth, the rectangular lobe, and the feather-
like bristles together with those from the opposite mandibl.e encircle a space and
cause every particle swept down into the lower part of the buccal cavity by the
combing teeth and the fringe to be caught within this space from which it is not
able to escape.

The maxillae are large flattened plates; they are not of such a complicated
structure as the mandibles, but as to form and equipment with hairs they differ in
the different species more than the mandibles. They are often roughly conical,
longer than broad, but may also, as in T. annulata, be broader than long. They are
furnished with a longitudinal suture, and carry outwardly a small basal appendage,
generally indicated as palpe. In all these species, which find their food in the water
layers, living on. suspended material, the apex of the maxillae carries a long thick
tuft of hairs; these hairs may be feathered as in C. pipiens and nigritulus; the same
tuft may also be long in most of the species which partly seek their food on
the bottom; still the tuft here is never so well developed, consisting as it does of
shorter hairs ; it may as in T. annulata be wholly absent. On the inner edge of the
maxillae is commonly inserted a series of long stiff hairs, and the whole space
between the above-named suture and the inner margin is covered with a coating of
long, soft hairs, now and then arranged in bands (C. pipiens and nigritulus). In
F. geniculata the whole upper and inner part of the maxillae are covered with a fel-
ted coating of very short hairs; outside the terminal brush is inserted a thorn-like
hair, very conspicuous in Tceniorhynchus. The palpe bears on its top four or five,
little digit-like prolongations undoubtedly of sensory function. The maxillae cover
the mouth from beneath; they are but slightly movable; when the catch- or brush
apparatus of the labrum is not used, it is folded in, and the large maxillae form
the floor of the space, in which the labrum and the other mouth-parts are concealed.
When the brushes are to be unfolded, the maxillae are unclapped, then the brushes
appear, and a moment later these begin to act. During the movement of the fla-
bellae the maxillae are quite immovable; together with the long apical hair-brushes
they border the space, in to which the particles are swept. It may further be ob-
served that the two maxillae never reach each other, but leave an open space be-
tween them; this is mostly covered by the above-named hairs along the inner
margin ; but lowest and nearest to the attachment of the maxillae a triangular space
is left hair-free. If now we direct our attention to this point on a feeding larva,
we shall be able to see that an irregular row of small pellets passes through this
little cleft. The pellets do not come at regular intervals, but irregularly, now and
then in long chains. These pellets represent all the material swept down into the
buccal cavity, which the larvae are unable to use. We therefore see that these
larvae too are able to select out of the captured material what they wish to use;
as, by means of the binoculary aquarium microscope, we are able to observe those
pellets which pass the oesophagus and the swallowing movements during the feed-
ing process, I have also noticed that there are periods in which all material, caught

20

by the flabellse, passes the above-named triangular space. At other times almost all
material is swallowed.

Behind the sharp transverse ridge to which the maxillae are attached we find
the mental and labial structures. Mesially are found four chitinous structures, ac-
counted for by RASCHKE (1887 p. 10) and MEINERT (1886 Tab. I. fig. 5) and men-
tioned in all works on mosquito larvae: 1. a delicate, roughly triangular plate with
a marginal hair-fringe and protruded into along tooth at the middle. 2. behind this
the mental sclerite, a heavily chitinised, dark, roughly triangular dentate plate.
3. behind this a complicated plate with teeth and spine-like structures, commonly
regarded as labium and. 4. at the margin of the pharynx the hypopharynx, a simple
chitinous cone (Howard, Dyar and Knab I. p. 87).

Of these organs No. 2, the mental sclerite or mentum, is very conspicuous; it is
commonly triangular, on its apex provided with a rather conspicuous thorn and with
the sides bordered by a number of shorter spines ; the form of the mentum and the
number of lateral spines have some significance as a means of classification; and are
therefore often mentioned in systematical descriptions. The Danish species of the
Genus Culex may always be distinguished by means of its high form of the men-
tum with rectangular sides; T. annulata by its many small lateral teeth, and
Tceniorhynchus by its very few large ones; in the genus Ochlerotatus it is triangular
with about from ten to fifteen small teeth; as far as I can see, it cannot be used
to distinguish the species of this genus from each other. Beneath the mentum is found
the very peculiar organ (3) which has been figured by MEINERT (1886 PI. I. fig. 5)
and better by RASCHKE (1887 fig. 13. Tab. VI) but never thoroughly described; it
consists of a tube, probably provided with a central pore. It is surrounded by a collar-
like part, consisting of plates of chitin which overlap each other and are furnished
with teeth along the edges. The organ rests upon a dome-like body, supported by
two lists of chitin, and inwardly provided with a thorn-like process. Thorns of
chitin are also present on the dome-like part. Meinert's drawing exhibits a circle
of hairs rising from the apex of the tube; when cut horizontally, the organ shows
a cushion-like layer of cells with large nuclei beneath the dome-like part. Two
divergent muscles run to the organ, serving to push it forward and to retract it. Its
appearance differs but little within the different Culicin larvae.

How these four above-named different parts act, I do not know; I have never
during the feeding process seen the mentum carry out any movement; the tube
with the collar-like expansion lies directly at the entrance to the pharynx; I sup-
pose it has a secretory function. The above-named pellets which leave the tri-
angular space between the maxillae during the movements of the flabellae, are wrapped
up in a mucous substance, and I suppose that it comes from the above-named
pore. Further I call attention to some peculiar movements of the larva, easily
to be observed and often figured in old as well as in new literature. When the
larvae are hanging down from the surface, we often see them release their hold;
the body is bent, and the apex of the sipho is put into the mouth. In this position

21

the larva sinks to the bottom, rests here for a moment and swims upwards to the
surface again. I have often been surprised at the facility, with which the apex of
the sipho, when it touches the surface-film, pierces it, and the rapidity with which the
flaps are folded out. I suppose that the apex of the sipho is oiled and that the oil
comes from the pore of the above-named tube. I have vainly tried to see if there
is any real connection between tube and sipho and do not think that this is pos-
sible to observe, but I have often seen that the sipho is pierced into the buccal
cavity, and that the flabellae are folded round it. As far as I can understand, we
have here to do with two processes: a cleaning and an oiling one, either one of
them or most probably both: first a cleaning and then an oiling process.

With regard to the tracheal system, thoroughly described by Meinert (1886
p. 391) and by RASCHKE (1887 p. 16), I shall restrict myself to the following short
remarks. The thickness of the tracheae and the form of the transversal cuts differ
widely in the different species; in some species they are circular, in others elliptical,
the tracheae being then converted into broad flattened bands; this more especi-
ally holds good for F. geniculata. In the thorax, in particular, the tracheal system
presents great variations from species to species.

The tracheal system of the mosquito larva has a double function, respiratory
and hydrostatical; the last-named in almost all mosquito larvae is but slight. In
recent years the respiration of the mosquito larvae has been subjected to many
valuable explorations (BABAK 1912; KOCH 1919; KROGH 1920).

Referring to this literature, dealing with problems which only touch the ex-
ploration which is here published, I shall only deal with a few points. BABAK (1912
p. 84) as well as many others remark that during the ventilation of the tracheal system
respiratory movements are wholly wanting. The most recent observations, (KROGH
1920 p. 95) confirm this. Some authors (BABAK 1912 p. 85) suppose that the re-
novation of the air in the large tracheal trunks takes place owing to the strong move-
ments of the abdomen, by means of the pulsation of the heart and owing to the
movements of the intestine. KROGH (1920 p. 96) has however pointed out that all these
movements do not suffice for the necessary ventilation and that we must try to
find other ways if we are to understand the ventilation here and in all those insects
where respiratory movements are not visible. Basing on his excellent studies on
some large insect larva? he has pointed out that diffusion alone is sufficient to pro-
duce the air transport in the tracheal trunks.

Babak (1912 p. 90) has shown that the two main tracheal trunks, when the larvae
are forced away from the surface, are flattened and emptied of air. With regard to
the summer larvae I have made quite the same observation. It is however in con-
tradiction to an observation of KOCH (1919 p. 467) according to which, instead
of gradually emptying during submersion, the tracheae are filled still more, and
when they are quite full, small gas bubbles escape from the sipho which there-
fore is not always completely closed under water. The author supposes that this
air cannot be oxygen, and that it must be regarded as air that has already been

22

breathed and is now stored up in the tracheae. Further observations are here neces-
sary. I only wish to make the following remark: In the winter- larvae of C. mor-
sitans which for weeks hang down from the submerged leaflets of water plants without
leaving their place I have never seen a flattening or emptying of the tracheae; they
are always filled with air and an air-bubble is often seen at the apex of the sipho.

In his interesting paper (1919 p. 463) KOCH, as one of his main results with
regard to the respiration of the Culex larvae, mentions the following: »Die Culex-
Larven sind Saprozoen, die vorwiegend im Schmutzwasser leben, das infolge der
sich darin abspielenden Famines- und Zehrungsprosesse ausserst wenig freien Sauer-
stoff gelost enthalt. Die Cufer-Larven konnen nur eine relativ kleine Menge Sauer-
stoffes bei der Submersion aus dem Wasser aufnehmen und zur Energieproduktion
benutzen. Hoher Partialdruck von 02 (bei niedrigem C02-Gehalt) verlangert zwar die
Zeit bis zum Eintritt der Lethargic, bietet aber nicht die Moglichkeit zu einer gros-
seren durchschnittlichen Energieproduktion sondern scheint im Gegenteil die Beding-
ungen dazu zu verschlechtern«. Most probably these statements are quite correct
with regard to the larva of C. pipiens; it must however be maintained, that most
probably they are quite wrong with regard to all those mosquito larvae which live
in natural ponds, often with green bottom, and cannot be correct with regard to
the mosquito larvae of those species which regularly hibernate under the ice. With
regard to the respiration of these larvae, I refer to C. morsitans. Like many before him
KOCH has taken the biological and physiological results relating only to C. pipiens
as a prototype for all mosquito-larvae; this is in my opinion inadmissible.

Used hydrostatic the tracheal system in the mosquito larvae has a loco-
motorical significance. The specific gravity of the mosquito larvae is almost that
of the surrounding medium; gravity compensation depends upon the size of the
larvae, the degree to which the intestine is filled with food, and the condition of the
tracheae; every one \vrho has studied large and small mosquito larvae in a vessel,
has almost always had an opportunity to see that the larvae of the first and second
moult are mainly or often supercompensated; old larvae after the last moult are very
often undercompensated; it may further be shown that larvae in Nature are very often
supercompensated, in aquaria with a rich supply of food often or mainly undercom-
pensated ; if kept for days in pure water undercompensated larvae will, as the intes-
tine is emptied, be altered into supercompensated ones. With regard to the hydro-
static function of the tracheal system, KOCH arrives at the following result: »Der
jeweilige Fiillungsgrad der Tracheen bei Cu/ex-Larven wird einzig und allein durch
die physicalisch-chemischen Vorgange bei der Atmung bestimmt; die dabei auftre-
tende Gewichtsverschiebung, die wiederum eine bestimmte Anderung der passiven
Geschwindigkeit der Larve nach sich zieht, ist nur eine Folge des Atmungsmecha-
nismus, hat also keinen Selbstzweck. Der Fiillungsgrad der Tracheen wirkt zwar
mitbestimmend auf die passive Geschwindigkeit der Cw/ex-Larven wahrend der
Submersion, es muss bei den die Hydrostatik bedingenden Faktoren in Rechnung
gestellt werden, aber eine automatische Regulation der passiven Sink- und Steig-

23

geschwindigkeit infolge Gasdiffusion durch die Tracheenwande wie bei Corethra
fmdet bei Cu/e;r-Larven nicht statt".

Generally these statements are most probably quite correct ; many of the experi-
ments which KOCH has carried on, I have occasionally had an opportunity to ob-
serve. It is quite right that the larvae of many mosquitoes, when they leave the
bottom for the surface, rise slowly in a vertical position without any motion;
the head is always downwards; that the sipho plays the role of "Schwimglocke"
is most probably quite correct; many species, f. i. C. morsitans, can often be seen
in quite the same manner sinking from the surface down to the bottom; but here
the head is also directed downwards and not upwards as KOCH supposes; in this
case the sipho has no significance as "Schwimglocke". With regard to 0. rusticus
I have very often seen the larva with an air-bubble at the top of the sipho rise
vertically from the bottom and without making any actual movement reach the surface.
But of this species I have also seen larvae, which first passively sank downwards and
then, before they reached the bottom, stood still for a moment in the water layers and
then again passively rose to the surface. I have only observed this in this same larva;
that the tracheal system in this case played a hydrostatical role is in my opinion un-
questionable. I am inclined to suppose that the mosquito larvae, with regard to the use
of their tracheal system as a hydrostatical apparatus, differ from each other. A more thor-
ough exploration of the tracheal system of the different mosquito larvae and the greater
or less use of it as a hydrostatic apparatus would probably give good results. It may
further be pointed out that the most elaborate tracheal system is found in those larvae
which live under bad respiratory conditions (tree-holes, polluted water, on the bottom
with the sipho pierced into the tissues of water plants, Tceniorhynchus). In these
larvae the tracheae are more band-like, especially in the thorax, the meaning of which
may probably be, that tracheae of this structure are able to store up larger amounts
of air than those whose transversal cuts are circular. We shall here only deal with
the highly remarkable tracheal system of the Tceniorhynchus larva.

Between the thorax and the first abdominal segment are situated two large
bladders. At the first glance these bladders resemble those of the Corethra larva, but
differ from these in being connected with the two main tracheae by two smaller,
rectangularly curved tracheae. The point of insertion is situated at the line between
the thorax and the abdomen. Fig. 12 and 13 Tab. XV illustrates the description. It
will be seen that the front parts of the bladders are furnished with some few, short,
slender tracheae, and that the two large longitudinal stems of the body are broad,
band-like in the thorax and the first part of the abdomen. In fact these main
tracheae are double, their double derivation being still indicated by a longitudinal
fold; in the thorax each of the two trunks is further divided by another fold. The
result is two broad, flat, band-like bodies, terminating in front in three tracheae, the
first of which has a lateral course, whilst the second is directed forward and sends
branches to the head; the third, inner, branch is smaller and communicates with
that from the other side. In the abdomen each of the main tracheae sends a smal-

24

ler branch to the alimentary canal and a larger, outer one with branches in a star-
like manner; one of these branches is stronger than the others and runs into the
preceding segment. In the eighth segment a strong trachea branches off, running
into the anal segment, sending out branches to the gills.

The function of this very peculiar tracheal system is difficult to understand.
I have tried to understand the mode of action of this peculiar tracheal system, it
being as far as I know unique among the insects. Later on Prof. KROGH has been
kind enough to read my manuscript and has discussed the problem with me.

From the very broad band-like tracheal trunks it can only be concluded, that
the larvae must be able to produce a very powerful respiration. This may probably
be of great significance for the larva, because the air in the plant from a respira-
tory point of view is a very bad medium, by no means rich in oxygen. This has
been ascertained by EGE (1915 p. 183). The main result of his investigation is "that
the composition of the air in the intercellular spaces of different aquatic plants is very
variable. The oxygen percentage is low, rarely higher than 10 °/0 and may especi-
ally in winter sink to about 1 — 2 °/o and even still less". When we remember that
the larva probably fixes itself to the plant until September and probably detaches
itself in May, the animal living as imago or egg during the time May — September,
it will be understood that the larva is dependent on the plant air, especially at
the season when the oxygen percentage is lowest. For a long time I therefore
thought that the tracheal bladders might be used to pump the air from the plant
into the body of the larva by pressure and dilatation. Prof. KROGH has now at my
request been kind enough to go into the matter and tells me that this however
cannot be the case. He pointed out that the larva, as far as he could see, made
no visible respiratory motions. He varied the composition of the air in the inter-
cellular spaces of the plant, but even then, if the amount of oxygen only was
three per cent., no respiratory motions were traceable. If the larvae got only nitrogen,
all motion ceased and the brushes stopped; if then atmospherical air was again
conducted through the plant, they were soon restored. If the larvae were exposed
to various different pressures, it could be shown that the tracheal system really
would be somewhat compressed; but the compression of the tracheae which was
the result of the pressure, possible for the larvae themselves to procure by
the contraction of their body, (not more than 0'2 atmospheres), is so inconspi-
cuous that it would be without any practical significance, even if the larva made
respiratory motions. Furthermore it could be shown, that it was only the flat band-
shaped tracheal trunks and not the bladders which were compressible.

It must therefore be taken for granted that the transport of oxygen from the plant
to the larva only can take place by means of diffusion. The bladders on the tracheal
system are said in Tceniorhynchus to have quite another function. They augment
the respiratory surface and the amount of air which is at the disposal of the larva.
Further they act hydrostatically ; they diminish the weight of the animal, more especi-
ally of the anterior part, which would otherwise be much heavier than the posterior.

25

Moults. As far as we know hitherto, all mosquito larvae moult four times
and transform into pupa with the fourth moult; the moulting. processes, the different
aspects of the larvae in the different larva stages, have been mentioned by different
authors. I more especially refer to the very valuable paper by EYSELL (1911 p. 320),
to the remarks in HOWARD, DYAR and KNAR (1912 p. 97), and to the most recent
investigations by LANG (1920). The ripe larva ready to pupate is always easily
recognisable, the body being more opaque; the compound eyes are dorsally drawn
out into a sharp point, and the trumpets appear as dark spots below the larva skin
and near the anterior angles of the thorax.

Here I only wish to call attention to a few facts, hitherto as far as I know
overlooked.

It has been mentioned that two of our Culicin larvae, Culicella morsitans and
Ochlerotatus rusticus, hibernate in the larva stage. These larvae are hatched in Sep-
tember or late autumn, but they have commonly passed the third moult before the
winter sets in. The wintering generally takes place in the last larva stage before
the pupation. In the long time from November — December to May — June when
C. morsitans pupates, the larvae, at all events in my aquaria, do not moult. The
same remarkable fact I have observed with regard to the Perlidce, Ephemeridce
and Zygopteridce, which are hatched in autumn and are ready to leave the water
in spring. In the course of the autumn as the temperature sinks they hasten to
reach the last larva stage before winter sets in. It seems as if all these different
insects are under the same law, that hibernation can best take place in the last larva
stages. It is very remarkable that the first larva stages are often passed in the course
of a few days, whereas the last may take more than a half year. The larvae eat in
the last moult as well as in the earlier; in the first, the result of the nutriment is
growth and new moults, in the last there is no, or extremely little, growth. With
regard to Perlidce and Ephemeridce the phenomenon is intelligible, because the re-
productive organs ripen during the last months; in the last days before the nymphs
leave the water, the abdomen bulges with ripe eggs. In the Culicin larvae this is
however not the case; here the process is by no means carried so far, the repro-
ductive organs in the pupa too being only small; as far as we know the imagines
of the Culicidae regularly use a fortnight or more to ripen their eggs after meta-
morphosis.

Further it is peculiar to see how all the larvae of the same species in a pond
keep time with each other with regard to the moults; they are hatched almost on the
same day and moult on the same day; in the course of a few days all larvae are
altered into pupae and in one or two days all animals leave the pond as imagines.
When therefore in these spring-ponds with older larvae, new broods of larvae in the
first stage suddenly arrive, it has been ascertained, that these young very often belong
to another species, the hatching temperature of which is higher than that of the first
hatched. Only when heavy showers have raised the water line, and some eggs of
the first-arrived species, have thus been reached by the water, it happens that

D. K. D. Vidensk. Selsk. Skr., naturvidensk. og mathem. Afd. 8. Raekke, VII, 1. A

26

new material of newly hatched larvae of the very same species which now fills
the pond with full grown larvae, appears. Then it is interesting to see how fast the
development of these newly hatched larvae goes on; especially if the weather is fine,
it happens that all larvae, the old ones and the newly hatched, all pupate almost
simultaneously; the old having taken about three weeks for their development, the
others, only five or six days; this is of course due to the temperatures, by which
the young larvae have been hatched and lived their lives, which were much higher
than those which regulated the rate of development of the older larvae.

Especially the first larva stage is in spring passed in the course of a very short
time, commonly only a few days. If we fill an aquarium with thousands of 0.
communis larvae, in the course of a few days we shall find the bottom of the
aquarium covered with thousands of small, black larva heads, provided with their
egg breaking tooth and thus proclaiming themselves part of the skin of the first
larva moult; of the rest of the skins we hardly ever see anything. Simultane-
ously we find in the larva swarms many larvae with very large, broad, flattened
and snow-white heads, which strongly contrast with the very short, dark and often
almost black body of the larvae. On more thorough study it proves that the head-
carapace is moulted much earlier than the rest of the skin, and that the new skin,
when leaving the old one, immediately after the moulting process, is rather dark,
whereas the head preserves its snow-white colour for days.

Summary: If we combine the knowledge we have now gained of the structure
of the Danish mosquito larvae, with our knowledge of their life, we shall in my opinion
come to the following result: From a biological point of view I suppose that our
mosquito larvae of the drying ponds may be divided into two groups: the surface-
and the bottom dwellers. This must not be understood to mean that these two
groups are quite distinct; on the contrary, they are connected with each other by
a long, unbroken series of intermediate stages: What I wish to point out by
means of the above-named statement is, that in these ponds there exist species
which almost always hang down from the surface, and others which generally
rest upon the bottom and only rarely come to the surface. Both groups use
the atmospherical air for respiratory purposes, but to the latter group the
respiration through the skin is of much greater significance than to the former;
further the nutriment of the first-named group takes place when the larva
is suspended from the surface, that of the last-named mainly from the bottom;
the first-named group are plancton- and suspended detritus feeders; the last-
named scrapes microscopical organisms and deposited detritus from the decay-
ing leaves, or twigs, or seeks its nourishment in the diatom-coverings etc. upon
living plants.

It is of course self-evident that animals which live their life in these two
entirely different wrays, cannot be constructed in the same way.

Larvae which always hang down from the surface, taking in atmospherical
air, need not resort to respiration through the skin. If we combine my own

27

observations with regard to the biology and anatomy of our own little mosquito
fauna with the remarks with regard to biology and the drawings in the large
work of HOWARD, DYAR and KNAB, we shall come to the general result that we
find the slightest development of the tracheal gills in the surface feeders, and the
strongest development of these organs in the bottom feeders. Only where we have
to do with larvae which are really surface feeders, but hibernate below the ice and
therefore for a great part of their life are shut out from the surface, do we find highly
developed tracheal gills. Larvae from brackish water Ochlerotatus caspius, 0. detritus
seem regularly to have very short, button-shaped tracheal gills.

As plancton-eaters the surface-dwellers must possess large, fanshaped organs,
by means of which water currents, which carry the organisms and detritus into
the mouth, are produced; this extremely fine material must further be caught by
organs which are so constructed that the same water currents do not release it
again. On the other hand the material is triturated to such a degree that a further
subdivision is almost unnecessary; we therefore find that in the surface dwellers
(Culiceta morsitans, Culex pipiens, nigritulus) the flabellae of the labrum, the fringe of
the mandibulae, and the apical hair-tufts of the maxillae are all highly developed,
whereas the triturating part of the mandibles is always feebly developed.

On the other hand, in the bottom feeders, the material destined for nutriment
is not suspended in the water layers, but of a much coarser solid condition, and
must be scraped off from solid bodies and not, like suspended material, be whirled
into the mouth; in accordance with that we find feebly developed flabellae, with
many of the hairs transformed into comb-bristles which we only rarely find
developed in the surface dwellers; the fringes of the mandibulae are more slightly
developed, and the hair-tufts on the maxillae may be wrholly absent (T. annulata).
On the other hand the inner edges of the mandibles are provided with strong
thorns which may be dentated, and the triturating part of the mandibles is very strong.

With regard to the main organ of locomotion, the great swimming brushes,
it would seem upon more superficial consideration, that this organ has not been
influenced by the different mode of life in the two groups ; still it must be pointed out
that some of those larvae which are very sluggish and live in extremely small water
masses, such as F. geniculata or the great group Sabethini, have either very few hairs
in the tufts of the swimming fan (F. geniculata only two) or totally lack the ventral
fan (Sabethini). In many of the bottom feeders, f. i. T. annulata, we find a highly
developed fan with a large number of hairs in the tuft (about fifteen).

Finally it may be pointed out that in the Danish fauna we always find the larvae
with the longest siphones among the surface dwellers, and those with the shortest
among the bottom dwellers; further that pecten and comb in the surface dwellers
differ very much from those of the bottom dwellers; as we are however quite un-
able to understand these structures, we cannot further comment on, though we are
forced to pay attention to, these facts.

On the other hand it must be taken for granted that there is a connection

4*

28

between life conditions and larvae structures on yet another point. In the bottom
dwellers we find a remarkable development of special hairs on the apical part of
the sipho which are either missing or only but slightly developed in the surface
dwellers. These hairs play a certain role in the life of the bottom dwellers, providing
them with points of support when they rest on the bottom with the dorsum down-
wards, or hang down from water plants.

b. The pupa.

It is a well-known fact that the pupa stage of the insects is mainly a resting-
stage. In total repose, without any supply of food and often in darkness, the great
alterations in external and internal anatomical structures are now to be accom-
plished. The power of locomotion in the pupa stage is therefore commonly very
greatly restricted. Many pupae are known to be quite unable to change their place.
Some of them, more especially those wrhich live in water, are able to make
respiratory movements, oscillations with the abdomen (pupae of Chironomidce a. o.).
The real power of changing locality is, if present, commonly restricted to the last
days of the pupa life. At this time these pupae push themselves out of their holes
and corridors to be as near as possible to the air and the sun when the last ec-
dysis takes place.

In the Culicidce we apparently find the most movable pupae stages known in
the whole animal kingdom. Strong power of locomotion demands a supply of food ;
it might therefore be expected that the mosquito pupae would be able to take food;
this is however not the case. The appendages of the head and thorax of the future
fly is wholly enclosed in a common chitinous covering. This apparent physio-
logical contradiction is in accordance with two facts which probably have not
hitherto been sufficiently estimated. Firstly the pupa stage is extremely short; in the
tropics there are species e. g. Psorophora which, according to HOWARD, DYAR and
KNAB, pass the pupa stage in a shorter time than one day, and even in our lati-
tudes it does not regularly last more than a few days. In periods of very cold and
rainy weather the pupa stage can be prolonged beyond a week or more, but this
is against the rule. Only once have I in my laboratory seen the pupa stage pro-
longed beyond three weeks; these pupae belonged to the last broods of C. pipiens,
taken as larva? into the laboratory on October the fifth; pupae arriving on October
the tenth, lived even on the fifth of November; a few reached the imago stage, but
the others died. The temperature of the room was not more than 10° C. and for a
week always less than 5° C.

Leaving a more thorough description of the mode of locomotion for a later
paragraph, we will here restrict ourselves to the following remarks. It may gener-
ally be maintained that we have highly overrated the power of locomotion.

HOWARD, DYAR and KNAB (1912 p. 98) write as follows: "The pupa is active
and capable of moving rapidly through the water" further: "The pupa is very easily
alarmed and at the appearance of a shadow or at a slight disturbance of the water,

29

it immediately darts towards the bottom". The statements are in accordance with
the common opinion and contain also what can be termed half of the truth, but
the thesis gives no expression to the other half.

It must be remembered that the mosquitoes pass from larvae to pupae imme-
diately below the surface, live their whole life as pupse in the same locality, and
even pass the last ecdysis from pupae to imagines in the very same place. As far
as I know this is not the case with any other insects but the mosquitoes.

If we keep mosquito pupae in aquaria, it can be shown that voluntarily they
never leave the point of support which they have once acquired, that is to say: if
the acquarium is never moved and if it always stands in the shade. I have in my
aquaria reared imagines from pupae which most probably have never made a single
somersault movement. I suppose that even in Nature it may happen that many pupae
moult without having made more than very few movements.

If we observe a pond where almost the whole swarm rests as pupae in the
surface, we see, in fact, that the single individual moves very little and that there
are long pauses wrhen we see no movement at all. Only two alterations in the
surrounding medium: different light reflexes and disturbing agencies of the water
layers, are able to make the pupae release their hold and alter their place below the
surface. The light reflexes are especially brought about by sunbeams which suddenly
strike the surface of the pond from a cloudy sky. As highly phototactic the pupae
often arrange themselves after a line, corresponding with the edges of the sunbeams
in relation to the shadow. The pupae are directed by their highly developed com-
pound eyes which do undoubtedly function, a remarkable feature by which the
mosquito pupae diverge from most insect pupae.

The disturbing agencies are mainly heavy raindrops, the circles of which pro-
duce a curious influence upon the swarm, and enemies of the pupae; of these they
have mainly three kinds. The Hydrometridce pounce upon the pupse from above
and insert their rostrum in the cephalothorax. It is very remarkable to observe how
numerously the Hydrometridce appear upon ponds where most of the swarms have
been altered into pupae; how suddenly they appear, and how suddenly they dis-
appear again as soon as the pupae have been hatched. From below the pupae are
preyed upon by Notonectidce and the larvae of various Dytiscidce, more especially by those
belonging to the genus Rhantus which are always found in great numbers in mos-
quito ponds; it seems as if their whole existence is dependent on mosquito larvae
and pupae, their whole development coinciding with the development of the mos-
quito larvae; this coincidence is adjusted to such a degree that the Dytiscid larvae
and mosquito larvae follow each other with regard to the single ecdysis; it is a
very curious picture to see the Dytiscid larvae, black with white venters, on a morning
when the total number of mosquitoes in an almost dry pond have suddenly
left the water, cross the water-masses like sharks in search of that prey which
they were deprived of almost at once, and which even on the foregoing day was

30

found in enormous masses. Then the larvae have only one thing to do: to dig
their holes near the borders of the pond and pupate.

It is further of interest to see how the larvae of a pond which belong to the same
species almost all follow each other with regard to the rate of development. In
periods of cold rainy weather the larvae can be forced towards their last ecdysis
and then stop in their further development, awaiting the days when the tempera-
ture is higher, when it is bright sunshine and calm weather. When such days
come, suddenly the whole bulk of larvae are transformed into pupae in the course

Textfig. 1. My mosquito cultures.

Textfig. 2. My mosquito cages.

of only a very few hours. When at nine o'clock in the morning I have passed
one of my experimental ponds, I have often found several larvae; when at twelve
o'clock I passed the pond again, the majority of the larvae had been transformed
into pupae. More than once when I have taken material from such a pond, in which
there still remained plenty of unaltered larvae, it proved that these larvae belonged
to another species whose temperature of transformation lay at a higher point than
that of those first transformed. This has more especially been the case with the
larvae of the two species 0. communis and 0. cantans, the latter species being always
about one or two weeks later than the former.

Now when we remember that the whole period of life which the mosquitoes pass
in the pupa stage is normally restricted to a few days, and in the tropics often to

31

some hours, and if we remember that the power of locomotion is only used when
reflexes of quite a definite kind are released according to definite variations in the
surrounding medium, it will be understood that the postulate, that the above-named
paragraph in HOWARD, DYAR and KNAB only contains half of the truth, is really
correct. The pupae are able to move, but commonly they do not for the whole
period of their life actively use this power. They are much more stationary than
one would think; as stated above, this more especially holds good for the last day
before ecdysis, the pupae being then almost glued to the surface.

If we will try to understand the peculiar pupa stage of the mosquitoes, we
must compare it with similar stages in the water insects ; it will then be clear, that
the pupa is constructed in accordance with the purposes which at all events we
are not accustomed to put in the first line, when we discuss the peculiar shape
and mode of life of these pupae.

If we survey all those aquatic insects which are going to perform the last ec-
dysis in the water before leaving this element for ever, we shall see that, just at the
time when the last ecdysis is to take place, there appear organs of quite a new
type; further we find old organs which are now modified in such a way that it is
clearly understood that they have only significance at the moment when the insects
leave the water; nay, in several groups of insects we find even more than that,
either peculiar biological phenomena or quite new developmental stages intercalated
between the old well-known stages.

In all those aquatic insects which leave the water as larvae, climbing on shores,
we find none of these peculiar structures and phenomena. We may only note that
some of the Perlidce crawl out of the water, throw their whole anterior part of the
alimentary canal out of the mouth, fasten it to stones to which it is glued, now
using this organ in this quite uncustomary manner as a cable by means of which
they crawl out of the nympha skin. Other Perlidce use their larval gills as glutin-
ating organs, by means of which these insects are fastened at the same moment
for the same purpose to the slippery stones.

A second group of aquatic insects live as nymphs or as pupae in the water
and complete their last ecdysis upon the surface of the water; to these belong the
Ephemeridce, the Trichoptera and some Diptera (Chironomidce). As a transition stage
between the aquatic and aerial life we find in the Ephemeridce intercalated the highly
peculiar subimago stage. In this stage, which only lasts for some hours or, rarely, for
a few days, the legs and nervatures of the wings are often covered by a coating of
minute thorns which hinder the wings from getting wet; a remarkable oily appea-
rance, f. i. on the wings of Ephemera danica, has the same purpose. These struc-
tures are undoubtedly inconvenient when the wings are used as flying organs
during the mating processes and egg-laying phenomena. Lying in my boat on
calm summer evenings, I have seen the large Ephemera danica nymphs rise to the
surface from a depth of from four to five meters ; with undulating movements of the
abdomen they lie for a few seconds below the surface-film fastened to it by the out-

32

spread tracheal gills and peculiar thorns upon the dorsal side of the abdomen.
Then the skin bursts and in the course of a second the subimago stands upon the
surface, whereupon it takes wing and reaches the coast. A few hours later the
subimago undergoes a new ecdysis, and the aerial wings appear, hyaline and
without thorns.

I am inclined to suppose that even many naturalists are unacquainted with
the fact that the Trichoptera pupae, after a resting stage in the closed and fastened
larva cages on the bottom of the water, are free-swimming organisms for a short
time of their life; as such, without using air in any way, they actively ascend to
the surface; the swimming apparatus is the second pair of legs, furnished with a
brush of long swimming hairs; at the very moment the surface is reached,
the tracheal gills, the lateral line of long hairs round the abdomen are thrown out
upon the surface; partly by means of these organs, partly by peculiar thorns and
plates on the dorsal side of the abdomen, the pupa is now fastened to the surface
and supported by the surface film. In this position the cuticula bursts in the middle
line over the thorax; its lateral parts are, just as in many Ephemeridce and Culi-
cidce pupae, spread out upon the surface; a swimming bridge, a point of support is
thus gained; by means of reception of air the imago pushes itself out of the
skin, using the broad outspread thoracic plate as a support for the legs; some of
these pupae (Leptoceridce, f. i. Mystacides a. o.) ascend vertically from the bottom at
such an almost incredible speed that they only use their legs for three or four
strokes; the moment they arrive at the surface, the skin bursts with an audible
sound, and the imago is almost hurled out of the skin into the air, where it
immediately takes to its wings. In these species the free-living pupa stage is almost
incredibly short, the time from the moment it leaves the pupa-case till it is, so to
speak, thrown into the air as a flying insect, may be counted in seconds. But even
in these few seconds of life a swimming apparatus is necessary, and just and only
for that purpose and, as far as we can see, for these three or four strokes of the
middle legs, these legs are formed as swimming legs with broad tibia and brushes
of long soft hairs.

The Chironomidce from the bottom of our deepest lakes act almost in the
same manner; there is only this difference that the pupae do not reach the sur-
face by active motions, but ascend passively and perpendicularly to the surface by
means of air formed between the pupa- and imago skins ; here they occupy a hori-
zontal position; the thorax bursts and the mosquito creeps out and stands for a
moment upon the outfolded pupal thoracic skin. Lying in a boat on calm sum-
mer evenings I have heard a sound of bursting bubbles round the boat, and
convinced myself that it originated from the bursting pupal skins when the air
escaped.

To this same group of water insects which complete their last ecdysis upon the
surface of the water belong also the Culicidce; from the Ephemeridce Trichoptera and

33

Chironomidce they differ only in so far that the pupse do not ascend from the bottom
of the water but live their whole life fastened to the surface -film.

There is yet a third group which are hatched as imagines at the bottom of
the water and as such ascend through the water layers to the surface ; to these belong
the Simuliidce and the few aquatic Lepidoptera. The Simuliidce use the air from the
pupal tracheal system as air-bubbles wrapped up in which they ascend as
imagines to the surface with an extraordinary rapidity. The moment this is reached
the bubble bursts, the fly stands dry upon the waves, whereupon it takes to
its wings.

The few Lepidoptera which undergo the last metamorphosis in the water, also use
an air-bubble by means of which they reach the surface; but these insects are
not wrapped up in this bubble; they only hold it between the wings and thorax
in a manner similar to that in which the bubble is held by the Culicid pupse.
Moreover the whole body of the butterfly, at the moment it leaves the pupa
case, is covered by a wax-like substance which prevents the body from getting wet
and which for a moment remains as a column in the water after the butterfly has
left the water. All the above-named structures and biological phenomena, appearing
in the aquatic insects on the threshold between aquatic and aerial life: the peculiar
fastening of the alimentary canal in Perlida", the subimago stage in the Ephemeridce;
the free swimming part of the pupa life of the Trichoptera with the peculiar modifi-
cation of the second pair of legs; the store of air in the pupa of Chironomidce, the
air-bubble of Simuliidce and Lepidoptera, and the wax covering of the last-named
insects are in my opinion all phenomena which tend to the same purpose: to carry
the insects rapidly and in dry condition up into the new element. Just this perfectly
dry condition, more especially with regard to the wings, is a conditio sine qua non
for all the insects which are unable to change element if the wings are wet.

It is from this point of view that the peculiar free-swimming pupa stage
of the Culicidce must be interpreted. Like all other pupae the mosquitoes in the
pupa stage are quite defenceless; in contradistinction to most other insects which
at this very stage hide themselves, the pupse of the mosquitoes live in quite the
same localities as the larvse, exposed to quite the same dangers. The pupa is
therefore adapted to escape from these dangers by means of active motions, but
as the pupa stage is simultaneously a resting stage in which the great alterations
from larvse to imago are to take place, the power of active motion is only used if
dangers appear or in search of water with the highest temperature. Otherwise the
pupse are at rest, and the stage is also used by these insects as a real resting-stage.
As however the pupse even as such are to pass their lives in an element which
is hardly ever perfectly calm, a series of peculiar physiological and anatomical
structures must be formed, by means of which the pupse even in a locality so mo-
bile as the surface of the ponds can be fastened to the spot where they have once
got hold.

We shall now study the power of locomotion of the mosquito pupa a little

D. K. D. Vidensk. Selsk. Skr., naturvidensk. og mathem. Afd. 8. Rsekke, VII, 1.

34

more closely. It will then be seen that it is really of a very peculiar kind. As
briefly mentioned above and often pointed out by earlier authors, it must firstly
be remembered that the specific gravity of the pupae in contradistinction to that of
the larvae is smaller than that of the surrounding medium. They are always super-
compensated, more especially as they approach the last ecdysis; this is due to secre-
tion of air beneath the pupa skin (silvery gloss). By means of this supercompensa-
tion the pupae are pressed against the surface, this being their natural plane
of support, just as the bottom of the ponds is the support of all undercompensated
animals.

The supercompensation is due to a large air globule, already mentioned by
MEINERT as "Flydekugle" (1886 p. 389) but more thoroughly described by HURST
(1890). The air-globule comes from the air in the tracheal system of the larva.
In a manner not hitherto thoroughly studied, it is carried down between the wing-
sheaths and legs of the pupa, being in connection with the trachealsystem of the
pupa through two large spiracles. As mentioned by HURST the air globule has
probably mainly a hydrostatic function (p. 7), but also serves to keep the pupa
afloat in a particular position, with the thorax uppermost and the apertures of
the trumpets at the surface of the water; further, to enable it to ascend to the surface
passively in a vertical direction and with the broad cephalo-thorax lying horizontally.

The supercompensation is however so great that it would force the pupa out
of the water, on to the surface, if it were not counterbalanced by other forces. If
the pupa, after one of its somersault-movements downwards, again passively ascends
to the surface, the motion always takes place along a vertical line; the animal
is always directed in such a wray that the broad cephalo-thorax turns upwards;
reaching the surface the pupa will always touch it with four points lying above the
rest of the body, viz. the edges of the openings of the trumpets, and the two
stellate hairs on the first abdominal segment. By .means of these four points the
body is fastened to the surface and prevented by the surface film, from being forced
out of the water.

The pupa never voluntarily leaves its place below the surface unless forced
either by light reflexes or by currents in or upon the waters, produced by enemies.
More especially in the last hours before ecdysis, the pupa is almost glued to the
surface film, being supercompensated to so high a degree that its power of loco-
motion is too slight to take it downwards.

Otherwise, if variations in the surrounding medium force the pupa away from
its resting place, active motions set in. These are really very peculiar. They are
restricted to a series of downward-directed somersaults, but whether these somer-
saults are to conduct them to the left, to the right, or vertically downwards, the
pupae are not able to determine; they cannot direct their motions, being un-
able to produce any steering motion in any direction; they are only able to dart
away from the point to which they were fastened. The moment the activity ceases,
the pupae rise following vertical lines as do air-bubbles to the surface.

35

No one can observe a mosquito pupa without being struck by the peculiar
disproportion between the bulky cephalo-thorax mass and the slender abdomen; it
is upon this incongruity that the peculiar somersault motion depends. When the ec-
dysis is going to take place, the thorax splits in the middle line, the large sides of
the chephalo-thorax are clapped downwards and now rest upon the surface of. the
water; they thus form a swimming point of support upon which the imago may
rest during the ecclosion and a few minutes immediately after. The actual process
of ecclosion of the imago \vill not be mentioned here; with regard to that point I
refer to the excellent paper by EYSELL (1913 p. 320).

In the above I have tried to elucidate some points in the biology and anatomy of
the mosquito pupa. Its many peculiar anatomical structures: its highly remarkable
form, the air-globules belowr the wing-sheaths, the use of the tips of the trumpets as
points of support, the stellate hairs, combined with the short life-time of the stage
and the peculiar manner of motion may all be regarded as adaptations directed
towards the same great general end : to bring the imago as soon as possible and in dry
condition out of the water. The common significance of the pupa stage of insects : that
of being a stage of repose, has in the pupa stage of the mosquitoes been subordinated
to this purpose; it is the life as free-swimming organisms exposed to dangers of
every kind, very different from the common pupa life of insects, which has made
this subordination necessary. It is often very difficult to distinguish the species from
each other in those immature stages which have the shortest existence. In the
development of the mosquitoes the pupa-stage, as is the case with other insects, is
the shortest. It is a well-knowrn fact that it is almost quite impossible to distinguish
the species in this stage; even species which belong to different subfamilies: Ano-
phelines and Culicines, are extremely alike in the pupa stage. This has also been
pointed out by HOWARD, DYAR and KNAB (1912 p. 103). These authors remark that
there really are some striking differences between the pupae, of the two tribes Culi-
cini and Sabethini; further, that there are some differences in the shape and length
of the trumpets and of the paddles. The greatest diversity may probably be found
in the number and arrangement of the setse on different parts of the body; by
this structure MEIJERE (1911 p. 1146) has tried to distinguish the pupa? of C. morsitans,
Theobaldi, C. cantans and communis but, as far as I can see, without any result. I
have been unable to detect real differences between the pupae of the Danish species.
The very large pupae of C. annulatus and C. morsitans can, if they appear in the
swarms of C. communis, be distinguished only by their size. With regard to the
pupae of Tceniorhynchus I refer the reader to that genus.

5*

36

Chapter II.

The Danish Culicines Systematically and Biologically Described.

Genus I. Aedes.
Tab I.

1. A. cinereus Meig.

A. cinereus occurs in North and Central Europe. Over this area it may easily
be recognised among all other mosquitoes more especially in the male sex, the palpi of
which are not longer than those of the female; but also the female is easily recognis-
able, especially owing to its minute size, the black colour of its abdomen, and the
rusty brown or reddish colour of the thorax. In the male sex the thorax is black.

The species varies a good deal with regard to colour; several species have
been established upon these variations (A. obscurus Meig., rufus Gimmerthal, leucopygos
Eysell) which now are regarded as synonyms for the species. With regard to the
dentition of the ungues the reports differ greatly. KERTESZ (according to SCHNEIDER)
indicates that the hind ungues of the females are uniserrate, THEOBALD (1907 p. 539)
that the ungues of the female are equal, simple and not uniserrate; GRUNBERG (1910
p. 90) the same.

EYSELL (according to SCHNEIDER) GOETGHEBUHR (1910 p. 86) (EDWARDS 1912
p. 261) and SCHNEIDER (1914 p. 24) state that the ungues of the female on all legs
are uniserrate and the latter author gives a figure of the claws. He gives the follow-
ing formula ? 1.1 — 1.1 — 1.1. c? 1.0 — 1.0 — 1.1. With regard to the Danish specimens
I have got quite the same result as the latter author.

Larva. Head rounded, wider than long; a notch at insertion of antennae ; front
margin arcuate. Antennae rather long, tapering at front, spinose; tuft moderate, in-
serted nearer to the base than to the apex; on apex three hairs and a digit. An-
tennal tuft multiple; frontal hairs long; lower and upper frontal tuft multiple with
six or seven hairs. Eyes large.

Thorax long, rounded, angled at hair-tufts. Hair formula of frontal margin
321100001123. No real hairs upon frontal margin, only two extremely small tufts
consisting of from two to five hairs; the other nearer the lateral margin strong.
Lateral hairs in multiple tufts; some single, strong hairs.

Abdominal segments narrow, almost equally long.- Lateral tufts of first segment
with four hairs, second with two, third to seventh with one single hair; subdorsal
hairs: a series of very short hairs between lateral tufts. Tufts of eighth segment in
common arrangement, the dorsal tuft double. Lateral comb only consisting of about
twelve to fifteen scales, commonly arranged in a row, each scale with a spatulated
base, very long, without median spine, but feathered along the borders. Sipho long,
four times longer than broad, tapering a little at apex; pecten very long, reaching
over the middle of the sipho, consisting of about twelve to fourteen thorns; the

37

thorns, more especially those nearest to the apex, not being in line; these thorns at
greater distance from each other than the following; the thorns of the middle part
of the pecten with one single tooth. Anal segment much longer than wide, almost
ringed by a plate. The dorsal tuft with two long hairs; the ventral brush in the
barred area with about ten rays, carrying from five to seven hairs; before the
barred area two small free tufts; lateral tuft consisting of a single hair; anal gills
very long, acute, equal.

Lateral tufts of labrum long, distinctly divided into two parts, but without
comb teeth; palatum covered with very long hairs. Mandibles quadrangular with
two strong spines and a shorter one before collar; a row of long cilia from a col-
lar. About ten long thorn-like bristles; before them a dagger-like thinner thorn;
a few long feathered cilia below; process below indistinctly furcate with strong
hair-tufts; a group of hair at base. Maxillae elliptical, divided by a suture; at apex
a brush of long hairs; a seta near the apex beyond the brush; near the inner
margin between it and the suture a coating of long hairs and at the margin a series
of long stiff thorns; palpe rather small with three digits. Mentum high, triangular,
without any conspicuous median tooth and with fourteen to sixteen teeth on each side.

Colour almost white or yellowish white, head black and sipho and plate of
anal segment yellow. Length 6'5 m.

The description and figures of the larva agreed well with those of MEIJERE
(1911 p. 148), his description being one of the most accurate of the hitherto published
of European mosquito larvae. The larva has probably been observed by GALLI VA-
LERIO in Svitzerland (1907). He has not however given any description of it; he
only says: "Die Larven sehen denen von Culex pipiens zum Verwechseln ahnlich;
sie haben denselben langen charachteristischen Atmungsfortsatz und die gleiche
Haltung; die Analdruzen (i. e. anal gills) sind etwas langer und schlanker und viel
durchscheinender. Die Farbe der Larve ist ein belles Gelbbraun und lasst sich leicht
gegen den dunklen Grund erkennen; wahrend die starker pigmentierten Larven von
C. nemorosns und anmilipes sich den Blicken vollkommen zu entziehen wissen".
Further it has been described by SCHNEIDER from Bonn. The rather short descrip-
tion agrees well with MEIJERES and mine. In 1919 it has been briefly described
from Strassbourg (ECKSTEIN 1919 p. 294).

Biology. Aedes cinerens is a little mosquito, which STAEGER has mentioned
as rare in Denmark. As far as I know, nobody has found it later in this country.
In the days from 23/y to 2/vi 1918 A. cinereus was found flying over different
small ponds in North Seeland; the ponds were all almost quite dry, only containing
a few litres of water; about 15/vi they were dried out. On Vvi 1918 I found the species
in enormous swarms over the vast meadows at Lyngby on the southern coast of
Arrese. The above-named ponds were dry until 15/x and were icecovered almost
the whole time from about Vi 1919 to Viv 1919. In the time from 15/x to 1/1 the
ponds contained no A. cinereus larvae. Being interested in finding the larva I explored,
in 1919, the localities where the imagines were found in 1918. On the meadows at

38

Arreso I never found the larva, but with regard to the above-named ponds (Mo-
chlonyx-pond I), the Bidens-ponds at Clausen's brick-factory and the ponds in
Stenholtsvang I had better luck. In the time from 20/v to 31/y I found a very
little larva here, at once recognisable as something peculiar by its almost black
head and white abdomen. The larva grew no larger, and on 3l/v A. cinereus was
hatched. About 20/Vi all the ponds were dry; none of them got water again 'before
the last fortnight of October. On 20/y, when the larvae were found, the depth of the
ponds was only about a decim. In the last part of June 1919 I saw very little of
the imago, but on my return to Hillerod in September I found the imago in enor-
mous swarms over the same ponds where they were hatched in the spring. Large tufts
of Cyperacece covered the ponds, which were wholly dry; sitting on one of the tufts
in hope of observations relating to the egg-laying process of 0. cantans, I found
my hand covered with a number of these very small vampires. They were deep
down in the Cyperacee-tufts, crawled more than they flew; after having sucked
themselves so full that they resembled little blood pearls, they were so thick and
so heavy that their power of flight was only very slight. Many of them which
were caught in my vessels, only crawled and did not try to fly. The sting was
almost imperceptible and they had great difficulty in getting blood, the skin being too
thick; afterwards, as my hands had got more than fifty punctures, it was covered
with a common purple colour and rather aching. On %/iv I only found a few
specimens but on lo/ix all had disappeared, and I did not see them any more this
year. In 1920 I got the larvae in the same ponds in May, and in July I found the
species on the island Lolland. The same observation which I had an opportunity of
making that year, I had made the year before at Arres0; the mosquitoes sit deep
down in the grass, and do not fly up before they are disturbed by some one
walking through the grass. They attack only that part of the body which is
moving through the grass, the legs, when walking, and the hands when they are
held down in it; this was the case in the brightest sunshine and in twilight about
7 o'clock. Especially in the forest it was very remarkable that I never saw them
flying; if I sat only a few meters from the pond, I was fiercely attacked by 0. can-
tans, but not by a single A. cinereus. Only when I placed myself in the centre of
the pond, on one of the tufts of Cyperaceae, the attack took place.

Having never been able to find the males in Nature, I have only observed
them in my hatching-cases. I have got the impression that this tiny mosquito
is much more bound to the ground than our other Culicidae. The difficulty with
which they got blood seems to indicate that blood can only be sucked from animals
with rather thin skin. I suppose that small rodents and insectivores are perhaps
their principal prey.

The life-history of A. cinereus is in our country most probably as follows: Males
and females die off before autumn; the males most probably already in June —
July; the larva stage is extremely short, only from eight to ten days; the pupa-
stage lasting normally only a few days; the species hibernates only as egg; the eggs

39

are hatched rather late, not before the last part of May; the pools, in which
they are hatched, are dried up a fortnight later; the eggs must therefore be laid
upon dry land and undoubtedly singly; most likely there is not time for more
than one generation; this generation has only one brood, and this brood lives for
three or four months.

In the literature the reports with regard to the life-history are very contradic-
tory; GALLI VALERIC and ROCHAZ DE JONGH in Switzerland maintain that they have
found hibernating single eggs, attached to fallen leaves in depressions of the ground
SCHNEIDER (1914 p. 28) and ECKSTEIN (1919j p. 68 19192 p. 100) state that the species
has probably "mehrere" generations in the course of the year. For Strassbourg
this is also highly probable but for our country this supposition is undoubtedly
wrong. SCHNEIDER says that he found the first larvae at Bonn on 1. March; they
were newly hatched and pupated already in the course of twelve or sixteen days ; the
first imagines arrived on 16. March. He has also found the larvae in the middle of
July, and this seems to prove the correctnes of his supposition. In our country
where the larvae do not appear before the last part of May, and the ponds nor-
mally are dried out before the end of June, more than one generation cannot be
the rule.

With regard to the blood-sucking process THEOBALD contradicts himself. In
1901 Vol.' II (p. 225) he implies that probably neither male nor female attack
animals or man "as a rule". This supposition is stated by FICALBI, who maintains
that they do not attack man or mammalia. On p. 235 in the same volume (1901)
THEOBALD says that A. cinereus (female) bites viciously. This last statement is in
accordance with that of all observers from recent years. EYSELL (according to
SCHNEIDER 1914 p. 26) maintains that it is very bloodthirsty and so does SCHNEIDER
(1914 p. 26). He has given a description of the attack of many specimens very
like my own. ECKSTEIN says with regard to the neigbourhood of Strassbourg that
it "tragt mit einem Hauptheil an der Stechmiickenplage". LANG (1920 p. 80) main-
tains "that the general situations, indicated in the British records, suggests that A.
cinereus mainly is a river-haunting species". This is by no means in accordance
with the observations in our country; it may be found in the forests, along the
shores of larger ponds and upon the open plains; I have never seen any special
predilection for river valleys.

Geographical distribution: known in almost all European countries. It
is probably identic with Aedes fuscus Osten Sacken North America.

Genus II. Ochlerotatus.
Tab. II.

1. O. caspius (Pallas).

Description. Female: Proboscis moderate, subcylindrical, uniform, labellae
conically tapered; vestiture of blackish-brown scales intermixed with a few creamy-

40

white; labellae dark; setae minute, curved, black. Palpi short, smaller than one-
fourth of the length of the proboscis; vestiture black, with a few white scales inter-
mixed, seta? moderate, black. Antennae moderate, with the joints subequal, rugose,
pilose, blackish, the second joint a little longer writh a yellow base; tori subspheri-
cal, with a cup-shaped excavation, bright brown, shaded with blackish scales; the
inner half covered with flat, sordid-white scales. Clypeus rounded-triangular, pro-
minent, blackish brown, nude. Eyes at all events on the newly hatched individuals
(in May — June) metallic green. Occiput rather broad, black, densely covered with
narrow curved coarse scales, nearly pure white in a broad median zone; brown
laterally and with a patch of flat, blackish ones on the sides; a series of black
bristles along the hind edge of the eyes and long, snowr-white bristles between them ;
on the occiput many erect, broad, and rather short white forked scales centrally,
a few black ones laterally.

Prothoracic lobes narrowly elliptical, remote dorsally, clothed with narrow
coarse brown scales at tip, whitish ones below and with short, brown bristles.
Colour of mesonotum extremely variable ; four main varieties.

1. Mesonotum black, densely clothed with coarse, narrow curved, dull-yellow-
ish scales, laterally golden-brown ones in a broad median stripe, horded by a
yellowish-white narrow stripe, running from anterior angles to near the root of wring;
scales pale in the region of antescutellar space.

2. Mesonotum brown, either densely clothed with coarse, narrow curved, dull
white scales over the whole surface or with a bright brown and usually narrow
median stripe.

3. Mesonotum covered with almost snow-white scales with an almost black,
narrow median line.

4. Mesonotum covered with almost snow-wrhite scales, with an almost black,
broad median line and laterally with two other black lines much shorter, only half
as long as the median line.

Bristles dark, brown or yellowish white. Scutellum trilobate, luteous, clothed
with coarse dull white scales, each lobe \vith a group of about twelve very pale
bristles. Postnotum elliptical, prominent, nude, brownish luteous. Pleurae and coxae
brownish, clothed with flat, white scales and pale bristles.

Abdomen: Subcylindrical, flattened, posterior segments tapering. Also the co-
lour of the abdomen extremely variable. The main form as follows: dorsal vestiture
of flat, sordid-white scales with two large patches of black ones on each segment,
the patches becoming smaller posteriorly and may be absent on last segment; first
segment almost white with many long white hairs; venter clothed with sordid-white
scales, a very narrow median broken line of black ones or row of rather large,
black spots; cerci black; setae mostly pale. Two colour variations are especially
common: 1. the whole dorsum of abdomen snow-white, only with small black,
divergent lines near the borders, most developed on segments two to six. 2. the wrhole
dorsum black, only with small basal bands of white scales.

41

Wings rather broad, hyaline, very irridiscent; petiole of second marginal cell
and second posterior cell both a little shorter than their cells; vestiture of black
and white scales; in some individuals almost all scales are white, in others the
black preponderate; outstanding scales narrowly lanceolate, both black and white;
fringe commonly grey, with white reflexions which give a mottled appearance.
Halteres yellowish with white-scaled knobs.

Legs rather slender; femora clothed with whitish scales, mixed with a few
black ones dorsally, these predominating at apex; extreme tip narrowly white; tibiae
with whitish scales with black ones intermixed and a small annulus before tip of
hind ones; tarsi black scaled, with a white ring at base and apex of each joint;
hind tarsi with the first joint also largely white scaled in the middle, the last joint
almost quite white; fore tarsi with apex of second and all of last three joints black;
mid tarsi with apex of third and all of last two joints black. Claw formula: 1.1—1.1—1.1.

Length: Body about 5 mm, wing 4 mm.

Male: Palpi exceeding the proboscis by nearly the length of the last joint,
which is somewhat swollen; vestiture blackish with white scales intermixed; end
of long joint and last two joints with long blackish or greyish hairs: Antennae
plumose; the last two joints long and pilose, the rest short, blackish at insertions
of hair- whorls; hairs long and dense, grey and black. Coloration similar to the
female, but the variation not so- great. Wings narrower than in the female, the
stems of the fork-cells a little longer, vestiture less abundant. Abdomen long de-
pressed with dense, pale, lateral cilia tion. Claw formula 2.1 — 1.1 — 1.1.

Length: Body about 6.5 mm.

Genitalia : Side-pieces more than twice as long as wide, apical lobe well devel-
oped, rounding, running uniformly down to base; basal lobe quadrate, protuberant,
clothed with short, coarse setae from tubercular bases, from its lower angle a stout
thick spine and a shorter one. Clasp-filament slender, long, slightly swollen medianly,
distally serrate and bearing several short setae, a long slender, articulated terminal
spine. Harpes rather narrow, concave, slightly curved, margins revolute, inner one
thickened, curved over at tip in a short point. Harpagones slender, columnar, uni-
form, with an articulated filament at apex, which is ligulate, a little expanded beyond
the middle and tapered to a point at tip, shaft with a few setae. Unci approximate
with revolute margins, forming a short stout cone. Basal appendages narrow, with
short stout spines at the tip.

Larva: Head rounded, rather small, wider than long; a notch at insertion of
antennae; front margin arcuate. Antennae short, slightly tapering at apex, spinose;
tuft inserrated only a little below the middle, small, consisting of about ten hairs.
At apex three hairs and two digits; two of the hairs a little below apex. Ante-an-
tennal tuft short, multiple; lower and upper frontal tuft with only one single hair;
the lower always, the upper rarely with two hairs. Eyes large.

Thorax wider than long, angled at hair-tufts; hair formula at frontal border
3121551213. Lateral hairs in multiple tufts and some single strong hairs. Tuft 5

D. K. D. Vidensk. Selsk. Skr., naturvidensk. og mathem. Afd. 8. R.-ekke, VII, 1. 6

42

with the hairs in different sizes and different numbers; from three to six, but five is the
most common number. Lateral hairs in multiple tufts and some single strong hairs.

Abdominal segments broad, almost equal, the first two a little shorter than
the others. Lateral hairs on the first segment with tufts in common arrangement.
Lateral comb consists of about twenty to twenty-five scales, arranged in rows,
covering a triangular area. The scales are spatulated, very broad with the median
thorn only a little longer than the two lateral ones.

Sipho short; about two or two and a half times longer than broad, slightly
tapering at apex; a long pecten reaching over half the length of the sipho; all thorns
at line, the first and last without thorns, the middle with from one to three, very
feeble thorns. A tuft of five hairs between end of pecten and apex. Anal segment almost
isodiametric, ringed by a remarkably small plate. Dorsal tufts well developed with twro
long stiff spines. Ventral brush in the barred area with about twelve rays, each ray
carrying about eight to ten hairs; before the barred area a few free tufts. A lateral
tuft consisting of one single, strong hair. Anal gills extremely short, budshaped.

Lateral tufts of labrum rather long, the inner part modified in comb-hairs, ar-
ranged as a crown round the palatum, which is bordered with long, soft hairs.
Mandibles quadrangular, elongate, spinose at base; two curved spines before a col-
lar and a row of strong spines (nine) from margin. Dentition five strong teeth and
before them a very long curved spine and a short dagger-like one; a remarkable
group of minute thorns at base; a few curved setae within and a row of long hairs
at base. Process below, distinctly furcate, with strong hairs at apices; a group of
hairs at base. Maxillae broader than long with rounded apex; divided by a suture,
furnished with two teeth-like processes. At apex a tuft of hairs and at the base of
the tuft one spine. The space between suture and margin covered with short hairs;
na spines from margin. Palpe well developed with three or four digits from apex:
Mentum high, triangular, no especially developed median tooth and from ten to
twelwe almost equally large, lateral teeth.

The skin of the abdominal segments covered with transversal series of minute thorns.

Colour greyish dark.

Systematical remarks: STAGER (1838 p. 554) has only found this species
on the shores of the island Amager near Copenhagen. He states that it is "not rare"
in the months of June and September; in August he has found the larva in
countless numbers in small water reservoirs along the coast line of Amager. It was
described as C. dorsalis Meig.

In 1917 HOWARD, DYAR and KNAB (p. 634) reported that they have had speci-
mens from the Zool. Museum in Copenhagen and compared them with the two
American species Aedts onondagensis and A. Curriei. These two species are identical
as imagines, but as larvae they differ from each other; the first-named species have
both pairs of dorsal head-hairs single, whereas in A. Curriei they are multiple; there are
also differences with regard to the structure of the skin and the anal gills. Moreover,
of the two American species, A. onondagensis breeds in brackish water along the

43

sea-coast, curriei breeds in temporary pools of snow-water or rain-water on the
prairies. The American authors suppose, as MEIGENS specimens of C. dorsalis derive
from Berlin (freshwater), and subsequent authors (STAGER, MEINERT, THEOBALD a. o.),
state that it breeds in brackish water, that also in Europe we possess two species,
the relations of which cannot be cleared up before the larvae have been studied.

C. dorsalis was described by MEIGEN, but already in 1771 PALLAS described
a species from the Caspian which is most probably identic with the above-named;
it has been deemed necessary to revive the ancient name O. caspius. As C. dorsalis
it has been indicated by STAGER in Denmark, by ZETTERSTEDT in Sweden, by
SCHINER in Austria, bei VAN DER WULP in Holland and by FICALBI in Italy;
it was last found by ECKSTEIN near Strassbourg. The Danish specimens are much
more in accordance with the description of MEIGEN and ZETTERSTEDT than with
the later one by THEOBALD. The larva has only been described by ECKSTEIN
(1919 p. 293). He says that the larva very much resembles that of C. nemorosus
and C. cantans. "Die Striegelborsten am 8 Segment, etwa 25, haben ebenso wie die
der C. nemorosus-Larva lauter fast gleichlange Zahnchen, doch ist der mittlere
meist ein wenig verdickt. Dagegen fehlt ihnen das Basalblattchen das fur C. nemo-
rosa so characteristisch ist".

With regard to the biology of the European C. dorsalis we do not know much.
PIFFARD (1895 p. 227) states that at Aldeburgh on the Suffolk coast it is known
as the Norway mosquito, having lived here for at least the last twenty-five years.
"A tradition" says PIFFARD "assigns its introduction to a particular yacht, which
used to ply between this port and Norway". Also in Sweden (Lund-Lomma) and
in Norway (Christiania) as well as in Denmark it is restricted to brackish-water
pools near the sea-shore. Later on, in a paper which I have not been able to con-
sult, DYAR and KNAB (Insec. Inscit.'1917 p. 122) have maintained that the descrip-
tion of 0. curriei larva in the monograph (Howard, Dyar and Knab) was founded
on a misidentified species of 0. canadensis. The correct description of the species is
under onondagensis (ace. to letter from Mr. Edwards 22/4 1920). As the American
authors, as stated above, have got material of O. caspius from the Royal Museum
of Copenhagen (1917 p. 634), and all this material derived from Amager, they have
determined the specimens from this locality, where the species still lives, as 0. cas-
pius; later on EDWARDS has done the same. According to me this material is homo-
genous, but on the authority of Mr. EDWARDS and in accordance with him and Mr.
LANG I have separated the specimens with thorax without brown coloration and
with broad white bands on mesothorax from 0. caspius as 0. curriei (Coquillet).
Of the American species, which seem to be either identic with the two above-named
European species or at all events very closely related to them, A. onondagensis lives
as larva on the flat marshes of the Pacific coast in pools of salt water, left by high
tides: a set of larvae appear after each high tide. QUAYLE (H. D. K. 1917 p. 632)
has given a description of their life. A. curriei inhabits the open arid country; the
larvse live in temporary pools. In the north there is but a single annual generation

6*

iii the snow-water of early spring. Southward the appearance of the larvae is govern-
ed by the formation of pools by heavy rains and consequently occurs at irregular
intervals. It has especially been studied by KNAB at Saskatchevan with other mos-
quitoes of the large prairies (1908 p. 540).

Biology. For a long time it has been a well-known fact that countless mos-
quito-masses are a real plague to all the suburbs of Copenhagen, especially those
lying near Kalvebodstrand, the strait between Copenhagen and Amager; one of these
suburbs, Valby, has given the mosquitoes of this district their name, they have
been called the Valby mosquitoes; they appear almost every year, more especi-
ally at the beginning of August; later on they spread over Copenhagen, being most
common in the large park Frederiksberg-garden, the Royal Garden, at Lange Linie
and northwards along the shores of the Sound. These mosquitoes belong almost
entirely to one and the same species 0. caspius. Curiously enough they have hitherto
only been found in the vicinity of Copenhagen, and it has hitherto not even among
zoologists been a well-known fact that Copenhagen had its own special mosquito,
hitherto only found in it and in its neighbourhood; indeed we also find C- pipiens
and T. annulata, but these two species do not, as far as I know, attack people, at
all events not like the above-named species; a few specimens of 0. communis,
lutescens and canlans may be found in the parks, but they are of no great conse-
quence. - - It was of course most natural to search for the hatching areas of 0. caspius
in the old locality of Amager where STAGER had found them almost a century ago.
As I wished to make a special study of our brackish-water mosquitoes and my
time was too much occupied with other mosquito-work, I asked Mr. KRYGER in
1920 to explore the brackish water coast of Amager and Seeland from Copenhagen
and southwards towards the bay of Kj0ge at regular intervals in the time from
medio Marsh to September. In the time from 24/m to 8/vn he made twenty ex-
cursions at regular intervals; then he was on a journey in Jutland from 8/Vn to
l/vin and in the time from 2/Vm to 2<Vix five excursions were undertaken. From
every excursion he brought living material to my laboratory, and thousands of
specimens were hatched in the hatching cages.

Most of the explored area belongs to the Amager common lying between Kalve-
bodstrand and the little village of Taarnby; it is used by the soldiers for gunpractice,
and is now therefore rather difficult to use for study of nature. The whole country
is extremely flat, the height over the sea leavel being only a few feet; formerly the
sea often covered the whole area and after heavy showers, especially in spring, it is
even nowadays changed into an almost inundated area which is difficult to cross.
From the plain it is now separated by a dike along which a channel runs land-
wards. Between the dike and the sea numerous brackish water pools are to be
found; on the other side, scattered over the flat ground, countless small holes may be
seen. After June the whole plain is commonly quite dry, and cattle and horses are
driven over the rich meadows. The area between the dike which prevents the sea
from inundating the plain, is filled with brackish water pools; after June commonly

45

wholly dry ; the pools are however often filled with brackish water which is stagnant
for months in winter and spring, but soon evaporates in summer. In rainy sum-
mers the pools hold the water for a shorter or longer time.

In autumn again most of the pools are often red from pur-pie sulphuric bacteria
and are bordered by Scirpus maritimus, Aster tripolium a. o. plants. At certain periods
they contain thick layers of green algse, and it is only in those pools, the bottom
of which are covered with a layer of algse in decomposition, that we find the huge
masses of larvae. The above-named dike forms a very distinct border-line between
the mosquito fauna of the area; landwrards in the numerous drying ponds enorm-
ous swarms of 0. communis are hatched. The first larvae were found on 24/ni; they
pupated and were hatched as imagines in the time from 21/jy to Vv. The whole
area was inundated and almost impossible to cross. As the water fell again clouds
of 0. lutescens appeared, and a very few belated larvae were found on 9/vi. jn fae
last part of May and in the first part of June 0. lutescens has most probably popu-
lated the numerous ditches. As 0. rusticus was found in the last part of May as a
regular tormentor on stretches bordering the meadows, it is probable that some of
the holes have been hatching localities for this species.

Outside the dike between it and the sea no larvae of mosquitoes were found
during the whole of April and first part of May; in the brackish water pools Nereis
diuersicolor, Crangon vulgaris, and other marine animals were common, but always
in company with Corixce, various Hydrophilidce and Dytiscidce. On 26/v mosquito
larvae were for the first time pointed out in these ditches; in the samples were
enormous amounts of newly-hatched larvae, some halfgrown larvae but no full
grown ones; most probably the hatching process was not more than a week old.
Already by 12/vi many of the pools were dried up, and by 16/vi all pools were wholly
dry. In the time from 26/v to about 15/vi, i. e. about three weeks, enormous masses of
0. caspius were hatched; in the material also appeared the supposed 0. curriei, but
I was never able to find any differences in the larva material, though many thou-
sands of larvae have passed under the binoculary microscope; once only I also
found a larva of 0. lutescens, and on the coast of Sealand nearer to human dwellings
larvae of C. pipiens and of a few T. annulala often appeared. In the two first weeks
of June numerous 0. caspius were sitting in the grass round the holes; in the last
part of June they left the locality and began their attack nearer the town where
we in the evening, were attacked by them, 0. lutescens and rusticus.

In the time from 16/vi to 8/vii all pools were quite dry; then when Mr. KRY-
GER returned to the locality on 2/vm the pools were full again after the rainy
summer; they now contained incredible numbers of larvae, the water was black; again
the holes were visited, and in the last part of August the whole stock was hatched.
Again enormous masses of 0. caspius were hatched; in the last part of August they
were found nearer the human dwellings, and in the whole of September they tor-
mented the inhabitants of Copenhagen. In order to clear up the manner of hiberna-
tion I explored and got information from many buildings in the outer part of the

46

town. It was shown that 0. caspius was often' to be found in cellars etc. till the
last part of November and even the beginning of December. In the last part of the
winter it seemed as if the material had everywhere died out; only C. pipiens and
T. annulata were left.

Regarding it as almost certain that egglaying processes have taken place in
the last part of July and most probably also in September, there can be no doubt
upon the point that 0. caspius and most probably also 0. curriei, if this species
can be separated from 0. caspius, both have two broods, the one hatched in the
first half of June, the other in the last part of August. In summer and winter there
is a resting period which is passed as eggs.

Having elucidated the life history of the Valby mosquito the question was, whether
0. caspius was really restricted only to the brackish water pools near Copenhagen.
This was of course very improbable. In the two years 1919 and 1920 Mr. KRYGER
and I explored different parts of the Danish coasts. It can now be stated that
it has been found near the coasts of Roskildefiord; on the southern coast of Lol-
land, on the coast of the straits of Guldborgsund, which separates Lolland from
Falster; along the eastern coast of Jutland, more especially in the deeper parts of the
fjords. Most probably it may be found everywhere in brackish water pools, along
the shores of Kattegat and the Baltic; I could not find it in the brackish water
pools along the North Sea. It has never been found away from the coast. It is al-
. ways accompanied by 0. curriei but in spring rarely by any other mosquito. In
autumn, at Guldborgsund and upon Amager and at Roskildefjord, I found it as-
sociated with 0. detritus, which also otherwise has often been found with it.
(England: EDWARDS, LANG). The localities are always the same: tidal brackish
water pools, which are often exposed to complete desiccation. According to the more
casual observations it seems as if two generations are typical for our country. At
Roskildefjord I have found the two generations in the last part of June and in the
last part of August; the last generation was found at Guldborgsund.

Geographical distribution: Found in almost all European countries, Asia
and Northern Africa. With regard to the peculiar biology of the Saltmarsh mos-
quitoes I further refer to the papers of BUTTRICH (1913 p. 352), SCHMIDT (1913),
HEADLEE (1916 p. 339 and 1917 p. 211) and CHIDESTER (1917 p. 299).

2. O. curriei (Coquillet).

This species is in my opinion indistinguishable in the imago-stage from 0. cas-
pius. It especially represents variety 4 on pag. 40. As I however possess almost all
intermediate stages in the above-named four varieties, it is with the greatest hesitation
and upon the authority of Mr. EDWARDS that I maintain the species. It has hitherto
been regarded as species, differing from 0. caspius, partly because of the larva, partly
because of a different habitat. HOWARD, DYAR and KNAB firstly indicated (p. 637), that
in the larva of 0. curriei both pairs of dorsal head-hairs are multiple, and that the
lateral comb of the eighth segment has about twenty-five scales in an irregular patch,

47

whereas in 0. caspius the dorsal head-hairs are all single, and the scales of the
eighth segment are many and arranged in an elongate patch, moreover in 0. curriei
the single scales have a long central spine whereas in 0. caspius the central ones
are equal and not differentiated. According to the later report '(see p. 43) the larva
must be regarded as unknown.

From the numerous brackish water pools I have had unlimited amounts of
larvae for my observations. I have never found a single larva with the characters
indicated by HOWARD, DYAR and KNAR for 0. curriei.

According to HOWARD, DYAR and KNAR 0. caspius is a brackish water species;
flat salt-marshes being essential to its occurrence. 0. curriei on the other hand
inhabits temporary pools throughout the arid regions.

As all Danish mosquitoes with white rings, involving both apex and «base of
each tarsal joint, only belong to brackish water pools, and mosquitoes of this kind
have. never been found in the poor remains of an arid region which our country
still possesses, I for my own part would be most inclined to refer all these spe-
cimens to one single species 0. caspius (= dorsalis). When I suppose it to be most
correct provisionally to maintain the species for the Danish fauna, it is because
EDWARDS, without having got the larva, has done the same for England, has looked
over my specimens and indicated them as 0. curriei; further because I must con-
fess that this variety, more especially with regard to the colour of the thorax, really
is more sharply defined than the other varieties.

Here as - - according to a letter from Mr. EDWARDS - - in England the two
species occur in the same pools and simultaneously, but 0. curriei is much rarer.
In more than twenty-five samples of mine, hatched in my laboratory, in the time
from May to July I have never got more than about fifty 0. curriei as compared
with thousands of 0. caspius.

Geographical distribution: Sweden, England, North America.

3. O. cantans (Meig).
Tab. III.

The three species 0. cantans Meig., 0. annulipes Meig. and 0. vexans Meig. are
in their different colour varieties very difficult to distinguish. 'Many authors, STAGER
(1838 p. 554), ZETTERSTEDT (1850 p. 3461) a. o. have been inclined to regard 0.
annulipes as a variety of 0. cantans. The confusion has been augmented because
FICALHI has redescribed 0. annulipes and 0. vexans, and these descriptions have
been adopted by THEORALD.

As far as I can see, the old descriptions of MEIGEN are much more in ac-
cordance with the specimens found in our country than those of FICALHI, whose
descriptions perhaps are more in accordance with specimens from more southern
countries. The typical 0. cantans with its banded legs, dark thorax, covered with
reddish and golden-brown curved scales, the brown abdomen with its pale basal
bands is an easily recognizable species among the Danish Culicidae. In the old des-

48

criptions of MEIGEN (1818 p. 6) and ZETTERSTEDT (1850 p. 3461) we always find
statements, relating to two black or brown lines running over the mesonotum;
these lines, more or less conspicuous, I have found upon all my specimens, but I
often miss them in the later descriptions.

MEIJERE'S description (1911 p. 144): a broad brown median stripe is in ac-
cordance with many of my specimens but this stripe is then often bordered by
lines frequently yellowish-white. This is also indicated by EDWARDS (1912 p. 218).
When Eckstein (1918 p. 65) states, that the last abdominal segment always pos-
sesses "Andeutungen von Schuppenbindern am hinteren Rande" I cannot verify this.

From 0. vexans Meig. 0. cantans Meig. may probably always be distinguished
by means of the white tarsalbands which are always very narrow in the first
named species, whereas they are broad in 0. cantans; further 0. vexans Meig. is
of a very small size being only about 5 mm. whereas 0. cantans is about 7 — 8 mm.
Also the male genitalia of 0. vexans are very peculiar, the claspers being forked.

The two species 0. cantans and anulipes merge with regard to the colour, and
are rather indistinguishable more especially in the autumn. The best character is that
the distal joint of harpago is flattened, about twice as long as wide in 0. anulipes
whereas in 0. cantans it is not much flattened and has a large, membraneous expansion
on one side. - - Besides the reader is referred to the description of 0. annulipes.

Larva. Head rounded, strongly vaulted, large, wider than long, conspicuously
notched at insertion of antennae; front margin slightly arcuate. Antennae short; spi-
nose, especially on the innerside, tapering at apex; tuft small, only consisting of a
few, about 7 hairs. Near the apex a long hair, three short hairs and a digit.
Anteantennal tuft short, multiple, lower frontal tuft with four hairs, upper double,
the hairs being very strong. Eyes large.

Thorax subquadratic, angled at hair-tufts. Hair formula of frontal border
131114411131; tuft four consisting of one long hair and three very short ones;
hairs after tuft 4 always very short; the others strong. Lateral hairs in multiple tufts
and some single strong hairs.

Abdominal segments broad, the first much shorter than the last. Lateral hairs
on the first and second segments triple, on the third to sixth double; subdorsal
hairs absent. The eighth segment w7ith tufts in common arrangement; lateral comb
consisting of about 30 — 40 scales, arranged in rows, covering a triangular area; the
scales are spatulated at base, obliquely rhomboidal, bordered by long bristles; in
the middle a rather short spine, only insignificantly longer than the bristle nearest
to the middle thorn.

Sipho about three times longer than wide; tapering at front, on basal third a
pecten highly developed, consisting of about twenty strong thorns with four or
five large teeth and some smaller ones at their base; a tuft of about six hairs
between end of pecten and apex. Anal segment almost isodiametric, ringed by a
plate. Dorsal tuft consisting of a tuft of short, soft hairs and two very long and
strong ones. Ventral brush in the barred area composed of about 16 rays, every

49

ray carrying about six to nine hairs; before the barred area five free tufts; a lateral
tuft consisting of a single hair. Anal gills long, acute, equal.

Lateral tufts of labrum short, the inner part modified in comb-hairs, arranged
as a crown round the palatum which is covered with long, soft hairs. Mandibles
quadrangular, with two strong spines before the collar; a row of short cilia from
a collar and a row of about ten strong spines from margin. Dentition : four or five
strong teeth and before them two spines; a series of bristles below. Process below
distinctly furcate, with strong hair-tufts on both tips; a group of hairs at base.
Maxillae subquadratic with almost straight sides, divided by a suture. On the top a
tuft of long, soft hairs; at its base a thorn; area between suture and inner border
covered by long soft hairs; inner margin furnished with a series of long, strong
spines. Area between suture and outer margin with tufts of soft hairs; palpe well
developed with four digits at top. Mentum large, high, triangular, with the median
tooth rather small, borders arcuate, carrying about twelve to fourteen rather small teeth.

Colour bright grey, often milky; that of the head always yellowish red; by
means of this colour it can commonly be distinguished from O. communis, with
which it has the structure of sipho in common; but also the more vaulted head,
the armature of eighth segment, and the more straight sides of the maxilla, may be
used as distinguishing characteristics.

The larva has been shortly described by MEIJERE (1911 p. 144) by SCHNEIDER
(1914 p. 29) and ECKSTEIN (1919 p. 392). The descriptions quite agree well with
each other and also with the above given; the number of scales on eighth segment
varies very much.

Biology. More than ten years ago I had observed that, at a time when
0. communis had almost ceased to sting, another larger mosquito with white-banded
tarsi appeared. The bite of this species (0. cantans) was much worse. Everywhere
in the forests of North Seeland as wrell as in probably most of our Danish forests
0. cantans is extremely common in July and August; it is a well marked forest-
mosquito which only rarely leaves the woodlands. For more than a year I could
not detect, from where the myriads of these troublesome vampires came, and only
regular hatching experiments revealed the fact

In 1917 to my great astonishment I saw7 that all my aquaria, filled in April
with \vhat I supposed was only 0. communis material, which produced immense
numbers of 0. communis on the first day of May, now in the time from about
!0/v to 25/y only produced 0. cantans. A more thorough examination of the material
showed that in all my cultures there were really two species of larvae, the one
first hatched with only one single hair in the frontal tufts, and the other, the last
hatched, \vith four and two. Also in the structure of the scales the two species
differed a little from each other. Testing these observations in Nature I saw that the
ponds after having given off 0. communis, still contained a lot of larvae, wrhich almost
everywhere were never hatched till a fortnight later than O. communis. In the two
following years the relation between the two species was more thoroughly studied.

D. K. I). Vidensk. Selsk. Skr., naturvidensk. og mathem. Afd. 8. Rjekke, VII, 1. 7

50

I now feel convinced that all the mosquito-larvae which appear during the
winter or the first days after the ice has melted, all belong to 0. punctor,
0. commimis, 0. prodotes. Later on, commonly not before 5/iv — i/v at a time when
the larvae of 0. punctor — communis are almost fullgrown, very small, newly-hat-
ched larvae appear. These larvse are larger than those of 0. communis, the head is
yellowish-red, and the body brighter. As they are hatched later than 0. communis,
the volumina of wrater, in which the larvse and especially the pupae live, are often
extremely small, being often only a few deciliters. At the beginning of a dry period
the development may be shortened, the pupa stage .not lasting more than a few
days. Very often I have observed the peculiar fact that the species wrhich bites belongs
to 0. communis, where as the species which is hatched from pupa is 0. cantans.
If we sweep the catcher through the vegetation, we shall see that all that we get
near the pond is 0. cantans which is sitting deep down in the grass near the ponds,
whereas the mosquito wrhich makes our sojourn in the forest and round the
pond intolerable is 0. communis. Flying out of the dark shades of the wood, they
anounce their attack by their burz, their smell having directed their way. Their
real resting places were far away from the ponds on the trunks of the large beeches
and below their foliage.

With us 0. cantans uses more than a fortnight to be able to sting. Then there
may be some weeks when 0. communis and 0. cantans attack simultaneously and
side by side; little by little 0. communis disappears and 0. cantans predominates.

There is undoubtedly only one generation in the course of the year. The
larva is hatched in the middle part of April and the imagines about a month
later; the life of the imago lasts about three months; the eggs are not ripe before
two or three weeks after hatching; then the ponds dry out, and in summer (July-
August) the eggs are laid on the dry bottom; here they hibernate; when in autumn
the ponds get water again, this has no influence upon the hatching of the eggs. I
have never found a single 0. ca/i/ans-larva in autumn, the eggs must undoubtedly
pass a freezing period before being hatched.

The larvae live as the 0. co/n/mi/j/s-larvae, in the surface, hanging down from
this by the sipho. - - Still I suppose that they are more pronounced bottom fee-
ders than those of O. communis.

In 1920, as cold and rainy weather was a hindrance to the hatching of 0.
communis, there was a week in which the larva-swrarms in our forest ponds were
composed of almost equal numbers of 0. communis and 0. cantans; then the 0.
communis larvae changed into pupae, whereas the 0. ca/ifa/js-larvae remained un-
altered for one or twro weeks. Even then it was by no means difficult to distinguish
the O. cantans larvae from those of 0. commimis, the first-named being larger,
brighter and having a red head which immediately distinguished them from those
of 0. communis with their grey heads.

With regard to the biology BRESLAU (1917 p. 524) states that there is only
one generation in the course of the year, that the eggs are laid singly or in small

51

batches and upon almost dry land. Already SCHNEIDER (1914 p. 31) has pointed
out that the species winters as egg and ECKSTEIN (1918 p. 65) confirms this. GALLI
VALERIC (1909 p. 91 and p. 345) maintained that the eggs were laid in batches, EYSELL
(1908 p. 717; 1909 p. 203; 1910 p. 21) that they were laid singly; -the last-named author
is undoubtedly right. - - ECKSTEIN (1919 p. 100) has arrived at the same result as I
"dass die Weibchen die Eier erst in der 2 Halfte des Sommers ablegen". He has
further observed that the eggs are laid remarkably high up above the water level.
Geographical distribution: As LANG (1920 p. 86) remarks 0. cantans has
been so confused with 0. anmilipes that it is not possible to determine its range
with certainty. Most probably it is distributed over the whole of Europe.

4. O. annulipes (Meigen).
Tab. IV.

Description, Female: Proboscis moderate, subcylindrically flattened, the la-
bella? conically tapered; yellowish-white in the middle, black at base and apex,
brown hairs in the white part and white in the black especially at base. Palpi
stout, about one-fourth as long as the proboscis, clothed with blackish-brown hairs,
with scattered white ones especially at tip. Antennae with the joints equal, second
joint a little larger and thicker, yellow, the remaining joints rugose, brownish
pilose; tori subspherical, with a cup-shaped apical excavation, luteous, bright brown
and with a patch of small white scales on the inner side. Clypeus brown, conical,
prominent, nude. Eyes black. Occiput brown, clothed with curved, narrow, red-
golden scales and many slender, erect, black, brown scales, on the vertex; cheeks
clothed with flat, red golden, a little brighter scales; bristles bordering the eyes
black, a tuft of bright yellow hairs, projecting between the eyes.

Prothorasic lobes elliptical, remote dorsally, blackish brown, clothed with
bright, yellowish-red hairs not brown as in cantans. Mesonotum dark brown,
almost black, very hairy, clothed with a uniform tomentum of red or red-brown
hairs either without any darker lines or paler scales at the margin or with lines
yellower and brighter than in 0. cantans. Scutellum trilobate, luteous, each lobe
with bright yellow bristles and curved pale yellow scales. Postnotum elliptical, short,
luteous. nude. Pleurae and coxae pale brown, clothed with elliptical white scales.

Abdomen subcylindrical, flattened, posterior segment tapering; chitin uniformly
bright brown, very hairy, reddish-brown, with more or less obsolete bands of crea-
my white basal bands; no indications of apical bands on the last abdominal
segments; venter clothed with creamy white or yellow scales, mingled with some
black ones especially on the last segments and forming a continuous median stripe
in every segment with slightly lateral projections. Wings rather large, hyaline, with
a yellow tint; veins yellow, clothed with yellowish-brown scales; petiole of second
marginal cell shorter than its cell; that of second posterior cell almost of the length
of the cell; basal cross-vein almost its own length distant from anterior cross-vein;
fringe yellow, halteres entirely pale. Legs yellow, femora yellow with intermixed

52

black scales especially distally and dorsally; no dark scales proximally and ven-
trally (as in O. cantons); tibiae and metatarsi yellow with some more intermixed
black scales; tarsi almost black at apex with three or four white basal bands,
progressively narrower in the lower joints; the last joint commonly quite black.
Claw formula I'l— I'l— I'l. Length 7—8 mm.

Male. I have only had badly conserved specimens of this species in the male
sex and have been unable to distinguish them from males of 0. excrusians. According
to Mr. EDWARDS the males of O. annulipes may be distinguished from 0. cantons
by the structure of the genitalia. In 0. annulipes the harpes are long and strap-
shaped, in 0. cantans however they are shorter and provided with a large, mem-
braneous expansion near the tip; in this particular my few badly conserved speci-
mens agree with Dr. EDWARDS' indications, but, as far as I can see, they are rather
difficult to distinguish from those of O. excrusians.

Larva: Head broad, rounded, wider than long, restricted before eyes, and
slightly notched before the antenna?; front margin slightly arcuate, almost straight;
Antennae short, strongly attenuated at apex, spined, serration none or a very indistinct
one along inner border; tuft almost in the middle consisting of from four to six
hairs; at apex two long spines, one shorter and a digit; yellow between base and
tuft, dark between tuft and apex. Eyes large, transverse, pointed. Anteantennal tuft
multiple, lower frontal tuft with four, upper with two thick hairs. Thorax rounded,
wider than long, angled at hair-tufts; -hair formula of frontal border most probably
3111441113; in tuft four, three of the hairs short, and hair 1 after tuft four, short.
Lateral hairs in tufts; besides some single strong hairs.

Abdomen moderate; anterior segment short, posterior ones narrower and elon-
gate: hairs rather long, lateral hairs of the first segment triple, on the second to
seventh double; subdorsal hairs double on fourth to sixth segments. Eighth seg-
ment with tufts in common arrangement. Lateral comb consisting of about forty-
five scales, occupying a triangular space; the single scale spatulated at base, ending
in a very strong and long spine and furnished writh a series of long, remarkably
strong lateral spines; sipho long, slender, about three and a half times longer than
broad, remarkably straight, not so much tapering at apex as the siphones of 0.
excrusians and 0. lutescens; pecten reaching less than halfway, all spines at the same
distance, all wide at base and with from four to six large basal thorns without
any smaller one at base; in contradistinction to the larva of 0. lutescens also the
two last spines have basal teeth; a large tuft at middle of tube beyond pecten.
Anal segment almost twice as long as wide; the dorsal plate almost covering the
sides; dorsal hair-tuft consisting of a coarse tuft, and two strong and long hairs;
ventral brush large in the barred area, consisting of about from twelve to fourteen
rays, each ray carrying about six or seven hairs; before barred area six free
hair-tufts; the lateral hair-tuft consisting of one single strong hair; four gills equal, acute.

Lateral tufts of labrum short; the inner part modified in comb hairs, arranged
as a crown round the palatum, this is covered with short soft hairs. Mandibles

53

remarkably high in the interior part; with two strong spines before collar; a row
of rather short cilia from collar, and about eight to ten rather feeble spines from
the inner edge; dentition: four, strong spines; before them a long dagger-like thorn ;
hairs below, process distinctly divided, with hairs on both apices ; a group of hairs
at base. Maxillae almost undivided at the apex, a rather long tuft of hairs and, at
its base, one spine. The whole space between suture and inner border covered
with long soft hairs and long bristles along the inner border; between suture and
palpe an area covered with soft hairs. Palpe well developed, short writh four digits.
Mentum triangular, an indistinct median tooth and from ten to twelve lateral thorns.

Systematical remarks: 0. annulipes has always been a very disputed spe-
cies. Described by MEIGEN it has later been found in Austria, Germany, Russia,
Sweden, Holland, England; THEOBALD was not able to find it in England but later
on EDWARDS has described it from there. STAEGER like many others regarded it as
a variety of 0. cantons; differences in the male genitalia and in the structure of
the larva makes this supposition untenable. It may be mentioned that the STAGERS
specimens, now in the Royal Museum at Copenhagen, have been reexamined by
EDWARDS and myself; they are unquestionably 0. excrusians ; this may probably be
so in many other cases.

Biology. I have only found this disputed species in various localities near
Arrese in North Seeland. My material was never good and not large enough for
me to make a more thorough study of the biology.

It is quite in accordance with my own experience when LANG (1920 p. 88)
maintains that the larvae of 0. cantans are to be found in shaded pools of thick
woods, those of 0. annulipes in open pools.

Geographical distribution: See under 0. cantans.

5. O. vexans (Meigen).

It is only with the greatest hesitation that I include this species among the
Danish Culicidse. STAEGER (1838 p. 554) mentions it and indicates that the species
is to be found in the forests, and that it is rather rare.

Most probably STAEGER has only been able to distinguish it from 0. cantans
by means of its smaller size and very narrow white bands upon the tarsi. Speci-
mens of this kind I have also found in our forests; a little pond near Tjustruplake
was regularly visited for more than two years, more especially because I thought
that this pond contained what I supposed was the true 0. vexans ; the specimens
which where hatched in July were very small, only five or six mm. and the legs
were narrow banded. I have never seen the male; as the claspers are forked, the
species is, in the male sex, easily distinguishable from all other Danish mosquitoes.

According to EDWARDS (1912 p. 195) its occurrence has not hitherto been
demonstrated with certainty in England, but according to LANG (1920 p. 85) it has
now been found there but is rare. In Germany it seems to be common. In the
neighbourhood of Strassbourgh it is said to be one of the most troublesome mos-

54

quitoes; its life-history has there been worked out by BRESSLAU in an excellent
study (1917 p. 507). It is hatched in the large meadows which are flooded with
water twice a year, in spring and summer, owing to the hayharvest. It was ascer-
tained that no mosquitoes were flying before the first inundation took place; only
two days after this the wrater teemed with larvae which, at a tp. of 20 — 25° C., in
the course of from 14 to 18 days, gave enormous swarms of mosquitoes. In June
and July no other brood appeared in the small waterpools which remained in the
now dry meadows. The mosquitoes were to be found at first in the meadows, later

Textfig. 3. Pond near Tjustrup. O. vexans, communis, cantons, stamm phot.

on in cottages and stables. In June the mosquitoes appeared again over the mea-
dows, and the egg-laying process took place; the eggs were laid upon wrholly dry
ground. Experiments showed that the eggs were laid singly or in small batches,
and that they had no apparatuses which could be used for floating purposes.
After the second inundation the water teemed with larvaB again and, owing to the
higher temperature, in the course of a week this generation was hatched. In the
middle of July this second generation visited the meadows and laid their eggs. The
species most probably hibernates as eggs, but it is possible that they also hibernate
as larvae. SCHNEIDER (1914 p. 33) maintains that he has found females in December.
GALLI VALERIC on the seventh of March. — I refer also to the interesting supplementary
remarks by ECKSTEIN (1919 p. 97). The larva has been described by SCHNEIDER
(1914 p. 32) and ECKSTEIN (1919 p. 294). The larva must resemble that of 0. can-

55

tans very much, but the two or three last thorns in the pecten are said to be de-
tached from the other thorns. It may be added that the larvae from the little pond
in which my supposed 0. uexans was hatched, had no detached thorns in pecten;
apart from their small size and remarkably late occurrence' (July) they were in
full accordance with the larvae of 0. cantans. As pointed out by EDWARDS (1912
p. 195) and stated by HOWARD, DYAR and KNAR (1917 p. 699) the species is identi-
fied with the American species Aedes sylvestris (Theobald) (Dyar and Knab).

Geographical distribution: It seems widely spread over the whole of
Europe, but has as far as I can see a more southerly range. It also appears over
the greater part of Asia.

6. O. excrucians (Wlk.).

A. abfitchii (Felt) Dyar and Knab.

Tab. V.

Description. Female: Proboscis moderate; vestiture of brown-black scales.
Palpi rather stout, short, about one-fourth as long as the proboscis clothed with
black scales, tips and bases of joints with yellowish-white scales. Antenna? with
tori subspherical, with a cup-shaped apical excavation, luteous, brown, and with a
patch of small white scales on the inner side. Occiput blackish, broadly clothed
with narrow, curved creamy-white scales in the middle, a diffused patch of browrn
ones laterally, and many slender erect forked black scales on the vertex. Bristles
bordering the eyes black.

Prothoracic lobes elliptical, remote dorsally, blackish, clothed with pale yellow
scales and black bristles. Mesonotum dark brown, clothed with narrow curved
scales, a broad median stripe of golden brown ones, anterior margin narrowly and
the whole of sides of disk as well as the antescutellar area with pale yellow ones;
bristles moderate, black. Scutellum trilobate, luteous each lobe with a group of
black bristles and clothed with narrow, curved, pale yellow scales.

Abdomen subcylindrical, flattened, posterior segments tapering; dorsal vestiture
of black scales with a few pale ones intermixed, each segment with a broad basal
band of creamy-white scales and a narrow row of pale scales at tip; on the sides
the basal bands widen into large triangular spots, particularly on the , sixth and
seventh segments; first segment writh a large patch of white scales and many pale
cilise; venter clothed with creamy-white scales and with median segmental spots of
black ones, tending to form a longitudinal stripe. Cerci black.

Wings moderate, hyaline; petiole of the second marginal cell somewhat shorter
than its cell, that of second posterior cell about as long as its cell; basal cross-vein
less than its own length distant from anterior cross-vein; outstanding scales long,
broadly linear, with blunt tips. Halteres entirely pale.

Legs moderately slender; femora clothed with creamy scales belowr, black and
whitish ones about evenly intermixed above, the tips narrowrly white; tibiae \vith
black and whitish scales intermixed, the black ones predominating at the apex, the

56

stiff outstanding setae mostly black; tarsi black, each joint of hind legs with a broad
basal ring of white scales; the first joint with many white scales scattered over the
surface and tending to form lines; on the front and middle tarsi, the basal bands
are narrow and nearly obsolete on the last joints. Claw formula I'l — I'l — I'l.

Length: Body about 6 mm, wing 4,5mm.

Male: Proboscis slender, straight. Palpi exceeding the proboscis by about the
length of the last joint; end of long joint and the last two joints somewhat thickened
and bearing many long dark-brown hairs; long joint clothed with black scales and
white ones intermixed, a broad white ring at middle and near base; last two joints
with many white scales at their bases. Antennae plumose, the last t\vo joints long
and slender, black, rugose, pilose, the others short, largely pale; hairs of whorls
long, dense, black, with yellowish brown bristles. Coloration similar to the female.
Wings narrower than in the female, the stems of the fork-cells longer, vestiture
sparse. Abdomen long depressed, the basal bands broader, lateral ciliation long and
abundant, pale yellow. Claw formula I'l — I'l — I'l.

Length: Body about 6 mm.

Genitalia. Side pieces over twice as long as wide, slender, distal lobe roun-
dedly prominent, continued along the inner margin, narrowly to the basal lobe;
basal lobe quadrately expanded, bearing many small setae with tubercular bases,
but without a stout spine. Clasp-filament slender, bearing a few small setae out-
wardly, at the tip a long articulated terminal spine. Harpes slender, concave, the
inner margins revolute, hooked at the tip, the point directed outwrard. Harpagones
with a slender cylindrical base, curved, minutely pilose, bearing a terminal filament
which is nearly as long as the stem and angularly expanded at middle. Unci ap-
proximate, revolute, forming an indistinct basal cylinder. Basal appendages stout
and approximate bearing a row of stout setae at the tip. (After H. D. K.).

Larva: Head rounded, wider than long; restricted before the eyes; a notch
at insertion of antennae; front margin broadly arcuate. Antennae short, attenuated
at apex, tuft small, only consisting of a fe\v, about six or seven, hairs inserted
almost in the middle of the antennae; spinose; the spines remarkably long and with
a fine serration along inner edge. Near the apex two long spines, and at the apex
three short ones and a digit. Anteantennal tuft multiple, lower frontal tuft with
three or four hairs, upper double. Eyes large. Thorax rounded, wider than long,
angled at hair-tufts. Hair formula of frontal border 221113311122 or 231213312132.
The median tuft three, with one long hair and two very short, tuft 1 after the
median tuft three, also very short. Lateral hairs in multiple tufts and single strong
hairs. Abdomen rather broad, the first segments much shorter than the following.
Lateral hairs of the first segment triple, on the second to the seventh double, eighth
segment with tufts in common arrangement. Lateral comb consisting of about
thirty-forty scales, arranged in rows, covering a triangular area; the scales spatulat-
ed at base, ending in a very strong spine and furnished with rather long spines at
the borders of the spatulated part. Sipho about four times longer than broad,

57

strongly tapering at apex; on basal third a pecten, rather short with about fifteen
to eighteen thorns, the first of them without lateral thorns, the others rather broad
with four strong ones. The last two thorns large, detached, out of line and with a
much greater distance between than the others; a large tuft at middle of tube,
consisting of seven hairs.

Anal segment longer than broad, covered by a rectangular plate, almost
reaching the barred area of the ventral brush; dorsal hair-tuft consisting of a coarse
tuft and two very strong and long hairs. Ventral brush in the barred area con-
sisting of about ten rays, each ray carrying about six or seven hairs, before barred
area six free hair-tufts; the lateral tuft consisting of one single hair; four gills,
equal, acute.

Lateral tufts of labrum rather short, the inner part modified in comb-hairs,
arranged as a crown round the palatum; this is covered with short, soft hairs.
Mandibles quadrangular with two strong spines before collar; a row of short cilia
from collar and a row of strong spines, about ten, from margin. Dentition four
strong spines, the first much stronger than the others ; before them three long acute
dagger-like spines, one of them faintly dentated; a series of bristles below. Process
below distinctly divided with hairs on both apices; a group of hairs at base. Max-
illre elliptical, divided, by a suture; on the apex a long tuft of hairs and at its
base one or two short spines. The whole space between suture and inner border
covered with long soft hairs; long bristles along the inner border; between suture
and palpe an area covered with soft hairs. Palpe well developed with four digits.
Mentum triangular, an acute median tooth and from ten to twelve lateral teeth.
Colour commonly green, often milky, very transparent, the head also green, the
sipho yellowish-red.

Systematical remarks. The description of the female and male is taken
from HOWARD, DYAR and KNAB (A. abftchii) with which my specimens have been
careful compared; they have been determined by Dr. EDWARDS. As far as I knowr,
the species has hitherto not been described from Europe; most probably it is con-
cealed in one of the fairly numerous insufficiently described older species. With
regard to the imagines there is full accordance between the American specimens
and the Danish ones; with regard to the larva? there are some discrepancies. H. D. K.
(p. 690) indicate that both frontal tufts are double; in my larvae the lower frontal
tuft has always three or four hairs; further, the lateral hairs on the abdomen on third
to sixth segments are single in the American specimens, double in the Danish specimens.
Biology: In North Seeland we often find, on the plains in the forests or in
the outskirts of the wood, small ponds, the bottom of which is not decaying leaves,
but grass; the ponds are always extremely shallow and dry up in May, often before
other ponds are laid dry. They are almost always dry from May to January,
and the water these ponds contain is almost only melted snow; it disappears again
in the course of one or two months. In these ponds, the true habitats of Bran-
chipus Grubii and Limnetis brachyura, we find the above-named grassy-green Culi-

I). K. D. Vidensk. Selsk. Ski-., naturvidensk. og mathem. Afd. 8. R.-ekke, VII, 1. 8

58

cin larvae which, when hatched, always give 0. excrucians. In one of the ponds the
larvae appeared 16/iv 1918 (Hestehave Hiller0d), a few days after the ice had dis-
appeared; they were full grown 30/iv and pupse Wv. At that time there was only
a few centim. of water in the pond; though the temperature of the air was only
eight degrees C., the temperature of the water was twenty. In 1919 the develop-
ment was quite the same as in 1918; pond icecovered 25/iv; full grown larvae 2/y; pupae
i°/v. The pond was dried up by i/vi. In 1920 the ponds were already icefree in
the latter part of February, but the 0. excrucians larvae did not appear before the

Textfig. 4. Pond: Hestehave, Hillerad. O. prodotes, O. excrucians, O. cantans.

middle of March; they were fullgrown in the first days of April; bad weather was a
hindrance to further development; pupae did not arrive until 8/v; imagines not
before Wv. In May 1920 I found the O. excrucians larvae in the ponds of the Ere-
mitage plain. Now and then I have also found the larvae in the common forest
ponds teeming writh 0. communis larvae. It was on 2l/y in such a pond, in Arne-
have forest near Tjustrup, that I observed this fact. On a day with bright sunshine,
standing near a pond with huge swarms of 0. communis-\ar\se hanging down from
the surface, I saw that below the layer of the perpendicularly hanging 0. co/n/nums-larvae
there was another layer of almost horizontally standing Culicin-larvae; they were
larger and almost white; most of them rested on the bottom or got support from
the fine leaves of Hottonia. These larvae were caught, isolated, and eight days later
gave O. excrucians.

59

It may be pointed out, that the 0. excrucians-\ar\3d, in contrast to those of
O. communis, almost always lie on the bottom, often on the dorsal side, or very
often are found hanging down from water plants; they rarely come to the surface,
brushing the bottom and the plants free from detritus. - The life history of the
species is the same as for the other mosquito larvae in drying ponds. They are hatch-
ed immediately after the melting period, probably a little later than O. communis,
they left the pond on 15/v; a few days afterwards the ponds were quite dry and
did not get water before the spring. The mosquito have only one generation. In one
of the ponds which got water in December, a few larvae developed but did not
hibernate, dying out under the ice. The number of larvae in the ponds hitherto ex-
plored is always slight ; I have never found them in huge swarms ; also as imagines
the mosquitoes are rare; I have only found them in the vicinity of the ponds
where they were hatched; they bite vigorously, sitting deep down in the grass, and
flying out when this is moved. A few have been observed in the latter part of August.

Geographical distribution: It has hitherto only been found in North-
eastern North America (H. D. K. 1917 p. 691).

7. O. lutescens (F.).

0. fletcheri (Coquillet).

Tab. VI.

Description. Female: Proboscis moderate, vestiture of browrn-black scales.
Palpi stout, rather long, more than one-fourth as long as the proboscis; vestiture
of black scales with a few pale ones. Antennae with tori subspherical, with a cup-
shaped apical excavation, ocher yellow7, on the inner side black and with small,
flat, broad whitish scales. Occiput rather broad, clothed very broadly with dense,
narrow curved brassy scales on the vertex, a large patch of golden brown ones on
each side close to the eyes; bristles bordering the eyes pale brown.

Prothoracic lobes elliptical, well separated, brownish, clothed with narrow, gol-
den scales below, golden-brown ones above and pale bristles. Mesonotum black, a
broad median stripe of narrow curved golden-brown scales, a detached stripe of
similar scales on each side on posterior half; sides of disk and ante-scutellar space
clothed with pale brassy scales. Scutellum trilobate, each lobe with a large group
of whitish bristles. Pleurae gray, the coxae pale brown.

Abdomen subcylindrical, flattened, the posterior segments tapered; dorsal vesti-
ture nearly wholly of dull ochraceous white scales intermixed with a few black
ones, these latter predominating along lateral margins, forming an ill-defined stripe
becoming obsolete towards the tip; no traces of bands along the borders of the
segments, venter similarly coloured, the black scales forming an ill-defined median
longitudinal stripe. Cerci black.

Wings rather broad, hyaline yellow irridiscent; petiole of second marginal
nearly half as long as its cell, that of second posterior cell about as long as its
cell; basal cross-vein nearly its own length distant from anterior cross-vein, out-

8*

60

standing scales linear to ligulate, very long, both black and pale. Halteres pale with
blackish white scaled knobs.

Legs rather long, clothed with pale, ochraceous scales, the long outstanding setae
black; femora with some black scales on upper side, which predominate towards tip;
tibiae similarly coloured; first tarsal joint clothed with ochraceous scales with black
ones intermixed which predominate at tips, the other joints black, with basal white
rings, the hind tarsi having the basal halves white, the rings narrower on the
other legs and nearly obsolete on the last joint of front legs. Claw formula 1.1 —
1.1—1.1.

Length: Body 7,5 mm; wing 6 mm.

Male: Proboscis slender, nearly straight. Palpi exceeding the proboscis by about
half the length of the last joint; vestiture of ochreous and blackish scales, the latter
very sparse, tending to form rings near the false articulation of the long joint and
at the apices of the other joints; apex of long joint and last two joints with long,
dense, golden and brownish hairs. Antennae plumose, the last two joints long and
slender, rugose, pilose, black, the others short, black at the thickened insertions of
the hair-wThorls ; hairs long, dense, brown, shining. Coloration similar to the female.
Wings narrower than in the female, the stems of the fork-cells longer, the vestiture
sparse. Abdomen long, depressed; dorsal vestiture of sordid yellowish white scales,
with an ill-defined, narrow median stripe of black and golden brown scales; lateral
ciliation long, fine, and dense, pale yellowish. Claw formula 2.1 — 1.1 — 1.1.

Length: Body 7 mm; wing about 6 mm.

Genitalia: Side-pieces nearly three times as long as wide, the tips conically
rounded. Distal lobe large, prominent, conical with short setae. Basal lobe a rather
large, but slightly elevated area, bearing numerous dense, short setae with tubercu-
lar bases; a stout spine with hooked tip within the basal lobe, accompanied by
two slender hairs. Clasp-filament slender, attenuated above base, a long stout arti-
culated spine at apex, nearly one third as long as filament; three small setae sub-
apically. Harpes elliptical, edges recurved and thickened, tips pointed and directed
outward. Harpagones with stout base, tapering outwardly, minutely hirsute, bearing
at its tip an articulated filament which widens, broadly lanceolate, with a short,
somewhat recurved branch on inner side near middle. Unci invisible. Basal appen-
dages small, rather approximate, bearing about six stout setae.

Larva: Head rounded, wider than long, restricted before the eyes and slightly
notched before the antennae; front margin arcuate. Antennae short, attenuated at
apex; finely spined, a fine serration along inner edge; the hair-tuft a little below
the middle, consisting of six hairs. Near the apex one long hair; three short ones
and a digit. Anteantennal tuft with from five to seven hairs ; lower frontal tuft with
five, upper with two hairs, all hairs remarkably long. Eyes large.

Skin of body very smooth. Thorax rounded, wider than long, angled at hair-
tufts. Hair formula of frontal border 132114411231; the median tuft with four hairs,
two of which are long and two short, the one often indistinct; at the base of the

61

first median single hairs two or three smaller ones. Lateral hairs of the first seg-
ment triple, on the second to sixth double. Eighth segment with tufts in common
arrangement. Lateral comb of about forty scales, arranged in rows, covering a tri-
angular area; the scales are spatulated at base, ending in a strong spine and fur-
nished with rather long spines at the borders of the spatulatea part. Sipho stout,
a little less than four times as long as wide, slightly tapering at apex ; pecten rather
fine, consisting of about twenty thorns, reaching nearly to tne middle of the tube,
the last two teeth but slightly detached without dentitions, the others with from
three to four teeth followed by a large tuft, consisting of six or seven hairs. Anal
segment longer than broad, covered by a large dorsal plate, dorsal hair-tuft con-
sisting of a coarse tuft and two very strong and long hairs ; ventral brush large, in
the barred area consisting of about 11 rays, each ray carrying about six or seven
hairs; before barred area six free hair-tufts; the lateral hair-tuft consisting of one
single strong hair; four gills, equal, acute.

Lateral tufts of labrum rather short; the inner part modified in comb-hairs,
arranged like a crown round the palatum; this is covered with short, soft hairs.
Mandibles quadrangular with two spines before collar; a row of rather short cilia
from collar and about twrelve spines in rowr from inner margin; dentition four strong
spines, the first strongest; before them two dagger-like thorns, the one dentated.
Process below distinctly divided with hairs on both apices; a group of hairs at
base. - - Maxillae indistinctly divided by a suture; at the apex a rather long tuft of
hairs, and at its base one or two spines. The whole space between suture and inner
border covered with long soft hairs and long bristles along the inner border; between
suture and palpe an area covered writh soft hairs. Palpe well developed, short writh
four or five digits. Mentum triangular, an acute median tooth and ten lateral thorns.

Colour bright yellow, rarely gray; the strongest chitinized parts of the body
yellowish -red; body highy transparent.

Systematical remarks. The description of the female and male is mainly taken from
H. D. K. (1917 p. 675) (A. fletcheri) with which my specimens have been carefully
compared; they have been determined by Dr. Edwards. Most probably the species
is identical with Culex flavescens Theobald (1901 p. 410). With regard to the ima-
gines there is full accordance bet\veen the American specimens and the Danish
ones, writh regard to the larvae there are rather significant differences. I have never
seen any fine hairs on dorsal surface towards base of the sipho as indicated by
these authors for the American specimens; the number of scales are greater in my
specimen (30 — 40 against about 25) ; further the last two thorns are but slightly detached
from the others; and the frontal hairs are not triple in both tufts as indicated by the
American authors, but double in the upper, and with five hairs in the lower, frontal tuft.

As however the imagines also with regard to the male genitalia are indistin-
guishable from the American specimens, I suppose that it is temporarily most cor-
rect to refer the Danish specimens to the American species.

Biology. I have mainly found the species in four localities resembling each

62

other very much: in the meadows near the outflow of Susaa in Tjustruplake, on
the large moors south of Arres0 and on the southern coasts of the island Lolland.
The large meadows near the outflow of Susaa in Tjustruplake only a kilom. from
my summer laboratory are regularly inundated in the winter; ice covers the whole
area and in spring it is changed into a large lake. In May the water disappears,
and herds of horses and cattle graze in the vast meadows, dry from June to No-
vember. Some of the pools left were under direct observation for almost three years.
In the spring of 1917 the ponds contained plenty of larvae which were full-
grown in the first part of June; the larvae were hatched in my laboratory and gave
0. fletcheri. In Nature they wrere hatched about Wvi, on i/vn the pond was dry,

Textfig. 5. Pond near Tjustrup-lake. O. lutescens, rusticus. stamm phot.

and the bottom was covered with grass which wras cropped by the cattle. The
pond was never filled with water before the middle of November, and by iVn 1918 the
pond contained many mosquito larvae, but only O. communis; from the middle of
January and till the latter part of March the pond was ice-covered, and when the
ice had disappeared crowds of mostly fullgrown 0. communis larva? appeared. On
12/iv I found a great number of newly-hatched yellow larvae; they did not swim
as the O. communis larvae and only rarely hung down from the surface, but moved
in smaller or larger circles along the sides of the aquarium; the larvae in my cul-
tures were fullgrown by 23/iv and metamorphosed into pupae on 30/IV. On 4/v the
imagines appeared. In Nature the whole stock of larvae died off. On so/iv the
temperature fell below zero and heavy snow fell at 9 o. cl. a. m.; the low tempera-
ture retarded the development and, as the pond was wholly dry about 15/v, the
whole mass of larvae died off. - - Other ponds near this, which were somewhat
deeper, were filled with water till July, and in these ponds the development was

63

accomplished. The pupae appeared on 20/v and before the 1st of June all 0. lutescens
larvae were hatched. The imagines sat in a rather restricted zone round the pond,
especially below the Ca///ja-bushes. The mosquitoes did not begin to bite before
about 15/vi. The ponds were dry till November; contained no'O. lutescens larvae in
the winter of 1919, and were open about the first of April. On 16/iv the ponds
teemed with 0. lutescens larvae halfgrown, fullgrown on 3/y, and on 19/v the ima-
gines were hatched. - - In the rainy summer many of the ponds contained water,
and in some of them a few 0. communis larvae were hatched. In a few of them
there was no water, but the cattle had made deep holes with their hoofs and in
these holes there was some water, only about half a deciliter. These holes contain-
ed rather few 0. lutescens larvae; the larvae were found on 29/vii and the imagines
were hatched on i/viu. An-
other of the ponds got water
on lo/vii; larvae appeared on
20/vii; they were hatched in
my aquaria and gave imagi-
nes by 28/vn, but in the pond
no larvae were developed, they
all died off because the pond
dried up. The ponds were dry
the whole of the autumn, at
all events till 15/x.

I do not know with cer-
tainty if we have here to do
with a new second brood or
only with larva; derived from
eggs which have only now
got developmental conditions.

I suppose that the latter supposition is most correct, and that the species in our
country normally has one single generation.

I have further studied the species on the moors south of Arreso. On 20/vi 1919 as I
was driving through the forest Neiede Vesterskov, almost bordering the lake, the horses
suddenly became extremely nervous. Clouds of large, yellow mosquitoes rushed over
them, attacking especially venter and the inside of the thighs. The mosquitoes
made any stay in the forest impossible. Some hours later I was driving over the
meadows and arrived at the hatching area of the mosquitoes that had attacked me
in the forest. This area, too, is in spring covered with water, but in summer the
water dries, and only some ditches and pools remain; herds of cattle live here the
whole summer. The mosquitoes were probably hatched in one or two weeks; the
landowners told me that they had even begun to sting; and that every year they
stood like clouds over the grass making any stay for people or cattle almost im-
possible. They pounced upon us in vast numbers and bit us very severely.

Textfig. 6. The vast meadows at Arreso. 0. lutescens.

64

In the following year I was again examining Neiede Vesterskov, and the mea-
dows south of Arreso. The water-line had receded, but in the ditches there was
still plenty of water; in this I found many yellowish-grey larvae, from which was
hatched 0. lutescens on 2l/y. 23/v when I was in the same locality, the meadows
were dry, and only a few holes had water. In one of them I found a great num-
ber of pupae, and in the grass over the pond plenty of newly-hatched O. lutescens.
On 29/v the mosquitoes were on the wing, but they had not begun to bite. The
meadows were quite dry from 29/v to the latter part of October. On a visit in the
last part of June I was fiercely attacked by clouds of 0. lutescens which stung vigorously.
Another locality where I have studied this species is the southern coast of
the islands Lolland-Falster: Time: June. Here we find large meadows, bordering on

the shores of the Baltic; in spring
the water goes over the mea-
dows, in summer they are com-
monly dry. Everywhere in the
large forests of Phrag mites, dee-
pest down in the old, now al-
most dry, fjords, often surroun-
ding smaller lakes, and in the
forests I found 0. lutescens in
enormous masses. I hardly ever
saw any other mosquito; more
especially on damp evenings, in
the large Phragmites svamp be-
hind the castle of Aalholm, the
mosquitoes were extremely trou-
blesome. Here, as well as near
Maribolake, and on the long

peninsula of Knudshoved, on the southern coast of Seeland, I observed that the
species attacks cattle and horses much more than man. Near Maribo I had an
opportunity to make sure that 0. communis, cantons and lutescens were simultane-
ously on the wing. Whilst we in the forest were attacked by the two first-named,
O. lutescens attacked the horses in the meadow bordering the lake; more than forty
were simultaneously sucking one horse.

On the island of Amager near Copenhagen man and cattle in the meadows
are attacked by clouds of 0. lutescens. In the Royal Museum of Copenhagen some
large yellow mosquitoes from Stsegers time are labelled C. annulipes. As we know
that Staeger has explored Amager with regard to mosquitoes, it is most probable
that these specimens really derive from this locality. Most probably the species is
widely spread over the whole island; at all events I have found it on both sea-
shores and in the middle. The island is bordered by numerous brackish pools, in
which the huge masses of 0. caspius and curriei are hatched. Often separated from

Textfig. 7. The vast meadows at Aalholm. Lolland. O. lutescens.

these pools by means of dikes, which preserve the low-lying island from inunda-
tions, we find hundreds of freshwater pools all over the meadows, more especially
in spring, in which 0. commnnis are hatched in early spring, and later on 0. lutes-
cens; I have only taken the larva of lutescens in one single brackish pool and
only one specimen; it seems as if the above-named dikes form a very conspicuous
barrier between 0. curriei and 0. caspius on one side and 0. lutescens on the other.
Later on, as imagines, they have the same flying areas.

From these observations we are able to state that the home of 0. lutescens
seems to be the open meadows bordering on lakes and sea-shores; they do not dwell
in forests, the outskirts of which is the natural home of 0. excrucians, only on
very warm days do they now and then seek them. There is unquestionably regu-
larly only one single generation, hatched in the latter part of May and on the wing
the whole summer, attacking cattle and horses more than men. Curiously enough,
this species, which has not hitherto been described in our country, is perhaps the
one which forms the greatest swarms, standing in clouds over the meadows; the
males disappear before the last part of June, and the females begin to throw their
numerous single eggs over the vast plains, then dry, but inundated before January,
at all events in the following spring.

Geographical distribution: England, Germany, Russia, and Scandinavia;
it is identic with 0. fletcheri Coq, hitherto found in North America. H. D. K. (1917
p. 678) indicate Prairies of western Canada and north western United States.

Systematical remarks with regard to the four last-named 'species.
In the above-named localities I found, in 1917 — 1919, the larvae of the now men-
tioned three species O. lutescens, excrucians and annulipes; these larvae were at that
time unknown. By means of the remarkably long siphO and short antennae I was
always able to distinguish the larvae of these three species from those of cantans,
communis and Theobaldia morsitans-, I first regarded the three larvae as belonging
to the same species. A closer examination showed that, between these long siphoed
larvae there were slight, but conspicuous, differences; later on I therefore regarded
them as belonging to different species, and made drawings of them. As the ima-
gines appeared, I immediately saw that I had at all events two species before me;
regarding those from the small ponds at Hillerad as differing from those from the
meadows near Arres0 and Tjustrupso. Later on I was inclined to regard some of
the material from the ponds in North Seeland as belonging to two different species,
one being 0. annulipes; if this was right, however, I was unable to distinguish this
species from 0. cantans, taking an intermediate position between 0. cantans and
0. excrucians. - - Later on, when in July — August I examined the same localities,
where I had gathered the larvae in spring, and from which I had hatched the pre-
sumed three species in the latter part of May, the case was much more trouble-
some. The males had disappeared; at that time we find only females in all the
above-named localities. When the lust of blood of this sex has been satisfied,

I). K. D. Vidensk. Selsk. Skr, naturvidensk. otf mathem. Aid. 8. R.-ekke, VII, 1. 9

66

when the mating and egg-laying processes are finished, the females of all three spe-
cies have another appearance. The scales of the thorax have almost all fallen off,
and the blackish brown colour of the mesonotum especially in lutescens and ex-
crucians appears; simultaneously the whole uniform tomentum of the abdomen of
0. lutescens disappears, the yellow strongly shining chitin, often a little darker at
the base of the segments, appears. The abdomen of excrucians and annulipes gets a
rather similar aspect; the scales of the legs and proboscides are torn off; the legs
are no more white banded but uniform yellow and only reminiscenses of the whitish
rings appear; this more especially holds good with regard to 0. lutescens and annu-
lipes. It will therefore be understood that at this time of the year it is impossible
to distinguish the three species from each other. — As the three species were un-
questionably distinguishable from each other in the larva stage, and were conspicu-
ously different when newly hatched as imagines, I was inclined to regard them as
three species, but was unable to determine them. After having sent them to Dr.
EDWARDS I was interested to hear, partly that the separation of the three species
was correct, and partly that my material contained the two above-named species
0. lutescens and O. excrucians. He wrote to me that he had arrived at the same
result as I, that the three species in the female sex are almost indistinguishable
from each other later on in the year, after the abdomen has been filled with blood
and enormously distended, the females of the three species having lost most of their
hair-coating.

Th6 best distinguishable species is 0. lutescens with its uniform ochraceous,
tomentum of the abdomen and the dark mesonotum; also annulipes with its red
tomentum, consisting of upright standing hairs is easily recognizable for a long
time in the summer; but in very many cases 0. annulipes takes the intermediate
stage between O. excrucians and cantans, and the three species are then very diffi-
cult to determine. As far as I can see, the male genitalia do not help very much,
the structure of the side pieces and clasp-filaments is almost the same in the four
species, and only the structure of the harpagos (basal appendages) differs a little in
the four species; they are long and strap-shaped in 0. annulipes; in the other three
species they are provided with a large, membranous expansion near the tip, and
this expansion has a somewhat different appearance from species to species.

The two species 0. cantans and annulipes have always been difficult to sepa-
rate from each other; roughly s.peaking the two species differ from each other by
0. cantans being more greyish-dark, O. annulipes more yellowish-red; but with re-
gard to the colour most probably every possible intermediate stage may be found.
0. annulipes is a more robust species than O. cantans, and this species may occur
in pond-races of only very small sizes (from five to six mm.); this I have never
seen with regard to O. annulipes. It may be added that O. cantans is a forest mos-
quito par excellence, 0. annulipes only found on the large fens and moors; more-
over O. cantans appears at a somewhat earlier date than annulipes, and is trouble-
some at an earlier time of the year than this last-named species.

67

Also as larvae the four species are difficult to distinguish from each other;
the best characteristics are the following: In 0. cantans the sipho is much shorter
than in the other above-named species; it does not reach more than about three
times its own width at base; those of the others about four times. Among the other
three species annulipes is distinguishable by means of the pecten, the two last spines
not being detached from the others, and provided with lateral thorns like these.
The two other larvae, those of 0. lutescens and excrucians are difficult to distinguish
from each other; I refer to the descriptions given above. - It will be seen that
whereas it is difficult to distinguish O. lutescens and excrucians as larvae from each
other, the difficulty is not so great with regard to the imagines; otherwise annu-
lipes and cantans are easily recognizable as larvae, whereas as imagines it is often
impossible to recognize them.

8. O. detritus (Haliday).
Tab. VII.

Description. Female. Proboscis moderate, cylindrical uniform, dark brown
almost black, sprinkled with white scales especially near the base. Palpi black with
many whitish scales and some black setae. Antennae filiform, the joints subequal,
rugose pilose, black, sprinkled with, whitish scales; second joint thicker, but scarce-
ly longer than third, pale; tori subspherical with a cup-shaped excavation, lute-
ous, darker within, outwardly sprinkled with many white scales, hairs of whirls
black. Clypeus rounded prominent, black, nude. Eyes black. Occiput black, covered
with lanceolate, curved, creamy scales; on the sides broader; generally an ill-defined
lateral black spot; bristles on the occiput and along margin of eyes black, those
between the eyes yellow.

Prothoracic lobes elliptical, remote dorsally, black, clothed with narrow white
scales and dark bristles. Mesonotum black with a monotonous coating of yellowish
brown or reddish hairs, without distinct brighter or darker lines; scutellum trilo-
bate, black, each lobe with a group of bright bristles. Postnotum elliptical, promi-
nent, blackish, nude; pleurae dark brown, coxae luteous, both covered with patches
of elliptical, flat, white scales.

Abdomen subcylindrical, tapering posteriorly; dorsal vestiture with broad white
basal bands, tending to expansion in the middle line; seventh segment almost
yellowish white; sprinkling of the darker parts of the abdomen with numerous
white scales; venter yellowish-white with a median series of three dark spots and
with two other more inconspicuous dark spots in each apical corner of each seg-
ment. Wings rather broad, hyaline, petiole of second marginal cell and second
posterior cell shorter than their cells; basal cross-vein distant less than its own
length from anterior cross-vein; scales black, but with numerous white scales scatter-
ed over all the veins, especially over the subcostal vein which may be almost
pure white.

68

Legs moderately long and slender, dark, brightest below, no conspicuous knee-
spots; covered with numerous white scales, especially conspicuous upon hind tibia
and tarsi.

Size 5'5 mm.

Male: Palpi and proboscis, black; end of long joint swollen, black, sprinkled
with white hairs. Abdomen broadest on sixth to seventh segment; coloration similar
to the female; lateral ciliation long, abundant, pale; wings narrower than in the
female; stem of the fork-cells longer.

Size 6'5 mm.

Male genitalia: Side pieces almost three times longer than wide, tapering di-
stally; apical lobe well developed with some few, rather short hairs. Clasp filaments
slender, slightly expanded in the middle and bearing a long articulated terminal
spine; a few extra large bristles at proximal end of the basal lobe; stem of har-
pago long, blade strap-shaped, not much shorter than stem.

Larva: Head rounded, wider than long, a notch at insertion of antennae;
front margin arcuate. Antennae short, antennal tuft small, only with from five to
seven hairs inserted below the middle of antenna; on apex four hairs, two long,
and a digit. Anteantennal tuft multiple ; lower frontal tuft consisting of twro or three
hairs, upper of one. Eyes large.

Thorax subquadratic angled at hair-tufts, hair-formula of frontal border
311144113; in tuft four two long and two short hairs. Lateral hairs in multiple
tufts and some single strong hairs. Abdominal segments rather broad, the first of
them shorter than the last. Lateral hairs on the first two segments four or three,
on the others, two; subdorsal hairs in double tufts. Tufts of eighth segment in
common arrangement; lateral comb consisting of about twenty-five scales, arranged
in a triangular area; scales blunt, without any peculiar, developed median tooth.
Sipho rather short, not fully three times longer than broad, tapering at apex. At
basal third a pecten consisting of about twenty thorns, all in line and with from
five to six teeth of unequal length at base; a tuft of hairs between end of pecten
and apex.

Anal segment longer than wide ; the dorsal plate subquadratic, not covering the
two thirds of the segment; dorsal tuft large, two very long stiff hairs beneath; ven-
tral brush consisting of about fifteen rays, every ray carrying from seven to nine
hairs. Before the barred area two or three free tufts; Anal gills four, extremely short,
bud-shaped, equal, almost isodiametric.

Lateral tufts of Jabrum short but dense; the inner part with a crown of comb-
hairs; palatum large, covered with long soft hairs. Mandibles quadrangular with
two strong spines before the collar; a row of short cilia from a collar. About ten
thorn-like bristles from margin, the last very strong, curved; dentition five, strong,
blunt thorns and one longer, more acute; long cilia below thorns. Process below
indistinctly furcate with strong hair-tufts on tips and a group of hairs at base.
Maxillae elliptical, at apex a brush of very long hairs; a seta near the apex; near

69

the inner margin a coating of long soft hairs; an inconspicuous row of thorn-like
bristles along the margin; palpe well developed with four or five apical digits. Mentum
triangular with rather large median tooth and about 13 small teeth on each side.
Biology. This peculiar mosquito, easily recognizable by the white scales
scattered over the wings, abdomen, and legs, I have for a long time vainly searched
for in our country. It has been described as Culex salinus Ficalbi (1896 p. 29) from
Italy, from the Mediterranean (see LANG 1920 p. 89), and from England where it
seems to be abundant, more especially in the South of England. It is a brackish
water species with sea-side habitat; it has very often been found with the larvae of
0. caspius and O. curriei.

During the regular exploration of the island Amager I always expected that
the species would occur sooner or later, but till the last part of August 1920 we
never found the species there; nor did all simultaneous exploration of the sea coasts
along Roskilde Fjord and various fjords on the east side of Jutland, and the brackish
water pools in the southern parts of Lolland and Falster, ever disclose the species.
Finally, only a few months (on 20/vn 1920) before the work was sent to press, I
found the species abundant in pools on the shores of Guldborgsund, which sepa-
rates the two islands Lolland and Falster; the pools were often filled with the
brackish sea water and contained numerous larvae and pupae. When hatched the
pupae all gave 0. caspius, and I supposed that the larvae would give the same;
then suddenly another mosquito wyith unhanded legs appeared in my cultures, and
these were now more thoroughly studied. I then saw that the larvae really did not
belong to 0. caspius, having all blunt scales and more than one hair in the frontal
tufts. Isolated they soon gave the above-named mosquito; a very short examination
then showed that the wings and legs were sprinkled with white scales and that
the abdomen on the underside possessed a series of black spots. The species was
then determined as 0. detritus (Haliday); in the latter part of August samples brought
me from Amager and Roskilde Fjord all contained numerous larvae of 0. detritus,
and many specimens were hatched in the laboratory. It seems that the species in
our country has only one generation, the imagines appearing very late; owing to
this it had nearly been overlooked.

LANG (1920 p. 89) supposed that O. detritus winters. as a larva or an egg (in
my localities almost certainly as egg) and that the species at least is double brooded
"for larvae and emerging ilies have been taken in September".

Geographical distribution: 0. detritus has hitherto only been found in
Italy and England.

9. O. communis (De Geer).

Tab. VIII.

Description. Female. Very similar to 0. punctor (Kirby), but the scales of
head and thorax are darker brown, and the coating of the mesonotum more homo-

70

geneous, the blackish brown stripe being less conspicuous and often almost obsolete.
The scales on the lateral parts of the thorax are more greyish than those of 0. punctor.

The abdominal bands are pure white, not creamy, forming straight lines
without any contraction in the middle line even on the apical segments. Underside
of abdomen usually all white. Femora darker than in O. punctor. Tibiae and tarsi
with more numerous pale scales.

Size 6 mm.

Male. Palpi entirely black; mesonotum covered with an almost homogeneous
greyish-brown tomentum. Abdomen and legs as in female. Genitalia: Side pieces
more than twice as long as wide; outer edge straight; apical lobe rather well
developed with only a few long hairs at tip; basal lobe well developed with long
hairs; clasp-filaments slender, slightly expanded in the middle, bearing a long arti-
culated terminal spine. Stem of harpagones very long, columnar; terminal filament
hardly more than half as long as stem, slender and bearing two ridges. Size 6'5 mm.

Larva: Head rounded; wider than long, a notch at insertion of antenna?;
front margin arcuate. Antennae short, antennal tuft small, with only a few hairs;
on apex three hairs and a short digit. Anteantennal tuft multiple; lower and upper
frontal tuft both consisting of one hair, or lower of two, upper of one hair. Eyes
large. Thorax subquadratic angled at hair-tufts; hair formula of frontal border
3131441313. In tuft 4 two hairs shorter than the others. Lateral hairs in multiple
tufts and some single strong hairs. Abdominal segments rather broad, the first of
them much shorter than the last. Lateral hairs on the first segment four, on the
second three, on the third to seventh two. On fourth to seventh segments subdorsal
hairs in double or. triple tufts. Tufts of eighth segment in common arrangement;
lateral comb consisting of about forty to fifty scales, arranged in rows occupying
a large triangular area; scales blunt with many almost equally long apical teeth.
Sipho short, straight, tapering at apex only a little more than double as long as
wide rarely three times longer than wide. At basal third a pecten consisting of
about twenty thorns all in line, and most of them with from 1 to 4 teeth of un-
equal length at base; a tuft of hairs between end of pecten and apex.

Anal segment longer than wide; the dorsal plate subquadratic, covering the
two thirds of the segment; dorsal tuft large, two very long stiff hairs beneath.
Ventral brush consisting of about 17 rays, every ray carrying from five to seven
hairs. Before the barred area about six free hair-tufts; a lateral tuft with two hairs.
Anal gills rather long, acute, equal. Lateral tufts of labrum short, but dense; the
inner part with a crown of comb-hairs; palatum large, covered with long, soft
hairs. Mandibles quadrangular with two strong spines before the collar; a row of
short cilia from a collar. About twelve thorn-like bristles from margin. Dentition: four
or five strong teeth, before them two short, acute thorns; long cilia below thorns.
Process below distinctly furcate with strong hair-tufts on both tips; a group of
hairs at base. Maxillae very broad, obtuse at front, at apex a brush of long hairs,
a seta near the apex, beneath the brush; near the inner margin a coating of

71

soft hairs, an inconspicuous row of thorns along the margin. Palpe well developed
with four apical digits. Mentum triangular with median tooth and about 14 small
teeth on each side.

Colour commonly greyish or brown, the head almost black.

Biology. Even in January, when the lakes are covered with thick ice, and
the landscape white with the snow, we are, on bright frosty days, able to feel the
heating power of the sun. If then on such a day, we examine the south exposed
borders of small ponds, lying in the beech-forest but in bright sunshine we shall
see that there is often a little stripe of water between the borders of the pond and
the ice edge; if the frost is severe, the stripe will disappear a few hours after
sunset, but will be formed again the next day if the weather is fine. By means of
a thermometer we are further able to ascertain the peculiar fact that the tempera-
ture in this stripe of water, only few inches from the ice edge, at the brightest
hour of the day, may rise to 7 — 10° C. ; sometimes I have even found 17° C. In
this stripe of water we find very many hibernating organs of the freshwater fauna :
Statoblasts, resting eggs, turions of water plants (Stratiotes, Myriophyllum etc.);
besides w,e also find a great part of the freshwater fauna which has hibernated
under the ice and now, in the water stripe, get the first feeling of approaching
spring. (Larvae of Odonata, of Ephemeridce etc. ; many small Mollusca, Crustacea etc.).
The enjoyment is but short; at four or five o'clock the temperature at the south
exposed borders of the ponds falls again, often below zero; but the above-named
temp, has been enough to hatch many of the hibernating organs, swept in autumn
by the wind on to the borders of the ponds, where they have been frozen in the
ice in November — December. This is the case with many Cladocera, and I suppose
also with the eggs of Phyllopoda. Simultaneously with them some insect eggs, which
have hibernated with them are hatched; among these eggs we shall in this connec-
tion especially pay attention to the eggs of 0. communis.

It is a rather common fact, at all events for my district of exploration, to
find in January the borders of trie partly ice-covered ponds teeming with newly-
hatched Cu/ex-larvae ; all the larvae still carry their egg tooth; they are hatched on a
sunny day from twelwe to three o'clock, but run the risk of not meeting this
temperature again for months. In the winter of 1918 — 1919 the ponds thawed in
the first days of January and were open till 22/i; the larvae were observed in
these three weeks. In this period the air-temperature never rose above 2° C.; we
had only very few sunny days, and the hours in which the temperature in
ponds was above one or two degrees, were certainly very few. By 22/1 the ponds
were frozen again, and did not thaw before the first days of April. Examining the
same ponds again, we still find the borders of the ponds teeming with very small
newly-hatched mosquito larvae. All are almost of the same size, a few have passed
the first ecdysis. From material taken into my laboratory on 13/1 and wintered here
at low temperatures, near zero, we learn that the larvae do not grow at these
temperatures. I therefore suppose that a great part of these larvae found in the

72

ponds in the first days of April, which look as if they were newly-hatched, are
really about three months old. In animals of such a small and delicate structure,
the need for atmospherical air is by no means as high as for larger ones which,
for a long time of their life, are covered with a much thicker cuticula; the respira-
tory conditions for cutaneous respiration in these ponds are also much better at
low temperatures than at higher. In early spring, immediately after the melting
of the ice, all our small ponds in our woods, the bottom of which is covered with
decaying leaves, teem with mosquito larvae; at that period in most of the explored
localities these almost all belong to one single species, the most common of all our
mosquitoes 0. communis. In the three years 1917 — 1919 the ponds thawed at diffe-
rent times, in 1917 from 5/iv |o 25/IV, in 1918 already in the last days of March,
and in 1919 Viv. Nevertheless C. communis was hatched as imago almost at the
same time all three years, in 1917 about 6/y, in 1918 about 15/v, and in 1919
about 10/v. In 1920 the temporary ponds were open already by Wn and then con-
tained huge masses of halfgrown larvae of 0. communis. In a mild period in the
first half of April they pupated; then a very cold period came, tp. of air hardly
ever more than five to seven dg., and the development was great retarded. The
ponds were often visited; a layer of living pupae covered the surface but ima-
gines did not appear before lo/v. I got the impression that an enormous amount
of pupae were destroyed by larvae of Dytiscs, by Phryganids (Phryganea minor) by
Hydrometridce and Notonecta.

At the beginning of the period we often find newly-hatched and halfgrown or
even fullgrown larvae among each other; side by side we further find ponds in one
of wrhich all larvae are fullgrown, whereas in the other many larvae are almost of
the same size; the pupation takes place almost on the same day, or at any rate
in the same week. Further it is very interesting to see, that the hatching of ima-
gines in the different ponds, but in the same latitude, almost everywhere in the last
part of the period takes place simultaneously; in North Seeland hundreds of forest
ponds have sent out their O. nemorosus material almost in the same week, and in
the years 1917 — 1920 this always lay between 6/v and 15/v.

The different development at the beginning of the period is intelligible, because
heavy showers suddenly raise the watermark line in the ponds, carrying a new
border of eggs outwards, giving them conditions for development. But also the
peculiar fact that, in spite of the different time for hatching from eggs, all larvae
are ready to pupate simultaneously, is intelligible. For it must be remembered that
these latest hatched larvae grow up under much higher temperatures and much
better conditions for rapid nutriment than those hatched in winter in ice and snow.
From my observations in my numerous cultures in my laboratory I can show that
I am always able to control the rapidity with which I wish the development of
the larvae to take place. Kept at temperatures between 0 and 5 degrees, the develop-
ment lasts about four months; kept at 15 — 20 degrees it is finished in at fortnight;
at low temperatures the water in my aquaria is very limpid and undoubtedly poor

73

in organic matter; at higher temperatures the sides of the aquaria are covered with
algae, and the water contains numerous Infusoria.

On the other hand we often find ponds where life conditions for the mos-
quito-larva? are so difficult that they highly influence the development.

On an excursion in Gripskov 15/iv 1919 I found many ponds with almost
fullgrown 0. communis larvae; a single pond lying in thick forest, and never getting
a single sunbeam, was still ice-covered; in the free stripe of water near the border
were many newly hatched 0. communis larvae, hatched almost a fortnight later

Textflg. 8. Pond in Store Dyrehave. O. communis, rusticus, cantons.

than in all ponds in the neighbourhood. The cold influenced the size of the ima-
gines, this being only half of the normal.

Of two of my Mochlonyx-ponds one lies free on the top of a hill, without
forest and fully exposed to the sun; the other lies in a deep hole, overshadowed
by willows and hardly ever sun-lit; the first is very shallow, has never more than
about one or two decim. water and dries up in May, the other is about one m.
deep, and dries up three or four weeks later; on sunny days the tp. in the former
is about 10 degrees above that of the latter. In 1919 the imagines were hatched
already on 6/y in the first pond, and the whole vegetation was covered with numer-
ous 0. communis; a few days later, the pond wras almost quite dry. In the second
pond the pupae did not arrive before 26/y then the pond was covered with a thick
layer of millions of pupae, and not before 29/y were the pupae hatched.

D. K. D. Vidensk. Selsk. Skr., naturvidensk. og mathem. Afd. 8. Rrekke, VII, 1.

10

I have often observed that the whole bulk of larvae, when the pond is almost
dried up, .are metamorphosed into pupae in the course of very few days and often
probably in the course of a few hours; in these very small water reservoirs, black
with the pupae, often lying in layers over each other, the temperature rises in the
sunshine to about 28° C.; the pupae-stage lasting only one or two days.

Further I have observed ponds which had a good deal of water in 1918, and
from which enormous masses of 0. communis were then hatched, but were dried up in
1919 during the whole of spring, and only in July got a decim. of water in the
deepest holes of the bottom. These holes were often formed by the cattle plodding
in the mud. In these very small water reservoirs a small part of the enormous
egg masses which covered the whole bottom was hatched; in the course of only
eight or ten days, by the drying power of the sunshine, in our hottest summer-
months, the whole metamorphosis was finished; at last the little water-mass was
packed with pupae, these being so numerous that they lay in layers over each
other, pressed together to suffocation; the whole mass is in a constant circulation,
the deepest layer always trying to reach the surface. In the greyish dried, up sur-
face of the pond these small holes shone black from the masses of black pupae.

The huge masses of larvae in the last stage as well as the pupae are of course
extremely good as food for many lower animals. Whereas the pupae of Chirono-
midae when they come up to the surface from the great depths of the lakes are
a welcome prey to the dikeswallows, I do not know of any insect-eating bird
which has learned to catch its food in the ponds teeming with mosquito larvae or
pupae; at all events I have never disturbed our singing birds on the drying mos-
quito-ponds; for the blackbird, which comes in late autumn and winter to the
same ponds to search for the larvae of Trichoptera, the mosquito larvae are prob-
ably too small. On the other hand, the surfaces of these ponds, near the hatching
time of the mosquitoes, are covered by pondscaters which dig their huge probos-
cis into the fat forepart of the pupae. As most of the pondscaters are wingless, we
must admire the speed with which they are able to find these small and often
sheltered ponds. But also different Dytiscidae more especially of the genera Colym-
betes and Rhantus as larvae prey almost exclusively upon O. com /n urns-larvae; the
eggs are laid in early spring, and it is interesting to see how these larvae in their
development keep time, so to speak, with the mosquito larvae; they are hatched
as larvae at the same time as these and they are ready to pupate a little after the
mosquito larvae have metamorphosed into pupae. It is very interesting to find these
ponds which, a few days before, have delivered the whole mass of mosquitoes to
another element, teeming with black and white coloured Dytiscid-larvae. An-
other fat morcel would have been desirable before pupation, but such a one can-
not now be obtained, the mosquitoes all being out of their reach; now they
have only one prey upon which to satisfy their hunger, viz. their own comrades.
This is exactly what happens, woe to the larva which, when the mosquitoes have

75

left the pond, has not passed the second ecdysis; it will unquestionably be devoured
by more vigorous comrades.

As always in the Culicidae, the males appear a few days before the females;
during the first days the vegetation round the ponds is covered with males; then
they disappear and we next find them in large dancing swarms in the glades and
on the wind-protected edges of the wood. Especially if the weather is cold, we do
not suffer from 0. communis till a fortnight after ecclosion (see later); then sud-
denly comes the week, when the lust of blood awakes in the millions of mosqui-
toes hatched in May from the numerous woodland ponds. In the vast forests of
North-Seeland I have observed how the swarms in May are restricted to the very
ponds in which they are hatched; but later on, especially in the middle of June,
the swarms are fused together and, everywhere in the forest, horses as well as men
are attacked. As an exclusive forest mosquito it hardly ever goes out of the forest;
according to my experience, the attack is always worst in the biggest and darkest
part; here in the deep shade the attack on a sunny day at noon is just as severe
as in the evening. In late spring and early summer man and cattle are almost ex-
clusively injured by this single species.

The mighty attack of 0. communis lasts only two or three weeks; before the
end of July other species displace it, but even in September, though rarely, we are
subject to its sting.

When, in July, the female is going to deposit her eggs, she commonly finds
only quite dried up ponds everywhere; where, in spring, bright little mirrors of
water broke the monotonous green carpet only greyish-brown spots surrounded by
or quite overgrown with Cyperacese etc. are found on the forestground.

For three years I vainly tried to see the process of egglaying. Not until the
summer of 1919 on 3/vii did I have an opportunity to observe it in one of the
wholly dried up Mochlonyx-ponds. The females were sitting under the dry leaves;
here, as many times before, I had placed myself on one of the Carex-tufts eagerly
observing every grass-stem and every leaf, hoping that here I should see something
of the process. Once after having turned over the withered leaves, I found, in a
layer of leaves below those rolled up by the sun, some mosquitoes which slowly
flew away. Looking at these leaves with a lens I found them sprinkled with the
wrell-known black mosquito eggs. Later on, leaves which wrere cleaned were brought
into the laboratory and placed in a vessel together with several females; the next
day I found the same black eggs scattered over the bottom under the leaves.
Therefore we can now take it for granted that this species probably, like all our
other Ochkrotatus-species, lay their eggs on dry earth and singly. I interpret the
life-cyclus of 0. communis as follows:

The eggs are hatched in midwinter or in very early spring; many of them
do not hatch before April; owing to the rising tp. the latest hatched overtake the
first, and in the two first weeks of May the mosquitoes are hatched. The mating
process takes place shortly after hatching, but the craving for blood does not appear

10*

76

before June, often not till the latter part of June. The eggs are laid singly and
often in the same pools in which the imagines are hatched, but these pools are now
dry, and the eggs are deposited upon dry bottom from July — August to December —
January and do not hatch before a freezing period; the males probably die off
shortly after the mating process ; the number of males I have seen after June being
very limited. In some ponds, and more especially in rainy summers, larvae may be
found after June, but the number is always very limited and has no great signifi-
cance, neither for the species nor for man.

0. communis has as a rule not more than one generation. In the very rainy
summer of 1919 many of the ponds were never dried up, and a good many had
plenty of water almost the whole of the summer. Of course we should now expect
that a new generation would be hatched, but this, as far as I can see, is not the
case. - - In these ponds I have really found 0. co/miwms-larvae in the months of
July — August; but the number was always small, and I never found those vast
swarms of larvae and pupae which coloured the ponds black in spring. The 21st of
July was the last day I found 0. nemorosus larvae; to these lately hatched 0. commu-
nis larvae, I refer most of those imagines which torment us in August and Septem-
ber. Even on 12/ix a single 0. communis stung me in the Royal Park at Hillerad.
In autumn when the small ponds are filled again, as a rule we find no 0. commu-
m's-larvae; here and there I have seen a few, and once I got a pupa which meta-
morphosed into imago n/xn in one of the aquaria.

I am inclined to regard all these larvae which appear after the great hatching
period in spring, not as belonging to a new, second generation, but to the same
generation as those which were hatched in spring. I suppose they derive from eggs,
which have had a rather unfortunate situation, which the water has reached too
late, or which have been buried too deep under the remains of the decaying vege-
tation. I do not think that we have to do with a new generation, hatched from
eggs laid in summer, whilst only very few larva? are hatched, and whilst the same
ponds in which these larvae are hatched, teem with larvae the next year.

It may be added that more than once I have observed ponds which had
water till June in 1917 and which were hatching-places for swarms of mosquitoes
about 7/v; in 1918 the very same ponds did not get any wrater and were dry the
whole year. In 1919 in April the ponds got water again and nowr teemed with
larvae in May; I suppose that these larvae belong to eggs which have preserved
their vitality from 1917.

That 0. communis really can have two generations in a year, we shall see
from the following fact.

On an excursion 25/x 1918 through the forest Store Dyrehave near Hillerod I
found many small ponds filled with water; heavy showers during the last fortnight
had given so much water that the bottom in the hollows could not take up more.
To my great astonishment in two of them I found enormous masses of black, al-
most fullgrown mosquito larvae. The ponds were overshadowed by high spruce firs,

77

the bottom of the ponds were covered with spruce-needles; the depth of the water
was only about a decim., and the area of the pond about fifty yards.

In regard to its short sipho and its black colour it differed very much from
C. morsitans, the only mosquito larva which was common at this season; a closer
examination of the sipho further showed that it could not be 0. rusticns; that the
larva would only be that of 0. communis did not occur to me. It was therefore to
be expected that the larva must be a new one. In the time from 15/x to *5/xi the
ponds were often visited. The temperature fell from seven to two degrees; at that
constantly sinking temperature, and in a pond which never got a single of the
really very few sunbeams of the season, these larvae reached their maximum size;
at the water temperature of 2° C. the larvae metamorphosed into pupae. At an air-
temperature of only 4° C. and a water temperature of 2° C. I saw the imagines in
nature come out of the pupae, very slowly fly a few yards and settle themselves
on the cushions of Sphagnum near the borders of the pond. The males appeared
first, a few days later the females. By 15/xi came a short frost-period; the ponds
were ice-covered, and all the pupae in the pond were killed. In December the ponds
thawed again, but not a single larva or pupa could now be detected. In the time
from 15/x to i-Vxi I visited many similar forest ponds lying in forest of spruce firs,
and I often found the same larvae in these ponds; these were always in very cold
localities where the damp autumn-fogs hung under the spruces almost the whole
day. Though I especially paid attention to that point, I could never see the mating
process; but opening the Sphagnum cushions near the ponds, I found the female
sitting there very indolent and half sleeping. The larvae had all blunt scales in the
comb and one single hair in the upper and lower frontal tuft. The colour of the
larvae and pupae was black as tar, but apart from this colour they were in-
distinguishable from the typical 0. communis larvae. The next spring, in the first
part of April, when the ponds were still partly covered with ice, I examined the
locality and found the water teeming with minute larvae. By 8/y they contained
enormous masses of larvae and pupae, on iVv the pupae were hatched.

If now we compare the imagines from the autumn of 1918 with those from
the spring of 1919 and 1920 we shall see that the first-named are larger, darker
and more hairy; a closer examination will however show that tenable differences
between the two groups of imagines hatched in autumn and spring do not occur;
both belong to the same species, our common 0. communis; I do not think that
the imagines have hibernated ; most probably they have died off, imagines in spring
deriving from eggs which have not been hatched in autumn.

For a time I thought that in the autumn-generation I had had 0. nigripes
Zett. before me. This was more especially the case because only a few kilometers
from my localities STAEGER (1839 p. 553) in the Royal Deer park near Copen-
hagen has indicated that he has found 0. nigripes. Owing to the peculiar fact that
the larvae metamorphosed at temperatures between 4° and 2° C. and that the ima-
gines appeared at the same temperature, in this tract, which was quite extraordinary

78

and unique for a mosquito of our fauna I saw a phenomenon which strengthened
my supposition. After having sent the specimens to Prof. SIMON BENGTSON in Lund
and asked him to compare them with the specimens of O. nigripes in the collection
ofZetterstedt, he kindly told me that a very similar specimen was caught in Scania
and was determined as 0. nigripes but differed from this by a brighter colour and
in not being so hairy. In a small preliminary paper the specimens were then des-
cribed as 0. nigripes. Later on I learned that this determination was wrong. The
Royal Museum of Copenhagen possessed mosquito larva? from Greenland, from
where we have hitherto only got one single mosquito species: C. nigripes; they were
kindly given me by Inspector LUNDBECK and will be described in the following; it
will then be seen that the two larvae differ very much from each other.

It seems therefore that 0. communis in our country really can have two
generations and that the late autumn generation differs a little especially with
regard to colour from the spring generation.

As described in the anatomical chapter the Iarva3 have very short flabellse;
and are very well equipped with comb-hairs. Nevertheless they are not bottom-
feeders, but live mainly in the surface of the ponds, hanging down from it by
means of the flaps of the sipho. In this attitude the ecdysis takes place too, also
the last one from larva to pupa. The larva often hung down in such countless
numbers from sunlit surfaces of the forest ponds that they almost touched each
other. The millions of flabellse, all in activity about a centimeter under the surface,
must produce an uninterrupted water current, lifting a deeper water layer upwards
to the surface. The flabellae of O. communis being very small, they act in quite a
different way to the large flabellae of Culiceta morsitans. Whilst the flabellae of the
last-named species strike about 100 to 130 strokes a minute by summer tempera-
tures, the flabellae of 0. communis strike with such an enormous rapidity that it is
quite impossible to count the number of strokes. Besides, the larva has also an-
other method of using the flabellae, and according to my view this is more signifi-
cant when the organ is to be used for gathering nutriment. We see that there are
always certain larvae which, when kept in aquaria, constantly hold the apex of
the sipho in the surface, suddenly bend the head upwards and now press also the
flabellae against it. Immediately after the bending of the corpus in a bow, the whole
body begins to describe a circle round the sipho which is held quite still; during
the circular movement the flabellae are pressed against the surface and used as
brushes which clean the underside of the surface of all adherent particles.

Geographical distribution: The species has been so confused with O.
punctor (Kirby) that it is almost impossible to determine its range with certainty.
Most probably it is the most common forest mosquito with unhanded legs in North
and Central Europe.

79

10. O. nigripes (Zetterstedt).
Tab. IX.

Larva: Head rounded; wider than long, a notch at insertion of antennse;
front margin arcuate. Antennse short; antennal tuft small, with only a few hairs;
on apex four hairs, one long, and a digit. Anteantennal tuft multiple; lower
and upper frontal tuft both consisting of one single feeble hair. Eyes large. Thorax
subquadratic, angled at hair-tufts; hair-formula of frontal border: 3231441323; hair
one after tuft four very short. Lateral hairs in multiple tufts and some single strong
hairs. Abdominal segments broad; the first of them much shorter than the last.
Lateral hairs on the first segment four; 011 the second three, on the third to seventh
two. On fourth to seventh segment subdorsal hairs single in two series. Tufts of
eighth segment in common arrangement; lateral comb consisting of about twentj'
scales arranged over a little triangular area; scales formed as sharp strong thorns
without any lateral thorns or hairs. Sipho short, straight, tapering at front only
about two and a half times longer than broad. Pecten long consisting of about
fifteen thorns; the last of them out of line at greater distance from each other;
most of them with a short basal tooth. A tuft of hairs between end of pecten and
apex. Anal segment broader than long ringed by the dorsal plate ; dorsal tuft rather
feeble but with two strong hairs; ventral brush consisting of about eighteen rays,
every ray carrying from seven to ten hairs; no hair-tufts before the barred area;
anal gills extremely long, acute and equal.

Lateral tufts of labrum short but dense ; the inner part with a crown of comb-
hairs; palatum large, covered with long soft hairs. Mandibles quadrangular with
two strong spines, before collar a row of rather long cilia from a collar. About
eight thorn-like bristles from margin. Dentition: four acute teeth, before them a
long acute thorn; long cilia below thorns; Process below indistinctly furcate with
hair-tufts on both tips, a group of hairs at base. Maxillae very broad, almost qua-
dratic with a brush of rather short hairs at apex and a seta; near the inner edge a
coating of long soft hairs; stronger dense haircovering along margin. Palpe thick,
high with four small digits at apex. Mentum triangular with inconspicuous apical
tooth and many small almost equal lateral ones.

Geographical distribution: Greenland; most probably circumpolar.

11. O..punctor (Kirby).

O. sylvce Theobald.
Tab. X.

Description: Imago: Very similar to 0. communis. Scales of head and
thorax mostly yellowish-brown, brighter than in 0. communis. Thorax with a more
or less commonly well-defined median stripe of dark brown scales on mesonotum.
The white bands of abdomen with a creamy tinge, not white as in 0. communis;
most of the bands at least them on segments 5 — 7 contracted or even interrupted
in the middle so that the bands are almost changed into creamy, yellowish, tri-

80

angular spots. Venter with a more or less well-defined dark median line not all
white as in 0. communis. Femora yellowish white, without dark scales scattered
over the light parts ; tibiae and tarsi dark, with scarcely any light scales ; in 0. corn-
munis tarsi have several numerous pale scales. Length 5.5 — 6.5 mm.

I have never seen the male; according to indications kindly sent me by Mr.
EDWARDS the male genitalia of 0. punctor differ very much from those of 0. corn-
munis. The side pieces have only a rather faintly developed apical lobe, with many
short hairs; clasp-filaments with some hairs (three) along the outer edge; a large
densely haired basal lobe; blade of harpags not much shorter than the stem. See
also LANG (1920 Fig. 64).

Larva. Head rounded, wider than long; a notch at insertion of antennse; front
margin strongly arcuate. Antenna? short, only slightly tapering at front; antennal
tuft nearer to the base of the antennse; consisting only of a few hairs. At apex, three
short hairs and one or two digits; colour yellowish-brown, not brighter at base.
Antennal tuft multiple, upper and lower frontal tuft both consisting of two strong
hairs. Eyes large, triangular. Thorax subquadratic angled at hair-tufts. Hair formula
of frontal border 3121441213; tuft one after tuft four only consisting of one or two
very small hairs, the other hairs of frontal border all being strong. Lateral hairs
in multiple tufts and some single strong hairs. Abdominal segments rather broad,
the first of them shorter than the others; lateral hairs on the first two segments
three, on the third to seventh two. On fourth to seventh segments two series of
single, subdorsal hairs. Tufts of eighth segment in common arrangement; comb
consisting of about twenty-five scales, occupying a triangular area-; the scales are
very long, acute with a strong very acute median tooth and a few shorter ones.
Sipho short, straight, tapering at apex, three times longer than broad, often a
little more. A pecten consisting of about twenty thorns, all in line and most
of them with from three to four teeth at base. A tuft of hair between end of pecten
and basis.

Anal segment almost as long as broad, ringed by a plate ; dorsal tuft rather feeble,
with two very strong, long hairs beneath. Ventral brush consisting of about from
twelve to fourteen rays, every ray carrying from six to seven hairs. Before the
barred area about five free hairtufts, a lateral tuft with one hair. Anal gills moderate,
acute, equal.

Lateral tufts of labrum short, dense, the. inner part with a crown of comb-
hairs; palatum covered with short, stiff hairs. Mandibles quadrangular, with two
strong spines before the collar, a row of short cilia before collar. About fourteen
thorn-like bristles from margin; the last strong. Dentition: four strong teeth, before
them one acute thorn, serrated; long cilia below the thorns. Process below distinctly
furcate with strong hair-tufts on both tips, a, group of hairs at base. Maxillae broad,
obtuse, at apex a brush of long hairs and a seta near the apex below the brush;
the whole inner part of the maxillae covered with a coarse coating of long soft

81

hairs. Palpe well developed with three or four digits. Mentum triangular with a
rather small, median tooth and from thirteen to fourteen small lateral teeth.

Colour deep grey, often almost black.

Biology: Of 0. punctor, in the above-named sense, I- have only seen one
single specimen, brought me by Mr. KRYGER from Tisvilde-forest, near the shores
of the Kattegat. I immediately saw that this specimen differed very much from all
our other forest mosquitoes belonging to this group. Especially the restriction in
the middle of the abdominal bands was very conspicuous. Later on Mr. EDWARDS
corroborated my supposition, writing to me "that this was the first undoubted
specimen he had got from Denmark"; all the other related specimens belonged
either to 0. communis or 0. prodotes; I have never found the larva; the specimens
used for the table derive from Mr. EDWARDS' collection.

The real geographical distribution of the species is quite unknown.

12. O. prodotes (Dyar).
Tab. XI.

Description. Female: Proboscis moderate, cylindrical, uniform, black.
Palpi short, about one fifth as long as proboscis, black with few, whitish scales
intermixed; setae moderate, bristley. Antennae filiform, the joints subequal, rugose,
pilose, black with some whitish scales, second joint longer and thicker than third,
pale at base; tori subspherical with a cup-shaped excavation, luteous, darker within;
hairs of whorls black. Clypeus rounded, prominent, black, nude. Eyes black. Occi-
put black; scales on vertex lanceolate, curved yellowish white, on sides broad milky-
white throughout, now and then an ill-defined lateral black patch ; bristles on the
occiput and along margin of eyes black, those projecting between the eyes pale.

Prothoracic lobes elliptical, remote dorsally, black, clothed with narrow white
scales and dark bristles. Mesonotum black with a coating of brown hairs commonly
spread over the whole mesonotum and without wellmarked blackish lines. Scutellum
trilobate black, each lobe with a group of brown bristles. Postnotum elliptical, prominent
blackish nude. Pleurae brown, coxae luteous, clothed with patches. of elliptical flat,
white scales and rows of pale bristles.

Abdomen subcylindrical, tapering posteriorly; dorsal vestiture black with broad
white basal segmental bands which in the middle have a rusty colour; first segment
almost white; venter whitish, scales with small black segmental medio-apical spots;
cerci black.

Wings rather broad, hyaline; petiole of second marginal cell shorter than
its cell, that of second posterior cell slightly longer than its cell; basal cross- vein
distant almost its own length from anterior cross-vein; scales blackish-brown, the
outstanding ones broadly linear. Halteres whitish, with yellowish knobs.

Legs moderately long and slender; femora yellowish-white; brightest below,
darker above, a black ring before tip ; tibiae with dirty-white scales below, bronzy black
above with a few white scales intermixed, tips black; tarsi almost black; the basal

O. K. D. Vidensk. Selsk Skr., naturvidensk. og mathem. Afd. 8. Raekke, VII, 1. J \

82

joint beneath with scattered white scales; terminal joints entirely black. Claw for-
mula 1.1—1.1—1.1.

Length: Body about 5.5 mm.

Male: Proboscis slender, rather long, straight, black. Palpi almost of the length
of proboscis, perhaps a little longer; end of long joint swollen dirty-white; the first
long joint yellow, black at apex; the second yellow, black at base, the last two joints
black with long black hairs with silky luster. Coloration similar to the female. Abdomen
elongate, broadest on sixth and seventh segments, narrowest at third; white basal
bands almost as in female, but first segment more black; lateral ciliation long,
abundant, pale yellowish brown. Wings narrower than in female; stems of the
fork-cells longer; vestiture less abundant. Claw formula 2.1 — 2.1 — 1.1.

Length: Body about 6 mm. wing 5 mm.

Male genitalia. Side pieces almost three times longer than wide; apical lobe well-
developed, with some few rather short hairs. Clasp-filaments slender, slightly ex-
panded in the middle and bearing a long articulated terminal spine. Stem of harpa-
gones very long, columnar; blade broad in middle, bearing only one median ridge.

Larva: Head rounded, strongly vaulted, wider than long with a slight notch
at insertion of antennae;, front margin feebly arcuate; antennae short, thin, black,
from base to apex slightly spinose, with the small antennal tuft (four hairs) in-
serted almost in the middle of the antennae. Anteantennal tuft only triple; lower
and upper frontal tuft consisting of only one hair. Medially and laterally are three
areas with a remarkable warble structure.

Thorax subquadratic, angled at hair tufts ; hair formula of frontal border most
probably 3131221313, one of the hairs in tuft two, strong, the other feeble and
short. Lateral hairs in multiple tufts, and some single strong hairs.

Abdominal segments rather broad, the first of them shorter than the last.
Lateral hairs on the first and second segments triple; on the third to seventh double.
Tuft of eighth segment in common arrangement; lateral comb consisting of about
twenty-five scales, arranged triangularly in two or three rows, the scales end in a
single strong spine, furnished at its base with two other shorter spines and with
the basal part fringed by numerous small hairs or bristles. Sipho almost three times
longer than broad, tapering at apex; pecten consisting of about twenty thorns,
furnished at base with three or four lateral teeth; between the tuft situated almost
in the middle of the sipho and the apex two single thorns, without teeth and with
much wider distance between than the teeth of pecten; a single short thorn dor-
sally near the apex of the sipho. - - As fig. 6b indicates, the free thorns are inser-
ted unsymmetrically, and their place differs from individual to individual; one side
may also have a thorn more than the other. Anal segment almost as long as wide;
the dorsal plate subquadratic, covering most of the segment; 'dorsal tuft rather
small with two very long stiff hairs beneath. Ventral brush consisting of about from
ten to twelve rays, carrying from four to six rather short hairs; before barred area three
or four free tufts; a lateral tuft with one single hair. Anal gills short, equal, acute.

83

Lateral tufts of labrum extremely short, the inner part with short comb-hairs;
palatum feebly developed with short hairs.

Mandibles quadrangular with two curved spines before the collar; a row of
rather short cilia from a collar; about seven to ten thorn-like bristles from mar-
gin; dentition five, almost equally strong teeth and before them a strong tooth;
long cilia below thorns; process below very indistinctly furcate with hairs on both
tips and a group of hairs at base.

Maxillae of remarkable form, broader than long, on apex a brush of long hairs,
which was commonly spread out as a flattened crown over the maxilla, all the
hairs lying in the same plane but with the hairs turning towards the inner surface
of the maxilla much longer than on the outer edge; near the inner margin a thick
and coarse coating of short soft hairs; inconspicuous thorns along the margin.
Palpi remarkably well-developed, almost cylindrical, furnished with four digits at apex.

Mentum triangular with middle tooth feebly developed and thirteen teeth along
the borders.

Biology. From one of the Hydrophantes ponds in Hestehave near Hillerod
0. excrucians and commnnis were hatched in 1919 in huge numbers. Among the 0.
communis material a good many were characterized by brighter bands, rusty in the
middle on the abdomen, and almost white, long joint in the palpi of the male. I regarded
them as an aberrant form of O. commnnis, but sent them to Mr. EDWARDS who kindly
told me that according to his opinion they were 0.' prodotes Dyar.

On examining my larva material from the Hydroplantes-pond I found a few
specimens of a highly characteristic larva, hitherto overlooked by me. Next year,
just after the ice had melted very many of these larvse were found and later on
hatched in my aquaria. Having found the species in this single pond I searched
for the larvse in a great number of ponds near Hiller0d, but found the species only
in a few of them and always in small numbers. On the other hand, on an excur-
sion in April to the many ponds on the Eremitage-plain in the Royal Deer Park
about 15 kilom. from Copenhagen, almost all the ponds teemed with 0. prodotes
larvse, and in more than one of the ponds I only found this very same species.

The species is hatched very early before 0. communis and 0. nemorosus. On
examining the ponds in the latter part of April and first days of May the ponds
contained huge masses of larvae of these two species but not a single O. prodotes-
larva. It is owing to this fact that I have overlooked the species in 1917 — 1919.
As far as I have hitherto observed, it seems that the species prefers temporary
ponds on plains, not overshadowed by trees, or ponds lying on the outskirts of
forests; I have never found them in the temporary pools in the deepest parts of
the woods, overshadowed by trees and only rarely touched by the sunbeams, locali-
ties where 0. communis preponderate.

The species has unquestionably only one generation in the course of the year,
lying almost the whole year as eggs; all ponds in which the species is found are
commonly dry from June to March. The eggs according to DYAR (1920 p. 10) have

11*

84

a rather characteristic appearance being ''thickly fusiform, rounded, one side flat-
tened, the ante-micropylar end more pointed than the other".

Geographical distribution: 0. prodotes has hitherto only been found in
North America. Its range "is to the north along the higher mountains of the Rock-
ies into the Yukon Valley, where it is the second species in abundance". (DYAR

1920 p. 9). In U. S. A. it is indicated as a "high altitude species".

*

13. O. rusticus (Rossi).

Aedes diversus. Theob.

Tab. XII.

Description. Female: Proboscis moderate, subcylindrical, flattened, uniform,
black, covered with scattered yellowish-white scales; nearest the apex and labellge
black; setae minute, black, curved, those on the labellae more prominently outstan-
ding. Palpi stout, rather long, about one-fourth of the proboscis; vestiture of black
scales with many pale ones; setae few, long, black. Antennae with the joints sub-
equal, rugose, pilose, black; second joint somewhat thickened, tori subspherical with
a cup-shaped excavation outwards, covered with small, broad whitish scales, on
the inner side black. Clypeus shortly conical, prominent, convex, black, nude. Eyes
bronzy black. Occiput covered with dense, narrow, yellowish-brown scales on the
vertex and many forked upright ones, a large patch of golden brown ones on each
side close to the eyes; bristles "along margin of eyes black.

Prothoracic lobes elliptical, well separated, black, covered with yellowish-
white scales and many long, black bristles. Mesonotum black with a dark, very
small middle line, two broad median dark lines and two small lateral dark lines
behind; between these lines stripes of yellowish-brown scales. Scutellum trilobate,
black, clothed with narrow, curved brown scales, each lobe with a large group of
long, yellowish-brown hairs.

Postnotum convex, black, nude. Pleurae black, coxae black, clothed with narrow,
elliptical, flat yellowish-white scales and short pale bristles.

Abdomen flattened, broad, the posterior segments tapered; dorsal vestiture of
blackish-brown scales, each segment with a basal band of creamy white scales,
wrhich spread out in the middle, forming together a more or less conspicuous
whitish middle line, and on the sides, where they form triangular creamy spots;
the seventh segment almost white with two dark spots; posterior borders with pale
golden bristles. Venter almost entirely clothed with pale creamy scales.

Wings large, veins covered with dark brown scales and pale lateral ones;
first submarginal cell much longer and narrower than second posterior cell, its
stem slightly shorter than the cell; stem of the second posterior cell shorter than
the cell, the forks of which widely diverge; supernumerary and mid cross-vein in
a straight line; the posterior cross-vein about half its own length distant from the
mid cross-vein; fringe brown, halteres ochraceous, with pale scales on the knob.

Legs: Femora creamy-yellow, especially beneath, with some dark scales above;

85

darkest at apex; knee spots yellow, large,, distinct; tibiae darker, yellow beneath;
metatarsi and tarsi blackish-brown, hind metatarsi not so long as the tibiae; ungues
equal. Formula 1.1 — 1.1 — 1.1.

Length 7 mm.

Male: Proboscis slender, straight black violet. Palpi exceeding the proboscis
about the length of the last joint; end of long joint and the last two joints thickened,
the long joint coated above with greyish scales; this and the two last joints bearing
long greyish hairs. Antennas plumose, the last two joints long and slender, black
with white rings ; hairs of whorls long, dense, black with greyish lustre. Coloration
of head and thorax similar to that of the female, but the dark lines of the ineso-
thorax more obsolete; coloration of abdomen similar to the female, but the ex-
pansion of the bands in the middle line often rather inconspicuous. Lateral hairs
very long, dense and yellow. Wings narrower than in the female, stems of the fork
cells longer. Legs as in female. Claws on the fore and midlegs unequal; on the
forelegs the large ones with two teeth, the smaller with only one; on the midlegs
both claws with two teeth ; the inner tooth of the smaller one small ; the large claw
strongly curved and highly developed ; claws of hindlegs equal and with only one tooth.

Male Genitalia: Side pieces with parallel curved outer and inner edges,
about thrice as long as wide, slender; the whole side piece being narrow, forming
the arc of a circle; Clasp-filament long, slender, curved not swollen medianly,
with a long articulated terminal curved spine; apical lobe of ventral flap indistinct,
distal part of basal lobe prolonged into a narrow arm-like projection with an ex-
panded hand-like end; tuft at the base of the basal lobe with extremely long brist-
les extending along the ventral flap as a fringe of very long hairs. Harpes slender,
rather long, margins narrowly revolute. Harpagones with a stout thick curved
columnar base with small setae on inner side; distal joint spatulate. Unci approxi-
mate, revolute, forming an indistinct basal cylinder; basal appendages stout and pro-
minent, bearing a row of stout setae at tip.

This very characteristic species, in the female sex easily recognizable by the
white middle line on the abdomen, in the male sex by the genitalia, and in the
larva by the characters of the sipho, is probably rather common at all events in
North Seeland.

Larva. Head rounded, wider than long, narrowed before eyes; a notch at in-
sertion of antennae; front margin arcuate. Antennae extremely short, straight, spinose;
antennal tuft small, inserted almost in the middle of the antennae; at the apex two
small hairs a long hair and a digit; anteantennal tuft multiple, lower frontal tuft
triple, upper double; epistome with a very characteristic coloration of the head
integument. Eyes well-developed.

Thorax much wider than long, rounded; hair formula of frontal border
5141331415 or 4131331314; hair 1 after median tuft 3 short, lateral hairs highly
developed; most of them in large multiple tufts, some of them single.

Abdomen moderate, the first segments much shorter than the last; lateral hair-

86

tufts on segments one and two multiple, on segments three to six double; a pair
of subdorsal hairs on segments one to six, largest on segments four to six. Hairs
of segment eight in normal arrangement. Lateral comb consisting of about 15 scales,
triangularly arranged in two irregular rows ; each scale with a broad spatulate base
and a very strong median thorn, two shorter lateral thorns and many shorter ones
bordering the spatulated part. Sipho straight, a little more than three times longer
than wide; pecten at basal third highly developed, consisting of about fifteen to twenty
strong dark spines, the first of them without lateral thorns, the others with one or two.
The pecten reaches to the hair-tuft; between it and apex two or three strong spi-
nes with large distance between each other; dorsal to the pecten and about half-
wray along it a small hair. On the opposite side of the sipho four pairs of hair-
tufts, more or less conspicuosly double, arranged in two lines. Anal segment much
longer than wide, almost covered by the dorsal plate. Dorsal tuft well-developed
with two very long, stiff hairs. Ventral brush in the barred area consisting of nine
rays each with from six to eight hairs; before barred area three or four free tufts.
Anal gills very short, broad, almost equal.

Lateral tufts of labrum short, a crown of comb-bristles nearest to the pala-
tum which is covered with long, soft hairs. Mandibles quadrangular, four stout spines
before collar, a row of long cilia from a collar; about ten spines from margin;
dentition very strong: four teeth, the first of them strongest, between them and the
marginal spines two strong spines; below the teeth a series of bristles. Process
below but slightly furcate, with strong hairs at apex; a group of hairs at base.
Maxillae of very remarkable form, almost wider than long, divided by a suture
with a large hair-tuft on the broad, oblique apex and a spine near it; coating of
soft hairs on both sides of suture; longest on the inner surface; no spines at inner
margin; palpe high, almost as high as maxilla; at the apex five conical digits.
Mentum broad, triangular with curved sides; a median tooth and 10 — 12 rather
large teeth on each side. Colour greyish, dark, often almost black with yellow head.

The species has been described by THEOBALD from England (1901 p. 73) and
refound by EDWARDS (1912 p. 219). It has also been found by GOETHGEBOUR (1910
p. 84) in Belgium and by ECKSTEIN at Strassbourg (1910 p. 67). The larva has been
shortly described by ECKSTEIN (1919 p. 293). The species is new to our fauna. In
accordance with my observation GOETHGEBOUR remarks que 'Tespece est la plus
precose dans nos environs. Je n'ai plus revu 1'espece a partir de la mi-juin".

Biology. In November — December 1918 I found, in two ponds near Hillered,
together with C. morsitans a huge, fullgrown, almost black mosquito-larva which I
immediately saw must give a species hitherto unknown to me; in the ponds
the larvae were always rare; and that year I found them only in the two above-
named ponds, lying near each other in the forest at the mainroad between Copen-
hagen and Hiller0d. Though the ponds were only about two hundred yards in cir-
cuit and were only a few decim. deep, and though I used my net for about an
hour, I could only get a few larvae. In December the ponds were frozen over, but

87

on 21/1, after a long period of thaw, they were half free from ice. Then I again
captured some few larvae, two of them were held in aquarium, but died during the
winter. In the last days of January the ponds were ice-covered again and did not
thaw before 5/iv 1919; at this date, when the pond was still ice-covered, I got
eleven larvae under the ice on one of the borders; they were all fullgrown and in
the following days (till 16/iv) on three excursions I caught all in all about twenty larvae.
On a journey to Suserup I got very many larvae in the same pond in which
C. lutescens was hatched, undoubtedly belonging to the same species. Further, on

Textfig. 9. Pond in Store Dyrehave. O. cantans, ruslicus, C. morsitans.

excursions to a little forest near Suserup, Arnehave, I found a pond which was al-
most exclusively inhabited by this larva; here it was present in thousands of spe-
cimens. All these finds were made in the time from 17/iv to 2l/iv. In the time from
Vv to 3/v there were no changes to note, but on 3/v I saw the first pupae, and
before 15/v all were hatched. On 6/y the first imago appeared in my cages; on 12/v
the last. By 21/y the ponds near Hillerod \vere both dry, by 7/vi all those at Suse-
rup; however, in the ponds where 0. lutescens was hatched, and which were now
covered with grass, I found numerous specimens deep down in the grass. After July
the first I have never seen a single specimen, neither at Hillerod nor at Suserup.
Probably we have to do with a rather rare and early flying species. Its life-history
may be summed up as follows: The imagines are hatched in May and may prob-
lyba lay their eggs on the dried bottom of forest ponds, rarely in ponds in meadows,

88

without trees around. The eggs are hatched, in autumn when the ponds get water
again. Before winter they are full grown, and as such they winter, living under the
ice exactly like C. morsitans. In the first days of May they pupate, and the mos-
quitoes appear in the first part of the same month. In the aquaria they almost
always lie upon the bottom and only rarely come to the surface; w7ith their short
flabellae they brush the bottom and gather their food in this way. If there are water
plants in the aquarium, I have seen them follow7 the leaves and stems, go round
the leaves, holding the axis of the body in a very acute angle to the leaf, simul-
taneously pressing the flabellae against the leaf and slowly move forward cleaning it
from adherent particles. It looks rather peculiar to see the larva without any cling-
ing or grasping organs slowly slide over the under side of the leaves, using the
flabellae simultaneously as an organ for nutriment and for movement. But in another
respect, too, the larvae are peculiar. More than the other, hitherto observed mos-
quito larvae they stand still in the water layers; \vithout reaching either the surface
or the bottom, the larvae, always standing perpendicular, first ascend a little and
then slowly sink downwards then swim a little actively and horizontally and then
again stand perpendicular for slow ascent or descent. I have tried to see, if an air-
bubble would appear on the apex of the sipho during these movements and prob-
ably alter its size, but I have never seen anything of that kind. When I had diffe-
rent species of mosquito larvae in the vessels, I was always able to distinguish the
larva of 0. rusticus from other mosquito larvae owing to this power of suspension
in the water layers below7 the surface.

Though I have rather often found the larva in the neighbourhood in Hillerod
I have hardly ever seen the imago in Nature. In 1920 (26/v) when I was on an
excursion upon Amager to my astonishment I was attacked by enormous masses
of 0. rusticus. Often more than twenty were sitting upon my clothes, trying to get
blood; they stung vigorously. The attack began at about seven o'clock and was
unaltered, when I left the place at half part eight. The specimens were larger than
those I have hatched from the forest ponds; their hatching ponds I did not succeed
in finding. — Collections from the first days in June did not show a single 0. ru-
sticus; at that time immense numbers of O. latescens appeared, which had just be-
gun to sting by 26/v.

Geographical distribution: The species has hitherto only been recorded
from Italy, Macedonia and England.

14. O. diantaeus (Howard, Dyar and Knab).

Tab. XIII.

Description. Female: Proboscis moderately long, curved, labellae conically
tapered, vestiture black, but with many intermixed greyish scales; labellae black.
Palpi short; only about one-sixth as long as proboscis; vestiture black, some white
scales at apex. Antennae filiform; the joints subequal, rugose, pilose; second joint
enlarged, bright; the others black, with grey scales and outstanding greyish hairs;

89

tori subspherical with cup-shaped apical excavation, bright brown with a patch of
brighter scales on innerside, hairs of whirls sparse black. - - Clypeus roundedly
prominent, nude, black; eyes black. Occiput black with narrow curved, pale-ochra-
ceous scales on vertex, and broader whitish ones on the sides; setae along margin
of eyes black; those projecting forward between the eyes black.

Prothoracic lobes elliptical, remote dorsally, black, clothed with yellowish-white
scales and black bristles. Mesonotum black, clothed with narrow curved pale bronzy
scales; with a broad middleline black, formed by two black lines fused together
but separated by an extremely small line only indicated by a series of few long
bristles ; sideways two shorter, more or less conspicuous black lines. The remainder
of the thorax covered by a coating of yellowish-white hairs. Scutellum brown, writh
creamy scales and dark brown border bristles, metanotum chestnut brown; pleurae
black, but almost covered by numerous patches of almost snow-white scales.

Abdomen subcylindrical, flattening, tapering posteriorly; dorsal vestiture of
black scales with basal creamy almost snow-white bands, narrow, almost disappear-
ing in the middle line but laterally widening in white spots; the underside banded
by bands of very broad, white scales ; posterior borders edged by yellowish-grey hairs.

Wings with the veins clothed with yellowish-brown scales; those of the costal
and subcostal vein black ; first marginal cell longer and a little narrower than second
posterior cell; stem a little shorter than the cell; stem of the second posterior cell
longer than the cell; supernumerary and midcross-veins forming a slight obtuse
angle with one another; posterior cross-vein about twice its own length from the
midcross-vein; fringe brown. Halteres grey with fuscuous, greyish bordered knob.

Legs with coxae covered by snow-white scales; underside of all femora yellow-
ish-white, on the upperside black, but at base all round yellowish-white; knees
bronzy; hindfemora in their half length almost white. Tibiae and tarsi black. Claw
formula 1.1—1.1—1.1.

Length: body about 5.5 mm.

Male: Proboscis long, slender, haired at tip, straight, black. Palpi slightly
exceeding the proboscis in length, blunt at apices ; vestiture almost black but in some
lighting showing a slight greyish tomentum; end of long joint and last two joints
slightly enlarged with dense, moderately long black hairs. Antennae plumose;
the last two joints long and slender, pilose black; the other joints short, pale
with blackish rings; hairs of whorls long, black with greyish silky luster. Occi-
put black, clothed with narrow, curved, creamy-yellow scales above; the sides
with broad flat, dull white scales; nape with many short, upright, forked, creamy-
yellow scales; a row of long, black bristles along margin of eyes; those projecting
forward between eyes pale, yellow.

Prothoracic lobes elliptical, remote dorsally, brownish, clothed with narrow
curved creamy-yellow scales and with few black bristles. Mesonotum clothed with
rather coarse, narrow curved, creamy-yellow scales; two narrow submedian lines of
brownish-black scales, which are smaller and denser; scutellum and posterior por-

D. K. I). Vidensk. Selsk. Skr., naturvidensk. og mathem. Afd. 8. Rjekke, VII, 1. 12

90

tion of mesonotum denuted. Postnotum nude, deep brown. Pleura? almost black,
coxae luteous; clothed with patches of flat white scales; the prothoracic epimera
with narrow curved, creamy-yellow7 scales.

Abdomen elongate, depressed; dorsal vestiture black with narrow, yellowish-white
basal segmental bands, obsolete centrally; venter whitish scaled, the segments with
apical median black spots; lateral dilation moderately long and abundant, brownish.

Wings narrow, hyaline; stems of second marginal and second posterior cells
longer than their cells; basal cross-vein its own length distant from anterior cross-
vein; vestiture sooty brown, with a few pale scales intermixed, rather sparse, out-
standing scales linear.

Legs rather long and slender; vestiture sooty brown, the femora pale, especially
beneath to near apices; fore femora palest; knees pale; tarsi dark but hind tarsi a
little brighter than the others. Claw formula 1.1 — 1.1 — 1.1.

Length: Body about 6mm.

Genitalia: Side-pieces nearly three times as long as wide, rounded at tip; api-
cal lobe roundedly prominent, without basal prolongation; basal lobe digitate, ap-
pressed, with a side-piece bearing two stout apical setaB. A group of dense hairs
arising at origin of apical lobe. Clasp-filament long, slender, with two small setae
towards tip arising from slight notches; a long articulated terminal spine. Harpes ellip-
tical, concave, inner margin thickened and revolute; tip pointed and outcurved. Harpago-
nes with a long stem, its basal and larger portion thick, angular and bearing a few
setae, apical portion slender, with a broad terminal filament which is expanded at
tip, the angles of the expansion pointed. Unci approximated revolute, forming a
basal cylinder. Basal appendages approximate, bearing several short, stout setae.

Larva. Head rounded, much wider than long, narrowed before eyes, a notch
at insertion of antennae; front margin arcuate. Antennae very long, longer than the
head, straight, not or only slightly curved, thorned; antennal tuft with few hairs
inserted almost in the middle of the antenna; terminal portion slender, carrying
two hairs near the tip and two thorn-like hairs on apex. Anteantennal tuft with
five hairs; lower frontal tuft with four or five hairs, upper triple. Eyes large.

Thorax rounded, angled at hair-tufts ; hair formula of frontal border 121114411121.
The median tuft of four hairs consisting of one very long hair and three small ones.
The next hair nearest 4 exceedingly small. Lateral hairs long, a few single, most
most of them in multiple tufts.

Abdomen rather broad, the first segments much smaller than segment six and
seven; lateral hairs on first two segments triple, double on third to fifth, single on
sixth. No subdorsal tufts. Eighth segment with tufts in common arrangement. Late-
ral comb consisting of about twelve scales, arranged in an arcuate row, each scale
spatulated at base ending in a long, acute spine with smaller spines at its base and
many small spines or hairs bordering the spatulate part. Sipho rather short, taper-
ing at apex, only two and a half times longer than broad, a pecten at basal third
consisting of about 13 thorns, the last two single, at great distances from each

91

other; the others with three or four lateral thorns; a large hair-tuft. Anal segment
longer than wide, dorsal plate square, only reaching halfway down the sides; dor-
sal tuft well developed with two very long stiff hairs. Ventral brush consisting of
thirteen rays in the barred area and before it three or four' free rays; every ray
carries from seven to ten hairs; anal gills long acute equal.

Lateral tufts of labrum well developed, no comb-hairs nearpalatum; palatum
covered with long soft hairs. Mandibles quadrangular, two stout spines before the
collar; a row of long cilia from collar; about ten spines from margin; dentition four

Textfig. 10. Pond in Stenholtsvang. Aedes cinereus ; Ochlerotatus cantans ; communis,
prodotes, rusticiis, diantteus, Cnlicella morsitans.

to five strong teeth and between them and the row of cilia three long thorns, the
last very long and acute; five strong ciliated hairs below the teeth, process below
furcate with strong hair-tufts on both tips, a group of hair at base. Maxillae elon-
gate, tips conically rounded, divided by a suture; at the apex a large brush of long
soft hairs, a strong seta near the apex belo\v the brush. Between the suture and
inner margin a coarse coating of short, soft hairs. No spines at margin. Palpes well
developed with five little apical digits. Mentum triangular with arcuated sides, the
median tooth but small and with about eleven teeth on each side. Colour of the
body red brown with bright yellow head and golden brushes on labrum.

Biology: I have found this peculiar mosquito only in one locality in the little
bog of Stenholtsvang near Hiller0d. In the same sample 23/v 1919, in which I found

12*

92

the larva of A. cinereus I found, among the numerous O. cantans larvae, a remark-
able red brown larva with very long antennae, almost as long as those of C. morsi-
tans but almost straight, not elegantly curved as in this species. - I immediately
saw that I had to do with a new species for our country. In the time from 25/y
to 5/vi the pond was visited -almost every day; the larva was rare, and I never got
more than about fifty specimens; they were hatched in my cages before 5/vi. By
5/vi the pond was almost dried up and got only very little water till October;
practically it was dry. In the time from 20/vi to Vvn and later on in August I
have often tried to catch the imago among the vegetation which covered the dry
bottom. It was always in vain. I had quite given up finding the imago in Nature,
when suddenly on 29/tx 1919 I found it in another part of Grib forest. Dredging
in the northern part of Griblake my assistent and I were suddenly attacked by
mosquitoes. The boat was about thirty meters from land ; it was fine sunshine and
almost calm where the boat was. I had an opportunity to catch some of them ;
they undoubtedly all belonged to the same easily recognizable species.

In the winter 1919 — 20 up to June 1920 the pond was visited regularly; it
was open from February and contained enormous quantities of 0. communis till
about 20th May. On 5/v the first halfgrown O. diantceus larvae appeared in the
samples; by 25/y all were pupae; the larvae were much rarer in 1920 than in 1919;
I found only about thirty, which were hatched; among them were only two males.

For the present we must register this species among the forest mosquitoes,
hatched in spring in ponds which are commonly laid dry in June; they winter as
eggs and probably do not possess more than one generation. The late occurrence
on 29/jx is remarkable.

Geographical distribution: The species has hitherto only been found in
America. New Hampshire (H. D. K. 1917 p. 758). Only the male has hitherto been
known. The species has been determined by Dr. EDWARDS. The description of the
female is new; that of the male has been worked out in accordance with that of
HOWARD, DYAR and KNAB; the description of the remarkable male genitalia has
been quoted verbatim.

15. O. sticticus (Meig.) var. concinnus Steph.

Description. Female: Proboscis rather long, uniform, labellae conically
tapered; vestiture black, labellae grey; setae small, black. Palpi short, not one fifth
as long as proboscis, black, no brighter scales at tip. Antennae long, the joints sub-
equal, rugose, pilose, black, second joint a little larger; hairs of whorls rather short,
sparse; tori subspherical with a cup-shaped apical excavation, black with a few
greyish-white scales on the inner side. Clypeus rounded, triangular blackish nude.
Occiput black, clothed with coarse narrow, curved yellowish-white scales, margin
of eyes and the cheeks white, scales on lower part of sides flat; many slender, erect
forked black scales; setae along margin of eyes rather short, black.

Prothoracic lobes elliptical, remote dorsally with narrow yellowish scales and

93

man}' black seta?. Mesonotum black, covered with golden yellowish or bright red-
dish brown scales and with creamy ones at the sides; over the roots of the wings
tufts of golden brown bristles; scutellum deep brown, almost black, trilobate, clothed
with pale scales and each lobe with a tuft of golden-brown' bristles. Postnotum
black, pleurae dark brown with patches of pale scales.

Abdomen densely black scaled with clear white basal bands, not or only little
contracted in the middle line not forming distinct broad lateral patches; posterior
borders with clear pale golden bristles; venter white and black scaled.

Wings with brown, almost black scaled veins; first sub-marginal cell consider-
ably narrower and longer than second posterior cell; petiole of first submarginal
cell as long as the cell, that of second posterior cell a little longer; basal cross-vein
very close to the anterior cross-vein. Halteres with ochraceous stem; knob fuscous
with grey scales. Legs unhanded ; coxae brown with white scales ; femora and tibiae
densely covered above with greyish white scales; knee spots white, apices of femora
before the spots deep black; hind tibia with a very characteristic white stripe on
the outer side. Claw formula 1.1 — 1.1 — 1.1. Length of body about four mm.

I have never seen either male or larva; the last-named is unknown.

The species was brought me by Mr. KRYGER who caught it in the western
part of Jutland at Linding near Varde. He has only caught three specimens, which
I determined as Ochlerotatus nigrina (Eckstein). Mr. EDWARDS has been kind enough
to verify the determination. He refers it to 0. sticticus Mg. var. concinnus Steph. and
gives the following synonymy. O. sticticus = sylvce Theobald = dorsovittatus Ville-
neuve = ? nigrinus Eckstein. - The best distinguishing feature is the white stripe
on the outer side of hind tibiae. See further p. 96.

Geographical distribution: 0. sticticus Meigen var. concinn us Steph. seems
to be rare everywhere; Mr. EDWARDS states that it has hitherto been found in
England, Scotland, France, Germany and Siberia.

Genus III. Finlaya.

1. Finlayia geniculata (Olivier).

Culex latcralis Meigen.

Tab. XIV.

Description. Female: Proboscis rather long uniform, labellae rather long,
tapering at tip, vestiture black without pale scales intermixed. Palpi about one-sixth
the length of proboscis, black without white hairs at apex. Antennae filiform, vesti-
ture black; second joint scarcely thicker than the following; tori globose with a
cup-shaped apical excavation and white hairs on the inner side; hairs of whirles
black, long. Clypeus rounded, triangular, blackish, nude. Eyes black. Head black,
with creamy spindle-shaped scales in the middle and forming a row behind, pure
white ones at the sides; a pale patch just in front projecting betsveen the eyes.

94

Prothoracic lobes elliptical, remote dorsally. Mesonotum black, covered with
bright bronzy or snow-white scales; two median black stripes as long as the thorax,
separated from one another by a white line; laterally two other black stripes, half
as long and also separated from them by a white line; scutellum trilobate, black,
bordered by lines, the median line being forked; long golden hairs on the borders
of the midlobe and on the lateral lobes; post-notum deep black; pleurae black with
eight or nine distinct large patches of snow-white scales.

Abdomen violet black, covered with dusty black scales and long golden hairs
from the posterior border of each segment. Each segment with lateral snow-white
spots, most prominent when the mosquito is observed laterally; on the dorsal side
they never form bands; venter with brqad white bands.

Wings with the veins covered by long lateral black-brown scales, truncated at
the apex; those along the costa and base of the first long vein black; first sub-
marginal cell a little longer and narrower than the second posterior cell, its stem
about equal to half the length of the cell; stem of the second posterior cell nearly
equal to the length of the cell; basal cross-vein not twice its own length distant
from the anterior cross-vein; fringe dark brown; basal lobe of wing with a fringe of
flat, black scales and no bristles near the base of the first long vein.

Legs black, coxae covered with snow-white scales; bases of the femora and
the ventral surface for about half their length white; knees snow-white. Tibiae and
metatarsi black; hind metatarsus about two-thirds the length of the hind tibia. Un-
gues of the female, on the forelegs uriinserrated, on the other simple; on the male
unequal on fore- and middlelegs, on the forelegs the small ungues uninserrated,
the large biserrated ; so also on the middle legs, but the inner tooth indistinct ; the
outer on both claws remarkably rod-like and broader at apex; those of the hind-
legs simple.

Length of body 5 mm.

Male: Proboscis longer in male than in female; palpi black almost of the
same length as the proboscis. Antennae black; but with white bands upon every
segment; the white parts of the thorax more distinct; the white spots of the ab-
domen larger; the last segment almost snow-white. The ventral surface of the legs
white to a greater extent than in the female. With regard to ungues see under ? .

Length of body 5.5 mm.

Larva. Head rounded; almost isodiametric; hind angles rounded; sides arcuate
and front margin highly arcuate. Antennae small, cylindrical, only slightly tapering
at front, smooth without any spinosity. Antennal tuft consisting only of one single
hair, inserted almost in the middle of the antenna. Two hairs and two attenuated
digits at apex. Eyes small, the stripe of integument between the eyes often indistinct
or obsolete. Anteantennal tuft often only with two or three hairs ; upper frontal tuft
with two hairs, lower with one single hair; between the upper frontal tuft a small
tuft of about six hairs and a similar one over the eyes.

Thorax rounded, slightly angled at hair-tufts; hair formula at frontal border

95

21022012. Between 2 and 0 a .very small hair-tuft. Lateral hairs long, many single,
the others in multiple tufts. Two series of smaller tufts with one single or a few
hairs between the median and posterior tufts.

Abdomen rather broad; lateral hairs on first two segments triple, double on
third to sixth; short hair-tufts at the base of the lateral hairs. On the dorsal side
of the segments three pair of tufts, one pair at the anterior and posterior border of
each segment, and a greater pair almost in the middle of the segment; this tuft
always consists of four hairs commonly arranged rectangularly to each other; the
other hair-tufts mainly triple or with four hairs, the arrangement of these hair-
tufts is very regular, the tufts forming three series over the dorsal surface of the
abdomen; on the ventral side only the median tufts present, those of the anterior
and posterior border being absent. Seventh segment with some more irregular di-
stribution of the tufts and without lateral hairs. Hairs of eighth segment in com-
mon arrangement. Lateral comb consisting of about twelve scales arranged in an
arcuate, single row, each scale having a rather narrow base and terminated by a
long strong spine ; on both sides fringed with a long series of weaker ones or very
fine hairs. Air-tube moderate, almost one and a half times as long as eighth seg-
ment, tapering at the apex, three times longer than broad: pecten short, with 10 —
12 teeth, every tooth broad, flattened, yellowish-brown with white apices; at the
base furnished with a series of dark, short spines; a single hair-tuft of five hairs
at some distance from the pecten and a single hair on the opposite side. Anal seg-
ment very short, a little \vider than long; the plate small, not quite encircling the
whole segment; dorsal tuft consisting of about eight to ten hairs of rather different
length. The ventral brush very remarkable, only feebly developed, consisting of but
seven rays, each ray carrying two or three hairs; before the brush two or three
free tufts; lateral tuft highly developed with three strong hairs. Anal gills of un-
equal size; the two large ones almost twice as long as the anal segment, the two
others only half as long, all broad, flattened, obtuse.

Lateral tufts of labrum short but dense; the inner part with a little crown of
comb-hairs; palatum well-developed, covered with soft hairs. Mandible qua-

drangular, two stout spines before the collar, a row of cilia from a collar, about
seven to ten spines from inner margin; dentition four strong teeth, preceded by
two serrated filaments, one much stronger than the other; a strong spine before
these filaments. Four hairs within; process below slightly furcate, with strong hair-
tufts; a group of long hairs at base. Maxillae narrowly elongate, tips conically
rounded, divided by a suture; at the apex an elegant large brush of long hairs; a
seta near the apex beyond the brush. Along the suture, between it and the inner
margin, a coarse coating of short, soft hairs. No spines at margin, but the whole
space between it and the coating of short soft hairs covered with short, strong
spines, especially in the part nearest to the apex; palpus well-developed with five
small apical digits. Mentum triangular, straight sides, a large central tooth and from
ten to eleven small teeth on each side. The whole body pilose.

96

Colour commonly white with almost black head and sipho ; the tracheal trunks
very wide and flattened.

Systematical remarks. When I first found the species and tried to deter-
mine it, I felt quite sure that I had found Finlaya geniculata (Olivier) = C. late-
ralis Meigen; and even now after having studied the whole literature with regard
to this and allied species I do not think that there can be any doubt upon that
point; I cannot find any real discrepancy between MEIGENS' description and the
Danish specimens. THEOBALD too supposes that he has found the species again; as
his description is not however in full accordance with my specimens, I have given
a new one. It will be seen that my specimens do not agree with Theobalds with
regard to the drawing of the thorax, but are in accordance with Meigens' descrip-
tion; further that there is some discrepancy in the description of the wing between
THEOBALD and me.

In this connection it is however necessary to take into consideration two other
species Culex sticticus Meig. and C. ornatus (Hoffmanseg) Meigen.

C. sticticus is similar to C. lateralis, but differs from it in having .the white
lateral spots on the abdomen united in bands; the legs are brown, the hind tibia
with a white stripe on the outer side. The species was later adopted by SCHINER
(II p. 629) by FICALBY (1896 p. 120) lastly by SCHNEIDER (1914 p. 41); this author
maintains, that stictica is a good species and states that it is to be found in the
neighbourhood of Bonn. On the other hand THEOBALD (1901 p. 80) refers the spe-
cies to C. nemorosus and so does BLANCHARD (1905 p. 393). Having got the speci-
mens with white bands from Jutland I am quite sure that sticticus really is a good
species, to which most probably 0. nigrinus (Eckstein) may be referred. (See page
93) ECKSTEIN (1918 p. 67) maintains that the specimens of C. lateralis Meigen belong
to ornata. This view I cannot adopt.

C. ornatus (Hoffmgg.) Meigen has always been a very doubtful species, and it
is now very difficult to understand what the earlier authors really meant by this
species; the type-species does not exist anywhere any longer, In STAEGER'S collec-
tion at the Royal Museum, Copenhagen, there are some species labelled as C. or-
natus Meig. A closer examination has shown that there cannot probably be any
doubt that what STAEGER has determined as C. ornatus Meigen has really been
Finlaya geniculata Olivier, (= C. lateralis Meig.). In THEOBALD'S translation MEIGEN
has described C. ornatus as follows: "Thorax wrhitish, with twro black streaks; ab-
domen fuscous with basal white bands; legs blackish, with a white knee spot; pro-
boscis blackish-brown; antennae dark brown in the oT with brown hairs; palpi of
the cT blackish-brown, with long hairs and three whitish spots; thorax yellowish
white with two converging blackish stripes and two others further behind; pleurae
blackish-brown, with white spots and marks. Abdomen blackish-brown with white
basal bands. Legs brown with the coxae dull yellow; femora dark brown, knee
spots white, tibiae and tarsi dark brown. Wings with brown scales. Length 3 lines".
THEOBALD has never seen the species, but indicates that it resembles C. lateralis

97

from which it can at once be distinguished by the abdominal bands. It is stated
to have been found in Germany (MEIGEN, GRUNBERG 1909 p. 88), SCHNEIDER (1914
p. 42); Scandinavia (ZETTERSTEDT 1850 p. 3459), Denmark (STAEGER 1838 p. 553),
Holland VAN DER WULP), Austria (SCHINER), Russia (GIMMERT'HAL), England (STE-
PHENS, VERREIL; EDWARDS 1912 p. 220; LANG 1920 p. 97).

ECKSTEIN, too, (1919 p. 66) has recently tried to elucidate the question but in
my opinion without success. He maintains that the species "in den Waldern um
Strassburg nicht sehr haufig ist", and says that the species is characterized by
its "glanzed silberweissen Schuppenringen an alien Knien, wodurch C. ornatus leicht
und mit Sicherkeit, namentlich frische Exemplare von ahnlichen Arten (C. lateralis
= F. geniculata), nemorosa and' nigrina unterschieden \verden kann''. He maintains
that the authors after Meigen have determined the true ornatus as lateralis "sonst
wurde man nicht von scharfen, weissen Knieflecken lesen konnen". As MEIGEN
(1818 p. 5) however writes with regard to lateralis: "Knie blass" it is in my opi-
nion questionable whether he is really right.

As far as I can see ECKSTEIN has described as 0. ornatus what is really Fin-
laya geniculata (= C. lateralis Meig.); as his description, more especially of the
female, is however rather insufficient, this cannot be established from his descrip-
tion of the imagines alone; on the other hand, if this description is combined with
that of the larva and the statements relating to the habitat, as far as I can see,
there can be no doubt upon that point.

ECKSTEIN (1918 p. 66) says that the larva lives "in den manchmal recht klei-
nen Wasseransamlungen in hohlen Baumer zusammen mit solchen von A. nigripes.
Die Eier werden einzeln wenige Zentim. oberhalb des Wasserspiegels an dem feuch-
ten Mulm u. s. w. abgelegt". GALLI VALERIO and ROCHAZ DE JONGH (1912 p. 224)
as well as MARTINI (1915 p. 585) have also found the C. ornatos-larva in tree-
holes. This is just the place where I have found my F, geniculata (= C. lateralis)
larva. As North of the Alps we have hitherto never found other Culicin-larva in tree-
holes than this one1, I suppose that ECKSTEIN and I have really found the same
larva. We have only determined the species in different ways, he as 0. ornalus, I
as Finlaya geniculata 0. (= C. lateralis Mg.). That this is really the case, will be
clear if we compare the description of the larva of 0. ornatus by ECKSTEIN (1919 1
p. 291) with my description of F. geniculata. He describes this larva as follows.
"Die Larve fallt sofort durch die auffallend starke Beborstung des Korpes, insbeson-
dere des Abdomens auf. Jedes Abdominalsegment tragt namlich mehrere aus 6 — 9
meist aus 7 starren Borsten bestehende Borstenbiischel. Das Atemrohr is kurz ge-
drungen, nicht ganz 2 mal so lang als sein Durchmesser an der Basis, ziemlich
dunkel gefarbt. Der Dornkamm unterscheidet sich von den anderen Stechmucken-
larven ohne weiteres dadurch, dass die Dornen nicht wie bei jenen von der Basis
zur Spitze des Atemrohres allmahlig an Grosse zunehmen, sondern dass neben den

1 Apart from the remarkable discovery of the larva of Onthopodomyia albionensis Mac Gregor
and Stegomyia fasciata (Fabricius) from the same tree-hole in Epping Forest.

D. K. D. Vidensk. Selsk. Skr., naturviclensk. og niathem. Afd. 8. Raekke, VII. 1. 13

98

basalen sehr kleinen ohne vermittelnde Bindeglieder sehr grosze stehen. Alle haben
kleine Zahnchen; meist sind 4 kleine und 9 — 12 grosse Dornen vorhanden. Das
Haarbuschel des Atemrohres steht etwa in seiner Mitte. Am 8 Segment befinden sich
etwa 25 in zwei Reihen stehende lange lanzetformige in einer Spitze auslaufende
Striegelborsten". There are some discrepancies between these two descriptions. Eckstein
says that the hair-tuft on the sipho "steht etwa in seiner Mitte"; this is in accor-
dance with my description, but his own figure (Fig. 10) shows it at the base. Further
his statement: "dasz die Dornen nicht allmahlich an Grosse zunehmen, sondern
dasz neben den basalen sehr kleinen ohne vermittelnde Bindeglieder sehr grosse
stehen" is not in accordance with those of my Finlaya geniculata larva. Further my
larvae have in the comb only 12 scales arranged in one series.

The mosquito which ECKSTEIN has described as 0. lateralis (Meigen) has, as
far as I can see, not hitherto been found in Denmark. The descriptions of the fe-
male and more especially of the larva are so insufficient, that it will be very diffi-
cult to determine them; in the description of the male genitalia he has pointed out
some characters, by means of which it seems that his 0. lateralis (Meigen) can real-
ly be separated from his 0. ornata (Meigen) (1920 p. 237). Most probably he is
therefore right, when he says (1918 p. 67) that: "lateralis ist eine Art fur sich, und
ebenso ornata und nemorosa".

Biology. More than twenty years ago, when on an excursion to Jsegers-
pris, near the fjord of Roskilde, I found some mosquito larvae in a little hole of an
old oak; I supposed that the locality for these larvae was rather peculiar, the quan-
tity of water not being V* Ltr., black, brown and of an extremely nasty odour. Yet
I did not then thoroughly study the larva. Later on, when I read the work of
HOWARD, DYAR and KNAB, with the description of all the remarkable mosquito
larvae found in tree-holes, in the small volumina of water, among the leaves of
Bromeliaceae and other tropical plants, I remembered my observation of more than
twenty years ago. Having mentioned it to Dr. TH. MORTENSEN, he told me that he,
too, had found mosquito larvae in the holes of old trees in North Seeland. Dr. MOR-
TENSEN, wrho at that time was my guest at the Freshwater Biological Laboratory
at Tjustruplake, explored the forest near the laboratory with me. In the course of
July we then found about thirty holes with mosquito larvae. On the meadow be-
fore the laboratory more than hundreds of plants of Angelica siluestris were grow-
ing. As this plant is provided with the greatest sheaths found in our flora, and more
than any other Danish plant is able to hold the rainwater in the sheaths for about
a week, I supposed that mosquito larvae might also be found here. The plants
were regularly observed; in the collections of water were found great quantities of
Infusoria and some Rotifers, but never mosquito larvae. It must be supposed that
our flora of herbaceous plants is unable to retain rainwater long enough for mos-
quito larvae to live in.

The tree-holes are mostly to be found near the ground where the roots branch
off from the trunks, but I have also found them some meters from the ground,

99

where the trunk is cleft in large branches; many of these holes are never filled with
rainwater because it immediately sinks down into the ground, or into the decaying
wood; in very dry summers the holes hold no water or only very small quantities.
In some of them, more especially those in which the bottom itself is of wood, and
not part of the ground, the rainwater can be retained for months, more especially
when a little rain now and
then can replace the loss by
evaporation. In these holes
the bottom is almost always
covered with decaying vegeta-
tion, more especially leaves,
which in its deepest layer
form a black humus. The
water is dark-brown and of
an extremely foul odour,
smells strongly of hydrosul-
phuric acid; the volumina of
water are often less than a
deciliter, and never more than
from three to four liters. In
autumn the holes are filled
with leaves; from December
to May the contents of the
holes can with more accuracy
be described as moist leaves,
than as clear water; for more
than three months the whole
mass is frozen into a brown
ice ; at the bottom of the holes
I have however almost al-
ways found a layer of frost-
free, black humus. The tem-
perature of the water is re-
markably constant during the whole summer and always rather low; even on hot
days, where the ponds have temperatures of about twenty-five Celsius, the holes
rarely have more than about twelve degrees, and probably never more than fifteen.
This is due to the fact that the water in the tree-holes hardly ever receives a single
sunbeam. Though the water has a disagreeable smell, it is commonly clear, and
most closely resembles fresh urine. The bad smell is strongest when the bottom is
stirred up. What certainly contributes to the bad quality of the water is the huge
mass of drowned animals which first cover the surface of the wrater and later on sink to
the bottom and decompose. Every heavy shower carries large quantities of animal-

13*

Textfig. 11. Hole in a trunk. Finlaya geniculata and Anopheles

nigripes.

100

cules into the holes with the streams running down the trunks and passing through
the huge carpets of tree-mosses. Often the surfaces are covered with thick layers of
large Podura which later on form a decomposing mass on the bottom. Some gras-
hoppers f. i. Meconema varium, Carabidce, Oniscidce, which here, curiously enough,
meet with a few living Asellus aquatius but especially many snails f. i. Limax o. a.,
are swept down into the holes and drowned.

In dry summers f. i. 1918 the holes contain no water from the first days of
August to October; in the course of the autumn the holes were filled, but in De-
cember they froze and were frozen till the last days of March. To aquatic animals
in the free-swimming stage the holes are only habitable for about four months, but
in these four months long periods of drought may intervene, and the holes may be
laid dry for weeks and even months.

Curiously enough, these rather unpleasant localities contain a crowd of ani-
malcules which have here found a home and are adjusted to the remarkable con-
ditions these holes can offer their habitants. Now and then the water contains in-
fusoria in countless numbers, the animalcules forming stripes and clouds in the
water; also many rotifers are common, more especially those of the Philodinidce,
probably swept down from the mosses on the trunks; yet it is much more remark-
able that Copepoda and Ostracoda are very, common, the former in the water itself,
the 'latter on the bottom, living on the decaying leaves; the Ostracoda more espe-
cially are common; the species hitherto found are Cyclops bisetosus Rehberg, Cyc-
lops pulchellus Koch, Candona compressa Brady. I beg Dr. SVEN EKMAN Upsala to
accept my best thanks for the determination. Once I found a few Asellus aqua-
ticus in a single hole. In the upper layer of the bottom are found many hitherto
undetermined Nematoda, in the lower, various Oligochaeta. The greatest and most
interesting contingent is yielded by the Insects.

Very frequent are the larvae of different Chironomidce, further of Ceratopogon
and Eristalis (rattle snakes). These larvae, especially, may be present in great num-
bers; common are also the larvae of Helodes sp.

Amid this company we also find the mosquito larvae which, when hatched, give
the beautiful mosquito Finlaya geniculata hitherto unknown in our country and the
larva of Anopheles nigripes, mentioned later on. The number of larvae of F. geniculata
found in the holes is always very restricted; often I have only found two or three,
commonly about ten, in spring however I have often found fifty and only once
about eighty; the larvae are extremely slow and sluggish, difficult to observe in
Nature, always seeking back into the darkest parts of the small water volumina or
between the leaves; in my aquaria they only rarely come to the surface to breathe,
they lie on the bottom or search the bottom for food. When there, they only move
forward slowly; the body is commonly held obliquely, and the very short flabellae
are in constant motion, brushing off the surface of the bottom; the description and
drawings show that the larva differs very much from all other Danish mosquito
larvae; the antennae are extremely short; the eyes rather small, the anal' segment of a

101

rather peculiar form and the swimming-brush more reduced than in any other of
our Danish mosquito larvae; of the anal gills two are extremely large and broad,
and the hair-covering of the body, more especially that of the abdomen, unusually
highly developed; further, the colour of the larva is greyish-white and the whole
larva semitransparent. Finally the tracheae are remarkably broad, flattened. Many
of these peculiarities may also be pointed out in many of the tropical mosquito
larvae living under similar conditions ; this more especially holds good for the equip-
ment of hair-bristles, which are often more luxurious in tropical species, further
with regard to the small eyes, the slight development of the anal brushes, of which
the ventral one may be wholly absent, and the large broad trachea gills. There is
an easily comprehensible connection between the small eyes, the slight development
of the swimming-fan and the conditions under which the larvae live; on the other
hand the luxurious development of bristles, and more especially that of the large
anal gills, is difficult to understand. It must be taken for granted that respiratory
conditions on the bottom of these holes are extremely bad; it is therefore difficult
to comprehend how the cutaneous respiration, taking place either through the cutis
of the abdomen or through that of the anal gills, can help the larva to any con-
siderable extent.

Having found the larvae in the forest of Suserup, where the summer labora-
tory is, later on I found the larua in the neighbourhood of Hiller0d, by Dragsholm,
by Tidsvilde (North Sealand near the coast of Kattegat). The imagines have never
been found in Nature itself; all the specimens in my collection derive from my
aquaria; the imago is of course extremely rare and probably very difficult to detect.
In such a little wood as that of Suserup every single tree has been observed; the
wood does not possess more than twenty breeding localities; if there are only hatch-
ed about thirty-forty mosquitoes in every hole, it is intelligible that the imago
must be rare and almost impossible to detect. I have further observed that spiders
almost always weave their webs over the holes ; the webs standing only a few cen-
timeters from the surface, almost every flying animal leaving the surface must be
caught by the webs.

Having had the holes under regular observation for about two years, I feel
quite sure that we have only one or two generations the whole year round. In
1918 many of the holes were ice-covered during the last days of March; they were
filled with water during the first days of April and in the time from April the first
to about April the fifteenth very many larvae in the first stage were found in the
holes. In the first weeks of May many of the holes were almost dried up; the larvae
only grew very slowly, lying between the moist leaves at the bottom of the holes,
but without any water to swim in. In the latter part of June the holes got some
water and the larvae grew more quickly, but no pupae were observed before the
first days of July; in the course of July all the pupae were hatched, owing to the
extremely rainy summer the holes almost always held water. From the last days
of July no larvae could be observed in the holes. In 1919 and 1920 I found a few

102

halfgrown larvae in several holes in October — November. In December the holes
were frozen, and when they thawed in 1919 in March and in 1920 in Febru-
ary, they never contained larvae; I take it for granted that the larva? from the au-
tumn have died out in the course of the winter. In 1920 the holes which were ice-
covered in February contained no larvae before the first days of April; they were
filled with water till June, but no pupae appeared before this month. In August
1920 I saw the only sign of a second generation. A large beech was cut down in
May; in the stump was formed a hole, and this hole was filled \vith water in the
first part of July; during the last days of July I found almost fullgrown larvae
which were pupae in the middle of August and have most probably given a second
generation in the latter part of the same month. During the whole summer I
found larvae of very different size; at a first glance one would think that this must
be interpreted as if the mosquito had many generations in the course of the year.
I do not think this is the case; in our country the different sizes of the larvae must
in my opinion be referred to eggs which have arrived at their natural hatching
conditions at different times of the year.

When the imagines were hatched in my cages, they stung immediately; they
had great difficulty in piercing the skin and often tried from ten to twenty times
before they got blood. I had hoped that these gorged imagines would lay eggs in
the vessels placed in the cages, but this did not occur.

The eggs are laid in July — August and are to be found on the sides of the
holes, commonly a little above the water rim. Most probably the eggs are laid at
different times and by different females; under specially favourable conditions e. g.
in wet summers, in which the eggs are reached by the water rim at a very early
date, it may possibly occur that some of these eggs are hatched in the very sum-
mer in which they are laid, but I feel quite sure that the main part hibernate as
eggs, and are not hatched before the next year, commonly in March — April.

LANG (1920 p. 96) agrees with me with regard to the number of generations;
he maintains, as I, that there is most probably only one generation, and that the
larvae grow slowly. That this is not always the case, ECKSTEIN (1919 p. 101), has
tried to show starting from very careful observations; it seems that he has proved
that more than one generation can be hatched in the course of the summer; the
number depends upon the number of rainy periods; the first generation takes 36
days from hatching of egg to imago, the last only 10. I feel convinced that this is
not the case in our country. Whilst in Germany, in the time from 24/m to 23/v, five
series of eggs can be hatched, in Denmark no imagines appear before June; further
the high temperatures in tree-holes (21 — 24° C.), mentioned by ECKSTEIN, have never
been found in our country, the temperature most probably never exceeding about
15 degrees.

Geographical distribution: Most probably Finlayia geniculata is widely
spread over the whole of Europe; it is unknown from Scandinavia, rare in our
country and most probably has a more southerly range.

103

Genus IV. Tceniorhynchus.

1. Taeniorhyncjius Richard! (Ficalbi). '
Tab. XV— XVI.

Description. Female: Proboscis moderate; labellae moderate; vestiture of
broad scales blackish-brown with many black and a few yellowish scales; labellae
bright ferruginous, setae small, black; yellow on the labellae. Palpi brown, about a
fifth as long as the proboscis, with many outstanding bristles and creamy-yellow
scales. Antennae filiform, moderate, blackish-brown, joints at shaft subequal,
rather short, densely clothed with silvery hairs; second joint a little thicker, ferru-
ginous; tori globose, brownish with an inconspicuous group of flat white scales on
inner side; hairs of whirls sparse,
dark. Eyes black. Clypeus broad;
rounded, almost black, nude. Occi-
put brown, clothed with narrow,
curved, pale scales and numerous
forked black ones ; numerous black-
ish and pale brown bristles pro-
jecting at vertex.

Prothoracic lobes small re-
mote, similar to mesonotum. Meso-
notum chestnut-brown with scatter-
ed golden scales, more or less di-
stinctly arranged in rows, bristles

black. Scutellum trilobate, clothed Textfig. 12. Tceniorhynchus Richardi. Larva living; with
with narrow curved scales and the sipho pierced into the root,

bright, golden brown border-brist-
les. Postnotum elliptical, nude, clear, ochraceous brown; pleurae and coxae pale,
yellowish-brown, with a few pale yellowish scales.

Abdomen subcylindrical, flattened, slightly tapering towards tip, when denuded
dull ochraceous-brown, under certain conditions of light it is dark, shining, while
in other cases it may be black. When covered with dusky scales it is almost black
with now and then traces of apical bands. Five or six yellowish-white lateral, often
rather inconspicuous spots. Numerous golden brown hairs along the sides and the
hind margins.

Wings: The veins densely covered with rather broad, elongated oval, brown
and light scales; besides there are a few scattered yellow scales, especially along
the costal region; no long thin lateral scales. First submarginal cell almost as long
as the second posterior cell; stem of the former about half the length of the cell;
stem of the latter also about the same relative length; basal cross-vein only about
once its own length apart from anterior cross-vein; halteres pale, ochraceous.

104

Legs: The coxse yellowish, femora yellowish, the upward turning surface brown,
the apex white, the white band not involving the tibia. Tibia brown with scattered
black and dull yellow scales; metatarsi and tarsi yellowish, banded in the following

manner: fore metatarsi and first
two tarsi with traces of basal
bands. On the midlegs the bands
are more distinct; the bands on
the hindlegs are broader and
still more distinct, but there is
no broad, pale median metatar-
salband, such as THEOBALD states
with regard to T. Richardi;
ungues equal, simple. Claw for-
mula 0.0—0.0—0.0.

Length: Body about 5mm.
Male: I have hitherto only
found females and with regard
to the description of the male
refer the reader sto THEOBALD
(1901 p. 194).

Larva: Head subquadrate,
wider than long (5 : 3) antennae
long and slender; a large hair-
tuft nearer the base than the
apex, arising from a notch, ter-
minal portion slender, flagellum
like, very flexible and much
drawn out, one of the terminal
hairs situated not far beyond
the tuft; dorsal hairs all in mul-
tiple groups; the anteantennal tuft
large, multiple; lower frontal tuft
absent; upper frontal tuft com-
monly with five hairs, between
them four very small hair-tufts.

Thorax transverse, angled at hair-tufts. Hair formula for the frontal border of
the thorax 531105501135, between 5 and 0 a small hair-tuft; lateral hairs long, a
few of them single, most of them in multiple tufts; a few small tufts scattered over
the dorsal side.

Abdominal segments rather broad, when the larva is fastened to the roots,
almost inflated; the long lateral hairs double; dorsally and ventrally every segment
provided with two series of hair-tufts, every segment carrying four tufts eighth

Textfig. 13. Tceniorhynchus Richardi.

105

segment without these hairs. Lateral comb of eighth segment with ten to twelve
scales in a single, irregular row; each scale having a somewhat spatulated base and
terminated by a stout spine, at the base 'of the latter on both sides a commonly
smaller spine, followed by a series of still smaller weaker ones; hair-tuft behind
the comb consisting of from three to four, long hairs. Air-tube about twice as long
as wide; the basal part broad and strongly convex with black ring near base, the
apical portion attenuated, consisting of thick lamellae with a group of hooks at the
tip and with stout teeth on one side mesially. It bears a hair-tuft on each side
near the middle, and two pairs of filaments at base of apical projection; the one
pair strongly curved, inserted upon two cushion-like parts of chitin and very mov-
able. No pecten ; two strong hairs at the base of the sipho. With regard to the more
thorough description I refer to my paper (W-L. 1918 p. 277). Anal segment much
longer than wide, ringed by a chitinous plate; dorsal tuft of many long hairs, divid-
ed into two small and two large groups on each side, no particularly developed
long bristles; ventral brush great, consisting of about eight to ten rays, each car-
rying from eight to ten, very flexible bristles ; either no tufts or a few (two) very
feebly developed tufts before the ventral brush. Anal gills four, equal, slender arid
not as long as anal segment.

Mouth brushes very large, distinctly divided into two parts: the inner part
without comb-bristles; palatum coated with a covering of rather short hairs. Man-
dibles remarkably high, three, long, curved thorn-like spines near the collar, a row
a cilia from a collar and from inner margin a series of tubercles bearing rather
long, curved but feeble setae; dentition about four to five irregular dark highly
chitinized thorns, one of them very long, acute and dagger-like; process below di-
stinctly furcate, with hair-tufts on both furca. The maxillae very large; the apex
bears an elegant large brush of dense and long hairs and near the outer margin a
very strong spine. Surface between the longitudinal suture and the inner margin
covered with a coating of dense but short hairs; no particular fringe of long hairs
along the inner margin; the palpus short. Mentum provided with a very large
median tooth and very few (about six) but great lateral teeth. Colour of the larva
milky-white; head and thorax of almost the same colour as the abdomen; sipho
in the broad part yellowish, in the attenuated part almost black; most of the hairs
of a golden colour.

Pupa: Thoracic mass subpyriform, rather large, indented behind the insertion
of antennas. Abdomen serrate, the segments largely expanded posteriorly ; anal paddles
oblong, cleaved at apex; the whole pupa quite hairless. No hairs on the ce-
phalothorax; no fan-shaped dorsal tufts on first segment; no subdorsal hairs at the
ends of the abdominal segment and no tufts on the angles. The most peculiar point
in the structure of the pupa is the two airtubes; these are not as in other mos-
quito pupae trumpet-shaped, but end in a long, sharp, thorn-like process of a very
peculiar shape and structure. The tracheae runs through the \vhole tube, ending at
the apex in a minute, almost invisible aperture. The tube itself has in the different

D. K. D Vidensk. Sclsk. Skr.. naturvidensk. og mathem. Afd. 8. Rwkke, VII, 1. J4

106

Textfig. 14. Tceniorhynchus pupa, frontally.

parts a very remarkable, highly specialised structure; in the part nearest to the
cephalothorax the structure resembles that of a trachea, being striped transversely;
where the tube attenuates, the transversal stripes cease and are succeeded by a more

homogeneous structure with a very
fine irregular rhomboidal stripening,
resembling that of a common pupa
tube. A little before the spot where
the tube attenuates, passing into the
accuminated part, there is a weak
point, where the chitin is thin and
where the apical part breaks off very
easily. At the same spot a chitinous
ring runs round the tube, on the
inner side leaving a cleft open. Out-
side this ring the tube acuminates;
the inner half has almost the same
structure, as that on the other side
of the ring, but the outer part is
formed quite differently. It has a

broad fringe of long hairy excrescences and the utmost part, which is commonly
corkscrew-shaped, and lying in another plane, has a hyaline transversally striped
membrane on each side, which has inconspicuous saw-
teeth along the edges. It is this extreme part which must
be used as a piercing organ. The tracheal tube, vyhich
runs from the apical opening to the above-named chiti-
nous ring, has a rather narrow lumen, being only one-
third broader than the tube in this part; immediately
behind the ring it expands to almost the whole width
of the tube, but tapers again and now runs as a narrow
tube through the whole air-tube.

The tubes, which in the case of all other mosquito
pupae are directed outward and divergent, are convergent
in the Tceniorhynchus pupae (Fig. 16); the acuminated parts
are laid against each other when pierced into the stem;
it looks as if the two tubes only made one single hole
when piercing; perhaps it is not quite improbable that
the two acuminating parts act along each other when
piercing and in this way saw a hole in the plant-tissue.
At first I had* the impression, that each tube is hollow

only on its inner side, the two half pipes forming a common conduit when laid
against each other; without section it is difficult to decide this question, but I sup-
pose that the description, first given, is correct.

Textfig. 15. Tceniorhgnchus-
pupa, laterally.

107

Systematical and faunistic remarks. As my specimens have not pale
rings in the middle of the metatarsi, these being quite black, it is only with great
hesitation that I refer my specimens to this species. As how-
ever I have never seen the male, I suppose that provisionally
we had better refer them to the old well-known species.
On an excursion in September 1914, to one of the
little ponds near Donse in the north-eastern part of See-
land, a locality well known to botanists and zoologists, I
was sitting in my boat near a sunlit, prominent point of
the shore. Some plants were lafd upon a tray, half filled
with water. While searching for larvae of Coleopiera my
attention was now and again attracted by some large
mosquito larvae which crept over the bottom in a ser-
pent-like manner, when the tray was shaken. It struck
me that it was really a peculiar season to find fullgrown Textfig. 16. Tceniorhynchuspupa.
Cufer-larvse. I caught one of them and placed it in a Cephal°th°trrauxmp^h the tw°
high cylinder-jar. To my astonishment I saw that the

animal was undoubtedly heavier than the water and that it sank slowly downwards
and settled itself horizontally on the bottom. Moreover I saw that the animal did

not at all swim like a common C«/e:r-larva, but always
swam horizontally; it was extremely sluggish and had
a milky-white colour, very different from the brown
colour characteristic of most of our Danish Culex-
larvae. I observed that the sipho was of a peculiar
structure, but on using a lens with high power I
immediately understood that I had made one of the
most remarkable discoveries made in our freshwaters
for a long time past.

Some weeks before, I had received a separate copy
from DYAR and KNAB (Entom. News 1910 p. 259) re-
lating to a peculiar mosquito larva, Mansonia pertur-
bans; the paper was cited in my work on Aquatic
Insects (1915), then just in press. The larva is re-
cognizable at a first glance on account of its very
characteristic sipho which has been converted into a
piercing organ by means of which the animal perfo-
rates living plant-tissues; the air in the air-spaces is
used for respiration. The mode of life of the larva is
therefore quite different from that of the other mos-
quito larvae; it does not swim, but must really be re-
garded almost as a sedentary animal, sitting with the sipho bored into the plant-tissue,
near the bottom, often at a depth of one-third of a meter (Textfigs. 12, Tab. 16 fig. 10).

14*

Textfig. 17. Tceniorhynchus pupa.

Apex of one of the trumpets;

highly magnified.

108

In fact, the respiration takes place in quite the same manner as in the case of the
Donaciin larvae, the life of which has been so admirably studied* by my friend Dr. AD.
B0VING in almost the very same locality where the Tceniorhynchus larva was found.

Till 1914 the Mansoma-larvae have only been found in America, and as I knew
that the genus Tceniorhynchus (= Mansonia) has an almost entirely tropical distri-
bution, it will be understood I could not have been more astonished even if I
had drawn forth a representative of the Dipnoi from the mud of the Donse pond.

In the autumn of 1914 I made many excursions to Donse, and I found many
larvae. Frequently I had 30 — 40 larvae in my aquaria, where I had ample opportu-
nity of seeing the larvae creeping between the roots and piercing their tubes into
the plant-tissues. In one of the last pages of my paper on the Aquatic Insects I
gave a microphoto of the larva fixed to a root, and some drawings of the tracheal
system and the sipho.

The larva was rare; the greatest number I was able to procure after searching
for 4 — 5 hours was 10 — 15. Strangely enough I could never find it in any other
locality than where I had found it the first time. The vegetation was composed
of Acoriis, Ranunculus lingua, Glyceria spectabilis and Typha angustifolia. I have no
impression that the larva preferred any of these plants to the others; if so it would
probably be Acorus. In the aquaria the larva fastened itself to the most different
plants and often sat for a fortnight or more fastened to the same spot. It was al-
ways restricted to very shallow water. I never found it deeper than Vs meter. The
best method to get the larvae is to loosen the roots of the plants from the bottom
and then to shake them in high cylinder jars. When the material has sunk to the
bottom the larvae will be found creeping slowly over the decaying material. More
than once on examining the plants I saw the animals fixed in their normal position,
trying to detach themselves when the plant was brought onboard. I have never
found more than two or three on one plant. Altogether I have probably caught
about 100 larvae.

It was my intention to keep the larvae during the winter in my laboratory,
but in February they all died, probably because I had kept them at too high a
temperature. As soon as the ice on the pond had melted I went again to Donse to
procure fresh material. Behold, another great astonishment, though not so agreeable
as when I found the larvae. An enterprising man had bought the water in the ponds
with the intention of establishing an electricity works at the little brook. The still-
born project supplied the country with electrical light for some months, and the
water of the pond disappeared. Next year it was almost wholly dried up; not a
single larva was to be found, the water having receded far beyond the zone where
they lived. On summer evenings I lay in the grass, hoping that some mosquito,
new to our fauna, would come and suck my blood. All was in vain. Neither in
1915 nor in 1916 did the water reach the zone where the larvae were found in
1914. As long as the imago was not found, I did not like to publish my observa-
tions.

109

After many excursions in 1915 — 16 always without result, finally, in 1917, I
had the good fortune to catch the imago. On an early day in July I was sitting
some 100 yards from the pond where I first got the larva. After a heavy rain the
mosquitoes stung vigorously. 0. communis and cantans swarmed around me; then
there arrived three specimens of a dark-coloured mosquito which immediately at-
tracted my attention. I could not get more than the three specimens; but when
these \vere more thoroughly examined later on, it was established that I had found
the Tceniorhynchus for which I had waited patiently for three long years. The next
day I had to leave for my new laboratory at Tjustrup, and when I returned, I
found no more specimens. Still the animal could now be identified and the observa-
tions be published.

According to GILES (1900), BLANCHARD (1905) and HOWARD, DYAR and KNAR
(1912 — 17), the home of the genus Tceniorhynchus is almost entirely restricted to
the tropical or subtropical countries. The main localities are Brazil, West-Africa,
the neighbourhood of the great African lakes, India, China and West-Australia. Ac-
cording to HOWARD, DYAR and KNAR North America possesses only two species
T. ochropus Dyar and Knab and T. perturbans (Walker) Dyar. In about 1900 Euro-
pean dipterologists show that .the genus also occurs in Europe, and that a single
species lives far beyond the normal area of distribution. In 1896 FICALHI describes
a mosquito from Italy under the name of Culex Richardii. THEOHALD (1901 p. 194)
refers the species to the genus Tceniorhynchus and remarks: "FICALHI'S T. Richardii
comes in this genus in spite of the male ungues differing from those of ARRIHALZAGA'S
species" (1901 p. 190). According to THEOHALD (1901 p. 197) a single specimen of
this species was found in England near Sutton by Bradley and, probably, the species
also occurs at Toronto (Canada); finally in 1903 (p. 269) THEORALD states that the
species "seems to be common in some parts of the Norfolk Broads, England."

Later on EDWARDS (1912 p. 261) has recorded the species from different parts of
England, and LANG (1920 p. 99) mentions many other localities. Also ECKSTEIN (1920
p. 232) has found the species "in den Waldern bei Brumath (Unterelsass)"; MARTINI
(1915 p. 605) at Danzig and Hamburg; most probably the species is more common than
hitherto supposed. Just before this paper was going into print Prof. G. W. MULLER,
Greifswalde, wrote to me that he had found a peculiar pupa in that place the
previous summer and sent me two drawings of the trumpets. The drawings prove
that he has undoubtedly found a Tceniorhynchus-pupa and that he has interpreted
the structure of the trumpets in the same way as I have. In 1919, simultaneously
with my own paper relating to the Tceniorhynchus larva EDWARDS published a valu-
able paper on the same subject (1919 p. 83). In all main points we agree well.
EDWARDS has seen the larvae "when disturbed rise to the surface of the water and
hang suspended there in the manner of an ordinary mosquito larva." I do not
think that they ever do so in nature, but in 1919 and 1920 I have often seen the
larva in my aquaria in this position when the roots were bad. As far as I can see

110

we agree with regard to the morphology of the air-tube, the mode of affixion, and
the large airsacks in the thorax.

With regard to the peculiar Tceniorhynchus pupa this is mainly known from
American authors I. B. SMITH (1908 p. 22) and GROSSBECK (1908 p. 473), further
HOWARD, DYAR and KNAB (1917 p. 519) have especially studied that of T. titil-
lans, THEOBALD (1903 p. 270) has figured that of T. uniformis. The pupa of the
European species has not hitherto been thoroughly studied.

Additional biological remarks. With regard to the biology and anatomy
I refer to my above-named paper; some new observations may now be added and
compared writh others derived from authors from last year.

In June 1918 my assistant mag. sci. L. PEDERSEN found the larva of Tcenio-
rhynchus Richardi in a sheltered little creek in Funkedam near Hillerod. The loca-
lity was often visited, but also here the larva was rare, and I did not venture to
disturb it too often. A more thorough examination was made on an area only a few
square yards large. This spot was covered with submerged plants of Sparganium
and Scirpus; the bottom round this was covered with Fontinalis and a few Potamo-
geton natans. Among the Sparganium I could get about twenty larvae in one single
catch, outside it only one or two. Taking the plants out with my hand I more
than once got plants, on the roots of which I found the larvae fastened. These
plants were always Sparganium. Most of the larvae were fullgrown, but curiously
enough I got four minute larvae, of not more than three to four mm. With the
new living material in my laboratory I mainly tried to study the pupa and its life
conditions.

In accordance with the above-given description of the pupa it may now be
maintained that the most characteristic features in the anatomy of the hitherto
known T&niorhynchus-pupaz are that the trumpets do not diverge but converge, and
that the trumpets are provided with a long, strong chitinized hook for insertion
into the roots of the water plants. The two hooks meet each other, so that the two
trumpets form a half-circle over the cephalothorax. Another remarkable structure is
that the stellate hair tufts on the hinder part of the first abdominal segment are
wanting. The paddles are cleft at apex.

From the structure of the trumpets we must suppose that the pupae like the
larvae are fastened to the plants and for their respiration use the air in the inter-
cellular spaces. As far as I know, no one has hitherto seen the pupa sitting with
the trumpets pierced into the plant tissues. Further if it is right that the pupa,
too, is attached to plants, the question arises how. it is possible that the pupa can
pierce the siphoes into the tissues. Finally we do not know if the pupa, when the
last metamorphosis is going to take place, really leaves the plant and, like other
mosquito pupae, metamorphoses on the surface or finishes its metamorphosis fasten-
ed to the plant roots.

For two consecutive years (June, 1918 and 1919) I had about twenty full-
grown larvae of T. Richardi in my aquaria; during both years five or six specimens

Ill

metamorphosed into pupae. I very often tried to observe the moment when the ec-
dysis took place, but I was always too late. Every time I found the fresh yellow
pupa fastened to a root, and with the two siphos pierced into the plant. At all
events it was now established as a fact that the pupae like the larvae are really
fastened to the plants using the air in the plants for respiratory purposes.

I only wish to call attention to the almost incredible power of adaptation
which the Tceniorhynchus-species presents. Like other mosquitoes they have the re-
spiratory system formed in quite different ways as larvae and as pupae; as larva
the tracheae open in an unpaired organ, the sipho, on the eighth segment; as pupae
in paired siphones "trumpets" on the forepart of the body, on the cephalothorax. If
then the species in its two different stages as larva and pupa is to be adapted to
use a special source for air-supply, it is able to modify, not only the unpaired sipho
of the larva, but also the paired one of the pupa. One would be inclined to sup-
pose that the problem of making a piercing organ out of two divergent, loosely
attached appendices which, when used, were to act according to the new claims
as an unpaired organ, would have been almost insoluble even to Nature. And still
this problem has been solved and in the most elegant manner only by making the
two siphones convergent and by laying the acuminating points against each other.
I only regret very much that I have not been able to see how it is possible for
the pupa to pierce the trumpets into the plant. From our knowledge of the struc-
ture of the pupa-body and the different mode of locomotion it possesses I am un-
able to understand how it is possible for the pupa to get the necessary support,
which must be the condition sine qua non, if the pupa is to be. able to pierce the
trumpets into the roots of the waterplants. Any one who will try to force a needle
into a root to which a Tceniorhynchus-pupa is fastened, will find that this demands
no inconsiderable force. I have thought that the pupa might perhaps get some sup-
port in the larva skin, this being thrown off after the piercing process of the trum-
pets has been finished. But I do not possess any basis for this supposition.

When I touched the pupa with a needle, it struck out eagerly with the ab-
domen; I could take the whole plant out of water, the pupa was quite unable to
loosen its hold. The first year all the pupae died, attacked by Mucoracece; the next
year three imagines were hatched, but sad to say, the ecdysis took place at a time
when I was at my summer laboratory; as however I found the pupa-cases floating
on the surface and the hooks of the siphos broken off, there can be no doubt that
the pupae, when the ecdysis is going to take place throw themselves away from
the plants by means of the abdomen and rise to the surface. This is also in ac-
cordance with some observations made by EDWARDS just published (1919 p. 83).
Although he has not found a living pupa, he is able to record that several speci-
mens of T. Richardi were hatched in a pail which he had brought home full of
pond water and sods of grass. "The empty pupul skins were found floating on the
surface for the emergence of the adult. An examination of these skins showed that
in every case the terminal portions of the breathing-tubes were missing; hence it

112

must be inferred that they had been left behind in the roots." I can add that this
supposition of Dr. EDWARDS is quite right; in every case I found pierced into the
roots the pointed terminal portions of the breathing tubes; in the tubes there is a
conspicuous predestinated zone of weakness, where the tubes break off; then the
pupae rise to the surface. Most likely their barbed structure, while facilitating their
insertion, would prevent their being withdrawn. (Se also EDWARDS 1919 p. 83). It
is only difficult to understand how without hairs the pupae are able to be suffici-
ently supported by the surface film during the metamorphosis.

It is of some interest to remember that the Tceniorhynchus larvae are probably
not the only mosquito larvae which make use of the air in the intercellular spaces
of the plants. According to HOWARD, DYAR and KNAR (1917 p. 894), the larvae of
the genus Aedeomyia (A. squamipennis and catasticta) are to be found in shallow
ponds covered with the water plant Pistia "from which they probably derive their
supply of air although their habits have not been exactly determined". They do not
come to the surface, but hide between the water plants. The sipho presents no
peculiar structure, being shaped as the sipho of a common mosquito larva; only
the tracheae of the tube are said to be rudimentary. On the other hand, the an-
tennae have a very peculiar appearance in comparison with those of the other mos-
quito larvae, being strongly curved, inflated, hollow, with a stout spinose digit on
the tip. HOWARD, DYAR and KNAB (1917 p. 898) suppose that these inflated antennae
may play some part in the respiratory process.

In 1916 DETTE has made the supposition probable that a Tipulid-larva, Tri-
chosticta flavescens,. too, makes use of the air in the intercellular spaces of the plants.

How the peculiar method of respiration, especially with regard to the Tcenio-
rhynchus-larva, has arisen it is difficult to understand. Further studies will probably
acquaint us with larvae in which the modus of respiration as well as the shape
of the sipho represent the missing link.

For a long time I thought that we should have to study the tropics if we
wanted to solve these questions, and that it would be almost unreasonable to ex-
pect that it would be possible to find the solution of the problem in a little pond
in North Seeland, far away from the centre of the geographical distribution of the
genus. Later observations from this last winter have somewhat altered my opinion
upon that point.

In my aquaria I had some Myriophyllum, which were growing well. In the
same aquaria there were a great many C. morsitans larvae. One day in January I
removed one of the aquaria into the bright sunshine and now observed the well-
known fact that vertical series of air-bubbles from different spots of the plants rose
to the surface. The numerous C. morsitans larvae now fixed themselves to the plants.
The position was always the same; the two strong curved setae on the flaps of the
sipho were pierced into the plant-tissue and the apex of the open air-tube was
pressed against its cutis. The larvae were hanging down from the plant, quite as a
Tceniorhynchus larva. For more than twelve hours they did not rise to the surface

113

and when brought into darkness and cold they hung down from the plants for
weeks. The biological difference between the C. morsitans larva and the Tceniorhyn-
chus larva is in one respect but slight, in another really very large. The C. morsi-
tans larva sits with the hooks on the flaps pierced into the cutis of the plant and
the apex of the sipho pressed against it; it is only a fraction of a millim. distant
from the air-supply of the plant, but most probably it is never able to use it; still
it is a question, whether it cannot make use of the air-bubbles which rise from the
stem of the water plants in sunshine, from holes wrhich may be pierced by the
hooks for the sake of attachment, into the plants. The Tceniorhynchus larva sits
with the flaps of the sipho which have been modified into a piercing organ and
with the apex of the sipho directly pierced into the air spaces of the plant and is
able to use this air for respiration. Still it is a question how much the Tceniorhyn-
chus larvae actually use of this air-supply in the \vater plants; for respiratory pur-
poses it is, especially in winter, of a very bad quality. (EGE 1915 p. 183); perhaps
this air is not their daily food at all, but is only used on certain more solemn
occasions (f. i. during the ecdysis process) as the cutaneous respiration is of the
greatest significance also for these larvae. If so the difference in the mode of re-
spiration between a Tceniorhynchus larva and a C. morsitans larva is not either by
any means as great as should be expected at the first glance, the Tceniorhynchus
larva being also mainly restricted to cutaneous respiration during winter. After
this has been written it was of great interest to me to see that LANG (1920 p. 103)
has had quite similar thoughts. With regard to the larva of C. morsitans he writes :
"Evidently they shun the surface and may well be on the way to developping
similar habits to Tceniorhynchus. Mr. EDWARDS suggests, that it is even possible
that that genus may have been derived from Culicella." It has always been main-
tained that the sipho of the Tceniorhynchus larva lacks a pecten. In this connection
I wish to direct attention to the possibility that the saw teeth in the Tceniorhyn-
chus tube may really be the modified pecten. This supposition is weakened by the
fact that the pecten in a normal larva sipho is situated on the opposite side to
where it is situated in a Tceniorhynchus tube.

The life-cyclus of the species is probably as follows: The female deposits its
hitherto almost unknown eggs in the course of the summer. In autumn the eggs
are hatched. In September we mainly find very tiny larvae on the roots. Before
winter most of the larvae are fullgrown and in this stage they winter. The pupation
takes place in the latter part of May. Whether the imago winters we do not know
but it is not probable that it should do so. How to explain the very small larvae
in spring I do not know; that the larvae should be biennial would be quite excep-
tional. I am more inclined to think that the difficult life conditions render it ne-
cessary that not all eggs are hatched in autumn or rather, that not all larvae are
fastened under good conditions in autumn, so that the development is delayed and
only part of them pass the last ecdysis before winter.

D. K D. Vidensk. Selsk. Skr., naturvidensk. og niathem. Afd. 8. Rtekke, VII, 1. . 15

Geographical distribution : The species is described from Italy (FICALBI) later on
found by EDWARDS in England, in Germany by MARTINI (1915 p. 585) and by G. W. MULLER.

The eggs of Tceniorhynchus have been described by different authors (see DYAR
and KNAB 1910 p. 259). Further they have been thoroughly described by the said
authors in a special paper (1916 p. 61). The following remarks are taken from that
paper. The eggs of the three American species, Mansonia fasciolatus, Arrib. arribdl-
zagce, Theob., and perturbans Walk, do not differ very much in shape, arrangement,
and manner of disposal from eggs of typical Culex species. The egg-boats float upon the
surface of the water, one end usually resting against an aquatic plant; still there is
some difference in the arrangement of the eggs of the three species. The eggs of
M. titillans found by MOORE, are of quite another type; they are placed on the
under-surface of the leaves of Pistia and deposited in a mass, generally between the
ribs of the leaves. They are attached to the leaves with their bases very closely
crowded together and apparently kept by a cement secreted by the female. The
number of eggs in a cluster exceeds 150. MOORE has observed directly that at least
the abdomen was submerged when ovipositing. "The lower half of her abdomen
was submerged and bent or curved back, the segment somewhat extended, and was
being moved slowly from side to side; the eggs seeming to issue forth in rapid suc-
cession and to be as rapidly set up each in its place air bubbles were en-
tangled in the abdominal scales and on the leaf itself. According as the cluster en-
larged in her direction she drew her abdomen more and more up so that when
she finished at 6,35 not much more than the tip of it was curved under the leaf.
When she first started more than half of her abdomen would have been under
the water. The freshly laid cluster was white". DYAR and KNAB call attention to
the fact that the abdomen of the female of M. titillans is unusually hairy, the hairs
being well distributed and coarse. This is no doubt an adaptation, that by en-
tangling air between the hairs prevents the body itself from becoming wet while im-
mersed. MOORE supposes that the female, when at work on Pistia, really works in a
globule of air, for, owing to the dense pilosity of the leaf, the under surface is simply
aglow with air-bubbles, so that the leaf probably rests more on air than on water.
The egg-shell of this species presents no special structure; it resembles that of most
other Culicidw.

In the same paper DYAR and KNAB describe another egg also forwarded to
them by MOORE. The egg is furnished with a small neck from the upper edge
of which four pairs of horns project upon very short stalks; these horns appear to
consist of solid chitin and taper into a sharp point. Later on, MOORE found the
species which laid these eggs; it was described as a new species, M. hnmeralis Dyar
and Knab. These eggs are of interest because they resemble the eggs of Nepa and
Ranatra; as well known, these water-bugs pierce their eggs into half decaying plant
material, and the crown of spines round the tip of the eggs is commonly regarded
as a respiratory organ. DYAR and KNAB also regarded the spines of the egg of Man-
sonia as in some way connected with the problem of air-supply.

115

The eggs of T. Richardii are unknown; most probably they are laid in the
manner of the genus Culex in eggboats. ECKSTEIN (1919 p. 288) writes; "Es ist mir
gelungen T. Richardii aus den Eiern zu ziichten", giving no description of the eggs;
he refers to a future paper.

Genus V. Theobaldia.
Tab. XVII.

1. Theobaldia annulata (Schrank).

Imago. This mosquito is recognizable at a first glance from all other Danish
Culicinse by its spotted wings, a characteristic it shares with T. glaphyropterus
which has not hitherto been found in this country. It is the largest of all our mos-
quitoes ; its large size, its spotted" wings, the white banded legs make it one of our
most conspicuous and also one of our most beautiful species.

Larva. Head rounded, rather small, wider than long, a notch at insertion of
antennae, front margin arcuate. Antennae very short rather thick, tapering at front
spinose, tuft small, only consisting of about five to seven hairs, inserted directly
without notch on the antennae and below middle. Near the apex two hairs, on the
apex itself three hairs and a digit. Anteantennal tuft multiple; lower frontal tuft
with six hairs, upper with one very long, and two shorter ones. Eyes large; a re-
markably well developed tuft in the notch between the eyes and antenna ; a charac-
teristic coloration of the head integument (see fig. 1).

Thorax subquadratic, angled at hair-tufts. Hair formula of frontal border
341144441143; I have also found 341145541143; the median tuft consist of one long
and three or four very short hairs; the. next tuft of four hairs always short. Lateral
hairs in- multiple tufts and some single strong hairs.

Abdominal segments broad, the first of them much shorter than the last.
Lateral hairs on the first segment multiple, on the third triple, on the third to sixth
double; subdorsal hairs on third to sixth segment double; between them and the
lateral hairs a single hair; the eighth segment with tufts in common arrangement,
the upper double; lateral comb consisting of about forty scales arranged in rows,
occupying a triangular area; the scales are long, spatulated with a feathered base
without median thorn. Sipho rather short, straight, slightly tapering at apex. A short
pecten consisting of about ten, short, feeble thorns, without any or with very indi-
stinct teeth at base; then a series of about twenty long, soft, flexible hairs.

No tuft of hairs between apex and .end of pecten, but a large tuft at the basis
of the pecten. Anal segment broader than long, ringed by a plate. Dorsal tuft con-
sisting of a rather compact tuft of rather long, soft hairs, two very long stiff hairs
and some others much softer and almost equally long. Ventral brush large, con-
sisting of about 17 rays; on the barred area every ray carrying from 14 to 16 hairs;
before the barred area five short tufts; a lateral tuft with three short hairs. Anal
gills moderate, equal, acute.

15*

116

Lateral tufts of labrum short, dense; the inner part consisting of comb-hairs,
arranged as a crown around the palatum, covered with soft hairs. Mouth-parts
highly remarkable. Mandibles quadrangular with three strong spines before the col-
lar; a row of remarkably short cilia from a collar; a row of very strong spines
from margin; most of these spines dentated, furnished with strong thorns. Denti-
tion: a broad dark plate formed as the forelimb of a talpa with six almost equal
teeth; a series of bristles below; process below distinctly furcate with strong hair-
tufts on both tips; a group of hairs at base. Maxillae broader than long, almost
without suture; no apex and no tuft of long hairs upon it; fore and inner margin
furnished with a coarse covering of very short, soft hairs; a few hairs near the
palpe; a short bristle on the foremargin. The palpe well-developed with a few di-
gits. Mentum triangular, borders almost straight; median tooth small, about twenty
equal teeth on each side. Colour commonly greyish.

The larva has been described and figured by MEINERT (1886 p. 376). Owing
to his description of the sipho and pecten I must suppose that he really has seen
the larva, but with regard to the description as well as the figures, especially re-
lating to the bristles of the head and anal segment, there are such great differences
between his and my statements, that I have often supposed that he has unfortuna-
tely used a larva of another species to describe these details. Of the frontal tufts,
the lower so characteristic with its one long and two short hairs, is, according to
his description, the most feebly developed with three bristles; the habitus figure has
only one single very long bristle, and the more specialized figure (2) has a very
short tuft with three hairs, one of which is really longer than the others; the
arrangement of the tufts differs greatly in the habitus figures from the more detailed
figure (Fig. 2). On the mandibles (Fig. 7 — 8) he has correctly indicated that the
spines of the inner border are dentated, and the figure of the characteristic broad
maxilla (Fig. 6) is correct. He has further seen that the species has comb-hairs in
the flabellse. On the other hand the dorsal brush of the anal segment is quite diffe-
rent from what I have found; the two long bristles are wanting, and the division
in two parts is only problematically indicated in the figure.

SCHNEIDER (1914 p. 44) has a more correct figure of the two last segments
(Fig. 4). With ECKSTEIN'S statement (1919 p. 290) that the pecten consists of "7
mehrzahnigen Dornen" I do not agree well.

Biology. The biology of T. annulata is rather remarkable. If in winter we
examine the deep frostless cellars of our houses, we find among the numerous
C. pipiens a few much larger ones, highly characteristic because of their spotted wings
and white ringed tarsi. This is T. annulata, the largest of all our mosquitoes. I have
never found it in great numbers; yet it is by no means rare.

In December 1918 I took twenty imagines and placed them in a little shed,
where the temperature in the nights often fell^below zero; most of them died but
some hibernated.

Hitherto we have taken it for granted that the mosquito only hibernates in

117

houses, cellars and sheds; but this is undoubtedly not correct. In 1916 on one of
the last days in April, I was examining an old hollow beech and to my astonish-
ment saw that many T. annulaia were sitting in the bright sunshine on the wind-
sheltered part of the trunk. I prodded the hollow part of the trunk with a walking
stick and the mosquitoes rushed out of the trunk like smoke; all were females,
which undoubtedly had their winter-quarters there. When I passed the same old
beech late in Oktober 1919, I again saw many imagines of the same species but
now males as well as females, sitting and flying round the entrance to the hollow
part of the trunk; no doubt they were seeking their winter quarters there. I lost
the opportunity to see the egg-rafts and the egglaying processes, but in July — Au-
gust I found the large greyish larvae among the swarms of C. pipiens larvae; they
were hatched in Cement-reservoirs in dairy-farms and in cow-houses in farm yards;
the number is always rather small, perhaps about one T. annulata to a hundred
C. pipiens. They are found as larvae and pupae much later than C. pipiens (till 20/x
1918). This is in accordance with the fact that the imagines fly remarkably late,
and that I have often found the imagines sitting out of doors the last days of Oc-
tober, behind shutters, below veranda-staircases etc. I suppose that the imagines
pair before winter and then die out; in spring I have never seen a single male. The
development by no means always takes place in our houses; I have found them
together with larvae of C. pipiens, in ditches mainly consisting of urine near gates
sheltered by old oaks below which the cattle regularly sought shade against the
burning sun. But, apart from these unsavory localities, I have also found them in
great numbers in a little pond covered with Lemna but with very decaying mud
in the bottom. This pond has been under regular observation for three years, 1918
—20, but T. annulata was only to be found in 1918.

The pond was visited for 0. cantans from April to June in 1918 and during
that time I did not get a single T. annulata. When I visited the pond 10/vn to
search for the rare larva of Rana agilis living in the same pond, I was rather asto-
nished to see that the pond now contained a great many grey, halfgrown larvae,
which later on gave T. annulata. The larvae were not hatched before the middle of
August. I always found small and large larva? among each other, and I got the
impression that the egg-laying took place at all events in September; curiously
enough I could never find the egg-rafts. Also in ponds near Hillerod have I found
T. annulata larvae in September — October; one of them had clear brown peaty-
water; they lived here till 12/x, when the pupae appeared, giving imagines in my
laboratory on l?/x.

From these observations we are able to ascertain that T. annulata is hatched
in the cement-reservoirs indoors, as well as in ponds in Nature itself. I am inclined
to interpret the above-named facts in the following way. In our country T. annu-
lata has two generations. The hibernating generation appears in September — Octo-
ber, hibernates in our houses, and lays its eggs indoors in stables etc.; from these
eggs appear the summer generation, which disappears from our dwellings and lays

118

its eggs mainly in natural ponds; most probably this generation has several
broods, the egg-rafts being not all laid simultaneously, the males die off after the
mating process but the females from all these broods return to our cellars and
hibernate there.

The biology has never been more thoroughly studied. All authors agree with
regard to the remarkably high susceptibility to domestication, breeding places in
Nature not being found hitherto. THEOBALD (1901 p. 335) states that both $ and
? hibernate but this has never been ascertained. I have observed this species in
many localities of hibernation but I have never seen a single male in winter or
early spring. With regard to the nourishment I refer to the following chapter.

Geographical distribution: According to THEOBALD (1901 p. 334) it is
common throughout Europe, from Scandinavia to Italy; it also occurs in India,
at 5000 feet above sea level. OSTEN-SACKEN states that it is also said to occur in
North America, but by HOWARD, DYAR and KNAB (1915 p. 496) the American species
are regarded as another species (Culiseta Dugesi).

Genus VI. Culicella.

1. Culicella morsitans (Theobald).
Tab. XVIII— XIX.

Description. Female. Proboscis long, uniform, pale near base, labellae
conically tapered almost black with some few bronzy yellow scales; palpi short; al-
most black, apex yellowish-white. 'Antennae brown, joints subequal, rugose, pilose,
second joint slightly enlarged, hairs of whorls rather long, spinose; tori sub-
spherical, bright ferrugineous. Occiput dark brown covered with yellowish-white
scales denser towards the sides; margins of eyes white scaled; many slender erect
forked black scales; setas along margin of eyes curved, black.

Prothoracic lobes elliptical, remote dorsally with narrow yellow scales and
many black seta3; mesonotum brown, with a median and two shorter curved late-
ral, rather indistinct and varying lines of bright bronzy-brown or creamy scales,
which are also found on the sides of the mesonotum. Scutellum trilobate, brown,
clothed with narrow7 curved shining yellow scales: each lobe with a large group of
brown bristles; postnotum pale, clear chestnut brown pruinose, nude; pleura brown,
covered with spots of creamy almost snow-white scales.

Abdomen subcylindrical, depressed, truncate at tip; dusky brown, covered with
fuscuous scales and with basal creamy yellow bands; their posterior borders edged
with pale hairs; venter covered with pale yellow scales.

Legs long, slender, dark, almost black; coxse, bases and ventral surfaces of
the femora more pallid; knee spots snow-white, tibiae black, apices of the tibiae
yellow, base of all tarsal joints narrowly banded, all the bands are very narrow,

119

broadest on the hind tarsi. Ungues of all legs equal and simple. Claw formula
0.0—0.0—0.0. Length of body 6.5—7.5 mm.

Wings unspotted, with veins covered with long, thin, black, lateral scales and
a dark fringe; both fork cells long and about the same width; second marginal
cell a little longer than the second posterior cell; base of the second posterior per-
haps a little nearer the base of the wing than that of the second marginal cell;
petiole of the second posterior about as long as that of the former cell ; basal cross-vein
about the same length as the anterior cross-vein, but not its own length distant
from it. Halteres with a pale stem and fuscous knob.

Male. Proboscis straight, uniform, brown, almost black at apex. Palpi longer
than proboscis. First joint of palpi in the first basal third part white; then a small
black stripe; again a white stripe and lastly black at apex; second joint white at
base, otherwise black; third joint white at base and black at apex, slightly spa-
tulate and truncated, the two last joints with black hairs. Antennae plumose, banded
black and white ; hairs long, dense black. Occiput black with a hairless line down
the centre; clothed with pale creamy curved scales on each side; flat creamy
white ones at the sides, but commonly with no brownish lines between these and
the curved ones, long brown upright forked ones, dotted about and golden hairs
projecting forward.

Mesonotum chestnut brown, with three rather distinct lines of yellowish gol-
den scales as long as the thorax and two other more distinct bright yellowish, only
half as long as the former ones, bordered by black scales ; long black hairs scattered
over the whole thorax and over the roots of the wings; scutellum brown, trilobate,
with tufts of long black hairs at the border.

Abdomen blackish brown, covered with brown scales, each segment, except
the first, with a basal band of creamy- white scales, broader on the last segment;
posterior borders of the segments with long golden hairs and the sides with long
brown hairs.

Legs with the coxae brown; femora at the base and beneath grey, at the upper
side dark brown; knee spots white; tibiae dark, covered with dusky brown scales,
apex bright yellow. All the basal joints with creamy white apices, but without
white bands at base; hind metatarsus about two thirds the length of the tibia;
metatarsus of the front legs distinctly longer than the remaining four joints together;
ungues of fore and midlegs unequal; the larger one with two, the smaller with one
tooth; hind ones of moderate size equal and simple. Claw formula 2.1 — 2.1 — 0.0.
Length 7.5 — 8 mm.

Wings long; the veins clothed with yellowish-brown scales, the lateral scales
mostly long; second marginal cell narrower; but about the same length as the se-
cond posterior cell; its stem only three-fourths of the cell; its base a little nearer
the apex of the wing than the base of the second posterior cell ; petiole of the latter
as long as the cell and almost as long as the stem of the second marginal cell; the

120

basal cross-vein about its own length distant from the anterior cross-vein; fringe
brown with pale reflexions along the inner border towards the base. Halteres ochra-
ceous-brown with a slightly fuscuous knob, stem elongated and thin.

Larva: Head subquadratic, almost twice as wide as long, a notch at in-
sertion of antennae; front margin almost straight, slightly arcuate. Antennae very
long, longer than head, elegantly curved, covered writh spines, especially between
antennal tuft and head; the part of the antenna between the head and tuft ivory
coloured, the narrower part brown; tuft very large, inserted near the apex, consis-
ting of more than twenty five very long feathered hairs ; the terminal portion slender,
carrying two long hairs before apex, on apex itself one long and one short hair;
between them a short digit. Anteantennal tuft almost in line with the frontal hairs
multiple; lowrer frontal tuft writh four hairs, upper double; the points of insertion
of the hair-tufts forming a curved line over the epistome. Eyes large.

Thorax subquadratic, angled at hair-tufts; hair formula of frontal border
231124421132. Lateral hairs in large multiple tufts some single, strong hairs.

Abdominal segments rather narrow, lateral hairs on first two segments multiple,
single on third to seventh; subdorsal tufts double on third to seventh segment. Tufts
of eighth segment in common arrangement, but all remarkably feebly developed. Late-
ral comb consisting of a great many, about a hundred scales, arranged in rows
occupying a large triangular area; each scale with spatulated base and elegantly
feathered broad tip. Sipho straight, extremely long, 6 — 7 times longer than broad; a
tuft of five hairs at base; the pecten extremely short, consisting of only about six to
eigth thorns, all broad obliquely feathered, no tuft of hairs between pecten and apex.
Anal segment longer than wide; ringed by a dorsal plate; dorsal tuft in two parts,
the upper part consisting of a tuft of many, rather short hairs, the lower of 6 — 8
hairs, unequal, two very long. Ventral brush in the barred area consisting of 12 rays,
each carrying about twelve hairs; before the barred area about six detached hair-
tufts. No lateral tufts. Anal gills long, acute, equal.

Lateral tufts of labrum very large, distinctly separated in two parts the inner
part without any comb-bristles, palatum large, covered with short, soft hairs. -
Mandibles quadrangular, with four strong spines before the collar; a row of long
cilia from a collar; about 10 scales from margin, but no distinct spines: dentition:
five teeth, two of them strong, before them a very long, arcuate thin thorn. Long
cilia below the teeth; process below distinctly furcate, with strong hair- tufts on both
tips; a group of hairs at base. Maxillae elliptical, tips conically rounded; at apex a
large brush of long, soft hairs. No spines at margin. Palpus well-developed with
five little apical digits. Mentum high triangular, the median tooth large, with 10
or 11 teeth on each side.

Colour of the body brown or green, brushes on labrum golden.

Systematical remarks: From the description above it will be understood
that there are same distinct differences between THEOBALD'S species C. morsitans
and the Danish specimens. The greatest variations are to be found in the white

121

bands on the palpi of the male, in the banding of the legs, further there are some
smaller differences with regard to the nervature of the wings. Otherwise there is
full accordance between Theobald's description and the Danish specimens. Among
all other Danish mosquito larvae the larva of C. morsitans is distinguishable at the
first glance owing to the antennae, the sipho and the structure of pecten and comb.
It has already been described by MEIJERE (1911 p. 138), EDWARDS (1912 p. 261)
and later by SCHNEIDER (1914 p. 35) and ECKSTEIN (1919 p. 288); it is perhaps one
of our most remarkable mosquito larvae.

Most probably the species is widely spread over the whole of Europe but it
is not very common in our country.

I have hatched many hundreds of this species in my laboratory, especially
from larvae which have hibernated in my aquaria, most of them there gave ima-
gines in April; in nature they did not hatch before the latter part of May. Later
on in the course of the summer I gathered several flying specimens. Between these
specimens hatched in my laboratory in April — May and those gathered in summer,
there were rather conspicuous differences. Those from April were smaller, only
about 6.5 mm, of a more brown colour, and with the bright scales almost white;
those from May and later were much larger, about 8 mm, almost as large as C.
annulatus and much darker.

For a long time I thought that I had more than one species in the material.
As according to MEIJERE himself (1911 p. 142) and EDWARDS (1912 p. 262) C. fumi-
pennis Stephens is said to resemble T. morsitans very much, I particularly thought,
that this species was concealed in the material. More especially some specimens
found in August 1918 in an old house in the park at Dragsholm Castle differed
very much from the true C. morsitans owing to their more yellowish colour. Un-
fortunately all these specimens were old; the hair-coating of the thorax was almost
wanting, and that of the abdomen was inconspicuous; all the specimens were fe-
males. Mr. EDWARDS has been kind enough to look over my whole material, and
maintains that all specimens may be referred to the single species C. morsitans.
This view is strengthened by the fact that in the large larva material I have never
been able to find more than one larva type. According to MEIJERE and EDWARDS
the t\vo species are easily distinguishable in the larva stage, C. fumipennis having
five to six spines beyond the pecten. I have never found larva? with siphones of
this structure in Denmark. As the species however is found in Holland (MEIJERE)
in Scotland (EDWARDS 1912 p. 262) England (LANG 1920 p. 104) and in Germany (ECK-
STEIN 1919 p. 289) I suppose that further explorations will also reveal this species
in our country. LANG (1920 p. 104) maintains that the two species are almost in-
distinguishable from each other as imagines. He maintains that it "would be of
great interest to determine .... if these two species always bred true, and that they
were not one species with a dimorphic larva".

Biology. C. morsitans has been studied regularly for more than three years
in a great many ponds, more especially those of Stenholtsvang, the Str0dam ponds,

D. K. D. Vidensk. Selsk. Skr., naturvidensk. og rnathem. Afd. 8. Rsekke, VII, 1. }g

122

those of Gronholthegn ; the Mochlonyx ponds, those of Store Dyrehave, of Gripso,
of Hestehave and of Suserup. To these many regular observations I can add many
accidental ones, gathered on excursions often undertaken for quite different purpos-
es. In almost all localities the life history of the mosquito is on the whole the same.

When the ponds in the time from about i»/ix to 15/x get the first insignificant
volumina of stagnant water, the first Culicin larvae which appear are those of C. morsi-
tans. The quantity of water, in which the eggs are hatched, is often extremely
small, only some few liters; the height of the water is so inconspicuous, that the
larvse are unable to swim, living the first days of their life as creeping animals,
winding themselves over the diatom-covered withered, yellow grasses which cover
the bottom of the ponds. As the water rises during the autumn, and the waterline
reaches eggs lying above the first waterline, new eggs are hatched. If heavy show-
ers fill the little water basin in the course of a few days, almost all the eggs are
hatched simultaneously, and the larvae are almost all of the same size during the
growth. If the filling of the basin takes place slowly through a long time, egg por-
tion after egg portion is seized by the water line and it then happens that newly
hatched larvse are found with fullgrown ones.

In the time from about Vx to about Vxn the larvae grow up, pass the three
ecdysis-stages and are commonly fullgrown before the ponds are covered with ice.
During the whole autumn the C. morsitans larva is the most common of all our
mosquito larvae, and in most of the ponds it is the only one occurring at that time
of the year.

It often happens, as in 1919, that a little rain in the beginning of October
fills the water basins; 'in the course of a few days the C. morsitans larvae are hatch-
ed. They grew up to the second ecdysis, then in November we got a period of
frost, and the pond froze to the bottom; then the whole larva material died out;
when the ponds were thawed again in the latter part of November, not a single
larva could be found. Then when snow and rain in December had filled the water
basin to the brim, new lots of eggs were hatched, and new larvae appeared. As
many of these mosquito ponds are extremely shallow, it often occurs that a good
many freeze to the bottom; in this case all the C. morsitans larvae died and when
in early spring the basins were again filled with water and snow, other mosquito
larvae especially O. communis took the place of C. morsitans. Then we had an op-
portunity to observe the very peculiar phenomenon that these ponds, when freezing,
are filled with thousands of C. morsitans larvae; whereas, when again thawed
up, they only contain those of 0. communis. This was more especially the case in
the winter of 1918 with almost all the ponds in North Seeland; in a mild winter
f. i. in 1920, when the covering of ice was but slight and the ponds open in Fe-
bruary, the wintering of larvae is a much more common phenomenon. But whether
the winter is severe or mild, it is a rule that in April — May we hardly ever find
the larvae of C. morsitans in the larva swarms of 0. communis; undoubtedly very
many of the C. morsitans larvae die out during the winter; and this is, I suppose,

123

the principal reason, why the imago is comparatively rare in our country and much
rarer than the larva. But the peculiar circumstance that we hardly ever find the
larvae in the swarms of 0. communis, though they are by no means rare in the
ponds, is caused by the fact that the larvae of C. morsitans • conceal themselves
between the decaying leaves and only rarely come to the surface. This is in ac-
cordance with observations made by ECKSTEIN (1918 p. 533), and LANG (1920 p. 102).
In my aquaria the imagines from larvae taken into the laboratory in December,
appeared already in the two first weeks of April; I therefore thought that this
would also be the case in Nature. It therefore astonished me extremely to find that
in the last days of the hatching period of 0. communis black and much larger
pupae appeared from which later on C. morsitans were hatched. A more thorough
study of my temperature observations this year and new observations next year
showed, firstly, that these ponds were all filled with water during the winter
and further, that the larva of C. morsitans in spring as in winter hardly ever
came to the surface, but lived near the bottom or were hanging down from the
plants. If this is a general rule, the life as larva of this species may be remark-
ably long, lasting from the last fortnight of September to the last half of May; in
the five last months, as far as I know, that larva does not moult. That the pupae
in May really derive from hibernating larvae and not from a new spring generation
I regard as certain, the pond in April — May being under regular observation almost
every week.

I therefore feel sure that C. morsitans in our latitudes has only one generation ;
laid as eggs in the summer months, living as larvae from September to May, as
pupae only a few days, and then from June to autumn as imagines, the latter dying
out before autumn.

As imago the mosquito, as stated above, is rather rare; this is the case at all
events in North Seeland. I have taken it from June to the middle of August, but
always only in small quantities; in July the mosquitoes where filled with eggs. I
suppose that the egg-laying process took place in July — August; the eggs were laid
upon wholly dry soil, the ponds where the larvae appear in September all being
dried up during the summer months. As a female in a vessel without water, but
with the bottom covered by dried leaves, had laid her eggs singly or in small
batches, I take it for granted that the females also in Nature throw their eggs
singly or perhaps in small lots between dried leaves and withered grasses on the
spots where they were hatched in spring, and which will again get water in autumn.

As the mosquito lives as larva at very different temperatures, from about
15 — 20° C. in May and September and near zero in winter, we have an excellent
opportunity to study the different manner of life at different temperatures. As regards
respiration there is a great difference between the behaviour of the larva in autumn
and winter and in spring. Like most of our other mosquitoes C. morsitans is sup-
ported by the surface film in the autumn and like other Culicin-larvae breathes
atmospherical air. When winter comes as the temperatures falls, the larvae dis-

16*

124

appear from the surface and fasten themselves to the water plants or to the sides
of the aquaria. They are also to be found at the bottom of the water, lying on the
dorsal side, supported by the apex of the sipho and the long hairs of the head.
At temperatures near zero it can be observed that the larvae, often for more than a
fortnight, never alter their position; this is also the case if the surface of the aquaria
is covered with a slight layer of ice. The larvae never or only at rare intervals seek
the surface; they only satisfy their respiratory claims by means of cutaneous re-
spiration; the anal gills are spread out, and the large flabellae maintain the water
currents.

In these hibernating larvae it is interesting to observe how the number of
strokes with the flabellae quite automatically increases or diminishes with the rising
and falling temperatures. At a temperature of 3° C. all larvae had the flabellse drawn
in; at a temperature of 5 to 6° C. the number of strokes per minute was 30, at
temperatures between 14 and 20° C. the number of strokes increased to 114 and
when the sunbeams fell directly upon the larvae, to 136. As the water in winter is
extremely clear and contains very little detritus or animalcules, the larvae get ex-
tremely little food by means of the flabellae. In the winter-larvae we therefore also
observe very few swallowing movements, easily observed under the binoculary aqua-
rium microscope in autumn or spring. During the winter the flabellae therefore
serve mostly for respiratory purposes.

More than any other of our mosquito larvae the larvae of C. morsitans live
upon suspended detritus and plancton; only rarely we see the larvae brush off the
plants from the bottom; the fiabellae are not suited for that, being quite destitute
of comb-hairs. In autumn we find the large larvae hanging down from the surface;
the head is held almost horizontally; in large elegant curves the antennae project
from the head, and the large antennal tufts form beautiful wheels on both sides of
the head; the large flabellae are almost always in activity striking in summer 120
to 140 strokes a minute and offering an excellent opportunity to study the feeding
processes and other phenomena connected with them. I refer the reader to pag. 16 — 19.

The larvae are fastened to the substratum by means of two curved hooks on
the flaps of the closing apparatus of the sipho; this is sufficient when the substra-
tum consists of small twigs or leaves; on the sides of the aquaria the hooks do
not yield the necessary hold, th'e manner of attachment is then commonly another.
It may be observed that the larvae often swim round with a little air-bubble at the
apex of the sipho; when the larvae arrive at the sides of the aquaria this bubble
is drawn in, and they are then glued to the aquaria by means of the diminished
space and the pressure of the air.

Undoubtedly the green waterplants are of the greatest significance to the larvae
during the winter. In shallow, slowly running brooks, with the bottom covered with
carpets of Callitriche and other green water plants, I have observed that the plants
carry hundreds of C. morsitans larvae, even where the ice covers the surface of the
water, and the plants are partly frozen in the ice. In sunshine little air-bubbles rise

125

from the plants, and it is possible that this air too, caught and drawn in by the
sipho, is used by the larvae. I have never directly observed this phenomenon, but
the supposition is rather obvious, because these air-bubbles play a prominent part
in the respiration of many other insects in winter, more especially Dytiscids.

Geographical distribution: It is very difficult to clear up the range, of
C. morsitans. LANG (1920 p. 103) designates it as a mainly British species, which is
further found in Ghent, France, Holland and Macedonia.

Genus VII. Culex.

1. C. pipiens Linne.
Tab. XX.

Imago. This species may be regarded as our only, true house mosquito
the temperate zone of the old world. It is introduced into North America in
from Europe and according to HOWARD, DYAR and KNAB (p. 366), has there con-
quered the northern cities, breeding in various receptacles containing water. In
America it is usually rare or absent in the rural districts, being largely replaced
by C. restuans.

Taken in the widest sense the species is easily recognizable from all other
Danish species and most probably from all species of Northern Europe, by its ex-
tremely long and narrow second marginal cell, the fork of which is at least seven times
as long as the stem and much longer than the second posterior cell. Also the brick-
red or reddish-brown colour of the mesonotum, unique in our mosquito fauna,
makes it easily recognizable. In the domesticated and most common form the
mesonotum has generally three lines of black bristles, but especially in older speci-
mens they are inconspicuous or obsolete. Also the flaxen-yellow bands of the ab-
dominal segments dorsally and the same colour of the venter helps to distinguish
this species from the whole of the other mosquito fauna.

Formerly we have here in Europe described very many species, which now
are all referred to this very same species C. pipiens Linne (C. uulgaris Linne, C. alpinus
Linne, C. agilis Bigot, C. ciliaris Linne, C. communis de Geer, C. rufus Meigen, C.
phytophagus Ficalbi, C. domesticus German). As most of these species, owing to the
descriptions, are irrecognizable, this method was most probably the most correct. On
the other hand I feel quite sure that C. pipiens, as we now regard it, is really a collec-
tive species, which further explorations will dissolve into several smaller ones. This
more especially holds good if we also take the larvae into consideration, which
differ much more 'from each other than the imagines do. The larva of the main-
form may be described as follows:

Larva: Head rather large; subquadrate, a little broader than long; sides bulg-
ing; a notch at insertion of antennae; front margin arcuate. Antennae long, highly
arcuate; basal thirds rather thick, spinose; apical part slender, a large tuft inser-
ted remarkably near the apex; two long setae before apex; on apex itself a long

126

seta, a short one and a small digit. Anteantennal tuft, lower and upper frontal tuft
all multiple, number of hairs in the two last-named tufts generally five and gener-
ally inserted over each other, the six tufts commonly not lying in an arcuated line;
two small single hairs, between upper frontal tufts. Eyes rather large. Thorax round-
ed, wider than long. Hair formula of frontal border 221123321122. Hairs in 3 very
long, reaching far beyond the brushes when extended ; lateral hairs single and in tufts.

Anterior abdominal segments short, posterior ones elongated; lateral tufts of
first two segments multiple, two hairs on third to sixth. Subdorsal hairs in the
domesticated races double on third to sixth segment. Airtube very long, about five
times longer than wide ; pecten consisting of about ten teeth, short, only on basal
third, single tooth oblique, triangular, feather-like, with from five to seven branches.
Hair-tuft of air-tube with four or five hairs. Between the hair-tuft and apex four
tufts double, the one of them out of line. Comb of eighth segment consisting of
numerous scales in a triangular patch, the single scale with feathered tip; hairs of
eighth segment in common arrangement. Anal segment a little longer than broad,
ringed by a plate. Dorsal hair-tuft feebly developed, consisting only of from six to
seven unequally long hairs; a single lateral hair; ventral brush well-developed, con-
fined to the barred area, without free tufts before it. The brush consists of about
10 — 12 rays, every ray carrying about five to seven hairs.

Lateral tufts of the labellum very large distinctly divided in two parts, but
the inner part without comb-bristles; palatum covered with rather short hairs.
Mandible quadrangular, three stout spines before the collar and some short hairs
arising from their base; a row of long cilia from a collar; outer margin with about
ten scales bearing short hair-tufts. Dentition: three teeth on a process, the first of
them very large; a long serrated tooth before; process below undivided with a few
hairs; angle below sharp; a group of hairs within and a row at base. Maxilla high,
conical, divided by a suture. At the apex a tuft of very long, feathered hairs; along
the suture a series of shortening hairs. Inner half between suture and inner margin
with sharply defined series of long soft hairs; inner margin itself furnished with a
series of long stiff bristles; the outer half with a spot covered with soft hairs
and a short spine near apex. Palpe moderate, four terminal digits rather long.
Mental plate high with straight sides and triangular apex; a large central tooth
and from nine to eleven teeth on each side; the first three small and densely crow-
ded. Colour commonly greyish-brown, often almost milky-white.

Biology. Of all our European mosquitoes, this is the most domesticated spe-
cies. In some regards it is the best studied; it is on this mosquito, that REAUMUR
has written his classical memoir and its life-history has been used as a model of
all other European mosquitoes. Its anatomy is better studied than is the case with
most of the other mosquitoes. I refer more especially to the papers on the genital
organs by LOMEN (1904 p. 567); HEIMANN (1913 p. 1); KULAGIN (1901 p. 578); Kopf-
bau (KULAGIN 1905 p. 285). Of course we know the developmental stage for this
mosquito better than for all other larvae; if however we will try to describe

127

the life-history of the species in our country as well as elsewhere, it will be appa-
rent that this is still quite impossible. According to my experience it is the most
troublesome species to study; as far as I can see, here lies a special problem which cannot
be solved together with the life-history of all our other mosquitoes. The following remarks
may be regarded as points of support for such a future, more thorough, examination.

In November I have often found the females in numbers in summer houses
arbours etc., but during winter they commonly disappear from localities of this
nature. The females hibernate in deep sheltered, frost less cellars; hitherto, as far as
I know, we have never in winter found the mosquitoes in Nature. As long as the
temperature is above zero, the mosquitoes are able to fly when a light is brought
near them ; they hang down from walls and ceilings often in such huge masses that
these are covered with them; the hibernating localities in our houses must always
be dark, rather moist; and without any draught at all; it is not necessary that they
are frostless; if the temperature falls below zero, they fly deeper into the cellars;
during severe winters they often retreat to places of such a sheltered nature that it
is difficult to find them.

Now and then they may also be found in localities where we should not ex-
pect to find them. In an old, almost put down farm of which only the walls and
the chimney were left, in Dcbr. I found the chimney on its inside wholly covered
with a greyish layer of C. pipiens, intermixed with a few T. annalata. The tem-
perature has undoubtedly been below zero. It was very interesting to observe the
behaviour of these mosquitoes. They were wholly immovable; they sat as glued to
the walls; if they are taken off, they lie lifeless in the hand on the dorsal side.
With regard to thigmotropical phenomena see WEISS (1913 p. 36). If mosquitoes
are taken in from the deep dark cellars, brought into the light and kept at tem-
peratures about 15° C., they almost always die; probably owing to want of food. Most
probably they are not able to keep their metabolism at a point a slow as necessary, if
food supply is to be wholly denied. The hibernating mosquitoes are all extremely
fat; with regard to this point and to the blood sucking habits I refer to the foll-
owing. That it is only the females, which hibernate, that the males die out before
winter, and that the hibernating females are impregnated may all be regarded as
established facts.

On a beautifull sunny day in May all the mosquitoes leave the hibernating
localities in swarms; on 3/y, a day with bright sunshine, I was told that all the
mosquitoes left my cellar as a cloud; the next day I could not find a single one.
We do not know where they fly; it is most probable that they fly out to get blood,
not being able to ripen their eggs without blood nutriment. Nevertheless we do not hear
anything of attacks of C. pipiens in our country, and I myself have suffered no attack
from this species in early spring; most probably it satisfies its lust for blood upon
poultry, perhaps upon cattle. In June the eggboats are laid in cisterns, water barrels
etc. and the larvae appear; the females do not deposit all their eggs in one single
batch, but in three or four, and between these batches there passes some time of

128

varying length; most probably blood-nutriment is necessary or desirable between
every deposition ; we therefore find larvae in the cisterns in all stages of development.
With regard to the enormous amount of eggs which may be deposited, in some
localities, I refer the reader to a valuable paper by GLASER (1917 p. 531).

It is very difficult to make clear how many generations are produced in the
course of a summer. The common opinion is that the number of generations is
very large; I for my part regard this supposition as quite wrong. I do not think
that it exceeds three or rarely four; SPEISER (1908 p. 395) has arrived at a similar
result, he indicates two or three generations, but every one of these generations has
most probably from two to four broods. The cisterns teem with larvae and pupae
till about the middle of September; then all the larvae are almost of the same size
i. e. no more eggs are deposited. On 15/x the cisterns still contain pupae, but from
the first days of November all the broods disappear. These indications are in ac-
cordance with those from Strassbourg (ECKSTEIN 1919t p. 95). He maintains that
five generations may be the rule in a year. Here however the females appear in
Nature already by 20/m Tp. 11° C. Eggs were found on 7/iv; in the first part of
May the first generation appears. In our country the first generation does not ap-
pear before the middle of June. At Strassbourg the development from egg to
imago takes three weeks in April, in summer only two. With regard to the influ-
ence of temperature on the life cycle of C. pipiens see also KRAMER (1915 p. 874).
That the power of propagation may be regarded as extremely high is pointed out
by many authors: GLASER (1917 p. 531); DAVIS (1906 p. 368). When in German
literature from recent years we read about the enormous amounts of C. pipiens
females wintering iu houses, we may also conclude that our climatic conditions are
by no means able to produce such enormous C. pipiens swarms; though I have
examined numerous cellars I have never seen them in such incredible numbers as
indicated in literature.

It has often been pointed out that C. pipiens breeds in water of extremely
nasty condition, and my own experience is in accordance with this; often they are
found in localities where we should not expect to find mosquito larvae f. i. 66 feet
below ground (MAC GREGOR 1916 p. 142). See also MANOLOFF (1910 p. 52). I sup-
pose that a more thorough exploration will clear up the questions relating to broods
and generations. When it has not been done here, it is partly as indicated on p. 127
because it could not be cleared up simultaneously with the other explorations, partly
also from another cause. It is rather difficult in our country to find farms where
the explorations can be carried out in the course of some years; mosquito larva*
in the drinking water of the cattle and in the cooling- water of the dairies are with
some reason regarded as inexcusable and must be combated when found. More
than once I have found the water barrels cleaned, when some weeks later I came
back, all further observations on this spot being then almost useless.

Also in our country the water barrels and cisterns in the cow-stables are by
no means the only known breeding places for C. pipiens. In the so-called settlement

129

gardens near the large towns, almost every garden has its barrel filled with drain-
age-water. If in August we study this water, we shall find millions of mosquito
larvae and almost always C. pipiens larvae in them. But also in the dunghill pools,
where the sides of the pools are real dunghills, we often find the brown, nasty
fluid almost filled with mosquito larvae; they may here stand so thick that the
larvae almost touch each other; curiously enough the huge masses of larvae do not
seem to appear before August. On calm days such pools are often covered with a
green or reddish foam, originating from Euglena or other Flagellata. If so, it seems
as if all larvae in the course of a few days die off, the foam probably preventing
respiration, atmospherical air for larvae living under such conditions being a con-
ditio sine qua non. I have often found the borders of the pond covered with a
brown line of egg-boats. A more thorough exploration of how many times a year
this line appears, may probably give some information with regard to the number of
broods and generations. It is especially owing to the study of this line that I sup-
pose that the number of generations in the course of the summer is but small; the
examination is however rather difficult because geese and ducks have often con-
sumed almost the whole stock in the course of a few hours.

But even all these localities lying near the human dwellings are by no means
the only spots where this species may be found.

On examining clear, grassy ponds, which contain water the whole year round,
I have in August 1918 and 1919 near the border of the pond found very small
mosquito larvae, often in great numbers. All in all these larvae have all shown the
systematic characteristics of C. pipiens; still the whole exterior was different; they
were much smaller, of a more delicate structure, white or translucent.

These larvae never appeared before the latter part of July, but at that time
they were common enough; they were pupae in the first part of August and imagi-
nes a little later. At the first glance these imagines did not resemble those from the
cisterns etc. in our dwellings; they were much smaller, and of much more delicate-
structure. More thoroughly studied it was however quite impossible to find charac-
ters which distinguished them from the real C. pipiens. In August — September I
often found these small races in Nature, more especially over the ponds where they
were hatched; in our houses, on the other hand, I never saw them. In the latter
part of August the larvae disappeared from the ponds, and from the first days of
September the imagines disappeared.

I confess that the life-history of C. pipiens is dim and obscure. More especially
we do not know what are the relations between the larvae and imagines in Nature
and those of our dwellings, farms etc. As C. pipiens hibernates in our houses and
the first generation is undoubtedly hatched here, I have thought that the generations
following were divided into some stocks which remained as house dwellers and
others which flew out in search of breeding places in Nature itself. Nevertheless if
this was the correct explanation, it is extremely difficult to understand that the
racial stamp could really be preserved in this way. On the other hand the total

D K. D. Vidensk Selsk. Skr , naturvidensk. og mathem Afd. 8. Rsekke, VII, 1. 17

130

absence of real characteristics which might keep the forest-races apart from the
house races; the coincidence of the hatching of the summer generation of the house
race and its occurrence in the open air on the one side and the appearance of the
larvae of the forest races on the other suggests that there must be some con-
nection between these phenomena. I think it rather probable that here we have to
do with one of those rather rare examples of species, which just now are in status
nascendi where new species arise. Some of these races are already now of remark-
ably stabile nature. I allude especially to the peculiar yellow very delicate little
mosquito C. ciliaris and to C. nigritulus mentioned in the following pages.

2. G. ciliaris Linne.

It is with great hesitation and mainly from a biological point of view, that I,
in contradiction to all other authors from recent years, again separate C. ciliaris
Linne from C. pipiens, to which it has been referred as a synonym. Created by
Linne, it was regarded as good species by ZETTERSTEDT, SCHIENER, VAN DER WULFP
and WALKER. BLANCHARD, THEORALD and all later authors regard C. ciliaris as a
synonym for C. pipiens.

It was separated from C. pipiens owing to its smaller size, its ferruginous
thorax and yellowish-ferruginous abdomen. In the structure of the wings, legs and
claws there are no differences from the true C. pipiens.

Every year in the latter part of August and through the whole of September
a slender, very delicate mosquito arrives in the Royal Gardens at Frederiksborg.
Its head quarters are always in the well-known several hundred years old box-
hedges, from which it can be driven out even in October, when a walking-stick is
pushed in among the foliage. I have only seen the species here, explored all the
ponds in the vicinity, but have not been able to find the larvae. I have therefore
never hatched the imagines, and do not know the hair and scale coating of them
when newly hatched.

The mosquito is of a yellowish, faintly brown colour, but the hair and scale
coating always feebly developed; mesonotum is covered with a ferruginous uniform
coating; the abdomen has almost no scales, appears either unhanded or with faintly
developed basal bands almost only developed in the middle line; besides there are
no differences from the true C. pipiens.

I am unable to understand why the box-hedges should year after year, al-
ways in the same month of the year, September, be a centre of attraction to de-
nuded C. pipiens-forms. Further, as it must be remembered, that during the whole
of September I find both males and females in great numbers, and that the speci-
mens all differ from the true C. pipiens in the much brighter more ferruginous
colour and much smaller size, I cannot see better, but that for the present it must
be separated as a species differing from C. pipiens.

Geographical distribution: C. ciliaris has been recorded from Germany,
Austria, Holland and England.

131

C. nigritulus Theobald non Zett.
PL XXI.

Extremely small mosquitoes only 3 — 3.5 mm. in length, .dark with greyish-
brown thorax, without any reddish tint. Abdomen dark, dusky brown with rather
distinct pale basal bands, widest in the middle. Venter dusky, not yellow. Legs
brown, rather dark. Claw formula of female 0.0 — 0.0 — 0.0; of male 1.1 — 1.1 — 0.0;
those of fore and mid legs unequal. - First submarginal cell longer and narrower
than second posterior cell, but only about one-fourth longer; knees faintly yellow
not bright white.

THEOBALD (1901 p. 140) has referred some extremely small gnats found in
England to Zetterstedt's C. nigritulus. He says that it looks very distinct from C.
pipiens, ,,but when one comes to examine them, however, the structural differences
seem very slight". EDWARDS (1912 p. 263) maintains that these small gnats are cer-
tainly not C. nigritulus Zett., which he regards as a synonym of Aedes cinereus Mg.
I suppose that EDWARDS is quite right in this last supposition. As Edwards how-
ever further says "At first sight this variety appears to be totally distinct from C.
pipiens, as it is much smaller and darker, the thorax being without any. reddish
tint. No external structural differences are however observable, and after carefully
comparing the larvae of this and typical C. pipiens I could find no differences what-
ever" I do not agree with Mr. EDWARDS.

Having found the larvae in great numbers in August in a little pond in Arne-
have near Tjustrup I have hatched many of these delicate creatures. The pond was
very shallow, covered with vegetation; the larvae were always to be found in the
waterrim; they were extremely small, and the pupae much smaller than any mos-
quito pupae I have seen. Unfortunately a large Crabro had one morning eaten all
my needled specimens, put them in her nest holes and used them as food for her
young ones. No more specimens were hatched and in the two following years the
pond contained no water, and I have never seen the species again. The above given
description is only based upon my provisional notes.

As will be seen by the description of the larvae these differ very much from
the true C. pipiens larvae, but undoubtedly belong to the pipiens group. Owing to
the fact that these small mosquitoes never enter houses (already stated by THEO-
BALD 1901 p. 141), and to the very conspicuous differences in the larva, I do not
refer them to C. pipiens and suppose it is best to refer my specimens to C. nigri-
tulus Theob.

Larva: Head very large, subquadratic, almost rectangular broader than long;
a notch at insertion of antennae ; front margin slightly arcuate. Antennae very long,
highly arcuate, basal two thirds thickened, spinose-; apical third very slender, a very
large tuft, much nearer to the apex than to the base; two long setae before tip;
a long terminal seta, a short one and a small digit on a pedestal. Anteantennal
tufts and lower and upper frontal tufts almost at line. Anteantennal tuft always, lower

17*

132

frontal tuft often multiple, or with four or five hairs, upper generally with four
hairs; between them two single feeble hairs. Eyes large.

Thorax rounded, much wider than long. Hair formula of frontal border
221123321122. All hairs especially 33 very long, reaching beyond the brushes when
extended; lateral hairs single and in tufts.

Anterior abdominal segments very short, posterior ones elongated. Lateral tufts
of first two segments with four to five hairs; two or three hairs on third to sixth
segment. Subdorsal hairs on third to seventh segment in tufts of four to five, often
in stellate arrangement with angles of 90°. Eighth segment with hairs in ordinary
arrangement. Air-tube extremely long, six or seven times longer than broad; pecten
short, restricted to basal fifth, consisting of about ten teeth; single tooth short, not so
broad as in pipiens and only furnished with two, rarely three, branches. Hair-tuft of air
tube double or triple. Between hair-tuft and apex four tufts double, often two out
of line. Lateral comb of eighth segment consisting of numerous scales in a triangu-
lar patch ; single scale extremely long more than four times longer than broad with
feathered tip; restricted after the spatulated part. Anal segment much longer than
broad, ringed by a plate. Dorsal hair-tuft with a few short and two very long brist-
les; ventral brush well developed, confined to the barred area without free tufts
before. It consists of about 10 — 12 rays, every ray carrying from five to seven hairs.

Gills extremely long, narrow, acute often twice as long as anal segment.

Mouth brushes very large, distinctly divided into two parts, the inner part without
comb-bristles; palatum coated with rather short hairs. Mandibles quadrangular,
three spines before the collar; a row of long cilia from a collar; outer margin with
about ten scales; bearing short hair-tufts; dentition: from three to four teeth on a
process, the first of them very long; a long serrated tooth before; process below
undivided with a few hairs; angle below sharp, a group of hairs within and a row
at base. Maxilla conical, divided by a suture. At the apex a tuft of very long, fea-
thered hairs. Along the suture a series of shortening hairs. Inner half between su-
ture and inner margin with sharply defined series of long bristles; the outer half
with a spot, covered with soft hairs and a short spine near apex. Palpe moderate,
terminal digits long. Mental plate extremely high, straight sides and triangular apex
with a large central tooth and from nine to eleven teeth on each side; the first
three small and densely crowded. - - Colour milky white.

As will be seen from the description of the larva of C. pipiens and C. nigri-
tulus there are great and conspicuous differences!

The larva of C. nigritulus is always about two millim. smaller than that of
C. pipiens; the number of subdorsal hairs in C. nigritulus is from four to five, in
that of pipiens only two ; the scales in the comb are much longer in C. nigritulus
than in C. pipiens and the sipho is about one third longer than that of this species ;
further the teeth in the pecten are narrower. Also the arrangement of the frontal
tufts differ a little in the arrangement.

133

Chap. III.

Contributions to the Biology of the Culicines.
a. General Biological Remarks.

It is only during the last years that we have got some information with regard
to the longevity of the mosquitoes in the different stages of life; but the informa-
tion we have got is still but slight, and most of the remarks with regard to all
relations between the different stages and the seasons of the year still contradict
each other. This is mainly due to the fact that the determination, more especially
of the European species, has been very deficient; further, sufficient attention has
not been paid to the fact that species with wide areas of distribution are by no
means obliged to live their lives in the same manner near the southern and nor-
thern limits of their area of distribution.

In his admirable chapter in "Histoire des Insectes" relating to the life-history of
C. pipiens REAUMUR pointed out that this mosquito laid its eggs in egg-rafts, the
well-known egg-boats; the boats were laid upon the surface of stagnant waters. For
more than a century it has been regarded as a fact that this was also the case
with all other mosquitoes. This thesis was strengthened by some observations with
regard to T. annulate, the eggs of which were also laid in egg-rafts.

In Europe it wras especially GALLI VALERIC and his pupils who showed that
C. pipiens, with regard to the egg-laying process, could by no means be used as a
model for all other mosquitoes. The significance of the many papers of these
authors is weakened by the fact that the determination of the explored species
is very deficient; some of the communications are, as EYSELL (1907 — 1909) has
pointed out, undoubtedly wrong. It has however been shown that some of the
Culicidce of Switzerland hibernate as larvae or are able to hibernate as such, more
especially below withered leaves "in den eingetrockneten und mit Schnee angefull-
ten Pfutzen"; that larva? during the whole winter develop into pupae at a tp. of
4 — 6° C.; that eggs of Culicidce are able to endure desiccation etc. Some of the
statements are unquestionably correct, some disagree with those of other observers
and need corroboration.

In 1909 EYSELL showed that only those mosquitoes (C. pipiens and T. annu-
lata) which hibernated in the imago stage, laid their eggs in egg-rafts, the others
laid them singly. Later on HOWARD, DYAR and KNAB 1912 pointed out that it is
only the genera Culex, Culiseta and Tceniorhynchus, which form egg-boats in ac-
cordance with the type of C. pipiens and deposit the boats on the surface of stagnant
waters. In the vast group of Aedini the eggs are laid singly or in small batches and
hardly ever on the surface of the water, but on the moist mud of the ponds where
the imagines were hatched, and often upon wholly sun-dried ground, commonly
covered with withered vegetation. The above-named authors further showed that the
Aedini hibernate as eggs; the eggs rest until the following spring and are hatched

134

in the water from the melted snow; the Aedini have only one generation. An expe-
dition (KNAB 1908 p. 540) to western Canada was especially of great significance.

The statements with regard to the Aedini in North America are unquestionahly
correct; on the other hand there is no doubt that some of the Aedini at all events
in other parts of the world are able to hibernate both as larvae and as
imagines; some of them have more than one generation in the course of the year.
The European literature upon this point is difficult to use mainly because the
determination is very uncertain.

As mentioned above in recent years hibernating mosquito larvae have often
been found in Europe; most of the indications belong to A. maculipennis some to
the Culicines. Besides the above-named papers by GALLI VALERIC I refer the reader
to the following papers. DUPREE and MORGAN (1902 p. 1036), (1903 p. 88), EYSELL
(1907 p. 210), LACAZE (1918 p. 729), WATERSTON (1918 p. 1), ECKSTEIN (1918 p. 530).
WRIGHT (1901 p. 882) maintains that larvae of C. pipiens and T. annulata are to be
found in October; exposed to severe cold they survive if the water does not freeze
to the bottom. WRIGHT supposes that it is really the larvae that provide for the
continuation of the species through the winter in these northern countries and
probably throughout Europe; further, that it is during winter that the destruction
of the mosquitoes as larvae is to take place. This supposition of WRIGHT'S is not
correct. That C. pipiens can live as larva in October is really quite right, further
that it can endure a . freezing period, but no one has hitherto found the larvae of
C. pipiens and T. annulata below the ice; all in all a destruction of mosquitoes
during the winter in the larva stage is an impossibility in our latitude.

When finally proved, the fact that there exist mosquitoes which can hiber-
nate under the ice as larvae, was regarded as highly remarkable. The larvae being
hitherto only known as air breathing animals, we were inclined to suppose that
hibernation under the ice in this stage was hardly possible. In this connection
we shall call attention to the following considerations.

In accordance with the fact that the larvae in winter are almost sessile ani-
mals their claims of nutriment are but slight, and the process of combustion there-
fore also very slow. Judging from the behaviour of C. morsitans in my aquaria in
the winter months, this supposition may be regarded as highly probable. Further
it must be remembered that even the iceclosed waters are only rarely quite desti-
tute of air-bubbles containing a greater or smaller amount of oxygen than the
atmospherical air. These air-bubbles derive from the green plants and are sooner
or later deposited under the ice. I have often seen other air-breathing insects in
search of these air-bubbles, and it is possible that also mosquito larvae use them
for respiratory purposes.

Undoubtedly the mode of respiration of the hibernating larvae is mainly cu-
taneous. Exactly in the winter months the water is much better aerated than in
spring even in such drying ponds where all processes of decomposition on the bot-
tom have only a very slow course and where many green plants in drying ponds

135

more especially Hottonia greatly contribute to the aeration of the water. In this con-
nection attention must of course mainly be paid to the tracheal gills; with regard
to this point I refer the reader to pag. 15.

At the same time as the hibernation of the mosquitoes . in the larva stage
was pointed out it was also shown that mosquitoes could hibernate in the imago
stage. In addition to the above-named statements by HOWARD, DYAR and KNAB and
by EYSELL I more especially refer to the following authors: WESTWOOD (1872
p. XVI and 1876 p. VII); WADE (1888 p. 52); GRAY (1900 p. 250); ANNETT and
BUTTON (1901 p. 1013); CAZENEUVE (1910 p. 155); ECKSTEIN (1919m p. 530); most
probably most of the indications belong to C. pipiens and T. annulata; the modern
explorations in Germany commenced with a view to mosquito destruction (ECKSTEIN,
BRESSLAU; TEICHMANN, PRELL), all seem to show that all mosquitoes which hiber-
nate in our houses in Europe really belong exclusively to C. pipiens and T. annulata.

With regard to the Aedini, as far as I know, we have never in Europe found
any of them hibernating in houses; that they should hibernate as imagines in Na-
ture itself has often been supposed, but never thoroughly corroborated. On the other
side communications from the arctic regions, from the Siberian Tundras (FINSCH
1876) as well as from the arctics of North America (STERLING 1891, STEWARD
1891; with regard to this littr. see NUTTALL and SHIPLEY 1902 p. 63) seem to
show that the Aedini of the arctic region are able to hibernate in the frozen
masses of the tundras and in clefts and hollows of the snow, appearing in milli-
ons as soon as the first sunbeams in spring heat the surface of the snow. Further
explorations may show how these communications are to be brought into accord-
ance with those of KNAB with regard to the hibernation of the Aedini as eggs, if
not under arctic conditions, still under very hard climatic ones, with high degrees
of frost. Even in our country the possibility is not quite excluded that some of
our Aedini should be able to hibernate as imagines. I more especially refer to the
late broods of 0. caspius and communis.

With regard to the egglaying and related processes of our Central
European Aedini we have only very few observations. With regard to all those species
which lay their eggs in batches (C. pipiens and T. annulata) and about which we know
that the single batches are laid at smaller and greater intervals, we are able to speak
of a series of broods in the single generation. With regard to the Aedini this is
not possible; most probably the eggs are thrown off uninterruptedly during the whole
summer. As far as I know, more thorough explorations have only been carried on
with one single species, the yellow fever mosquito: Aedes calopus- (Stegomyia fasciata),
only found a few times in southern parts of Europe and last in England (LANG 1920
p. 112). MACFIE (1915 p. 205) indicates that the maximum life of the female is sixty
two days; FIELDING (1919 p. 25) has kept the species living for 93 day^. The first
blood-meal is taken on the second or third day, and three or four days elapsed
between each act of oviposition. Egglaying continued throughout life. Even with
regard to Stegomyia fasciata BACOT (1916 p. 1) has mentioned the fact, highly

136

remarkable also in this connection, that the whole development from egg to imago
can be completed in the course of only four days. From a biological point of view
it is highly interesting that the development of the very same species dependent on
outer conditions, in the one case can be completed in the course of four days, in
the other in the course of many weeks; further that among the mosquitoes there
are species which finish their whole development in four days, others which nor-
mally spend about eight months either in the egg-stage or in the larva-stage.

HEIMANN (1913 p. 31) has shown that the sex differentiation with regard to
C. pipiens takes place already at a very early stage of the development; cut series
show that already in larvse of 2 mm differentiations between ovaria and testes may
be shown; it may be pointed out that the observations were made upon a species
the larva of which only lives a few weeks and perhaps only a single wreek. It
ought to be investigated whether the rule also holds good for larvae which live for

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137

eight months or even more as is the case with C. morsitans. With regard to sex
differentiation see also ADIE (1912 p. 463 and 865).

Having now in the foregoing worked out the main poiixts in the biology of
our Danish mosquitoes I have in the table on p. 136 tried to sum up the results
of my investigations and hereto attach the following remarks. From a biological
point of view the Danish Culicidse are referred to three different groups. The first
and the greatest contains all the Aedini with the three genera: Aedes, Ochlerotatus
and Finlaya; only one species 0. rusticus belongs to the second group. A charac-
teristic of the first group is that all the species winter exclusively or mainly as
eggs. The species often spend more than seven months in the egg stages, the
other stages are all restricted to the five summer months. Of these the larva
stage only lasts from four to six weeks and is commonly restricted to April — May.
The imago stage lasts from the latter part of May to August, for some species, f. i.
0. detritus, only two months in autumn. In most of the species there is therefore
only one generation. Two generations occur regularly only in two species: the
brackish water mosquitoes: 0. caspius and 0. curriei. Our most common species O.
communis with regard to its life history differs very, much in the different localities;
in most of them it is in accordance with the other Aedini but it may have two
generations and is able to survive both as larva and as egg, probably also as imago.

In rainy summers most of the species which regularly possess only one gene-
ration may probably get a second generation; this may especially be the case with
0. lutescens; all in all this generation is very insignificant in comparison with the
spring generation. Apart from the above-named exceptions I for one am inclined to
refer the main part of almost all our Aedini larvae from July and later on, to eggs
which belong to the same generation as the spring generation, but which have been
deposited under bad hatching conditions.

The group contains the pronounced dwellers in the drying ponds which often
only possess water in the time from the snow-melting period to June.

All the Danish species are pronounced blood suckers attacking man as well
as horses and cattle. It is just among the members of this group that man has
some of his most tormenting enemies among the mosquitoes.

Some of the species are probably rather short living as imagines but most of
them live remarkably long, about three months or more, especially in damp summers.
It is a matter of fact that different species of Aedini hatched as imagines in April —
May contain eggs the whole summer till late in August or even in September; this
is the case with 0. cantans, annulipes, excrucians, lutescens and perhaps other species.
The eggs are laid singly, never in batches, probably always upon wholly dry land.

During the whole summer all the temporary pools of the forests, and mea-
dows are normally dry or moist but covered with dry leaves or grasses. Just in these
localities which to a human eye are often almost inseparable from the surrounding
ground, and which never get stagnant waters, the countless number of individuals,

L>. K. D. Vider.sk. Selsk Skr ., naturvidensk. og mathern. Afd. 8. Raekke, VII, 1. 18

138

especially those of the species 0. commanis, cantans and lutescens, must throw their
eggs above the ground during the whole of the summer. My own insufficient ob-
servations tend to show that the main part of 0. communis and prodotes throw
their eggs from the latter part of April to the beginning of July; 0. cantans from
the latter part of June to the latter part of August. When driving in my carriage
through the large forests of Gribskov near Hillerod I have visited several hundreds
of temporary ponds in spring and found larvae in all; later, in summer and autumn,
I found the same ponds covered with brown leaves, dry and indistinguishable from
the surrounding ground. It is most extraordinary that the huge masses of mosqui-
toes which almost make the sojourn in the forest intolerable in late spring and
during the whole of the summer throw their eggs in the summer months, the very
same eggs which cannot be developed without access to the water, upon wholly
dry land, in all the small inconspicuous hollows covered with dry leaves, and just
as dry in July and August as the small hills which border the hollows. It is as if
the mosquitoes, by means of their maternal instincts, were able to select all the
localities where water will appear half a year later and which to a human eye are
indistinguishable from the surrounding localities where there will never be water.

Owing to the enormous amount of larvae which appear in spring in our forest
ponds one would be inclined to think that it would be very easy to observe the
egg-laying processes over the dried up surfaces of the temporary ponds. As often
mentioned in the previous pages this is not the case; only with great difficulty and
rarely have I seen the egg-laying process of the Aedini; as far as I know no one
has hitherto observed it in Nature itself; that it should be confined to a special time
of the day is rather improbable; if so, it is most likely during the night. It is most
probable that the egg-laying process goes on during the whole of summer owing
to the remarkably long life period of these species as imagines, and that only a
few specimens are active at every time of the day.

Most of our Aedini belong to the forest ponds, some to the temporary ponds
on open land; two live in brackish water pools, one in tree-holes.

The second group consists of Culicella morsitans, 0. rusticus and Tceniorhyn-
chus Richardi. It is characterized by the fact that the species do not winter in the
egg but in the larva stage; the latter lasts from September till May i. e. eight to
nine months; the imago stage as in the foregoing group is restricted to the sum-
mer months; the egg stage is extremely short in this group, only lasting one or
two months; the imago from May — June to the latter part of September. There is
only one generation. The eggs of T. Richardi are laid in egg-rafts; how it is with
regard to C. morsitans I do not know, but I should suppose that they are laid
singly. The egg boats of T, Richardi are most probably laid on the surface of stag-
nant pools among vegetation, those of C. morsitans singly over the dry bottom of
temporary forest pools. As far as I know neither man nor cattle or horses have
been subject to attacks from this group in our country; further explorations will
most probably show that this is not correct.

139

The third group consisting of the two rnainspecies C. pipiens and T. annulata is
again of quite another type; here it is the impregnated female which hibernates; the
life of the imago with regard to the female lasting about seven months; the male hiber-
nates only in the spermatozoan stage. In spring the female lays her eggs, and these are
always laid in egg-rafts. Culex pipiens is the only Danish, and probably the only
North European s'pecies in which we have with certainty regularly observed a
series of generations in the course of the summer. Further south the same is the
case with T. annulata. EYSELL (1907 p. 198) says correctly: "Nur die im Imagosta-
dium iiberwinternden Stechmucken vermogen mehrere Generationen in einem Jahre
zu erreichen". As far as we know the two species in our country only rarely attack
man; C. pipiens probably mainly attacks poultry; T. annulata is best known as flow-
er visitor but also sucks blood from cattle.

With regard to the impregnated females hibernating in the imago stage it may
be added that parthenogenesis in the mosquitoes, at all events as a rule, is highly
improbable (KELLOG 1904 p. 59; LUHE 1903 p. 372).

It has often been said when the attacks of mosquitoes in the warmest sum-
mer time have been extremely fierce that this is due to the large amount of gene-
rations and broods which follow each other with incredible celerity. This supposi-
tion which has especially taken root among common people, but has really been
nourished by the scientists, is quite wrong. The huge masses of mosquitoes are
not due to new generations; almost all our mosquitoes except C. pipiens and the
brackish water mosquitoes have practically only one single generation a year; if a
second generation appears, this is against the rule, and the number of individuals
is much smaller than in the first. The huge mosquito masses in the summer months
are principally due to the fact that the different species, which are hatched after
each other, keep on adding to the amount, and for a short time of the year all
bite simultaneously; when this has not hitherto been understood, it is also because
we have in a very high degree underrated the longevity of the mosquitoes; as men-
tioned above it may, more especially in damp, cold summers when the lust of
blood is feeble, be prolonged to about three months. One would be inclined to
think that exactly in the rainy summers, when the ponds are filled with water, the
best conditions would be found for production of new generations and augmenta-
tion of the mosquito plague. This supposition seems however to be quite wrong as
regards our country. In 1918 we had a very dry summer, in which all the ponds
from the latter part of May till the latter part of October were dry; many ponds
were not filled with water before next spring. In 1919 many ponds were laid dry
in the latter part of May but got water again in July; then most of them were
dry again in Aug. — September and got no water before December. As mentioned
before after the complete desiccation in June 1919 we really found larvae of 0. commu-
nis and 0. lutescens in July, but the number which was hatched was extremely
small, and there is no doubt that the mosquito plague was greater in 1918 than

18*

140

in 1919. The mosquito attacks during the rainy period in July and on the beauti-
ful autumn days in August — September were but slight.

The regular examination of the above-named 40 ponds gave as main result
that there are a few ponds in which only a single species is hatched. This is how-
ever an exception; in most of the ponds a greater number of species are hatched.
I have made schemes for all forty ponds, but as they resemble each other very
much, I will only mention a single one of them as a model. It belongs to the
Stenholtsvangs ponds, about two kilom. from Hillerod. This pond, which was under
observation for four years 1917 — 1920, in 1917 — 1919, in all three years, gave quite
the same result. In this pond seven species are hatched; the seven species follow
each other with quite the same invariable regularity. In January there live plenty
of C. morsitans larvae and a few larvae of O. rusticus; in free water on sunny days,
between ice and land, diminutive larvae of 0. comnnmis. This fact is unaltered till
April when the ponds thaw. Then the ponds teem with larvae of 0. communis, the
water is practically a black living mass of larvae; the larvae of Culicella morsitans
have retired to the deeper parts of the pond; when dredging in the surface we only
get very few larvae of this species. Suddenly in the course of a week the whole
bulk of O. communis-larvsz are altered into pupse, and in the same weeks the in-
sects leave the ponds as imagines. But simultaneously with the metamorphosis into
pupa of 0. communis, and most probably a little earlier, eggs of 0. cantans have
been hatched; already a fortnight later this species, owing to the much higher
temperature, leaves the pond as flying insects. A little later the eggs of C. diantceus
and Aedes are hatched, and in June these species are imagines. Simultaneously with
them C. morsitans leaves the pond and so also 0. rusticus. In June the pond is
wholly dry.

The dry bottom of the pond contains no mosquitoes in any stage in June. In
the following three months the case alters again, and all the species find their way
to the pond again, laying their eggs on the dry bottom. Side by side, perhaps under
the same leaf, the eggs of the different species slumber the long summer sleep; in
autumn, when the rain begins, the deepest part of the bottom takes some water,
often only a few liters. This is enough to revive the eggs of C. morsitans and a
little later 0. rusticus. The larvae of these two species appear, but the moist condi-
tions have not the slightest influence upon the eggs of 0. communis, cantans, dian-
tceus and Aedes. Before the eggs of these species can be hatched, they must, besides
being burned by the sun, also be frozen in the ice, and not till January are any
of these eggs hatched. At this time only the larvae of 0. communis appear, the
others do not appear before they have passed the whole winter in the egg stage,
the larvae not leaving the eggs before April. The two species C. morsitans and 0.
rusticus pass the winter as larvae under the ice.

In 1920 the development of the mosquito life in the pond apparently gave a
picture of a somewhat different kind. The facts were the same as regards April;
larvae of C. morsitans and O. rusticus were found on the bottom, and the water

141

teemed with enormous masses of 0. communis. Owing to the warm weather in the
latter part of March and in the beginning of April the development was at a some-
what greater speed than in the foregoing three years. Then the weather wras bad,
and during the whole of April and in the first part of May .the temperature did
not rise above 6 — -8 degrees Celsius; the wreather was extremely rainy. Under these
conditions the 0. communis material was not hatched, and the pupa stage was
prolonged beydhd the normal limits to about two or three weeks; as the tempera-
ture of the water was however about six to eight degrees, all the other mosqui-
toes in the pond were hatched from eggs; before 0. communis left the pond as ima-
gines most of the larvae, belonging to the species 0. cantans, diantceus and Aedes,
were ready to pupate. Then when the fine summer weather arrived, all the mos-
quito species of the pond were almost simultaneously hatched, and in the course
of about a week all the species had left the pond. The pond had water the whole
summer but from about July to September not a single larva was found in the pond.

Having followed the development of the species in this pond for three years
and having followed it in about thirty forest ponds of quite similar appearance, I
have seen that the above-named scheme is a true prototype of the development
year after year in a great number of forest water ponds ; in some of them 0. rusti-
cus, 0. diantceus or Aedes may be lacking, but where they are to be found, they
are always intercalated in the very place in the developmental series where we
should expect them to appear.

Everyone who has tried to carry through an exploration of this kind, will
admire the almost incredible regularity with which the development of the species
takes place. Over an area of only a few square yards seven species have laid their
eggs. The eggs lie side by side in August, they are exposed to the same outer con-
ditions, the same burning sun, the thaw of the summed morning, the first moisture
from the autumn showers; one day the eggs of all the seven species can be brought
to swim in the very same little water-filled hole, or diminutive pond. But the seven
species are by no means hatched simultaneously; deep in their life history immu-
table laws are laid down which rule the life of each of the species. The tempera-
ture and degree of moisture, which forces one species to pass from one stage to
another, has no influence at all upon another species which only awaits its ap-
pointed time.

In the temporary ponds upon the plains and meadows not overshadowed by
forests I have never found this highly remarkable alternation of many species. In
these ponds as a rule we only find two or three species: in inland ponds, mainly
0. excrucians, lutescens and annulipes, now and then 0. communis and rusticus; near
the sea shore 0. caspius, curriei and detritus. As mentioned above, also here we
find localities where the temporary ponds in spring all teem with larvae of one of
these species, and where incredible myriads are hatched in the course of a few
days. The rule is however that in the open country, more especially far from the
coast, in many localities we find a great many temporary pools in which I have

142

never found a single mosquito larva. As late as April of this year I have travelled
over a great part of my area of exploration and visited several hundreds of tempo-
rary ponds scattered over the fields and meadows, and only found mosquito larvse
in ten of them. This is in contrast to the conditions in the forest ponds, where
almost every single pond in spring contains larvae often belonging to many species.
There is also this difference between the mosquito life in forest ponds and ponds
of the plains that the first-named almost always teem with myriads of mosquito
larvae whereas in the last named - - apart from the brackish water pools - - we
often find only very few specimens almost always belonging to the above-
named species differing from those which inhabit the forest ponds.

Finally I wish to call attention to the following results which, as far as I know,
are in accordance with those of all the authors who have made a more thorough
study of the biology of the mosquitoes. It is often maintained that the attacks of mos-
quitoes are more troublesome in the vicinity of large lakes, and that the mosqui-
toes are hatched especially in them. The fact is that our mosquitoes are
never hatched in lakes, but all belong to very small pools, most of them living in
ponds which are dry or frozen for about eight months of the year. Another thing
is that they often occur in the small ponds which border larger watermasses, and
which are cut off from them.

Further it has often been stated that the mosquitoes are actively able to
spread over large areas. For all our Danish Culicines this supposition is, accor-
ding to my opinion, not correct. They are almost all remarkably stationary animals;
many of the colonies never leave the vicinity of the pond where they are hatched;
we are only attacked when we place ourselves at the borders of the pond; this
especially holds good for Aedes cinereus. Where small, sharply defined woods are
spread over a rather wide a^ea f. i. in North Seeland, it often happens that different
species are prevalent simultaneously in the different forests. Most of us will also
observe that we are very rarely attacked in the open country, but that we are sub
ject to even very violent attacks if we seek the shade in one of the woods; the
more attentive observer will further notice that if we are attacked simultaneously
in the open country and in the forest, the attack in the former locality is almost
always due to 0. lutescens, whereas quite different species are prevalent in the
forests. In my opinion everything seems to indicate that our mosquitoes are really
very stationary animals, only rarely leaving the forest where they are born; per-
haps the mosquitoes of the open meadows have a somewhat greater power of
spreading, at all events passively, owing to the wind; this would most probably
hold good with regard to the brackish water species, more especially 0. caspius
which leaves the coast after hatching, flying landwards in search of man and
cattle. With regard to some of the Anophelince - in our fauna more especially
A. bifurcatus — the case is different. (See the following).

It is a well known fact that the mosquitoes in different parts of the world
occur in countless numbers and make the sojourn in these places almost intolerable

143

to people and mammalia; this is f. i. the case in the arctic region and in many
parts of the tropical world. But the plague is serious also in a great part of the
temperate zone and a long series of papers dealing with mosquito swarms and mos-
quito attacks have appeared. Some of them are cited in the • following. SWINTON
(1768); DALE (1833 p. 543), BOLL (1858 p. 186), HAGENOW (1860 p. 457), WEYEN-
BERGH (1871), SMITH (1890), DOUGLAS (1895 p. 239), BLUMMEL (1898 p. 15), WHEE-
LER (1894 p. 373), SINTENIS (1891), KNAB (1906 p. 123), WEBER (1906 p. 38),
MEISSNER (1908 p. 8), GERMAR (1913 p. 137, 1917 p. 336), ZETEK (1913 p. 5).
Some of these papers deal with phenomena of more biological interest; I more
especially refer to the paper of ZETEK, concerning the determination of the flight
of the mosquitoes and that of WHEELER dealing with anemotropical phenomena.
Connected with the swarmbuilding phenomena are also the peculiar auditory organs
described by JOHNSTON (1855 p. 97) and MAYER (1874 p. 577).

In our own country we only rarely have occasion to observe large swarms of
Culicidce; it is perhaps mainly the case with O. caspius, but for my part I have not
had an opportunity to make any observation of that kind. In recent years we have
received many accounts, especially from Central Europe, relating to the mosquito
plague, and a long series of papers dealing with the means by which the mosqui-
toes should be destroyed have appeared. I more especially refer to the following
papers: BRESSLAU & GLASER (1918 p. 290 and p. 327); ECKSTEIN (1919 p. 93 and
p. 530), SACK (1911); TEICHMANN (1919 p. 118), BRESSLAU (1917 p. 507), PRELL
(1919 p. 61).

In my own country \ve have hitherto never tried to destroy the mosquitoes,
and in my opinion the plague is not so great either that such a destruction should
be necessary in most cases. I only wish to make an exception with regard to A.
maculipennis in our stables. See later.

b. The Blood-sucking Habits of Culicines.

As pointed out by almost all authors from recent years, the mosquitoes have
originally lived upon a vegetable diet, plant juices, nectar etc. As well known all
the males are still exclusively vegetable feeders, the very few, rather doubtful, ex-
ceptions will be mentioned later on. This also holds good for probably more than
half of all the females of the mosquitoes; a long series, mainly of tropical genera,
are, as far as we hitherto know, exclusively vegetable feeders in both sexes. I refer
especially to HOWARD, DYAR and KNAB (1912 p. Ill) and to a paper by KNAB
(Mosquitoes as Flowers Visitors 1907 p. 215) where the whole of the earlier litera-
ture with regard to this subject is cited. Now and then it has been stated that also
some of the European species may be found upon flowers; this is more especially
the case with T. annulata. From observations from the last three years but especi-
ally from 1920 I am inclined to suppose that the meteorological conditions are
able to force the mosquitoes, more especially all the Aedince, to be flower visitors

144

at all events during a shorter or longer part of their life. In 1920 when the
immense swarms of 0. communis and 0. prodotes were hatched, the temperature
suddenly fell for a fortnight, never rising above about 6 — 8 degrees Celsius. Im-
mense swarms of mosquitoes, females as well as males, were sitting in the grass,
flew up when the grass was moved, but never tried to bite. At the same time
Taraxacum vulgare and Cerasus padns were in blossom. About ten days after the
above-named mosquitoes were hatched, these two plants, especially Taraxacum,
were regularly visited by mosquitoes; on the meadows almost every flower had
one or two females of 0. communis and many three or four; the females were sit-
ting on the flowers and pierced their proboscides into the heads now here now
there. The phenomenon lasted for about eight days here in North Seeland; simul-
taneously with my own observations Mr. KRYGER had an opportunity to make
quite similar ones on the large moors south of Copenhagen. Then we got fine
weather with a temperature of about 20° C., and in the course of a few days the
immense swarms rose, the higher temperature awaked their lust of blood, and
sojourn in the forest was almost made an impossibility. In the foregoing years I
have now and then, in the latter part of cold rainy periods, found a few mosqui-
toes upon flowers. In a cold rainj' period from 25/vn to 7/vm 1920 I was often
attacked by 0. lutescens and 0. cantans. It struck me that many of these specimens
were gorged with a fluid which could not be blood being clear like water. Squeez-
ing the females clear drops appeared. They were sweet like sugar and were un-
questionably honey. In the cold period many of the mosquitoes had been forced
to be vegetarians.

The fact of the matter is unquestionably that the lust of blood of the Aedini,
at all events in our country, is dependent on the temperature, and that vegetable
matter, more especially in the cold spring months plays a much greater role in
the diet of the mosquitoes than we have hitherto thought. (See also HOWLETT
1910 p. 479).

I have myself no observations with regard to the relation between mating
process, bloodsucking and egg-laying. Formerly most authors maintained that a
bloodmeal was necessary for the females to ripen their eggs; with regard to the
literature I refer the reader to NUTTALL & SHIPLEY (1902 p. 65). Now it has been shown
that females which were held upon a vegetable diet were also able to lay eggs
from which adults were reared in some cases (SEN 1917 p. 729; 1918 p. 620).
NEUMANN (1910 p. 27) has kept C. pipiens alive for two years in a large aquarium;
many generations have been hatched but they have got no nourishment. He further
maintains that also C. nemorosus is able to produce eggs without a bloodmeal but
in that case the eggs do not develop, and that Anopheles is also said to be able to
do so after hibernation. See also GRUNBERG (1907). GOELDI remarks that fer-
tilized eggs may remain dormant in a female for 102 days, if a feed of blood is
withheld. MACFIE (1915 p. 205) has observed with regard to Stegomyia fasciata
that the first blood meal was taken by females on the second or. third day

145

after emergence from the pupa. Fertilisation and a blood meal precedes oviposition,
and fertilisation preceded the blood meal. Eggs were laid on the sixth or seventh
day: After this they regularly fed once, soon after each batch of eggs was laid.
Three or four days elapsed between each act of oviposition ; . egg-laying was con-
tinued throughout life; the maximum length of life of the males being 28 days,
that of females 62. BACOT (1916) states that a female of S. fasciata, which had
subsisted on honey and white of egg 56 days without egg-laying, was given three
blood-meals; fertile eggs were deposited four days after the first blood meal. Be-
sides he remarks that all experiments to induce oviposition in the absence of a
blood meal met with negative results in this species.

Undoubtedly a generalisation with regard to the significance of a blood meal
for the ripening of the eggs in the mosquitoes is by no means allowable; every
thing seems to point to the fact that the species differ very much from each other,
and that there is a regular transition from species which are exclusively vegetable
feeders to such to which a blood meal is, if not a necessity, at all events the
most natural form of nutriment.

It is a very remarkable thing that we know species which, in a vast part of
their area belong to the most troublesome blood suckers, and in others never seem
to suck blood. This seems to be the case with C. territans, which according to
SMITH and FELT (1904 p. 309) is extremely annoying in North America, whereas
in Europe - - if the determinations are correct - - it is said never to sting man.
This has been pointed out by SCHNEIDER (1914 p. 46), ECKSTEIN (1919 p. 64), PRELL
(1919 p. 63).

In our own fauna, too, we possess species which seem never to use blood as
nourishment, others which do not suck from man; further, species which seem only
rarely and under special conditions to sting man, and lastly, species which seem
ready to sting almost at all times. To the first belongs one of our largest species:
Culicella morsitans, a species of wide distribution, but according to many authors
(THEOBALD, SCHNEIDER 1914 p. 43); never acting as blood suckers. I have hatched
this species in many thousands at my laboratory, I have been sitting in the very
same dried up ponds over which the females were flying and probably egglaying,
and I have caught them in the evenings when they came through the open windows
lacing the lake; moreover I have never found females, whose stomachs were red
and distended by blood.

For a long time I thought that this was also the case with T. annulata; I
have had the mosquitoes in hundreds in my hatching cages, have very often visit-
ed the ponds where the larvae wrere hatched, and in September gathered plenty of
them behind the shutters of the laboratory; further, numerous females on the walls
over the cisterns in which they wrere hatched; nevertheless I have never seen a
female gorged with blood, and I have never myself been bitten. FICALBI (1897)
has arrived at quite the same result with regard to Italy and so has SCHNEIDER
(1914 p. 43) with regard to the environment of Bonn. THEOBALD quotes an observa-

U. K. I). Vielensk. Selsk Skr., naturvidensk. og mathem. A til. 8, Rrekkc, VII. 1. jg

146

tion by HATCHETT JACKSON that on a warm sunny day in November they settled
on stems of periwinkle and wall flowers and, inserting their proboscides, were
apparently engaged in sucking (1907 p. 278).

On the other hand we often find indications in literature \vhich show that T.
annulata may be a very troublesome blood sucker. I especially refer to THEOBALD
(1907 p. 277) and to PRELL (1919 p. 65) who says that in Spa he has found
females gorged with blood.

According to THEOBALD the sting may be very troublesome; "cases have oc-
curred especially in women, where there have been four or five simultaneous punc-
tures, and the patient has felt so indisposed as to have to retire to bed with fever
ranging up to 101° F." These indications are in accordance with those of ECKSTEIN
(1919 p. 63), EDWARDS (1912 p. 261) and LANG (1920 p. 101) who states that it
may become troublesome in mild weather in the winter.

Last year, during my exploration of the cowstables, I found a great many speci-
mens of T. annulata, sitting on the ceiling and upon the walls together with A.
maculatus ; they were very often gorged with blood. They were common more
especially in Aug. — Sept. Later on Mr. KRYGER told me that he, too, had found
them extremely numerous in the stables in Jutland more especially on the east
coast; they were almost always blood-filled. He further maintained that he was
often stung by the mosquito, and that the sting was extremely painful. It seems
therefore that in our country nowadays T. annulata just as A. maculipennis is at-
tracted by the stables and mainly sucks blood from cattle.

The bloodsucking habits of C. pipiens seem to be of a very remarkable kind.
From a popular point of view it is often believed of the mosquito plague that, at
all events in Europe, it is mainly due to C. pipiens. My own experience, especially
in Denmark, and in recent years also that of other observers, especially in Ger-
many, is in contradiction to this supposition.

During the last five years I have studied C. pipiens and its behaviour in my
own cellar in winter, when it was brought up into my rooms with the peat, fur-
ther in May out of doors, when it appeared there after leaving the hibernating
localities, in the breeding places in the stables etc. During the whole summer and late
autumn not a single C. pipiens has done me the honour to puncture my skin. As
mentioned later on, I have never found a blood-filled mosquito in the cellars, and
the few I have seen I have caught on evenings in spring and summer months.
Only during winter, when the mosquitoes arrived in the rooms, have I been the
object of their attacks; wrhen I have heard that people have been attacked in their
rooms by mosquitoes in winter, and I have been able to examine them, it has al-
most always been shown that the trouble was caused by C. pipiens.

Studying the literature, also there we find very few trustworthy indications
with regard to the trouble caused by this very species. THEOBALD (1901 p. 135)
observes that it "is known to bite some years with considerable severity". HO-
WARD, DYAR and KNAB (1912 p. 106) state that even C. pipiens is among those

147

mosquitoes "which do not persecute man with the same persistence as certain other
species f. i. Aeries calopus". Owing to the enormous masses of C. pipiens which must
every year he hatched from the incredible number of larvae which fill almost all
the ditches and pastures near our farms, there does not seem to be the slightest
accordance between the number which are hatched and the annoyance caused
by them.

In 1919 an interesting paper by PRELL (1919 p. 61) appeared. He has made
quite the same observation as I have. In 1917 there were plenty of C. pipiens round
Spa, but there was no mosquito plague at all. On the other hand, in Stuttgart,
where the mosquito plague is now severe, and as far as I can see also partly caus-
ed by C. pipiens, the plague was unknown before 1900. PRELL correctly rejects
any attempt to refer "these peculiar facts either to different species" of C. pipiens
or to migration. He points out that C. pipiens like other and perhaps all Culex-
species has originally been a bird-mosquito; as it is an intermediate host -for Pro-
teosoma which produces bird-malaria, this makes the supposition very reason-
able; even now in many localities it occurs as a bird mosquito. See also HOWARD,
DYAR and KNAB (1912 p. 107), LANG (1920 p. 114). Its great power of living as
larva in polluted water has been a factor which altered its primary habits, accom-
modating it to the polluted water basins arising round human habitations. Still the
mosquito can keep its old customs of sucking blood on birds; its common appear-
ance in poultry houses makes this very probable. On the other hand its occur-
rence in human dwellings, more especially in stables, has now offered another
source from which it may satisfy its lust of blood, which is: domesticated mammalia
and man himself. The power and inclination in this direction is developed to different
degrees in the different countries and perhaps also in different years. I should be
inclined to think that in higher latitudes and at lower summer temperatures, the
old habits will be preserved. (See also HOWLETT 1910 p. 479).

It seems as if the lust of blood in the Aedini, at all events of our Danish
species, is much greater than that of the genus Culex, Culicella and Theobaldia.
American authors (HOWARD, DYAR and KNAB 1912 p. 107) come to the same result.
From every part of Europe we hear of severe attacks now from one and now from
another species; 0. nigripes from the far north, 0, communis, cantans, annulipes,
vexans, caspius have all a very bad reputation, everywhere attacking man or
large mammals; the landward migration of the salt marsh mosquitoes in search
of blood, the behaviour of the mosquitoes of the prairies, which are adjusted to fly
towards prominent objects, in that locality almost always large mammals or men,
point in the same direction. It need only be added, that the time of bloodsucking
in the life of the animals is really rather short.

In our country the bloodsucking period for most species does not last more
than about three or four weeks ; further it does not begin before two or three weeks
after hatching, a fact which I have observed in almost all these species (Exception Fin-
lay a geniculata see pag. 102). It may further be pointed out as a phenomenon common

19*

148

to all these species, that in the bloodsucking period there are really rather few
days, in which they try to satisfy their lust of blood; these days coincide with
certain meteorological data, great humidity of the air, a high temperature and rather
low barometer. When on such a warm damp day, especially about sunset, one
has witnessed the enormous masses of mosquitoes which from all sides dart upon
the wanderer or the horses, and have seen the eagernes with which the attack
takes place, one cannot get rid of the supposition that it is only a very small part
of the whole crowd of mosquitoes which really gets blood. More especially in cold
summers with heavy rains, falling in the main period of the flying time of the
above-named species, I should suppose that out of the millions only a very few
get a blood meal. A factor which helps the mosquitoes is their longevity, and that
their life is prolonged if blood meals cannot be obtained. This is in accordance
with my own experience, acquired in Nature herself; in very hot summers the
mosquito plague is in the. main at an end by the latter part of July, and all spring
flyers disappear before July, in wet summers, such as 1919, the mosquito plague
lasts till the latter part of August and spring species such as 0. communis are on
the wing and biting as late as the middle of August. As mentioned above accor-
ding to my opinion there can be no doubt about the fact that the attacks in Au-
gust do not come from new broods or generations, but are caused by the specimens
which are hatched in spring, but have had no opportunity to get blood.

In the literature a few examples are mentioned of males which are able to
bite; this is said more especially with regard to Aedes calopus (FICALBY cited from
HOWARD, DYAR and KNAB 1912 p. 109), but these authors suppose that the obser-
vation is wrong. Of our mosquitoes it is especially the males of O. nemorosus :
which are said to bite. STILES was bitten by an 0. nemorosus with long antennae
(H. D. K. 1912 p. 109), and later on EDWARDS (1917 p. 216) has been subject to a
similar attack. This last-named author shows that none of the three examined
males were normal, and that all three had one or more female characters on one
or both sides of the body.

With regard to the blood-nourishment and its significance for the ripening
of the eggs I wish to make the following remarks:

If we take an 0. lutescens, newly hatched, and make transversal sections of
the abdomen, we shall find a well marked fat body, filling the greater part of the
abdomen and a very thin alimentary canal, only occupying a very small part of
the abdominal cavity; the walls of the canal show the well known deep folds, the
transversal sections therefore showing a starlike figure. If then a fortnight later we
let the mosquito suck blood, and now lay the abdomen in transversal sections, we
see nothing of the fat body. The abdomen is enormously expanded; the ventral re-
servoir for the blood fills the whole abdominal cavity only leaving a very incon-
spicuous space for the nervous system below and the heart above.

If further we let an 0. lutescens suck blood, keep it for eight days in a hat-
ching cage, kill it and take transversal sections of the abdomen, we shall again get

149

quite a different picture. The ventral reservoir is again shrivelled up lying only in
the first or two first abdominal segments and the blood has now arrived in the
intestine; but also this is almost empty especially in its anterior part; in the
posterior part it contains a blood coagula of larger or smaller .size. But round the
intestine, where formerly the fat body was, the whole body cavity is filled with
hexagonal figures, cross-sections of the ovaries with numerous eggs. Roughly spea-
king in the course of from eight to ten days the blood nourishment has been
transformed into eggs. If then in September we catch one of the C. lutescens-fe-
males, which, waiting for death, are sitting deep down in the grass covering the dried
ponds where they were hatched in spring, and where they have now laid their eggs,
and we now take cross-sections of the abdomen, we shall again get another picture.
The intestine is empty, but so also is the abdominal cavity round the intestine;
the ovaries are shrivelled up to two thin strings ; the little mechanism has spent its force,
and is now only destined for one thing, to die and make room for another generation
now in preparation in the eggs slumbering in the dry mud under the withered grass.

If we now investigate the case of another mosquito, hibernating not as egg
like 0. lutescens, but as imago, like C, pipiens, we find an arrangement of quite
different sort. A cross-section of the abdomen of a C. pipiens in Sept., a few days
after it has left the pupa, shows a very thin intestine with strong folds of the wall,
a fat body with very small cells, strongly compressed; the sections further show
that the dorsal shields are much broader than the. ventral ones, which on the other
hand are much more vaulted. A deep cleft is conspicuous laterally between the
dorsal and ventral shields.

Already in the latter part of September the females of C. pipiens have found
their places of hibernation. If we now take one of these hibernating females from
my cellar, the cross-section gives quite a different result (Fig. 18 a). The intestine is
as formerly extremely small, and in many of the sections difficult to find. On the other
hand the fat body is of quite different structure; the cells are much larger; between
them are large intercellular spaces, and the content of oil globules is enormous,
the cross-section of the abdomen further shows that this is now extremely extend-
ed; the contour is circular; if we lay a hibernating mosquito from October in a
vessel with water and open the abdomen, enormous masses of oil globules will
pour out; in a living animal we are able to see the oil globules with a lens through
the extended body wall. In November — December the picture is quite the same; I
have got the impression, that the mosquitoes are at all events just as fat in Decem-
ber as they were in November.

The question is now: What is the source of this fat? Most people would
probably say that it derives from the blood nourishment taken in by the females
before hibernation. This may be the case, but I am not quite sure that this sup-
position is correct. Firstly I have never seen a mosquito with blood in its intestine
arriving at the hibernating places. Moreover, though in September I have very often
been sitting in my garden, observing the swarms of dancing C. pipiens males, and

150

caught the females which directed their way into the svarms, I have never got a
female with a blood-filled intestine. It seems as if C. pipiens upon this point is in
accordance with Stegomyia fasciata: first mating process and then blood nourish-

Fig. 18 a, b, c, d. A series of cuts through the abdomen of C, pipiens.

a, in the last part of October, a few days after the mosquito has been hatched, b, in April after having

hibernated, c, in the first days of June immediately after bloodsucking, d, eight days later.

a heart; b malphigian tubules, c ovaria, d intestine, e fat body, /"ventral cord in all the figures.

ment, quite the opposite of what we have seen is the case with 0. lutescens. I con-
tinued the observations in my garden, till the bad^autumn days arrived, and found

151

the C. pipiens females always without blood in the intestine; a few days after I
found the females in the hibernating places, also here without blood in the intes-
tine. I cannot see how we can combine these observations with the supposition
that the fat body derives from blood nourishment. We further know that the blood
nourishment of 0. lutescens is converted into eggs in the course of about eight days in
summer, and we shall see that this is also the case with the blood nourishment
in May in the case of C. pipiens. It is therefore in my opinion rather hazardous to
suppose that in the course of a few days the blood nourishment in September will be
transformed into diffuse fat-masses in the body cavity, and in May into egg-masses.

For my owrn part I am inclined to suppose that the fat-body of the hibernat-
ing C. pipiens females derive from those fat-masses, which the animal has accumu-
lated during the larva stage in freshwater, and which it, passing the pupa stage,
has taken over into the imago stage. I know very well that this supposition meets
with great physiological difficulties. The question is, whether fat in some more
condensed form, taken over from the larva stage into the imago stage, may be
further utilized in this stage in any way.

Even if the physiologists say that this is an impossibility, I should like a
thorough physiological investigation upon this point. It must be remembered that
the females of C. pipiens, which we catch in summer, are all relatively meagre,
differing much from those in the hibernating quarters; as the C. pipiens were hatch-
ed in the middle of September in the water barrels in my garden and immediate-
ly began the mating dances only a few meters from the water barrels, and as
only a few days later, after a rainy period, I found the females fat and with empty
intestine in the hibernating place in my cellar, I suppose that we here have to do
with a fact which strongly calls for a more thorough physiological investigation.

In the course of the winter the mosquitoes become more and more meagre
a transverse section (Fig. 18b) gives quite another picture; the form of the body
is another and the fat body strongly reduced. One day in April — May they leave
the wintering localities like a cloud. Never being bitten by C. pipiens in late spring
and summer I have only found the females gorged with blood on the walls of
cowstables and hen-houses; cross-sections (Fig. 18c) of the abdomen from blood-
filled C. pipiens and from those about eight to fourteen days later, show quite the
same picture as we saw in the case of 0. lutescens; an enormous gorged inestine
filled with blood coagula and eight days later an empty intestine and the body
cavity filled with eggs (Fig. 18 d). The above-named cross-sections of the ab-
domen of the female mosquito at different times of the year are of particular inter-
est with regard to the knowledge of the great phases in the life of the mosqui-
toes. In some ways they are even more than that. They represent cross-sections
through the life history of the mosquitoes; especially those of the blood-filled inte-
stine and of the abdomen, distended by eggs, represent pictures of the results of
the two great life preserving agencies: "Hunger und Liebe" the first acting as life
preserving factor for the individual itself, the last for the species; when both have

been satisfied, the individuals have done their duty and have now only one thing
to do: to disappear and make room for new individuals.

As well known the mouth parts and the sucking apparatus of the mosquitoes
have often been subjected to thorough investigations from Reaumur to our day. I
refer especially to the papers of DIMMOCK (1881), GRUNBERG (1907), LEON (1904
p. 730 and 1911 p. 7), MACLOSKIE (1888 p. 884), Mum (1883), THOMSON (1905
p. 145), WESCHE (1904 p. 28). A more thorough study of the mouth parts of the
different specimens is however still lacking. I have made slides of almost all
our species and studied them in preparations of Canada. There are really some
small differences in the different species; this especially holds good with regard to
the form and hair equipment of the labellae and to the number of saw teeth upon the
maxillae; but the differences are but slight and their constant number only to be
detected after very thorough investigation.

Mating process.

In the course of years, from 1760 (GODEHEU DE RIVELLE p. 617 and REAU-
MUR) and to our own day, many observations on the mating habits of the mosqui-
toes have been made. Most of the,m have been collected in the chapter upon mating
habits in HOWARD, DYAR and KNAB (1912 p. 120—132).

It has been pointed out that in many species the males congregate in swarms,
but that there also exist species in which no swarm-congregation takes place. Even
the manner in which the swarms are formed, their position in the air, the size
and the behaviour of the single individuals of both sexes, differ from species to
species. Of fundamental significance is the observation that the attitude assumed
during the copulatory act differs according to the structure of the claws of the
female: "In forms with simple claws (Culex, Anopheles) the position is end to end,
the pair facing in opposite directions. The forms in which the female claws are
toothed, copulate face to face, clasping each other with their claws" (HOWARD, DYAR
and KNAB 1912 p. 121).

Commonly it is only the males which congregate in swarms, whereas the
females make their way singly into the swarms from the outside. There are also
species where the males as well as the females form swarms, and the pairing takes
place when the single individuals drop out from the swarms and unite. Commonly
the swarms congregate near the ground and often over prominent objects: hay
stacks, isolated trees, church-steeples etc.; they often follows persons, walking over
the meadows and grow thicker and thicker as the person walks along. It has been
noticed that persons have been surrounded by swarms of females not reaching
above the knees, and with swarms of males around their heads. The swarms emit
high vibrating notes, often two distinct ones, corresponding to the two different
swarms and to the dancing up and down of the mosquitoes. A few species, f. i.
Aedes calopus, pair in the rooms of our dwellings and these species only can be
hatched and studied through many successive generations. The swarming of the

mosquitoes is especially dependent upon meteorological conditions. It is most con-
spicuous towards evening, more especially after calm fine days; on windy days it
may take place, but then only in sheltered places behind large trees, buildings etc.
In the swarms the mosquitoes are almost always directed facing the wind. Of great
interest is the old narrative of WAHLBERG (1847 p. 257), relating to the mating
habits of the mosquitoes of the far North. Undoubtedly it deals with one of the
Aedini, most probably with A. nigripes. He says that travellers, as known well, are
attacked by immense numbers of female mosquitoes, but that for a long time it
was quite an enigma to him where the males were to be found. A clergyman then
told him, that the females were often found upon the surface of the lakes, beaten
down by rain and wind in such endless numbers that when blown ashore, they
formed thick wind rows. WAHLBERG then observed, that no males were to be found
near the ground, just where the females in immense numbers tormented him and
his fellow-travellers. But from high up in the air he heard a loud singing noise
which wras found to be produced by immense swarms of mosquitoes dancing in
separate flocks. These swarms being examined they were found to consist almost
exclusively of males. This indicates that the males of the Culex, like those of Chi-
ronomids and some other non-biting gnats, keep to themselves in a higher stratum
of the air, \vhere they flock together in dancing swarms, more especially towrards
evening, and tempt the females to come up by the noise of their wingbeats.

During recent years I have often had an opportunity to observe the mating
habits of our mosquitoes; more especially those of C. pipiens, 0. cantans, 0. com-
munis, Anopheles maculipennis and A. bifurcates. I shall here only dwell upon the Culicines.

In the latter part of September small clouds of males of C. pipiens may be
observed on fine autumn evenings everywhere round Hillered. On five successive
evenings I have observed the swarms in my garden. The swarms always consisted
of males only; they always stood in sheltered places, commonly behind a large
lime tree; the mosquitoes always faced the wind which was very slight. The swarm
was formed about six o'clock, and was still hovering after it was so dark that I
could see nothing. The single individuals were flying up and down, commonly at
the same rather slow speed, but suddenly it could be observed how the whole
swarm got into the greatest excitement, all the males now flying at a much higher
speed. The swarm almost invariably stood in the same place, but I got the im-
pression that now and then some of the males left the swarm and settled on the
leaves of the lime; at all events many males were sitting here. The shape of the
swrarm was that of a column, commonly about two or three meters high and one
meter thick. The height from the ground was about five or six meters. I observed
the mosquitoes by means of a Zeiss (power x 8). I estimate the number of animals
from some hundreds at about six o'clock, to some thousands when the swarm was
largest, at sunset between seven and eight. In the course of these two hours I saw,
most probably about fifty times, larger and darker mosquitoes direct their way from
the outside into the swarm. I could observe the females about two or three meters

O. K. D. Vidensk. Selsk. Skr., naturvidensk. og mathem. Afd. 8. Raekke, VII, 1. 20

from the swarm; it was very interesting to see, how straight the lines were, along
which these mosquitoes made their way into the swarm; the mosquitoes were al-
ways females of C. pipiens; it was as if by some magic power the insects were forc-
ed to fly directly into the swarm of dancing males. Undoubtedly they were direct-
ed by the sound issuing from these males which I have often heard formerly and
which others, standing near me, heard very distinctly. Having lost my hearing for
very high notes, I am probably not able to hear these notes any more.

The moment a female had reached the swarm, a great excitement was notice-
able in it. Now here, now there, a ballshaped, thicker, little cloud was observed;
a few seconds later two mosquitoes, male and female, dropped out of the swarm,
slowly sank down into the grass or retired some meters from it carried by the slight
sunset-breeze. I could never directly observe that the mating position was end to
end, as indicated by KNA? (1912 p. 122); the insects were always curled up in a
ball and very soon reached the grass. Here the act was accomplished in the course
of a few seconds, after which the mosquitoes flew away.

In the first part of October we got a period of bad weather; the mosquitoes
disappeared; undoubtedly the males died off, and the females retired to the deep
cellars, the ceilings of which were covered with C. pipiens. In their spermateca the
spermatozoa survived the winter, next year giving rise to new generations. In this,
as in many other cases, where the males die off in autumn, and the females keep
and preserve the sperma in their bodies, I find our customary phrase, that the
males die off rather incorrect; I should suppose that it was more adequate to say
that the males only hibernated in the spermatozoan stage; this would be more in
accordance with the expression we use with regard to all those species, which die
out before winter, and with regard to which we commonly use the term that they
only hibernate as eggs.

With regard to 0. fletcheri I have made the following observations. On 15/vi
I was standing on the southern coast of Lolland near Aalholm Castle, on a little hill
covered with trees and lying in a vast fen, covered with reeds. Below the trees
the ground was covered with more than one meter high nettles. It was near sunset
at seven o'clock. The weather was calm; Tp. 20° C.; the day had been very warm.
Enormous masses of 0. fletcheri were sitting in the reeds; as soon as I came down
upon the little path, hundreds of females rushed upon me. Studying the nettles I
then saw that most of the leaves of the nettles either on the edges or on their tips
carried males of mosquitoes undoubtedly 0. fletcheri; the mosquitoes hung on to
the edges of the leaves by means of the two first pair of legs, the hindlegs were a-
straddle in the air and were now and then moved in circles; the females almost
always sat under the leaves. When I now moved the nettles with my walking stick,
both sexes arose, and to my great satisfaction I saw that if they touched each
other during the flight, pairing immediately took place. For three consecutive even-
ings I now observed the phenomenon during the time from 6Vz to 7 o'clock. At
6Va o'clock the males -and females sit on the leaves as mentioned above, about ?Va,

155

when the shadows grew long, and the sunbeams golden, the males arise and dance
up and down; the dance is very close to the ground, only about one-third to half
a meter from the tops of the nettles. The females alter their places; they now
hang out from the edges of the leaves, and the hindlegs are. often moved either
voluntarily or by the light evening breeze. On studying the females a little more
closely, we shall see that they are almost all very thick, with a blood-filled intes-
tine; the blood is black, i. e.
the blood-meal has taken pla-
ce some days ago; as mention-
ed above most of the scale
vestiture of the abdomen and
of the legs is lost; the mosqui-
toes shining a bright yellow.
More than once I saw a male
during the dance touch the
hindlegs of the female, stretch-
ed out into the air. At the
very same moment the female
released its hold, and the ma-
ting process took place; but I
also very often saw a female
voluntarily release its hold
and make her way into the
swarm of dancing males. The
pairing was always begun and
accomplished during flight; it
lasted only from 50 to 70 se-
conds; the position during the
act was vertical, and in this
position the insects floated up

and down, the line from the highest to the lowest point being only half a meter;
commonly the dance went on in the very same place, often the light evening breeze
carried the mosquitoes a few meters to one of the sides; in the vertical position
the sexes were placed face to face. Immediately after the two sexes had found each
other, they danced some seconds up and down, grasping each others fore and
middle legs; the hindlegs were streched straight out into the air; then I saw the
hindlegs being carried inwards, forming a bow with each other; immediately after
this the tips of the abdomens were brought against each other, and the pairing
took place. Still flying the two sexes released their holds, and both male and female
hovered alone in the air; immediately after I have seen the male seize another fe-
male and pair with her. BACOT (1916 p. 1) indicates that in S. fasciata one male
fertilized 10 out of 21 females. At the same moment I have counted about twenty

20*

Textfigure 19. The mating place of 0. fletcheri. Aalholm. Lolland.

156

pairs in mating position in the air. I was standing with my camera in my hand,
and more than once I could see the dancing pairs, on the focussing screen of my
camera, but it was too dark to get a photo of them. At 8.30 the phenomenon abated,
and at nine o'clock I saw no more dancing pairs.

In the forest which borders some of my experimental ponds near Hillerod
(Stenholtsvang) I have often observed the swarms of 0. communis and prodotes.
The swarming always took place about a fortnight after the mosquitoes were hatch-
ed; the swarms consisted only of from twenty to fifty individuals; but of such
small swarms there were many hundreds around the ponds; they were always
standing in the small open spaces between the trunks, mainly from one to two
meters above the ground; they could best be observed when suddenly sunbeams
fell down between the trunks. In the swarms the single individuals kept their
vertical position, only slowly gliding forwards and backwards in the same plane.
Also with regard to this species did I see the females from the shade of the forest
steer into the swarm and after a short battle drop out with a male. The mating
process took place in the deep shadow of the trees at every time of the day.

With regard to Theobaldia annulata Mr. KRUGER has sent me the following
interesting observation.

"On October the thirteenth a little past five, after noon, I arrived at Gentofte.
I then saw something that looked like smoke on two chimney tops on one of the
villas which I passed. A peculiar undulating motion in the smoke made me pay
a little more attention to the phenomenon. I then observed that it was two mos-
quito swarms which were standing over the chimney tops. A few moments later I
had opportunity to ascertain that all the cottages in the little town had mosquito
swarms over the chimney tops. By means of a fieldglass I saw that all the swarms
consisted of mosquitoes, that all were males and most probably all Culicines. Every
swarm consisted of about 200, rarely about 400 specimens. The swarm undulated
to and fro; the single mosquito moved forward and in small jerks back and down-
wards. The swarm was always standing a little aslant from the chimney top. All
the swarms were directed eastward, and all the mosquitoes facing in the same
direction; most probably because a very faint breeze seemed to come from this quarter.

Chimney tops from which it smoked had no swarms. My daughter had ob-
served the phenomenon before my arrival at my house; she thought that it began
at 5 o'clock. The swarm building was always begun at the gable head, but at sun-
set the swarm was standing over the chimney tops. Ascending the roof of my house
I got some of the mosquitoes: they were T. annulata, all males. At six o'clock the
swarm disappeared; the weather was beautiful, the air warm and soft; no wind; I
could never hear any sound arising from the swarms". The observation corrobo-
rates the often mentioned peculiarity that the swarms are formed over elevated
objects: hay cocks, persons walking over prairies and meadows, cattle etc.

II.

Anophelines.

Chapter IV.

Anopheles and Danish Malaria.

Of the genus Anopheles we have three species in our country: A. maculipennis,
A. bifurcatus and A. plumbeus. We cannot expect to find any more species. The
three species are so well known in the imago stage as well as in the larva stage
that redescription and drawings may be regarded as quite superfluous.

A. plumbeus Stephens.
A. nigripes n. sp. Staeger.

A. plumbeus is easily distinguishable from A. bifurcatus by its small size and
dark colouring. It has been described by STAEGER (1838 p. 552) from a single spe-
cimen taken in Charlottenlund near Copenhagen. In the Royal Museum is found a
series of the species but after 1838 no finds are recorded in literature.

Most probably A. plumbeus is rather rare in our country; I have found the
species in the Royal Garden at Fredensborg near Esromlake and in the forests bor-
dering the lake of Tjustrup. I have only seen it flying at sunset mainly when it
is so dark in the forests that the species may just be distinguished. It bites but
not so viciously as A. bifurcatus.

The larva has hitherto been unknown in our country; MEINERT (1886 p. 395)
has described a larva as A. nigripes but his figures show that the larva he has found
is most probably only a young A. macu//pe/?m"s-larva, at all events not the larva of
A. plumbeus.

The larva is hitherto mainly recorded from tree-holes where it lives together
with the larva of Finlaya geniculata. (EDWARDS according to LANG 1920 p. 78; LANG
1920 p. 78). ECKSTEIN (1919! p. 288), MARTINI (1920! p. 52). For a long time I have
vainly searched for the larva of A. plumbeus, the tree-holes only containing the larva
of Finlaya geniculata; finally in the latter part of July I found a tree-hole with a
great many Anophelin larvae which when more closely examined differed very
much from those of the two other Danish species; they had all the diagnostic fea-
tures of the larva of A. plumbeus; the post antennal hairs being exceedingly small

158

and simple; the outer anterior clypeal hairs too; the equipment of hairs on the
thorax and abdomen is much richer and the colour of the body is remarkably red-
dish brown; the whole larva has, as LANG (1920 p. 78) writes, a more stumpy look
than that of A. maculipenms and A. bifurcatus. I observed the tree-hole almost every
day till 15. August, the hole being only a few hundred yards from my summer
laboratory; there were about a hundred larvae in the hole; they pupated in the first
part of August and the imagines A. plumbeus were hatched before my departure; all the
larvae I saw in the tree-hole were fullgrown ; that a new generation of larvae should
appear in autumn is highly improbable. The larvae were always lying at the surface
but at the slightest shaking of the earth round the tree stump they darted away
from the surface and disappeared at the bottom of the dark brown water.

ECKSTEIN (19193 p. 532) supposes that the species hibernates as imago. Besides
I refer to EYSELL (1912 p. 421). The species is often but not exclusively found in
tree holes also in peat holes (BLANCHARD 1918, MARTINI 1915 p. 585, THEOBALD
(1910 p. 13), it has been recorded from most European countries lastly from France
(CORDIER 1918 p. 726; LANGERON 1918 p. 728). Its significance as Malaria carrier is
very small (BACOT 1918 p. 241); but BLACKLOCK and CARTER (1920 p. 413) have shown
that infection really is possible; the peculiar eggs differing from the eggs of other
European species in having a ring of floating cells all round have been described
by EYSELL (1912 p. 423).

A. bifurcatus.

A. bifurcatus is a well-known species recorded from Denmark already by
STAEGER (1838 p. 552); it is regarded as rare and this, as far as I can see, is the
case with regard, to most of the localities in Central and North Europe. - - In my
opinion it is not so with our country; insufficient knowledge of the biology has
caused the impression that the species is much rarer than is really the case.

The first specimens appear in the middle of May; I have not found specimens
after the first part of September; I have found the greatest number in June — July.
A. bifurcatus is mainly an outdoor species, the home of which is dark forests, old
gardens, the outskirts of old beeches, especially where these border on lakes. Even
if the locality contains numbers of A. bifurcatus during the twenty hours of the day
and night we shall hardly see anything of it; in a great many localities in Den-
mark I and some persons with whom I have been acquainted have made quite
the same observations.

Until a little after sunset we have all been tormented by the different Ochlerotatus
species; then when it is so dark that it is difficult to distinguish the different spe-
cies from each other, mosquitoes of very slender form and with very long legs
appear; it is A. bifurcatus - as far as we hitherto know in our country never
A. maculipennis - which now displaces the Ochlerotatus species; - their flight
is quite silent, and I have never had the slightest sensation of the mosquito
when it alighted upon my hand; the sting is very painful. Different people in the

159

neighbourhood of Hillered have told me that in the time from ten to twelve they
were stung in their bedrooms when the vindows were open by mosquitoes of a
remarkably slender form and with very long legs; unquestionably we here have to
do with A. bifurcatus, so much the more, as I myself have been, subject to attacks of
this species in my bedroom. In early spring when the evenings are cold, I have
also found the cobwebs in stables carrying numerous A. bifurcatus; at that time
A. maculipennis has not arrived here or is very rare. As soon as the evenings have
got warmer, A. bifurcatus disappears from the stables and is now a particular out-
poor species. In my opinion it is one of those mosquitoes of ours which have the
greatest power of flight. On calm very warm days with an overcast sky and sultry
air it may happen that the mosquitoes are on the wing even in the middle of the
day. On such days I have often been lying on the borders of our largest lakes and
watched how A. bifurcatus steered from the lake perpendicularly on the shore line;
I got the impression that the mosquitoes came directly from the lake having pas-
sed this and, if so, flown about two or three kilom.

Everywhere in North and Middle Seeland where I have studied the pheno-
menon I have had an opportunity to observe the attack of A. bifurcatus in the time
from nine to twelve evening; only rarely was I attacked by A. nigripes and never
by A. maculipennis. The species of the genus Ochlerotatus did not quite disappear,
especially 0. cantans was troublesome but A. bifurcatus did not arrive before eight
or nine o'clock, and in most localities it preponderated over the Ochlerotatus-species.

I have observed the males at two different times of the year; in the last days
of April and in the latter part of August and first days of September. The males
congregate in small swarms, commonly not consisting of more than from twenty
to a hundred individuals. On calm evenings or on days with warm weather and
overshadowed sky in the outskirts of the forests we may often find these small
swarms in the small "bays" in the foliage; these swarms of Anophelines are easily
recognizable from those of the Culicines owing to the picture of the position of the
body during the flight. Of a flying Culicin male we only see the body and the an-
tennae which are spread out laterally; a flying Anophelin male presents itself as a
much longer line, because the male palpi are pressed to the proboscis, and pro-
boscis and palpi appear almost as thick as the thorax and abdomen; this impres-
sion is augmented because also the antennae are held nearer to the proboscis
during flight than is the case \vith the Culicines. In the swarms the mosquitoes all
fly almost at the same distance from the earth, flying horizontally out and in
without altering the vertical position in the s'warm: More than once I have seen
the females following straight lines, steer their way directly into the little swarm
which is then in a moment altered into a ball in which the single individuals -are
pressed against each other; a few moments a pair drops out of the swarm, and
falls down into the grass where the mating is accomplished. On a calm day I once
saw such a whole series of dancing A. bifurcatus swarms all almost at line, all

160

standing in the small "bays" of beech foliage and all with the faces directed to-
wards the moors from which the females steered their way into the swarm.

From the middle of May the egg-laying processes go on ; as far as I know a little
later than the process begins for A. maculipennis. The larvae of the two species are easily
distinguished from each other by means of the clypeal hairs; in the larva of A.
bifurcatus the inner pair is simple, and the outer only cleft a few times; in A. ma-
culipennis the inner is cleft several times, the outer is a thick brush; moreover the
float hairs of A. bifurcatus have about sixteen leaflets, those of A. maculipennis
about twenty-two. Also in the comb of the two species there are great differences.
Moreover, as far as I know, the larva of A. maculipennis is always of a much
brighter colour, commonly green, whereas that of A. bifurcatus is darker. Further-
more it may be pointed out that most probably all fullgrown larvae of Anophelines
which are to be found in May-^-June mainly or only belong to A. maculipennis,
whereas all Anophelin larvae which occur from October and during the winter
months always only belong to A. bifurcatus. The two species meet each other as
larvse only in the month June — September; during this time, as far as I know, A.
maculipennis everywhere preponderates over A. bifurcatus; in the six winter months
the opposite is the case, and in the true winter months we only find the larvae of
A. bifurcatus. As well known (GRASSI 1901 p. 53; LEVANDER 1902 p. 11) most of the
Anophelin-larvse are found in the thick green layers of algae on the surface of smaller
ponds (Cladophora, Oedogonium, Spirogyra); as far as I know especially near the coast. It
is very difficult to observe the larvae in Nature; but from my boat when lying in
the Potamogeton region of our ponds I have learned to see the larvae between the
Potamogeton leaves. The larvae are often found together but those of A. bifurcatus
preponderate in clear cold localities.

It is a well known, often established, fact that whereas A. maculipennis hiber-
nates only as imago, A. bifurcatus hibernates as larva. See f. i. NUTTALL and SHIP-
LEY (1901 p. 452; 1902 p. 64); GALLI VALERIC and NARBEL (1901). In September I
have, especially in a little valley near Suserup, seen the swarms of males of A.
bifurcatus; then the females probably lay their eggs; at all events vast numbers of
small black Anophelin larvae occur; at that time these larvae appear almost
everywhere in small ponds rich in vegetation. Their home is the water rim, the
larvae lying, like the Dixa larvae, almost upon dry land; in this water rim the
females have deposited their eggs; these are rather difficult to see in Nature,
but if we take a piece of milky coloured glass or of white paper and bring it
under the surface, but as near this as possible, we shall see that the eggs are ex-
tremely common, further that the numerous black Anophelin larvae originate from
these eggs. The larvae now live in the water rim for more than two months, but
when the temperature of the water is about zero, they disappear and hide themselves
at the bottom of the ponds; at that time they have almost reached the fullgrown
size, the hibernation as far as I know always taking place in the last rarely in the
second larva stage. During winter the larvae do not grow, most probably they eat

161

very little, satisfying their respiratory claims through the air dissolved in the water.
- In spring the larvae appear again in the water rim, and in the detritus washed
ashore in the spring months the pupae appear together with those of Dixa, Cera-
topogon and many pupae of Chironomidcv . ECKSTEIN (1918 p. .530) has arrived at
quite similar results. MARTINI (1920 p. 63) indicates that A. bifurcatus most probably
quite like the Aedini hibernate as eggs which should then be hatched very early
at low temperatures. I do not think this supposition is correct. It seems as if
A. bifurcatus, both as imago and as larva, is more accustomed to low tempera-
tures than A. maculipennis, occurring partly as larva in cold, slow running moun-
tain streams and as imago higher up in the mountains. (See f. i. PRELL 1917
p. 243; MARTINI 1920 p. 67). How many generations are produced in the course of
a year I do not know, but I should think not more than two. - The one is laid
as egg in Sept., winters as larva, the larva life lasting about eight months, and is
imago in May; the other is laid as egg in May— June; the larva life lasting not
more than one or two months; and the imagines appear in mid-summer.

As far as we know there are only few of the Anophelince which hibernate as
larvae (see GRIFFITS 1918 p. 1996. LACAZE 1918 p. 729). LEGER 1917. NUTTALL and
SHIPLEY 1901 p. 452).

A. maculipennis.

When I began my investigations on the Danish Culicidce I supposed that A.
maculipennis was one of our most common mosquitoes; STAEGER (1838 p. 552)
writes "common from April to September; the female common on the windows of
houses". To my great astonishment I never saw A. maculipennis in Nature. The
single Anopheles species which for years I could find was always A. bifurcatus; in
houses I certainly saw a few but never any great number.

It is a well-known fact that in our country we have formerly had a very
serious malaria epidemic; we are therefore forced to suppose that at that time, not
a century ago, swarms of Anophelines must have been hatched every year. As for
the whole of Europe A. maculipennis is nowadays undoubtedly the chief malaria
carrier and as North of the Alps we have never found more than the three
Anop/ie/es-species mentioned in this work, and the significance of the two others as
malaria carriers, especially of A. niyripes, has always been but slight, we are almost
forced to suppose that it really was A. maculipennis which was the malaria carrier
a century ago; as my investigations however showed that A. maculipennis nowa-
days seemed to be an extremely rare mosquito, it really seemed that all those
naturalists and physicians were right, who maintained that one of the main causes
of the disappearance of malaria from more northern latitudes was really the dis-
appearance of A. maculipennis.

One day in 1918 I happened to enter a cowhouse, lying near my laboratory
at Tjustrup. To my great astonishment I then saw A. maculipennis in incredible
numbers hanging down from the ceiling of the stable and especially from all the

D. K. D. Vidensk. Seisk. Skr., naturvidensk. og mathem. Afd. 8. Rjekke, VII, 1. 21

162

cobwebs in the dark, windsheltered corners of the stable. A closer examination
showed that of Culicidce the stable only contained A. maculipennis; that almost all
were females and only a very few males; further that almost all females were
blood-filled.

In the following weeks I then explored about twenty farms lying in the middle
of Seeland; later on ten in the north of Seeland. In every stable I found the mos-
quitoes; the number varied, but was very often about 100 specimens upon one
square yard; very often I saw stables in which the number must be estimated to
be many thousands in all.

The fact interested me very much, never having thought that my limnologi-
cal studies would carry me away from the moors and lakes into the stables; that
however was the case for more than two years. I immediately saw that here prob-
ably was the clue to the enigma why one of the most terrible epidemics, from which
our country had suffered, had totally disappeared from the country in such a
relatively incredibly short space of time.

On two journeys to Lolland-Falster, formerly the real home of the malaria,
I studied the behaviour of Anophelines there; in 19191 explored another old malaria
centre, the marshes in the western part of Jutland. In 1920 I further requested Mr.
KRYGER, on a journey which lasted about a month, to explore the life modus of
Anopheles maculipennis in the southern part of Jutland, from Kolding along the east
coast to Skanderborg; further an area round the large lakes near Silkeborg, then
westward over the heath and finally near the large downs along the west coast
of Jutland.

For my own part I chose a single farmyard lying near my laboratory at
Tjustrup, used the stables as a laboratory and visited the stable in the time from
June to September, often almost every day and at all events every seventh day;
further I visited it now and then also at other times of the year, and moreover
at all hours of the day and night. I wish to give my heartiest thanks to the owner
of the farm, the chairman of the parish council Mr. JORGENSEN. Of course without
any scientific education, yet he was soon interested in the exploration, often looked
for the mosquitoes himself, and allowed me to begin, carry on, and complete my
investigations at every time of the year and the day. In this connection I also wish
to bring my best thanks to Mr. PETERSEN, veterinary surgeon at Ringsted, Mr. J0R-
GENSEN, Nysted, Mr. E. PETERSEN, Silkeborg, and Dr. HELMS at Nakkeb011e Fjord;
Prof. C. O. JENSEN, Copenhagen; they have all given me information of different
kinds. In April 1920 I delivered a discourse in the Royal Society at Copenhagen
on the malaria mosquitoes and their relation to the Danish malaria. Some weeks
later, Prof. C. J. SALOMONSEN called my attention to a paper by E. ROUBAUD published
in April 1920, the very same month in which I delivered my discourse. I immedia-
tely saw that it had happened that two scientists in two countries, without having
the slightest suspicion thereof, had studied quite the same phenomenon simultane-
ously and on quite the same principles. It was with the greatest satisfaction that

163

I saw that \ve have arrived at quite the same results. I do not think that the
excellent paper of ROUBAUD has made mine superfluous; the same theory which
already in 1918 I had worked out for myself with regard to the disappearance of
the malaria in North-Europe I have seen that ROUBAUD has also worked out for
France. His thoughts and mine upon this point can, as far as I can see, never be
more than a theory; but it is a matter of course that this theory is greatly streng-
thened by the facts that two scientists, in different parts of the globe, have arrived
quite independently and simultaneously at quite the same result.

In accordance with my discoveries and starting from the new facts gathered
from Mr. KRYGER'S note-books from his journey in Jutland, I shall now in a
somewhat abbreviated form give an account of my investigations, then mention the
results of ROUBAUD and finally discuss the relatively slight differences between his
and my statements. All in all I suppose it will be understood that the old saying
that two eyes see better than one has been corroborated also in this case.

With regard to the anatomy and general biology of A. maculipennis I refer the
reader to the many papers published upon this subject especially: GRASSI 1901 ;
IMMS 1907 and 1908; CHRISTOPHERS 1901, NUTALL and SHIPLEY 1900—1903 a. o. I
especially wish to point out the last-named admirable investigation relating to the
anatomy of imago and larva ; of particular interest is the study of the digestive organs.
(1903 p. 166).

1. The explorations have been carried on over North, Middle, and South-See-
land, over the islands Lolland and Falster, and over a large part of Jutland (see
above). From these explorations, carried out in more than a hundred farms, it may
be supposed that almost every stable in the country at special times of the year
harbours A. maculipennis. In the time from June — September A. maculipennis has
been found in every stable hitherto explored. From the exploration hitherto carried
on it has been quite impossible to point out special areas of distribution where A.
maculipennis either preponderates or is rare; I once thought that the mosquito was
more common in the southern part of the country, but this is certainly not right.
In the woodlands, on the vast meadows on the southern coast of Lolland-Falster,
in the marshes at the west coast of Jutland and over the sandy country of Mid-
Jutland the mosquito seems everywhere to be common. Most probably the peculiarly
regular distribution over the country is in accordance with the fact that breeding
places are to be found everywhere and that want of food cannot exist.

2. The mosquitoes appear in the stables on the first days of May, at that
time the number is but small and during the whole of May it is not augmented ; at
that time we only find females; in the middle of June the new summer generation
appears, making known its existence rather suddenly by means of rather numerous
males and an enormous amount of females. Any augmentation of females from the
latter part of July I cannot ascertain; the males almost totally disappear, but in the
last part of August I have got the impression that the number is again augmented.
From the middle of September to November the number of both males and females

21*

KM

diminishes and from the latter part of November it is almost impossible to get a
single specimen in stables which in July sheltered thousands of A. maculipeiuus.
The hibernation does not take place in the stables. When studying the hibernation
places of C. pipiens I only very rarely found A. maculipennis in them. The number
of A. maculipennis which I have seen in human dwellings in winter is also al-
ways extremely small; in the district of Silkeborg it has been maintained that the
females in late autumn fly into the rooms; otherwise I have never heard anything
of this and I take it to be highly improbable that our rooms are the real hiberna-
tion places of the species. On the other hand I have myself found the species in
small numbers in remarkably cold but always dark localities, especially out-buil-
dings. The veterinary surgeon Mr. PETERSEN has kindly told me that in the western
part of Jutland, near Ribe, on the farm Villeb01, on 23/n 1917, he found numerous
A. maculipennis, hanging under the ceiling of a peat house; it was in company with
T. annulata. I suppose that such localities are the real hibernating places, at all
events in our country, not the stables. - - Most probably this is in accordance with
the high temperatures in winter in the stables ; low temperatures being a life con-
dition for the mosquitoes, as they do not suck blood during winter.

That the hibernation as a rule does not take place in stables but in out-
buildings etc. is corroborated by many other authors. I refer especially to ECKSTEIN
(1919m p. 531); MARTINI (1920JJI. Also ANNETT and DUTTON (1901 p. 1013) maintain
that A. maculipennis hibernates in outbuildings, cellars, dairies; cheese rooms, pan-
tries; lumber rooms, ware houses, coal cellars. The two last named authors state
that the mosquitoes were very difficult to rouse during hibernation. Howr long the
mosquitoes remained in the same position during the winter months it was not easy
to determine, but it was noticed that many of the Culicidcc were wholly or partially
enveloped in a thick mould which had grown in and around their bodies thus
fixing them in the attitude described.

3. In my opinion the number of A. maculipennis is greatest in the hog-sties;
not so great in the cowhouses and smallest in the horse stables; often the num-
ber is also great in the hen-houses. As however the rearing of swine during these
last two years has been very greatly diminished, so much so that often there are no
hogs at all in the sties, it has been difficult for me to corroborate this supposition.

It is always so that dark and dirty, badly ventilated stables without draught
contain a greater number of A. maculipennis than light, clean, well ventilated stables;
newly whitewashed stables always contain only very few specimens. Mr. KRYGER
as well as myself have observed dark stables were A. maculipennis has been pre-
sent in thousands, we are almost inclined to say in millions; when the door has
been opened and we have tried to touch the ceiling with a net, crowds of mosqui-
toes have hovered around us. It further seems that the number is greatest in the
small stables with low ceilings, it is further greatest in stables with many animals,
much smaller in stables with only few cows or horses. The mosquitoes occupy the
ceiling more than the walls and always prefer the darkest corner; in particular

165

they hang down from the cobwebs; every cobweb often carries about thirty to forty
specimens; where it has been possible to count the number I have often found
about 80 to 100 upon a square meter.

Even in summer when the Anophelines are mainly to be found in the stables
the cattle is often in the fields; on the larger farms they are mainly out of doors
day and night, on the smaller ones the cattle is driven into the stable before night.
In the last case the number of Anophelines is exceedingly large. In every stable
there are however almost always a few pens in which young cattle or sick ani-
mals have been locked in. It is then very peculiar to see that even that part of
the ceiling and walls which borders on these pens contains a much larger num-
ber of mosquitoes than the empty pens. To get a true estimate with regard to the
number of Anophelines a very careful examination is necessary; it has been shown
that a great many mosquitoes hide themselves between the collar-beams and the
ceiling and similar localities which are almost excluded from examination. - It
can also be shown that where among a series of stalls, each with its head of cattle,
there are some empty ones, the number of Anophelines over these empty stalls is
smaller than over those which contain cattle; nor is the ceiling over the middle
walk so closely covered as the ceiling over the stalls.

4. Even in those farms where the stables contain large numbers of mosqui-
toes, the rooms occupied by the family are almost quite free from mosquitoes.
The opposite may be the case and more especially this has been the case upon
some large estates where all the cattle has been out in the meadows for a long
time, and the servants' rooms have been in connection with or very near the stables.

- As a common rule it may however be pointed out that on most of our farms
there is the most striking contrast between the number of mosquitoes in stables
and in the living rooms.

Accounts from excellent observers, in whom I have the greatest confidence, seem
to point to the fact that in localities where there are exceptionally many breeding
places for Anopheline-larvse, and where the number of cattle present in the vicinity
is but slight f. i. in the little town of Silkeborg (about 10.000 inhabitants), quite
surrounded by lakes and moors, it seems as if the mosquitoes here may enter
the houses ; this may especially be the case in autumn. Personally I have not myself
had any occasion to corroborate this assertion.

5. The mosquitoes of the stables are almost all blood-filled; extremely thick;
where I have tried to count I have always found that about 90 % have the sto-
machs full of blood and only 10 °/o have empty stomachs; in many of them the
contents of the alimentary canal is black, in many of them it is red. Rather often
we find specimens where the hind part of the contents is black, the fore part is
red. In my hatching cages I have seen that an A. maculipennis with red contents
of the alimentary canal in the course of twenty- four hours has altered it to black.
When therefore I find mosquitoes with contents half black and half red, I am in-

166

clined to suppose that the mosquitoes suck or at all events are able to suck blood
very often, most probably almost once in the course of twenty-four hours.

It is difficult to see the real blood-filling process ; I have never seen the mosquitoes
suck on bright days; nor have I been able to see the process during night, most
probably because it was always too dark in the stables and the mosquitoes had
left their victims when light arrived. On the other hand, in the time from ten to
twelve evening, very often when I came into the stable, especially in the hog-pens,
I have seen almost all the pigs rub themselves against the boards of the stall;
this I have only rarely observed in day-time. On dark days in dark stables I have
further often seen or rather just been able to catch a glimpse of the sucking Ano-
phelines; curiously enough I have most often observed them on the eye-lids of the
cows; more than once I have tried to catch them while they were sucking but
this was always an impossibility; the cows moved and the mosquitoes darted
away. - - I have not tried to determine the blood in the mosquito stomachs; I soon
learned to regard this as quite a superfluous investigation. Later on I learned that
already MUHLENS "konnte das Blut mit der Uhlenhutprobe als Schweine- bez.
Rinderblut anweisen" (MARTINI 1920i p. 60). It may be added that the few speci-
mens which I have found in the latter part of October have never been red but
have had a yellow coloured abdomen not distended with blood. The blood-sucking
period lasts only till about 15/ix.

6. The mosquitoes are always remarkably indolent, and sluggish; when en-
tering the stable the observer gets the impression that the mosquitoes sit almost as if
glued to the ceiling and walls. I shall not here discuss the well-known position which
the Anophelines generally adopt in contradistinction to the Culicines; (see especially
PRELL 1917 p. 242) but only once more emphasize the peculiar position when they
hang down perpendicularly from the cobwebs by only one claw of the forelegs.
The animals are quite motionless and do not alter their position for many hours;
the moment, however, the glass approaches the mosquito and the distance is dimi-
nished only a few inches we immediately see the hindlegs make oscillations and
often describe circles in the air; if then the vessel is not rapidly put over the mos-
quito it takes the wing; unquestionably the long outstretched hindlegs are used as
organs of feeling.

At first I thought that the number of mosquitoes which I should find at night
hanging indolent from the ceiling would be, smaller than by day; this may perhaps
really be the case but after all the difference is but slight. On lO/vin I marked the
resting places of 40 A. maculipennis ; time seven o'clock in the evening; the next
morning at nine o'clock twenty-nine of the mosquitoes had not altered their places.
I have got the impression that the females almost live their whole life in the cow-
houses, only fly out of doors to pair and for the purpose of egg-laying; on calm
evenings I have observed the mosquitoes from outside either fly through the open
door or against the windows, but I have never been able to observe a flight from
the stable into the open; Mr. PETERSEN writes to me that in the western part of

167

Jutland near Ribe he has made quite a similar observation; any general flight of
Anophelin females in the evenings round the farms or under the large trees which
are often found in the gardens near the farms I have never been able to observe.

7. Whilst the females, in my opinion, must mainly be regarded as stationary
stable mosquitoes during the summer, the males are rare in the stables; I have
never found more than about 10 % males; Mr. PETERSEN has come to quite a
similar result. At Nysted (Lolland) I have in the middle of June observed the small
swarms of males dancing behind and between shrubs; it was evening; sunset; the
observation was made about fifty meters from the stable in which, at the same
moment, about one hundred blood-filled females were hanging. Here too I had oc-
casion to observe a few females steering their course into the swarms, but these
females came from the outside, the swarms of males being between them and the
stable; as far as I could observe without catching them they were all lank, without
blood in the stomach. The observation of the swarming of the Anopheles-species is
of some interest; it has hitherto been denied; recently it has been corroborated by
BANKS with regard to Philippine species (1919 p. 283).

8. I have never directly observed the females egg-laying; having often tried to
see the process by day I am almost convinced that it takes place at night, and
especially in the early morning hours. This is also stated by LEVANDER (1902 p. 18).
In my hatching cages the females never laid eggs in the day time, but the water
reservoirs very often contained eggs in the morning. With regard to the structure
of the eggs and the form of the egg groups I refer the reader to earlier authors.
As far as I can see the eggs are often laid in the water reservoirs nearest to the
farm; it is only the distance from the stable which determines their usefulness; the
quality of the water is a matter of entire indifference to the mosquito. Any predi-
lection for clean water I do not find. Hitherto I have never, as is the case with
C. pipiens and T. annulata, found the eggs indoors in cemented water reservoirs but
I should not wonder if this will be the case some day. I have found the larvae in
the dunghill pools lying only abt. 10 meters from the stable; in these pools a great
many larva? are hatched. In most of our villages we commonly find pools very
rich in organic matter often covered with water bloom, our Danish "Gadekaer"; gener-
ally they are bordered by grassy vegetation. In these pools I have always found
the greatest number of the larvae of A. maculipennis. I suppose that these pools
are the nightly rendezvous places for all the egg-laying females from the stables
of the village; that A. maculipennis should not be bred in polluted water is therefore
not in accordance with my own observations (see GAVER and PRINGAULT 1914 p. 401
a. o.). I may add that I have often found a large number of larvae near the marshy
borders of larger ponds or small lakes. What mainly characterises the egg-laying
localities is that they are almost always sunlit, not dark as is mainly the case with
many of the localities for Cu/ex-larvae.

9. As is well known a C. pipiens throws its eggs in egg boats; we suppose
that every female produces about four eggboats. I regret that the far-branching

168

investigation of the biology of our mosquito fauna has not left time enough to
study the egg-laying processes of A. maculipennis in a more thorough manner. From
observations in my hatching cages, but never corroborated in nature, I have got
the impression that also the eggs of A. maculipennis are given off if not in rafts,
at any rate in series; that periods of egg-laying succeed periods in which eggs are
not laid; how many of such periods exist in the life of an A. maculipennis I really
do not know. At highest summer temp. I have observed that a blood meal almost
disappears from the stomach in the course of about four to six days; when then
opened, it has been shown that the abdomen was filled with eggs. I feel quite sure
that from the moment of blood-filling and to the moment of egg-ripening the
mosquitoes do not leave the stable, but it seems that they suck blood more than
once. As mentioned above in my opinion they do not leave the stable except for
mating and egg-laying, and it is most probable that, during flight, for one of these
two reasons they do not suck blood. If this is right it means that A. maculipennis
in most districts of our country does not suck blood out of doors. With regard to
larva life I refer to A. bifurcatus.

10. It is a very peculiar fact that of the owners and inhabitants of about a
hundred farms which Mr. KRYGER and I have visited, more than ninety have not
had the slightest idea that their stables contained mosquitoes at all. When we have
asked permission to visit their stables they have invariably answered "we have no
mosquitoes in our stables"; often the owners have been angry and said that they
wanted to see the mosquitoes before they would believe it. It has always been
rather a jolly moment when we studied their faces, after having presented them
with some hundreds; their astonishment was beyond all bounds. A few of them
were well aware that their stables were inhabited by mosquitoes, but these persons
have always maintained that the mosquitoes whic'h stung them in the forests and
in their gardens were of another kind ; that the mosquitoes of the stables were blood-
filled they have never observed.

11. The most striking fact elucidated from conversation with the owners was
that the mosquitoes of the stables never sting man. This is in full accordance with
my own experience: I have never in my life been stung by a single A. maculipen-
nis. Moreover, I have been sitting at the farms near the open stable doors, expect-
ing that the mosquitoes would use me as a sucking object. I never succeeded. I
have asked the herdsman, who was to attend the sows when they were to farrow
and was therefore forced to lie as near as possible to the sow, if he had ever been
stung by the mosquitoes. Even if the stables contained many hundreds, the answer
was invariably "No". There is not the slightest doubt upon the point that the
mosquitoes of the stables suck blood from our farm animals and not from man.

12. From this common rule we have only been able to get a very few excep-
tions. Mr. KRYGER has shown that there is evidence that A. maculipennis at all
events in two localities in Jutland still attacks man. In one locality the mosquitoes
were caught while sucking and determined by him as A. maculipennis; in two other

169

localities as well as in the thjrd, where the fact was ascertained, the nursery, the
bedrooms and the servants' rooms were full of A. maculipennis; the people main-
tained that during night they suffered horribly from mosquitoes, and that -their sleep
was disturbed by the insects. It has been maintained that A* maculipennis every-
where round Silkeborg attacks man. This more especially holds good in autumn.

Most probably the statement is quite correct. For all three localities it can be
pointed out that there is a want of cattle. In one locality, the great estate of N0r-
holm, the cattle was out of doors; the Anophelines have flown into the servants'
rooms and satisfied their lust of blood on man; of the two other localities one,
Silkeborg, is surrounded by water in an area where undoubtedly vast numbers of
Anopheles may be hatched and where the number of cattle to nourish the number
of Anophelines is but small ; the third spot was at Gudenaa where th'e same is the
case; here the house was in possession of a fish farm with large hatching ponds
which contained plenty of Anophelin larvae but no stock of cattle.

It seems therefore that in localities where special conditions prevail, .4. ma-
culipennis nowadays also attacks man, but we have here only to do with excep-
tions; the rule is that this is not the case.

13. As A. maculipennis is now ascertained to be an inhabitant of our stables,
the question is if they may be regarded as quite harmless insects; I am not quite
sure that this is the case. More than once we have explored stables which only
contained two cows. When in such stables we are able to count about 100 A. ma-
culipennis on a in2 and may estimate the number of mosquitoes at many thousands,
and 90 % of them are blood-filled, it may really be a question if the cow is able
to produce the same amount of milk, whether the stable is mosquito-filled or
empty of mosquitoes. If I estimate the amount of mosquitoes in such a stable at
5000 only, a number which is unquestionably too small, it means that about 5000
drops of blood are hanging on the ceiling and walls. If then I suppose that this
number is almost unaltered from the 1st of June to the 1. Sept. and that the blood
is renewed every fourth day - - this is probably too little - - this again means that
the cows have been tapped of more than 100.000 drops of blood. If we further
suggest that 100 drops are about 5 ccm blood, this again means that the mosqui-
toes have tapped the cows of 5 liters of blood during the summer. I suppose that
this may be regarded as rather strong, at all events rather unnecessary, bleedhig.

It may in this connection be kept in mind that quite similar calculations have
been made by WILHELMI (1917 p. 69) with regard to Stomoxys calcitrans, and that
BISHOPP (1913) for the same species and from explorations in North Texas has
shown that loss of milk production owing to the same cause should be estimated
at 40—60 %>.

With regard to the Anophelines it may in this connection be remembered that
a study of the literature from GRASSI (1900) up to our own day seems to show
that no conformity with regard to all indications as to the blood filling processes : -
how often they take place; the relation between egg laying and blood filling; the

I). K. D. Vidensk. Selsk. Skr., naturvidensk. og matheni. Afd. 8. Rsekke, VII, 1. 22

170

influence of temperature, can be aquired, in the present state of our knowledge. I
shall restrict myself to remarking that MARTINI (1902 p. 152) for North Germany
indicates that at tp. of 20° C. in the rooms the blood sucking process takes place
every fourth day till egg-laying, and that this goes on two or three weeks later on.

14. If now from a veterinarian point of view it will be admitted that the num-
ber of Aiiophelines in the stables has some significance, it may be added that it is
very easy to destroy the mosquitoes; the best means are white washing of ceiling
and walls, destruction of cob\vebs, draught and light. The number of mosquitoes
is always greatest in the dark, dirty, small stables without light and draught. In
large, fine stables, well ventilated and white-washed the number of mosquitoes has
certainly no practical interest.

It may also be added that the swallows play a prominent part in the destruc-
tion of the mosquitoes ; where there are many swallows' nests, there are few mosqui-
toes. I have often seen them pick the mosquitoes away from the ceiling. On the
other hand I have never seen the spiders destroy them and never found remains
of them in the webs, even where the mosquitoes in huge numbers hang down from
inhabited cobwrebs; see also KNAB (1912 p. 143). He mentions several other Nemocera
which are also found there. Only the Ceratopagonida> suck upon the prey of the
Aranea; \vhat the other Nematocera have to do there we do not know. That they
should find any protection there I find quite improbable.

15. Being no veterinarian I only venture to suggest the question if the thought
is quite unnatural that there may be occasions where the mosquitoes may be able
to play a role as disease-carriers.

16. It is a well-known fact that entomologists who have been punctured by A.
bifurcatus always maintain that the sting is much more painful than that of the
Culicines; further that the effect lasts much longer. See also NOCHT (1901 p. 908).
My own experience goes in the same direction. Here as everywhere we often
hear about venomous punctures of mosquitoes. It happens that quite suddenly many
people suffer from such punctures; in 1920 the field workers on a large estate suffered
greatly from venomous punctures of mosquitoes in September. In one of the above-
named localities at Silkeborg the families and especially the children got one veno-
mous puncture after the other and had to be treated by a doctor. In that very
locality an Entomologist, Mr. PETERSEN, pointed out that A. maculipennis was to be
found in the rooms. I should think that here we have fo do with a case, worthy
of special investigation.

17. From the Middle of Seeland as well as from Lolland I have gathered from
twenty to forty females in the stables and examined the alimentary canal, but I
have never seen cystes on the walls. As up to 1920 in the autumn I never heard
of a single case of malaria which must be regarded as indigenous, I ceased to make
these observations, regarding them as rather unnecessary.

18. Commonly A. maculipennis is sole master of the stables; only in spring
A. bifurcatus arrives too. Especially in the autumn C. pipiens appears, but now and

171

then T. annulata may be present in relatively large numbers; these large mosqui-
toes, which, quite like A. maculipennis, are almost always blood-filled, resemble
flies and are as sluggish as A. maculipennis. Also MARTINI (19204 p. 13) states that
he has rather often found A. bifurcalus in stables.

19. With regard to the number of generations in our country we only know
very little. The last broods of the last summer generation hibernate and most prob-
ably die out in June, living about eight months. The summer generation is born
in June and produces a series of broods; that these broods again produce a new
generation is in my opinion probable, but more than two generations a year I do
not suppose will appear. KULAGIN (1907 p. 867) has arrived at a similar result with
regard to Russia (one generation). PRELL (1917 p. 262) seems to be of a similar
opinion: he says: "dass die A. maculipennis Larva verhaltnismassig hohere An-
spruche an die Temperatur stellt als Culex und daher fur gewohnlich sich wesentlich
langsamer entwickelt. Bei einer durchschnittlichen Tp. von 20° C. war eine Zucht
allerdings bei schwacher Ernahrung nach 5 Wochen noch nicht fiber das zweite
Stadium gekommen". ECKSTEIN (19192 p. 94), MARTINI (1920i p. 63) indicate 2—3
generations at Strassbourg and Hamburg. Unquestionably the number of generations
in the south is much greater. GRASSI (1900 p. 81) found that the development from
the moment when the larva left the egg and to the transformatign to imago lasted
30 days at tp. 20 — 25° C. Twenty days later these flies in turn laid eggs. In the
long Italian summer there will certainly be time for a whole series of generations;
this has also been stated for England by NUTTALL and SHIPLEY (1902 p. 68) and
for Austria by KERSCHBAUMER (1901 p. 85).

If now we will summarise our knowledge with regard to the biology of A.
maculipennis in Denmark nowadays, we shall arrive at the following remarkable result.

A. maculipennis is almost for the whole of its life bound to human
habitats; in summer to the stables, in winter to outhouses, only leaving
the houses for mating and egg-laying processes. It sucks blood upon
the domestic animals, pigs, cattle and horses, not upon man; this is
only the case where opportunities to suck blood upon animals are
wanting or insufficient; nowadays the females are extremely sluggish,
hanging blood-filled, often in incredible numbers, upon the ceiling
and walls of the stables. They are hardly ever met with in Nature
itself and as a rule they do not fly through the windows into the rooms
in the evenings.

It is a well-known fact that malaria was formerly one of the worst epidemics
we have had in this country. Its history here has been treated by C. A. HANSEN
(1886) and by GOLDSCHMIDT (1886 p. 29). With regard to older literature I more
especially refer to COLD (1857 p. 109). I shall here by no means enter into detail,
but referring the reader to these papers only call attention to the following facts.

22*

172

Before 1818 there had been some malaria attacks but hitherto they had not
been very conspicuous. In 1826, after a very warm summer, a terrible epidemic
broke out. On the island Langeland about, one fourth of all the inhabitants were
attacked; the leading physicians supposed that the whole generation of the period
living in the middle part of Seeland would succumb. Again in 1831 the epidemic
ravaged Denmark as one of the most terrible epidemics we have ever had; the term
"Lolland fever" originates from that time. It lasted to 1834. In the years 1847 — 49;
1853 — 56, 1859 — 62 a series of smaller epidemics appeared. From that moment we
observe an uninterrupted fall of the curve though with some undulations and a
series of low vertices; nowadays endemic malaria does not exist in our country;
from abroad cases of malaria have been brought in; in the year 1914, 33 foreign
malaria cases have been treated; not a single one of them can be regarded as
indigenous. It is a disease nowadays extinct in our country.

How terrible was the epidemic about 1830 will be seen from the following
description (C. A. HANSEN) (1886 p. 151): After a few days of a nasty smelling
blighting fog in July the malaria suddenly attacked a very great part of the popula-
tion. As by a flash of lightning several hundreds were attacked in all directions in
the same parish. Upon Lolland there were two parishes with 2000 inhabitants of which
1800 were attacked and 98 died. The percentage of mortality was greater in the
Cholera year 1853 when more than 50 °/o of the attacked succumbed, but the actual
number of attacked persons was much greater in the malaria years. Suddenly
during work in the fields the workers dropped down. The whole stock of servants
even of larger farms and estates would be attacked simultaneously ; the cattle could
not be milked and any stranger who cared to was allowed to take the milk. In
Maribo county (Lolland) 28,788 persons were attacked i. e. about half of the
whole population; 1114 died. The malaria occurred mainly in the benign form, but
also perniciosa occurred. The malaria devastated the whole country, especially
Lolland — Falster, a district in Middle Seeland, North Seeland round Lyngby, the
island of Langeland and the area round Silkeborg, Jutland.

It is very peculiar to see that in the same county where formerly more than
28,000 people were attacked in one of the large epidemics, the medical officer of
the county was only able to count 300 attacks in the time from 1875 — 87, from
1887 — 1900 only 10 and after 1900 not a single one. Old people are still living
who have either had malaria themselves or have given me the most vivid descrip-
tion of the disease and its general character.

If now we will try to combine the description of the disease in old days with
what we nowadays know with regard to the transmission of the infection and with
the biology of the Anophelines nowadays in our country, we shall see that these
different facts, gained in very different ways, cannot be brought into connection
with one another.

Before discussing the matter I wish to call attention to the following fact.
Being no physician I am forced uncritically to accept the material at hand as it is.

173

I must take it for granted that the disease in the beginning and in the middle of the
nineteenth century really was a true malaria, mainly benign, but partly pernicious.
When however we read these reports on the old malaria epidemics we are, in my
opinion, almost forced to direct our attention to several points which seem in-
compatible with our recent knowledge of the disease and its manner of infection.
This especially holds good with regard to the extreme rapidity with which these
old malaria epidemics by all accounts set in. When we hear that SCHAUDIN in St.
Leme in malaria affected houses only found from 5 to 16 per cent, of the Anopheles-
material affected, and that in Macedonia, a country which is infected to a very high
degree with malaria, only 2 per cent, of the Anophelin material (MARTINI 19204 p. 72)
is said to be infected, how is this compatible with the old reports that, as by a
flash of lightning, several hundreds were attacked in all directions in the same
parish and that whole crowds of working men in the fields suddenly dropped dowrn
sick to the ground. This in the first place presupposes myriads of clouds of infected
Anophelines, and we may be permitted to ask from where these infected clouds
suddenly came; further this suddenness is dependent on a remarkable simultane-
ousness in the attack which must have occurred before those meteorological phenomena
(dense fog etc.) which are often tacitly regarded as partly responsible for the outbreak.

As however I have never seen any criticism of all these records of the old
malaria epidemics, it is only with the greatest hesitation that I write the above
lines. As matters now stand we are forced to regard all these accounts as really
relating to malaria, leaving it to future research to add to this criticism or show it
to be unnecessary.

If now we take it for granted that the old epidemics were true malaria, we
are also forced to take it for granted that, as it is stated about the disease nowa-
days so in former days, too, it can only have been transmitted by means
of mosquitoes; without having recourse to strict arguments of any kind it must
be admitted that at the present standpoint of science this is the only correct
point of view to set forth. It is one of the few cases in the kingdom of science in
which the old word: blessed are ye who do not see and yet believe, is in accor-
dance with the true spirit of science. If this is right, it must also be admitted that
the sole mosquito which has been able to bring disease or death to so
many people almost a century ago can only have been A. maculipennis. At
the present time we have only three Anophelines north of the Alps, of which A.
nif/ripes does not come into consideration as a plasmodium carrier, while A. bifur-
catus as such is to a very high degree subordinate in significance to A. maculipen-
nis. We are either forced to suppose that the malaria was transmitted by A. maculi-
pennis a century ago or to accept a scientific absurdity e. g. that a century ago we
possessed species north of the Alps which at that time transferred malaria, but
which have now disappeared.

These considerations being correct the great question arises: Why has A.
maculipennis in our country only three generations ago transferred mala-

174

ria to man whereas nowadays it has not the slightest significance as a
malaria carrier? The question however coincides with another, often put: Why
has malaria disappeared from our country? This question has been ans-
wered in very different ways. Disregarding a series of quite fantastic answers I only
wish shortly to call attention to the following.

1. The number of Anophelines has regularly diminished in the course of years.
This may be possible but, on the other hand, there is no doubt about the fact that
every farm in our country has enough mosquito material to infect its inhabitants.
German authors have arrived at a similar result (MARTINI 19204 p. 28).

2. The improvements in agriculture, especially the extensive drainage works,
have dried up the hatching localities of the Anophelines. This may be possible,
with regard to our country the answer however may be treated in accordance with
1. With regard to Germany MARTINI (19204 p. 22) states: "dass die Veranderungen
der Wasserverhaltnisse des Bodens es in erster Linie sind, die uns die Malaria vom
Halse verschafft haben".

3. The quinine treatment of the disease has killed the parasites in man and
the Anophelines have had no opportunity of getting parasites and of spreading the
contagion (KocH 1899 a. o.). This is unquestionably true; many physicians however
maintain that the quinine treatment has indeed weakened the virulence of the dis-
ease especially near the northern limits of its area of distribution, but do not think
that it can be made responsible for its total disappearance. (CELLI, SCHOO, SCHUFF-
NER in ZIEMANN 1918 p. 109). They more especially call attention to the fact that
the malaria is the same even in localities, where the farmers use quinine in abun-
dance: It may f. i. be pointed out that even in 1918 about 5000 cases were to be
found round Emden; (MARTINI 1920t p. 75). Further that formerly malaria has
disappeared from certain areas, and that at a time when quinine treatment was
quite unknown.

4. It has been stated that the improvement of the houses and dwelling rooms
has played an essential role in diminishing malaria. In this supposition there is
unquestionably some truth. MARTINI (19204 p. 22). says that formerly: "Knechte und
Magde in Verschlagen an der Diele schliefen, nach der auch die Stiille offenen Aus-
gang hatten und die Herrschaft in ahnlichen Verschlagen neben dem Hauptraum
des Vorderhauses". Especially "die wundervollen Unterschlupfe, welche diese Schlaf-
stellen den Mucken boten und die von Anopheles wimmelten" are significant. Also in
our country the houses have been of similar kind. Nowadays as the peasants live
in houses of much better construction, as the admittance to the sleeping rooms is
much more difficult for the mosquitoes, and the temperature in the rooms is lower,
great outbreaks of malaria epidemics are rendered difficult. MARTINI (192()4 p. 22)
correctly remarks as follows: "Der Hygieniker versteht nun auch warum in ganz
Deutschland die kleinen Leute die Fenster so angstlich zuhalten, besonders abends
und nachts. - - Die alte Volksweisheit die vielleicht alter ist als selbst die Malaria-
pandemien des letzten Jahrhunderts weiss, dasz durch #die offenen Fenster abends

175

die Fieber hineinkommen und dasz in den Marshen die laue Luft der schonsten
Juli und Augustabende giftig und krankheitsschwanger ist".

Even if all these considerations are correct, I for my own part am inclined
to suppose that the improvement of our houses cannot be regarded as the main
cause of the disappearance of the malaria. The number of Anophelines in the
stables nowadays is too great for that.

5. Another explanation of the phenomenon that the malaria has disappeared
from our own and adjacent countries is, that the mean temperatures of the summers
of the last 150 years has by degrees been lowered. It is especially FLENSBURG
(1911 p. 1244) who with regard to Sweden has shown that cold summers dimmish
the malaria attacks, warm summers accelerate them; a mean temperature of 15.3° C.
for July alwrays brings decrease or cessation, a mean temperature of below 15° C.
cessation. For the marshy country at the North Sea MARTINI (19204 p. 27) states that:
"angeblich eine Veranderung der mittleren Sommerwarme von 15 auf 16Vs, also
urn iVa0, in marschigen Gegend Epidemien erzeugen kann". Also MARTINI is therefore
inclined to see in the low summer temperatures after 1870 a factor which has
diminished the malaria epidemic. Formerly the Danish physicians, especially C. A.
HANSEN, have arrived at similar results.

These observations are in accordance with those of JANCSO (1905 p. 624) who
shows that if an Anopheles infected with malaria plasmodia is held at a temperature
of 16° C. no cystes are formed upon the walls of the alimentary canal; the infec-
tion of the mosquito may take place at tp. below 16° C. but only if the tp. rises
rapidly after the infection. It is in accordance with these observations that malaria
hardly ever passes the July isotherm of 15 — 16° C. As A. maculipennis in our country
is really near its northern limits of distribution, and we may have summers when
the middle tp. of July does not rise to 16° C., it will be understood that climatic
conditions in our country are able to produce undulations and changes in the viru-
lence of the disease. Yet it may be admitted that JANCSO'S statements have been a
little weakened by KING (1917 p. 495) and WELCH (1917 p. 98) who show that the
tertian parasites in A. maculipennis are able to endure, at all events for some days,
a tp. of 35° F. for 17 a tp. of 46.

That there really exists a very close connection between the climatic and meteoro-
logical conditions and a new outburst of epidemics has often been pointed out in
recent years. Especially the explorations of the SERGENTS (1903 a. o.) in Algiers have
sho\vn the very near relation between the degree of moisture of the air and the epide-
mics. The more moist and cold the summers in Algiers are the more serious are also
the epidemics; for this country the explanation of the fact is that the burning Afri-
can sun dries out the eggs and the larvae do not develop. In our northern latitudes
it is really the warm and moist summers which may be regarded as one of the
main conditions for an outbreak of malaria. With regard to Germany MARTINI (19204
p. 21) comes to quite a similar result. He says: "Ich selbst bin davon iiberzeugt,
das/ eine Senkung des Grundwasserspiegels nicht ohne eine erhebliche Verminderung

176 _

tier Miickenzahl abgehen kann besonders in den Marshen. Bringt doch auch ein
trockener Sommer sofort ein Schwinden der Anopheles, wie dass letzte Jahr zeigte.
Auch vom Ausland wissen wir, dass nasse Jahre Malariajahre werden".

6. A sixth ^explanation I have seen in print and also more than once heard ex-
pressed by physicians. It maintains that speculations as to the disappearance of
malaria are of no particular interest. Like all the other great epidemics this has had
its time of raging; its virulence is now over, its time has passed. - This explana-
tion is in my opinion unsatisfactory. In its old area of distribution, where it has
now mainly disappeared, it now and then breaks out again with epidemics by no
means quite insignificant; in the southern part of Europe it is still in many locali-
ties a terrible scourge for the nations, and in many localities in the tropics horrible
epidemics suddenly break out e. g. Sumatra (SCHUFFNER & SWELLENGREBEL 1917
p. 1) and California which have formerly almost been exempt from the disease,
but where the rice culture has created new possibilites for the development of the
Anophelines. - - (FREEBORN 1916 p. 247).

If now keeping in mind the above given facts 1 — 18 (pag. 163—176) with regard
to the biology of A. maculipennis we will nowadays try to answer the question: why
has malaria retreated in our country? why is A. maculipennis no more a carrier of
malaria to man? the question may be answered quite satisfactorily for this little
area. Because, according to its manner of life, it is nowadays quite un-
able to do so.

It will clearly be understood that a mosquito which generally only sucks blood
upon our farm animals and not upon man, which is to such a high degree dome-
sticated that during the blood sucking periods it takes its sojourn in the stables,
which now appears as an extremely sluggish animal, only leaving the stables for
the sake of mating and egg laying, is really quite unable to be the intermittent carrier
of a parasite from man to itself; it is unable to create those mighty epidemics
which formerly spread in all directions with the rapidity of lightning, and it is un-
able to keep even a relatively slight epidemic alive.

If however this is right it will be understood that the mosquito, if it has
transferred the malaria to man in our country a century ago and does not do so
now, must have altered its manner of life in the course of a 'century.
The question is then, why it has done so. Before we answer this question, we shall
call attention to the following fact.

The retreat of malaria in our country is, as well known, by no means a
phenomenon restricted to these parts; it is common to the greater part of Europe,
but especially to the part north of the Alps. In Norway it has always been ex-
tremely insignificant, if present at all. In Sweden just as in Denmark it was of
an extremely dangerous epidemical character a century ago or more. It raged
especially along the Gulf of Bothnia, round the large Swedish lakes and southwards;
the epidemic lasted longer in Swreden than here, i. e. from 1875 to 1908 no less

177

than 60.449 attacks are noted, then the curve falls rapidly; in 1909 only 45 cases are
known and nowadays it may be said that it has almost totally disappeared.
(FLENSBURG 1911 p. 1213).

In England the malaria was a real scourge a century ago; now England is
almost quite free from malaria; it seems only that a few cases may still be noted
in a few localities (Romney marsh)-. See NUTTALL & SHIPLEY (1901 p. 26); LANG
(1918); CARTER (1919 p. 2605).

Also in France malaria has retreated, but still there are rather large areas
where it is still prevalent but always in a very mild form (Bretagne, Vendee, Cha-
rente, Gascogne, along the Mediterranean coast, in the Valley at the Somme a. o. loc.)
I refer especially to the papers of ROUBAUD. The case is the same in Holland,
but small hotbeds of malaria are still present (SCHOO 1902).

In Germany malaria raged vigorously a century ago, now it has receded to
a high degree; but still there are many localities, especially along the river valleys
and along the coasts of the North See and the Baltic where malaria occurs; it may
retreat for some years but on special occasions (vast inundations, great engineering
works) it appears again. German physicians urge that even if the disease diminishes
its significance can by no means be underrated; it reduces the mental and bodily
power of man, and causes painful neuralgias which last throughout life. MARTINI
(19204 p. 18) calls attention to the fact that: "Kinder erkranken haufig so atypish, dasz
die anschlieszenden Kindererkrankungen nicht als das erkannt werden, was sie sind".

It is further stated that the farmers use quinine and only rarely apply to the
doctors; it is therefore difficult to see how widely spread the disease really is. With
regard to German and Austrian malaria from recent years I refer to CZYGAN (1901
No. 37) MARTINI (1901 p. 44; 1902 p. 147). PFEIFFER (1901 p. 246). GROBER (1903
p. 601). MUHLENS (1909 p. 166; 1912). STORCH (1914 p. 77). MALISCH (1914 p. 763).
EUGLING (1917 p. 65). STEUDEL (1917 p. 21). SCHAEDEL (1918 p. 143); I refer especi-
ally to the valuable papers of MARTINI (1920! p. 1 and 19204 p. 1).

Formerly the whole of Russia to the 63. degree of latitude suffered from the
epidemic, and curiously enough in Finland rather serious epidemics still appear
(se f. i. LEVANDER 1902 Nr. 3); more especially the districts of southern Russia round
the Black Sea and the Asow Sea are attacked.

In Italy malaria has receded to a very high degree but this is mainly due to
the very hard and extremely successful struggles of GRASSI and his school against
the disease; still the number of cases especially in the southern part of the country
is high.

On the Balkan peninsula it still rages with almost undiminished strength;
in Grece alone there are nowadays about 800.000 cases yearly. The disease is here
still of the greatest hygienic and economic significance. It is a well-known fact how
terribly the oriental army suffered in the Balkans during the world war (NICLOT
1916 p. 753).

We now know that the European malaria mosquito which more than any

1). K. I). Vidensk. Selsk. Skr., naturvidensk. og niathem. Afd. x Haekkc. VII. 1. 23

178

other is the transferrer of malaria to man north of the Alps as well as south of
the Alps, is invariably ^4. maculipennis; \\e must take it for granted that it trans-
ferred malaria north of the Alps a century ago and we know that it does the same
south of the Alps this very day. Our question set forth on pag. 186 why it does
not transfer Malaria any more in Denmark may therefore be amplified to: Why
does it. not with some few relatively insignificant exceptions transfer
malaria any more over the whole of the central European plain and
over North Europe as far as about the 63. degree of latitude. If the
question be put in this form every one will see that the above-named old explanations
are not satisfactory; this has also been clearly understood by almost all investigators
Irom more southern countries than my own.

Just as in our country it has been thought that A. maculipennis was rather a
rare insect everywhere. Fearing the outbreak of malaria from troops arriving from
Nubia or the orient and coming back to their homes, or sent back as prisoners,
the nations have during the war tried to clear up the conditions of new malaria
outbreaks in their countries. Indifferent countries the occurrence of .A. maculipennis
has therefore been studied. Curiously enough the attention has been directed speci-
ally towards the larvae. Without entering into details I shall restrict myself to remark
that in all explored areas the result is that want of Anophelines is never or
very rarely found. I refer the reader to the following literature: Austriche:
(STORCH 1914 p. 77); Suitzerland GALLI VALERIO (19172 p. 1566); France: ROUBALD
(1916 p. 203; 19182 p. 430); LEGER and MOURIQUAND (1917i p. 16); PETIT and TOUR-
NAIRE (1919 p. 332); LAGRIFOUL and PICARD (1918 p. 73); MANDOUL (1919 p. 779); Bal-
kan: NICLOT (1916 p. 753); Germany: I refer only to the list of litr. in: MARTINI (1920!).
In England SHIPLEY and NUTTALL (1901— 1903^: LANG (1918). JARVIS (1919 p. 40)
has pointed out that from Charing Cross as the centre and with a radius of nine
miles A. maculipennis has been found in London itself in 16 localities. See also
BACOT (1918 p. 241). That the summers should have been too cold over this vast
area during the last century is impossible. That the quinine treatment of the
nations should have been of such a perfect kind that malaria should have died out
owing to this cause is, as far as I can see, a supposition which appeals less and
less to naturalists and physicians the more southerly the area of exploration is
situated, and less and less the more the matter is discussed owing to new experience.
Even if the houses are nowadays better constructed everywhere and the mean
temperature of June — July should be lowered, it is highly improbable that malaria
from these causes should almost disappear from the half of Europe. It is therefore
intelligible that in recent years new explanations have been tried.

I shall here mainly deal with one set forth by the best names (GRASSI, SCHAI DIN,
CELLI, LAVERAN; see ROUBAUD 19172 p. 401 and 1920 p. 181). It maintains that the
Anophelines of the North, owing .to a natural or acquired quality have lost their
receptivity with regard to the Plasmodia. This explanation was however subverted
by ROUBAUD (19182 p. 430). He took Anophelines from Paris made them sting malaria

179

patients, pointed out that they got cystes on the alimentary canal, made them sting
himself and got malaria which, in spite of quinine treatment, persisted almost for
two years. Quite similar experiments were made in other countries and always with
the same results. The supposition that ^4. maculipenms should he divided in separate
geographical and biological races some of which have receptivity with regard to
Plasmodia, others not, is therefore unquestionably wrong.

It is also in accordance with the statement of ROUBAUD that the war with its
transport of troops etc. has actually as was expected carried malaria into areas where
it was not found; the troops have infected the Anophelines, after which these have
brought the malaria to natives, who for a long series of years have never set foot
on infected territories. I shall here not enter into details but only refer to the following
cases which may be augmented with a long series of others; most of them derive
from the west front or from England. JEANSELMK (1916 p. 693); ROUBAUD (191 1^
p. 171); CAILLE (1918 p. 282); PEJU and CORDIER (1918 p. 1039 and 1919 .p. 23); PEJU
(1919 p. 1267); BRULE and JOLIVET (1916 p. 2304); JAMES (1919 p. 37). BACOT (1918
p. 241). MALONE (1919 p. 202). MACDONALD (1919 p. 669). ROUBAUD (1920 p. 181).
DIBLE (1915 p. 577). ROBLIN (1919 p. 605). The interesting and very consoling fact
with regard to all these cases is, that they never give rise to greater epidemics,
and that from an epidemical point of view they have hitherto really been quite
insignificant. CARTER (1919 p. 2605) states that though in 1917 over 10.000 infected
men were imported there were only 231 cases of malaria contracted in England.
In France only 258.

If however great numbers of malaria carriers were spread over areas where
the Anophelines were abundant and, as we nowr know, able to be infected, the
question arises why these malaria carriers have not caused great epidemics. Even
the above cited new investigations have in my opinion contributed to its solution,
but as far as I can see without the investigators having any intelligence of the fact
themselves.

Already in the earlier entomological literature we find it stated that A. maculi-
penms does not suck blood; all these indications derive from the area north of
the Alps. England: THEOBALD (1901 p. 194). NUTTALL and SHIPLEY (1901 p. 10).
Austria: SCHINER according to SCHNEIDER (1914 p. 20). Germany: SCHNEIDER (1914
p. 21). Still in 191 82 (p. 430) ROUBAUD maintained that the Anophelines in North
France are only to a slight degree blood-suckers; it is very often stated that the
mosquitoes of both sexes are flower visitors. These indications are unquestionably
wrong, but still they contain a grain of truth.

Already in 1900 GRASSI (p. 82) pointed out that the Anophelines suck blood
upon all mammifers also birds especially fowls; they show no particular predilec-
tion for man; if a horse and a man be placed in the same room, the horse will
be attacked before the man, but if man and a rabbit are placed in the same room,
it is man who will first be attacked. It is the volume of the evaporating smelling
surface which guides the mosquitoes. Various authors further maintain that it is

23*

ISO

almost impossible to get the Anophelines to suck blood upon man. CELLI and
GASPERINI (1902 p. 141) indicate only 35 p. 100, and the same authors maintain
that in Toscana the Anophelines prefer cattle to man. The very same results
were also arrived at by ROUBAUD who maintained that A. bifurcatus attacked in
the open air, but this is not the case with regard to A. maculipennis. GILES says
that in England it is only in hot weather that mosquitoes show any strong ten-
dency to attack human beings. TANZER and OSTERWALD (1919 p. 689) have shown
that A. maculipennis have abandoned the rooms and retreated to the stables; they
suppose because the rooms nowadays are cleaner than formerly. JAMES (1919 p. 37)
maintains that houses as a condition for visitation by Anophelines must have a
large amount of domesticated animals. DOFLEIN (19182 p. 1214) shows that A. ma-
culipennis is constantly to be found in stables. MUHLENS according to MARTINI (1920!
p. 60) has as stated above ascertained by means of the Uhlenhut proof, that the
blood in the Anophelines of the stables really derives from swine and horses.

PRELL (1917 p. 242) has also arrived at quite similar results; his paper being
one of the most instructive with regard to the biology of our two most significant
^4nop/}e/es-species. According to him A. maculipennis is mainly to be found in stables,
not so much in outhouses, mostly in the cow-houses, not so much in hog-pens; in the
horse-stables they are most common in the clean well ventilated stables; just like
myself, PRELL has seen that swallows in stables diminish the number of mosquitoes.
They occur mainly on the ceiling, often in enormous numbers. He says: "In Abstanden
von knapp 1 cm, von einander sind sie dann manchmal unter moglichster Ausnut-
zung der Flache so dicht und gleichmassig verteilt, dasz sie geradzu in Reihen auf-
marschiert erscheinen und wie ein Schleier die Decke uberziehen". He has further
observed that the Anophelines hang down perpendicularly from the ceiling and use the
hind-legs as organs of feeling; also that almost all specimens are blood-filled and that
they are extremely sluggish: "Der vollgesogene Anopheles legt eine ausserordentliche
Flugunlust an den Tag. Jagt man ihn auf, so fliegt er oft nur einige Cm., selten
Tiber einen Meter weit fort". In the stables the mosquitoes ripen their eggs; he has
correctly seen that among the many red individuals also others are found which
have an almost white abdomen, owing to the ripening eggs. - - Curiously enough
the main result of my own observations that A. maculipennis nowadays really may
be regarded as a domesticated mosquito is not in accordance with PRELL'S view:
He says: "Anopheles ist eben keineswegs ein "Haustier" sondern eine "Wildart", die
nur zum Blutsaugen in Stalle kommt und beinahe mochte man sagen widerwillig
dort langere Zeit zuriickbleibt". I regard it as highly probable that this supposition
may really be correct for Wurttemberg where PRELL has made his investigations;
for my country, nearer the northern limits of the distribution area of the species,
it is not so, however (see later).

Among the many other observers from recent years who have arrived at the
same results as myself, I especially refer to the following: MANDOUL (1919 p. 779);
PEJU and CORDIER (1918 p. 1039). PEJU (1919 p. 1267). MACDONALD (1919 p. 669).

181 .

LANG (1920 p. 75). PRELL (1917 p. 244). VOGEL (1917 p. 1509) and hereto may also
be added some remarks by MUHLENS with regard to the malaria outbreak in Wilhelms-
hafen (1909 p. 169); MARTINI (1920).

Curiously enough in the great work: Studies in Relation to Malaria, the authors
of the first part (NUTTALL, COHHELT and STRANGEWAY-PIGG) seem to show that they
have never any idea of the occurrence of A. maculipennis in stables.

It will now firstly be understood that the main results of my own observations,
that the Anophelines do not attack man, that they suck blood upon our domestic
animals, and that they show a remarkable predilection for stables in comparison with
our dwelling rooms have all almost simultaneously been corroborated by a
great many observers; about the correctness of the observations there can now
be no dpubt. It may be regarded as a matter of fact that, wrhat I thought had validity
only for Denmark, is really valid for almost the whole of Central Europe, Great
Britain, and for some few areas to the south of the Alps (Toscana). To me how-
ever it is rather a remarkable circumstance that of these many foreign observers
all unknown to me, who have almost in some measure made my now published
investigations superfluous, and among whom many understand that all the old ex-
planations of the fact that malaria has receded from such vast areas of its former
territories, are insufficient, no one, as far as I know, have understood what, in my
opinion, must necessarily be inferred from all these investigations.

For it can now be proved that, over the vast area - - more than half of Eu-
rope - - where formerly A. maculipennis brought down disease and often death on
mankind, the peculiar phenomenon now prevails of an Anophelism without malaria,
already known as a remarkable exception in one of the fatherlands of malaria in
Europe. From these many investigations, carried on independently by each inves-
tigator without any knowledge of the researches of the other workers in the same
field, we are now able to show that the real cause why malaria has receded from
the greater part of Europe is that A. maculipennis has lost its co nnection with
man. If nowadays after the war no outbreak appears North of the Alps,
this must in my opinion partly be referred to this fact.

Secondly it must be understood that over vast parts of distribu-
tion a change has taken place in the habits and biology of the mos-
quito within the last century. That this has been the case can in fact
be shown.

Apriori it may be regarded as a matter of fact that when the Anophelines
even nowadays in South Europe especially in the Balkans, but also in Italy, yearly
transfers malaria to hundreds of thousands of people, it 'cannot live its life
there as it nowadays does in more northern latitudes. In his excellent
work GRASSI has elaborated the biology of A. maculipennis in an admirable man-
ner: "He writes (p. 58) that during the summer months numerous specimens of A.
maculipennis remain outdoors in Nature, p. 105 he further writes: "Die A. claviger stecken
sowohl im Freien wie in den Hausern und in den Stallen. In den Malariagegen-

den wiederholt sich sehr viele Tage hindurch gegen Sonnenuntergang das Schauspiel
unzahliger Schaaren von A. claviger, welche die sich an den Thuren unterhaltenden
oder Abenbrod essenden Menschen angreifen. . . . Im Freien konnen die Anopheles
claviger, nachdem sie gestochen haben, auf die in der Nahe stehenden Baume flie-
gen und sich dort verstecken. . Die Miicken ruhen sich haufig auch auf den
ausseren Hauswanden aus und bleiben dort mehrere Stunden sitzen, am nachsten
Morgen aber sind sie nicht mehr verhanden. . . . Wir sehen sie die Beute in von
weniger oder mehr entfernten Orten her kommenden Schaaren anfallen. Im Allge-
meinen steht fest dasz sie durch jene Fenster und jene Thuren in die Hauser ein
fliege die nach der Richtung des Wassers liegen u. s. w." SAMBON (1901 p. 195) says
as follows : "During summer the A. maculipennis do not seem to remain long in the
houses and stables. Their number varies greatly from day to day in the same room.
Fresh specimens arrive every evening, gorge themselves on the blood . . . hide for
some hours in the darkest corner they can find and go out again in the morning
or the next evening". -

At Maccarese GRASSI says that in July at 21 t. 30 he has hardly been able
to defend himself against A. maculipennis; this was the case whether he "was in the
house or out of doors. Also LEGER (1913 p. 41) records that he has caught A. m«-
culipennis in many hundreds in the houses and on the railway stations in Corse.
With regard to tropical Anophelines DONITZ (1902 p. 20) says: "dasz die Tiere sich
sogar, nachdem sie sich mit Blut gesattigt haben, die Hauser welche ihnen nicht
zusagen verlassen um sich in Freien -zu verbergen. Already in Poland MARTINI
(1920 p. 61) indicates that at sunset A. maculipennis was flying as well in through
the windows as out of them. With these statements in mind the above-named diffe-
rences between PRELL'S and my views with regard to A. m. as a domesticated mos-
quito are intelligible.

From these indications we now learn that A. maculipennis at all events round the
Mediterranean lives a life quite as we should expect the mosquito to live
if it were to be able to transfer malaria to man. At any rate it is here to
a rather high degree even nowadays an outdoor species which is on the wing to
find its prey over rather considerable distances, and to a very high degree it sucks
blood upon man.

It is thus actually proved that there is the greatest difference in the manner
of life of A. maculipennis in South Europe and at the northern limits of its area
of distribution. In my opinion it is neither quininisation of mankind alone, nor
water drainage of the field, nor lowering of tp., but just this alteration in the
biology of the species, the very peculiar transition from an outdoor
species sucking upon man to a stable insect sucking upon our farm
animals which has been the main cau se of the disappearance of malaria
from its northern limits.

The question now arises: what has caused this transition? I do not dare
to solve it for the niany foreign countries but I think I am able to do so for my

183

own country. Only with some doubt do I now enter territories of human know-
ledge which have nothing whatever to do with limnology and only very little with
zoology generally; we must now turn our attention to agricultural history, to
the great changes in agriculture which our country has been subject to in the for-
mer century. I beg Prof. Dr. JOH. STEENSTRUP to accept my best thanks for the help
he has given me upon this point. It is a well-known fact that in the eighteenth
century, and still in the first quarter of the nineteenth, the swine were driven to
the woods where they lived on mast; special swine stables were hardly known.
Horses and cattle lived the greater part of the year out of doors, many of them
the socalled "Udgangsog" (jades) the whole of the year. At that time Danish agri-
culture was based upon cereal culture; a little after the middle of the nineteenth
century, after the establishment of cooperative dairies, the stress wras laid upon the
greatest possible production of bacon, meat, milk and butter. Then it was no more
possible to let the farm animals live almost their whole life out of doors. Year
after year the stables became better and better; larger and larger; the number of
animals continually greater; the time in which the animals lived out of doors
continually shorter; the hogs were almost all their lives bound to the hogpens,
the cattle was often kept in the stables the whole year round or, apart from a
very short summertime, driven into the stables before night. The stables were bet-
ter and better lighted, during the last century often by electric light.

It will be clearly understood that this change in Danish agriculture must of
course be of the greatest significance to the Anophelines; for during a great part
of their flying time the large mammalia year after year disappeared
from their flying areas. But not only the domestic animals disappeared, man
himself by no means lived as much in the fields as hitherto; the agricultural ma-
chines make the extensive use of manual working power superflous. Where formerly
at harvest time long rows of harvesters and harvest women could be seen in the
fields for more than three weeks we now only see a few selfbinders going their
way round over the fields.

But simultaneously with the disappearance of all warm blooded animals from
the fields, in our warm well-lighted stables we created refuges which acted upon
the mosquitoes as large thermostats spread in many, many thousands
all over the country; the odour from all the large animals streaming out on
the still evenings through open doors and windows, the heat which thermically
attracted the mosquitoes, and the light which attracted them phototactically, con-
verted the stables for our Anophelins, which were on the wing in the evening in
search of prey, into thermical and lighted traps by which the mosquitoes
instinctively governed their flight. Inclosed inside the stables they found
all that they wanted for their life: plenty of food, a suitable temperature, darkness
and no draught; only the conditions for mating and egg-laying processes were
wanting, but apart from them life in the stables was really possible for flying in-
sects. Arrived in the stables and, owing to the much stronger odour and greater

184

heat, attracted more by the large mammals than by man, the mosquitoes with
great skill helped themselves to what was on the table. But simultaneously
with that the connection between man and mosquito was broken, and
malaria was bound to disappear from our country.

That there really is a connection between the alteration in agricultural methods
and the disappearance of malaria is made highly probable by the fact that the
rapid fall of the malaria curve coincides with the above-named alter-
ation in agriculture during the period 1860 — 1880. It is this alteration
which in my opinion is the real cause of the variation in their manner of life which
the mosquitoes especially north of the Alps have undergone. - - How little of mere
theory there really is in the above-named facts will be seen if we study the new
literature relating to the biology of mosquitoes. With regard to the influence of light
upon mosquitoes e. g. C. pipiens and A. maculipennis, WEISS (IQlSj p. 12) calls attention
to the fact that the mosquitoes only fly towards evening and are attracted by light of
moderate power; this is corroborated by BENTLEY (1914 p. 9) who states with regard
to the Anophelines in India that they are attracted by light. This is in accordance
with the fact that the ravages of malaria are more severe in open villages than in
those situated in forests; that hedges round the houses prevent malaria, that the strong
light from the bungalows of the Europeans attract the mosquitoes. See also HOLMES
(1911 p. 29) and MARTINI (1920X p. 21) who correctly states that the species in this
respect differ very much from each other. With regard to the influence of warm
air upon the Anophelines MARCHAND (1918 p. 130) shows that A. punctipennis, quite
like Stegomyia fasciata, is guided by thermotropisms in its instincts with regard to
bloodsucking; warm air which pours out from test tubes attract the Anophelines;
this is not the case with all mosquitoes e. g. not with those of Aedes (f. A. sylvestris) ;
finally as mentioned above GRASSI points out that the Anophelines are attracted by
the smell which radiates from animals, the more strongly the larger the animals are.
WALKER and BARBER (1914 p. 381) have shown that the role played by a species of
Anopheles in the transmission of malaria in any country is proved to depend chiefly
upon (1) its susceptibility (2) its geographical distribution and prevalence (3) its
avidity for human blood and (4) its domesticity : Whereas if the avidity for human
blood diminishes, the role as a malaria carrier disappears.

When really A. maculipennis in the course of less than a century has been able
to or perhaps rather forced to alter its life in our country the cause is in my opinion
that here it lives near the limits of the northern area of distribution.
The cold evenings in spring and autumn have most probable always been the time
of the year, especially in a rather long series of years with lower mean tp., which
have been difficult for the mosquitoes to pass through. Just at that time of the
year, before the cattle is driven out of doors, and in the autumn where it is driven
back to the stables we have in the middle of the last century created thermi-
cal refuges for the mosquitoes in the stables : I am inclined to suppose that in the
more southern countries the time in which the mosquitoes have profited by the

185

stables owing to the climatic conditions is much shorter than here. The length of
time in which the mosquitoes year after year have been able to accustom them-
selves to the new life conditions is greater the nearer they are the northern limits
of their area of distribution; in accordance with this the indolence and sluggishness
and the diminishing life out of doors is augmented in the direction from South
to North.

When further malaria has retreated almost completely from all countries north
of the Baltic, two other reasons have cooperated. Simultaneously with the always
increasing tendency to suck upon cattle the possibility to transfer malaria to man
in the transition period where man as well as cattle was stung became always less
and less owing to quininisation; the old malaria carriers died out and the number
of new cases became fewer and fewer year after year. But also upon another point
did the situation of our country near the northern limits of the area of distribution
of A. maculipennis influence the rapid disappearance of malaria.

Till 1915 it was unknown whether the plasmodia were able to hibernate in
the mosquitoes. This has been supposed and has been maintained even in recent
years. LENZ (1917 p. 830) maintains that the scizonts circulate in the blood during
the flying season of the Anopheline generation that has hibernated. In the case of
later generations of Anophelines the conservation of the plasmodia is ensured by
new infection. STEUDEL (1917 p. 21) maintains that among the hibernating Ano-
phelines in a locality on the east front there was a large number of carriers. As
far as I can see, the indications by LENZ and STEUDEL have not been scientifically
elucidated. On the other hand MITZMAIN and ROUBAUD have showrn that hibernation
does not take place in the mosquitoes.

MITZMAIN (1915 p. 2117) showed that with regard to A. quadrimaculatus this
could not be the case. Of 1100 specimens, gathered in negro barracks inhabited by
malaria patients, the intestines of all 1100 were quite free from cystes during the winter.
The first cystes appeared on 15. May. More thorough investigations in 1917t (1917 p. 29)
show quite the same thing. In 2.122 hibernating Anophelines not a single individual
with cystes could be pointed out; simultaneously MITZMAIN' shows that in exactly
the same area, of 1.184 persons 492 have malaria; the first infected Anophelines
do not appear before 15. — 26. May. In 19172 (p. 1400) MITZMAIN shows that low
temperatures during the hibernation destroy the cystes, and are a hindrance to the
development of the sporozoits in the cystes. In other words, mosquitoes which have
got blood with gametocysts during the winter will be sterile during hibernation.

The above-named results of MITZMAIN are in full accordance with the results
of the investigation of ROUBAUD (1918! p. 264) that in A. maculipennis infected with
malign tertian malaria the sporozoites will be destroyed if they are not very soon
carried out with the sputum; further that they are discharged through a relatively
small number of punctures. In 19182 (p. 430) ROUBAUD then showed that hiberna-
tion also in the salivary gland is an impossibility. The Anophelines which he in-
fected in October, and which in March — April during the hibernation only got water,

I). K. I) Vidensk. Selsk. Skr., naturvidensk. og matheni. Alii. 8. R.-rkke, VII, 1. 24

186

did not show the slightest sign of infection. He maintains that at all events in
France, and that most probably means in all more northern countries, the plasmo-
dia are only able to hibernate in man and not in the mosquitoes. REGENDANZ (1918
p. 33) comes to a similar result. He maintains that the temperature needed for the
plasmodia to develop in the mosquitoes in Roumania is not reached before the end
of June when the day tp. was usually over 25° C. and the night tp. was only ex-
ceptionally below 16° C.

It will clearly be understood how significant these indications really are; and
this especially holds good the nearer we are the northern limits of the area of
distribution. For it means that the Anophelin material, every year before
the blood sucking period begins, is totally free from plasmodia. Those
which had plasmodia before the winter are now free, and the new brood will as
imagines be born quite as free from plasmodia as their mothers were. Only when
sucking upon malaria patients will the Anophelines get plasmodia; the hibernating
females perhaps a second time; the harvest of the summer the first.

Those Anophelines which begin therr blood-sucking period in spring are al-
ways free from malaria; it is man himself who year after year must infect the
Anophelines again if the disease is to be spread. The longer the winter is, the
smaller is also the chance of a serious infection of the Anophelin material; the
shorter the time of the summer in which the temperature is above about 16° C.,
the smaller is the chance of the development of gametocysts, even if the Ano-
phelin material has been affected. It will be clearly understood that just at the
northern limits of the area of distribution, where the whole period of bloodsucking
is restricted at most to five months, it is of the greatest significance that the sum-
mer campaign of the mosquitoes begins with uninfected material. Just here a
treatment with quinine will in a comparatively short time restrict the chances of
disseminating the plasmodia, especially because the Anophelines are inclined to prefer
the blood of domesticated animals, and in this way loosen the ties which connect
them with man.

The question is now whether the view which I maintain with regard to the
retreat of malaria from our country also holds good with regard to the vast foreign
territory, from which it has also almost entirely disappeared. I suppose that the
same theory also holds good with regard to Sweden, but I do not venture to form
any opinion with regard to the other, southern countries. I only wish to call atten-
tion to the fact that in South Europe where A. maculipennis still attacks man, hor-
ses and cattle as far as I know live out of doors most of the year, and the stables
are not so large, so closed and so sheltered as in our country; the difference be-
tween the temperature out of doors and in the stables is not so great.

There are still some few points to discuss with regard to the biology of the
Anophelines living near the northern borders of the distribution area, and North

187

and Central-European malaria. As mentioned above, even nowadays small epidemics
of malaria now and then break out in the regions round the Baltic or North Sea.
(Holland, Ditmarshen, Wilhelmshafen, Finland); only Sweden and Denmark have
been spared. The curves of these epidemics are very peculiar. . Already C. A. HAN-
SEN showed that the climax of the malaria curves with regard to the old Danish
epidemics was in May, and FLENSBURG has shown the same with regard to Swe-
den; it was and is even nowadays the same with the greater part of Germany.
(See especially MARTINI 1902 p. 147). On the other hand in Italy the climax lies
in Aug. — September. In all cases we have to do with the curve of fresh cases (not
relapses) and with tertian malaria. ZIEMANN (1918 p. 123) points out that it seems
as if .the climax of the curve the nearer we get towards the north, has a greater
and greater tendency to be displaced towards the left side. KOCH (1899), who
is well aware of the phenomenon, supposes that it must be understood as follows:
The inhabitants north of the Alps, by heating their houses, create in them tempera-
tures for the mosquitoes lying above the temperatures to which the mosquitoes in
more southern countries are exposed at the same time of the year, and tempera-
tures by which it is possible for the parasites in the mosquitoes to develop.

SCHOO (1902 p. 1343) has arrived at quite the same result: He shows that
Anophelines caught indoors in Holland, and which were freshly infected, got "Sichel-
keime" in the course of twelve days. It wras only necessary that the mosquitoes,
immediately after the infection, only for two days should be exposed to a tp. of
25° C. If this was the case the tp. might sink from 22 to 10° C. without damage
to the parasites. At a constant tp. of 18° C. the parasites in Anopheles used 18 days
for development and at 30° C. only ten.

The suppositions may have been correct for the old malaria epidemics north
of the Alps; it is also possible that they hold good for the smaller epidemics in
Holland and Germany at the beginning of the last century. But I venture to remark
that if we in our country should get another malaria epidemic and the curve should
show the vertex in the same place (in May) as in the curve for the old epidemic in
the middle of the ninteenth century, this explanation could not be used. - - Our Ano-
phelines do not hibernate either in dwelling rooms or in stables, they hibernate in
outhouses and similar localities; here they hang till the latter part of April, not
leaving the hibernating places to enter our stables before then. They do not begin
to sting before the middle of May. For Finland LEVANDER states that the Anophelines
do not arrive in the rooms before the first days of July. It must be taken for
granted that they all are free from plasmodia and first must infect themselves. That
an Anophelin material of this kind should be able to cause a climax of the curve
already in May is highly improbable. On the whole I am not quite sure that the
explanation of KOCH and SCHOO of the malaria curve for North Germany and Holland
really holds good. Further explorations are desirable. - - It must be remembered that
we have not the slightest understanding of the fact that the enormous amount of
Anophelines which are hatched during summer, and in comparison with

24*

1 88

which the hibernating material is only a very inconspicuous fraction,
does not seem to influence or to have influenced the malaria curve in
any way. From our present knowledge of the malaria-plasmodia and the Ano-
phelines we are able to understand a malaria curve with its climax in August,
such as is the case with Italy, and a curve with two climaxes, one lower in May,
and a much greater in August— September.

Curves of this kind are in fact pointed out for several epidemics north of the
Alps (Ditmarshen 1842 bis 63; DOOSE in Hirsch 1881 p. 175); Wilhelmshafen (WENZEL
1870 p. 28) but they are not the rule. The very curve which in my opinion we
are not able to understand, a curve with only one vertex lying in May — June, is
that which seems to be the rule for all epidemics north of the Alps. It is only in-
telligible on two assumptions, which in my opinion are both equally improbable.
The due is that the Anophelines of the summer have sucked parasites into the
intestine, have formed their oocystes and hibernated with them on the walls of the
intestines and then in spring infected man. This is improbable according to all
more thorough investigations, which seem to show that the parasites hibernate
in man and not in mosquitoes. The other assumption is that the- summer-

broods really give malaria to man but that it is latently present till May; man
lives with the parasites during winter, but the outbreak does not take place before
May. This indeed is by no means in disaccordance with the nature of malaria; it
is a well-known fact that a very long time may pass before a malaria attack pro-
duced either by external or internal, physic or psychic conditions, really breaks out.
See e. g. the report by KIRSCHBAUM (1917 p. 1405) on the malaria outbreak in
North West Russia in February in ice and snow. Quite a similar result is arrived
at by WERNER (1917 p. 1375). Yet also this supposition must be regarded as an
absurdity. For we are quite unable to understand why the malaria transferred by
hibernating mosquitoes in April — May invariably should be able to influence the
curve after the course of a few weeks and produce the high-lying vertex in the
course of only a few weeks, whereas that malaria which is transferred in the sum-
mer months does not in any way influence the curve before eight months later; if
the summer-generations had transferred malaria we should have expected a second
vertex on the curve a few weeks later. See also MARTINI (1920! p. 69).

ZIEMAN has pointed out that if there was any possibility that the Anophelines
infected themselves, that the parasites from the mother mosquito were transferred
to the eggs and from them through larval and pupae into a new generation, the
malaria curves would be more intelligible. As well known, both SCHAUDIN and
DOFLEIN (1916 p. 933) have reckoned with this possibility. Moreover the supposition
is allowable because others of our great parasitical diseases, e. g. Texas fever, really
are spread in this manner. As far as I can see here is really a point where more
thorough investigations are desirable. But even if it should be shown that the Ano-
phelines are able to infect themselves this would not help us in our case. For north
of the Alps we have really only one malaria carrier i. e. A. maculipennis, and even

189

this species hibernates as imago and the new broods do not appear till simultane-
ously with or after the climax of the curve has been reached.

Coincident statements from almost all countries further show that the malaria
epidemics, like almost all epidemics, occur in time-waves of different length. It seems
that these waves occur almost simultaneously over a great part of Europe; it fur-
ther seems that these waves come a little later to the northern countries than to
the more southern ones. Great malaria waves occurred in 1812—16; 1819 — 21;
1830 — 32; 1846 — 48; 1853 — 62; from that time on it has, with a few exceptions,
almost disappeared from the area north of the Alps. Nowadays these waves can
only be understood in this way that the Anophelin material was also affected
periodically; we must suppose that in four or five periods of about two to six
years, the Anophelin material was affected by plasmodia; during the trough of the
curves the Anophelines have not been attacked or only to a slight degree; even if
we are now able to show that the great malaria years coincide with high tempera-
tures and great humidity of the air, it is rather difficult to understand that these
variations in external conditions are able directly to influence the actual percentage
of mosquitoes attacked by plasmodia.

With regard to our own country it is very difficult to understand from where
the enormous amount of infected Anopheles material which must be regarded as a
condition of the great malaria epidemics formerly, was derived. This more especially
holds good for Lolland and Falster, islands with very few lakes and moors. We
must suppose that a large amount of larva? have been hatched along the shores
of the Baltic. It is a well-known fact, that A. maculipennis does in fact breed in
brackish water. LEVANDEK (1902 p. 10) maintains, that the predominating breeding
places for the Anophelines in Finland are the small bays of the Gulf of Bothnia,
and still in 1919 I myself found many larvae of A. maculipennis in the small seclu-
ded bavs on the southern coasts of Lolland.

I have in the above only wished to call attention to the incongruity between
curves and our present knowledge with regard to plasmodia and mosquito life.
Perhaps the whole question is not of much consequence; how great credence we
can give to these old curves is doubtful; and with regard to new ones, they will
most probably be very difficult to use as working material, because they will be
influenced by the fight which we shall take up against the disease. If these investi-
gations are carried on, especially in North-Germany, it would be of interest to find
out whether it was only the hibernating Anophelines which in early spring sucked
upon man, where as the summer generations sucked upon cattle. If this should
really be the case, the peculiar malaria-curves in North Germany would be more
intelligible.

Whether we consider the malaria curves from the single years or the curves
for the whole of the last century we shall almost be forced to assume, more especi-

19(1

ally with regard to the northern limits of the distribution area both of the Ano-
phelins and of malaria, that, in our knowledge of malaria, there still remains something
unknown. This has also been corroborated by others. The old question of BACCELLI:
"Gesetzt die Stechmiicke infiziert den Menschen und der Mensch die Miicke, wer
infi/iert sie beide" (GRASSI 1901 p. 199) has in my opinion not been answered yet.

When this chapter was written and used for a discourse in the Royal Society
of Copenhagen in April 1920, Prof. C. J. SALOMONSEN kindly called my attention to
a new paper by ROUBAUD just published. To my great satisfaction I saw that in
our main results we coincide upon almost all points. As however ROUBAUD and I
have approached the subject from quite different points of view, our two papers
supplement each other in a remarkable manner.

As a foundation for ROUBAUD'S elaborate and highly meritorious work lies the
idea of studying the ''rapports nutritifs des Anopheles avec 1'homme et les animaux"
(1920 p. 187). Originally this was never my intention. During my studies relating
to the biology of the mosquitoes I was of course also in search of A. maciilipennis;
struck by the peculiar fact that I never could find it in Nature I accidentally found
it in a stable; in spite of my very cursory knowledge of Danish malaria and my
being without any knowledge of foreign malaria, my whole knowledge being really
restricted to the fact that malaria was formerly a terrible disease in our country
and had nowadays disappeared, I, in the course of a few days, understood that
here most probably was a possibility of understanding the main causes of the pecu-
liar disappearance of the disease. - - On very many points ROUBAUD and I coincide,
upon a main point we differ, and in the main result there is some discrepancy; this
is however only apparently, and is due to the fact that our areas of exploration are
in different latitudes; in my opinion our results really coincide.

ROUBAUD has in two localities examined the relation between the Anophelines
upon one side and cattle and man upon the other; one locality is the Vendee
region, the other the environs of Paris. It has formerly been remarked that A. ma-
culipennis is almost domesticated in Vendee, a locality which may be regarded as
classical with regard to malaria, whereas it rarely approaches man in the neigh-
bourhood of Paris. This different behaviour of the mosquitoes in these two locali-
ties has been explained as a result of the climate.

Even though this may be correct it must however be kept in mind that
malaria has raged and does so still in various regions of northern Europe, where
the temperature is much lower than that of la Vendee. The main question, there-
fore, which ROUBAUD tries to solve is: Why is Anopheles domesticated in Vendee,
tormenting man and transferring malaria, whereas in the environs of Paris it has
no connection with man. Perhaps I may here insert the remark that even if I
have commenced my investigation with the study of malaria, I have not been able
to solve this or a similar question, nay not even try to set it forth, because in our

191

country we have no malaria anywhere and because, as far as we know, A. maculi-
pennis is spread over the whole country almost in an equally large number. If now
we compare the results of ROUBAUD'S investigations on the life-history of A. maculi-
pennis with mine, we shall find great coincidence.

. He calls attention to the enormous amounts of Anophelines on the ceiling and
walls of the stables; they are rare in houses which are not inhabited by man or
cattle; here we only find some males; in the stables they originally only sought
shelter; now they also look for nutriment there. Even in houses which only con-
tain the stable and a single room for the inhabitants, almost all the mosquitoes are
to be found in the stables; there are none or only a very few in the room. Man
is not attacked by the mosquitoes; they only suck blood upon the domestic ani-
mals; the few mosquitoes which can be caught in the dwelling rooms have almost
always empty stomachs, those in the stables are almost always blood-filled (never
any less than 40 % and often over 90 %). In all these main points there is full
accordance between the statements of ROUBAUD and myself; it must only be remem-
bered that ROUBAUD has only studied the biology during summer and not like my-
self followed the life- history the whole year round. His indications that the Ano-
phelines do not occur in non-inhabited rooms are most probably only correct for
the time he has studied the mosquitoes; at all events in our country the Anophe-
lines entirely disappear from stables and inhabited rooms in the six winter months,
the hibernation taking place exactly in outhouses, unoccupied rooms; the presumed
cause is indicated on p. 164.

The most striking difference between ROUBAUD'S and my results is that the
Anophelines of Vendee are very active animals out of doors. However favourable
the conditions for nutrition may be on the spot where the female has spent the
period of daily rest, this is always abandoned for flight in the open air at night, so
that a new host must always be found for the meal before the next day's rest. The
Anopheline-population of any given shelter is therefore entirely or almost entirely
renewed every night. If therefore all the Anophelines present in a certain building
were captured and destroyed several days in succession, provided that the host
conditions are favourable, the numbers would be constantly replaced, probably
without any noticeable modification of the total. It has been proved by marking
some thousand individuals that the Anopheline fauna of any given spot, however
densely populated it may be, is entirely renewed within a few days; the regu-
lar flight in the open directly observed during night by ROUBAUD has been proved
to be indispensable to the life of A. maculipennis. It will be understood that ROU-
BAUD and I have arrived at quite opposite results upon this point; in Vendee
the Anophelines are on the wing every night during the summer, in Denmark
hardly ever, and only for mating and egg-laying processes ; I have hardly ever caught
an A. maculipennis out of doors. I am sure that both our observations for each
country are quite correct. The Anophelines of Vendee and Denmark differ from each

192

other upon this point in most localities; (Silkeborg?) the difference is due to the
much colder night in Denmark than in Vendee.

Like myself ROUBAUD sees the main cause of the phenomenon of Anophelism
without paludism in the secondary adaptation of this species to animals, especi-
ally in countries where domestic cattle are abundant, whereas the Anophelines
as I have supposed for Silkeborg, also in France, in territories where the
amount of cattle is small, and where vast numbers of Anophelines are hatched,
attack man. He says that in the Vendee region two different sets of conditions
occur; in the dry districts where the Anopheline-density is not very great, the
existing mosquitoes find sufficient nourishment in the cattle of the district; man is
practically free from attack and may even be unconscious of the presence of large
numbers of mosquitoes in his near vicinity; while in the marshy districts, where
the Anopheline density is too great to find adequate nourishment in the cattle pre-
sent, man is undoubtedly attacked, but even then the Anophelines seem to bite
with repugnance and without entirely satisfying their hunger. The conditions in
the Paris region offer a close analogy with those of the non-marshy regions of la
Vendee, namely the occurrence of Anophelines in fair numbers, characterised by the
exclusive adaptation of A. macnlipennis to bovine hosts which are present in suffi-
cient numbers. So complete is this adaptation that the presence of the mosquitoes
often passes entirely unnoticed by man; it is this last case which nowadays is the
rule for our own country. In a very convincing manner ROUBAUD shows how
malaria epidemics, the result of abnormal frequency of contact of A. maculipenms
with man, may suddenly arise in a region well stocked with cattle, merely in
consequence of an increased number of breeding places due to flooding, and a
consequent increase in the Anopheline population, requiring greater nourishment.
This has been known to occur in la Vendee. Further the immigration of small
settlements of people with but littFe cattle into a marshy zone, previously uninha-
bited, may give rise to the outbreak of fresh malaria epidemics. This explains the
occurrence during the war of several small foci of indigenous malaria, reported from
districts poor in cattle.

As a final result of his explorations ROUBAUD says on p. 222: "La constitution dans
1'Europe agricole d'une race d'A. maculipennis essentiellement adaptee au betail, a
permis, pour le plus grand bien de 1'espece humaine, la disjonction des rapports
habituels de 1'Anophele avec 1'homme. Cette variation physiologique n'a pas influe,
d'autre part, nous 1'avons vu, sur la receptivite de la race anophelienne a 1'egard
de 1'infection malarienne. Aussi la possibilite d'injection des Anopheles subsiste-t-elle
entiere. Mais pratiquement, au point de vue humain, le resultat favorable n'en a
pas moins ete acquis, puis qu'en modifiant leur habitudes de nutrition primitives
aux depens de Thornine, les Anopheles des regions a bestiaux out brise le cycle
ferme des parasites malariens".

It will be seen that ROUBAUD'S view and mine almost coincide. The total dis-
appearance of malaria from our country demands however another explanation than

193

that given by ROUBAUD; such an explanation I have tried to give hut I do not
know for how wide areas my explanation holds good (p. 182).

Upon one of the last pages in his work ROUBAUD and according to him les
SERGENTS (p. 222) has corroborated an idea which I have had but which I was
unable to verify. ROUBAUD has pointed out that the specimens of A. maculipennis
from more northern latitudes are of greater size than those in more southern
countries. It seems therefore, that the secondary adaptation of the species to
animals in countries where domestic cattle are abundant, has produced a particular
race of mosquitoes, which is distinguished not only by its tastes and affinities but
also by its greater size.

Most probably ROUBAUD'S indication is really quite right. In this connection
I take the liberty to call attention to the following fact. If we nowadays from our
country compare long series of A. maculipennis with those of A. bifurcatus there is
no doubt that the first named species is longer and larger than A. bifurcatus. This
is also indicated by THEOBALD. According to him A. maculipennis measures 6 to
7.5 mm. A. bifurcatus 5 to 51/* mm, with proboscis 8 — Sl/s mm. If we however take
the old descriptions by ZETTERSTEDT and MEIGEN we shall find that the contrary is
the case; here A. maculipennis is indicated as shorter than A. bifurcatus. MEIGEN
states (1818 p. 11) for A. maculipennis 3 lin. for A. bifurcatus 3l/s lin. ZETTERSTEDT
(1850 p. 3467) for A. maculipennis 21/*— 3 lin. for A. bifurcatus 3 lin. Nowadays there
is not the slightest doubt about the fact that the common size of A. maculatus in
our country is between 6.5 to 7.5 mm. and that the species is larger than A. bifur-
catus. If the indications cf the length of the two species by MEIGEN and ZETTER-
STEDT are really correct, it seems therefore that the average length of the
species has really increased in the course of the last century near the
northern limits of its area of distribution. This is only what we might
expect, according to ROUBAUD'S and my own statements, MEIGEN and ZETTERSTEDT
having measured the mosquitoes at a time when A. maculipennis was no sedentary
stable mosquito but, as nowadays in the Mediterranean countries, a free flying
mosquito.

ROUBAUD is inclined to regard the variations in the habits of A. maculipennis
as "une evolution lente et durable des habitudes alimentaires d'Anophele c'est-a-dire
d'une evolution d'habitudes acquises". I do not agree with ROUBAUD upon this
point. Firstly I wish to remind the reader of the fact that all mosquitoes have
unquestionably, from originally being flower visitors, in the course of time altered
their habits and, with regard to the female sex, are now in many species and genera
blood suckers. This biological variation is much greater than that which A. maculi-
pennis has undergone with us. Further it must be remembered that A. maculipennis
is by no means the only mosquito which has altered its habits over part of its area
of distribution; the same is said to be the case with C. territans, which is a very
angry bloodsucker in America, but does not attack man in Central Europe (SCHNEI-

D. K. D. Viclensk. Sclsk. Skr., naturvidensk. og niathem. AM. 8. Riekke, VII, 1. 25

194

DER 1914 p. 46). We have seen that variation in habits has most probably taken
place also with C. pipiens and T. annulata.

I suppose that the whole question with regard to variation in bloodsucking
habits in mosquitoes must be regarded from the same point of view, viz. that
species with a wide area of distribution are not forced to live their life in quite
the same manner as those of the northern and southern limits of their area. Fur-
ther that when some species are carried out of their normal distribution-area and
are suddenly forced to live in another area, their biological range of variation is so
great that they are able to begin life again under other conditions than those to
which they were originally adapted, and in the course of a short time conform
their whole organism to the new claims. Finally when a new factor appears in
their old distribution area and disturbs the once-sanctioned order of environment,
the organisms are to a certain degree able to accomodate themselves to the new
factor and this latter again is able, to a degree which almost seems incredible, to
alter the biology of the said species.

The peculiar fact that many hymenoptera of the order Fossoria use different
forage for their young ones and use the paralytical instinct here and upon Corse
in different ways (Bembex a. o.); the variation in instinct from fruiteaters to blood-
suckers of the Nestor parrots of New Zealand; the variation in instinct of the Au-
stralian Dingos, the variation in instinct in the biology of different species of beetles
(Haltica, Anthrenus) which, suddenly transferred from the old world to the new or
vice versa, grow to be noxious animals of great economic significance in their
new home, whereas in their original home they are quite harmless animals; the
alterations in the biology of the swallows which, from being originally inhabitants
of rocks and mountains nowadays owing to the building of castles, church steeples
etc. build their nests upon or in our houses over vast areas of distribution; the
variation in the life of Turdus merula in the last generation of man, are all ex-
amples of the same above-named common rules. With regard to the Anophelines
the above named changes in the agriculture of our own and adjacent countries was
the new factor which in our latitudes altered the biology of this Anophelin species.

When I consider the malaria curves in the time from about 1830 to 1900 and
see how rapidly the curves fall and remember that malaria has disappeared from
our country in the course of only one or two generations of man, I find that the
variations in the habits of A. maculipennis have taken place not as an "evolution
lente" but very suddenly and with an almost incredible rapidity. From ROUBAUD'S
investigations we are entitled to suppose that the variation in habits has at all
events also affected the animal morphologically; if this holds good for more
than the size we do not know; a more thorough investigation of the mouthparts,
especially the number and size of the sawteeth on the maxillae which are in fact
subject to variation, would most probably give interesting results. I think that it
must be admitted that in the variation in the habits of A. maculipennis there really

195

is a basis for the origin of a new type which, in the course of time, may perhaps
lose its connection with the maternal species and give rise to a new one.

Nowadays I am inclined to see in our .4. maculipennis, neither a subspecies
nor variety or race, but only stocks of individuals geographically and culturally bound,
stocks which nowadays play upon other strings of their life instrument than those
usually used. If we get similar life conditions as in the first part of the former
century they will however immediately revert to their earlier manner of life. It is by
no means an "evolution durable" it is an utilisation of other physical and mental
properties but no "evolution d'habitudes acquises". Actually the connection with
man is nowadays in the main broken in our latitudes but the circle can be closed
again. The probability of the great epidemics occurring is really very small but
the deep lying real life conditions for these epidemics are the same nowadays as
formerly in as much as they are dependent upon the Anophelines.

Postscript um.

After the printing of the greater part of the manuscript of the Culicines I got
from Dr. E. MARTINI his excellent papers relating to the classification and biology
of German mosquitoes. I am glad to see that in many respects we fully agree.
Only with regard to the synonymy there are, as might be expected, great differen-
ces. In the following I have tried to collate Dr. MARTINI'S species with mine; I
suppose that the references will almost all prove to be correct, because, according
to a letter to me, Mr. EDWARDS has arrived at quite the same result.

I add some biological remarks taken from the wrork of Dr. MARTINI, especially
those which supplement my own observations or which strengthen my views where
this seems to be desirable. With regard to the Anophelines the work has been con-
sulted in the foregoing pages.

Martini. W.-L.

Aedes cinereus Mg A. cinereus Mg.

lateralis Mg Ochlerotatus lateralis Mg. (?)

serus Martini diantceus H. D. K.

diversus Theob riisticus Rossi.

nemorosus Mg. communis Deg.

sylvce Theob punctor Kisby.

terriei Theob salinellus Edw.

salinus Fie detritus Hal.

nigrinus Eck sticticus (Meig.) var. con-

cinnus Steph.?

annulipes Zett lutescens Fabr.

25*

19H

Martini. W.-L.

Ae'des cantans Mg Ochlerotatus cantans Mg.

abfitchii Felt excrucians Wlk.

quartus Martini ?

dorsalis Mg caspius Pallas.

rusticus Rossi diuersus Theob.

vexans Mg vexans Mg.

lutescens Fbr lutescens Fabr.

ornatus Mg. . . . Finlaya geniculata Oliv.

rostochiensis Martini prodotes Dyar.

? annulipes Zett.

curriei Coquillet.

Culex pipiens L C. pipiens L.

territans Walker

nigritulus Zett.

Theobaldia annulata Schrank T. annulata Schrank.

glaphyroptera Schiner.

morsitans Theob. Culiseta morsitans Theob.

f'umipennis Steph

Mansonia Richardii Fie Tceniorhynchus Richardi. Fie.

It is of particular interest that the whole new mosquito fauna which I have
detected here in Denmark has now also been found in Germany; MARTINI menti-
ons five species: A. lateralis Mg. A. quartus n. sp. C. territans Wlk., T. glaphyroptera
Schiner and T. fumipennis Steph. which we have not found here in Denmark. Of
these species A. lateralis Mg. and A. quartus n. sp. are most probably very doubtful
species; this especially holds good for the first named. In our country we only
lack C. territans, T. glaphyroptera and fumipennis. T. glaphyroptera cannot be expected
in our country, but there is no doubt that the two others will be found. Most prob-
ably C. territans is in some way concealed in my forest races of C. pipiens, but provi-
sionally the larva does not allow this supposition. That I have not found T. fumi-
pennis must be regarded as simply accidental.

On the other hand my list includes three species which are lacking in that
of MARTINI. These three species are 0. annulipes Zett. 0. curriei Coc. and nigritulus
Theob. All these species are doubtful; I am not quite sure that what I have named
O. annulipes Zett. can be kept distinct from O. excrucians; still the larvae do not
coincide. 0. curriei is perhaps identic with O. caspius Pall.; the larva being un-
known; what the species determined as C. nigritulus really is, we do not know with
certainty; most probably it is related to C. territans but the larvae seem to differ
very much from each other.

With regard to the synonymy in the two lists this may be regarded as rather
indisputable in most of the cases; there are only two cases to which it is neces-

197

sary to call special attention. It is rather doubful if my species 0. sticticus is
identic with A. nigrinus, a species which according to the description is always
difficult to determine. The species 0. salinellus Edw. ha* not hitherto been men-
tioned in this work, but must now, most probably, be registered among the
Danish species.

After I had sent Dr. EDWARDS my 0. prodotes material from Amager he called
attention to the fact that the specimens differed somewhat from the true 0. prodotes;
I tried to get some males, but without success; later on Dr. EDWARDS wrote to me
that the specimens must most probably be regarded as a new species for which he
would propose the name salinellus. Later on he told me that these specimens were
identic with A. terriei Theob. and more thoroughly described by MARTINI (19204
p. 112). It is therefore now necessary to register the species among the Danish
mosquitoes; with regard to the description I refer the reader to MARTINI. With
regard to the chapter relating to the single species of Culicines I wish to call at-
tention to the following facts.

Aedes diversus Theo. = O. rusticus (Rossi). MARTINI maintains that MEINERT'S
figure of C. nemorosus belongs to this species. I think that this may be correct and
confess that I have overlooked this fact.

Aedes nejnorosus Mg. = O. communis (Deg.). It is of interest that MARTINI has
shown that below the withered leaves in the dried ponds other leaves were found
which were still moist; between these moist leaves "fanden sich Unmengen von
Nemorosus-Larven und Puppen, so dasz man den Eindruck hatte, die Entwicklung
ganz grosser Larven gehe fast ungestort weiter".

Aedes sylvce Theob. = 0. punctor (Kirby). MARTINI states that the home of the
larva is "in Torfmoorgraben zwischen Gras und Fadenalgen" not in drying ponds
in forests. This may be true, but I must confess that I have never found these
larvae there.

Aedes terriei see above.

Aedes dorsalis Mg. = 0. caspius (Pallas). It is of interest that also MARTINI has
shown the remarkably severe attack of this species in the autumn, a long time after
the other mosquitoes have ceased to sting.

Aedes vexans Mg. It is highly remarkable that this species, which has a parti-
cular significance for large parts of Central Europe, hardly seems to exist in our
country; the same seems to be the case in Great Britain.

C. pipiens. MARTINI states that MUHLENS has counted about 10.000 specimens
in one square meter in the hibernating places; he supposes that the species has
about four to six generations in Germany. He mentions the enormous swarms of
C. pipiens males in autumn; swarms which are indicated to be "Tausende von Metern
lang". MARTINI has observed one of more than 1 km. in length. Phenomena of this
kind have hitherto been quite unknown in our country. He has made the same
observation as so many others that C. pipiens only rarely sucks upon man and
mainly upon birds.

198

C. territans Walker. The statement that C. territans should mainly be a house
mosquito, makes it rather improbable that it should have any great distribution in
our country. Most probably it is an American species, which has been found in
Italy, at Bonn, Strassburg and Hamburg in recent years. In America it is a very
angry bloodsucker according to Felt; in Europe it does not seem to attack man.

Theobaldia annulata: MARTINI has found hibernating larvae; he also comes to
the result that it only rarely sucks upon man. On an excursion to Amager Mr.
KRYGER and I found a remarkable mosquito closely related to T. annulata; the white
scales were however yellow and the black brown. After this work was sent to the
press Mr. EDWARDS told me that the specimens were identic with specimens adapted
to desert conditions and hitherto found in Mesopotamia ; it may be named T. annulata
var. subochrea Edw.

I only wish to call attention to the remarkable mosquito fauna which has now
been ascertained to exist upon Amager in the immediate vicinity of Copenhagen.
In the drying ponds of Amager common we now know that the following speci-
mens are hatched: 0. salinellus, O. detritus, O. rusticus, 0. caspius, O. curriei, 0. lutes-
cens, T. annulata var. subochrea. It will clearly be seen how much this fauna differs
from that of the drying forest ponds where O. communis, 0. prodotes, O. excrucians,
0. cantans, 0. diantceus preponderate.

Ochlerotatus rusticus. After having read the paper of MARTINI I am not quite
sure that two species are not confused in my 0. rusticus Rossi material. It is pos-
sible that some of the material from my forest ponds should be referred to 0. fus-
culus Zett. ; I have hitherto regarded all my larva material as homogeneous; it seems
however that there are some small differences in the arrangement of the hairs
upon the dorsal side of the sipho; without delaying the publication for almost a
year this cannot be cleared up.

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Corrections.

P. 93 heading for Finlaya read Finlaya.

- 133 1. 10 from bottom for 1909 - 1907.

- 134 1. 12 from top for 1903 p. 88 dele.

- 134 1. 13 for Eckstein 1908 19022.

- 135 1. 9 for 1919m 19102.

- 135 1. 4 from bottom for p. 25 p. 259.

- 143 1. 7 from top for Weber 1906 p. 38 1906 p. 380.

- 154 1. 13 for Knab (1912 p. 122) Knab (H. D. K. 1912 p. 122).

- 158 1. 17 for (Blacklock and Carter 1920 p. 413) but has shown

read but Blacklock and Carter (1920 p. 413) have shown.

INDEX

Pag.

Preface ' 3— 8

I. Culicines 9 — 156

Chap. I : 9—35

Morphological remarks 9 — 35

a. The larva 9—28

b. The pupa • 28— 35

Chap. II •. 36—132

The Danish Culicines, Systematically and Biologically described 36 — 132

Aedes 36— 39

1. A. cinereus Meig . . Tab. I 36— 39

Ochlerotatus 39— 93

2. O. caspius (Pallas.) II 39— 46

3. O. curriei (Coquillet) 46— 47

4. O. cantons (Meig.) Ill 47— 51

5. 0. annulipes (Meig.) - IV 51 — 53

6. O. vexans (Meig.) 53 — 55

7. 0. excrucians (Wlk.) - .V 55 — 59

8. O. lutescens (F.) VI 59— 67

9. O. detritus (Haliday) - VII 67— 69

10. O. communis (De Geer) VIII 69— 78

11. O. nigripes (Zett.) IX 79— 79

12. O. punctor (Kirby) : X 79— 81

13. 0. prodotes (Dyar) XI 81—84

14. O. rusticus (Rossi) XII 84— 88

15. O. diantams (H. D. K.) XIII 88— 92

16. O. sticticus (Meig.) var. concinnus Steph 92 — 93

Finlaya 93—102

17. F. geniculata (Olivier) XIV 93—102

Tceniorlujnchus 102— 1 15

18. T. Richard! (Fie.) XV— XVI 102—115

Theobaldia 115—118

19. T. anmilata (Schrank.) - XVII 115—118

Culicella 118—225

20. C. morsitans (Theobald) XVIII— XIX 118—125

Cnlex 125—132

21. C. pipiens Linue .' - XX 125—130

22. C. ciliaris Linne 130—131

23. C. nigritnlns Theob XXI 131—132

I). K. D. Vidensk. Selsk. Skr., naturviclensk. og mathem. Afd. 8. Raekke, VII, 1. 27

210

Pag.

Chap. Ill 133—156

Contributions to the Biology of Culicines 133 — 156

a. General Biological Remarks 133 — 143

b. The Blood-sucking 143—152

c. The mating process 152 — 156

II. Anophelines 157 — 195

Chapter IV 157—195

Anopheles and Danish Malaria 157 — 195

24. A. plumbeus Stephens 157 — 1 58

25. A. bifurcatus Lin 158 — 161

26. A. rnacnlipennis Meig 161 — 195

Postscriptum 195—198

27. Ochlerotatus salinellus Edw 197

28. Theobaldia annulata (Schrank) var. subochrea Edw 198

List of Literature . . . 198—208

[). K. D.VIDEXSK. SELSK.SKH., NATURV.OG MATH. AKD., 8. R.VII. 1 [C.WESBNBEHG-LuND]

TAB. I

Aut. del.

Aedes cinereus. (Meig.)

I). K. D.YIOKNSK. SICI.SK. SKK., XATUHV. OG MATH. AFD., 8. R.VII. 1 [C.WESENBEBQ-LOND]

TAB. II

7

Ochlerotatus caspius (Pallas.)

K. D.VIDENSK. SEI.SK. SKR., NATURV. ou MATH. AKH., 8. R.VII. 1 [C.WESENBERG-LUND]

TAB. Ill

O. cant mis (Meig.)

D. K. D.VIOF.NSK. SEI.SK. SKR., NATURV. oo MATH. AKD., 8. R.VII. 1 [C.WESENBEHG-LUND]

TAB. IV

0. annulipes (Meig.)

Aut. del.

I). K. D.VIDKNSK. SKI.SK. SKH., XATURV. OG MATH. AFD., 8. R.VII. 1 [C.WBSENBERG-LuNp]

TAB.V

9

0. excrncians (Wlk.)

D. K. D.VIDKXSK. SIU.SK. SKH., NATUHV. oo MATH. AKD., 8. H.VII. 1 [C.WESENBERG-LUND]

TAB. VI

I). K. D.VIDENSK. SELSK. SKU., NATURV. oo MATH. AFD., 8. R.VII. 1 [C.WESEXBERG-LlWD]

TAB. VI I.

9

8

O. detritus (Haliday.)

I). K. D.YIDKNSK. SF.I.SK. SKK., XATITRV.OG MATH. AFH., 8. H.VII. 1 [C.WESENBERG-LuNb]

TAB. VI II

m 2

(). comninnis (De Geer.)

I). K. D.VIDKNSK. SEI.SK. SKR., NATURV. OG MATH. AFD., 8. R.VII. 1 [C.WESBNBERG-LlWD]

TAB. IX

0. nigripes (Zett.)

D. K. D.VIDENSK. SELSK. SKH., NATUKV. OG MATH. AKO., 8. R.VII. 1 [C.WESENBERG-LUND]

TAB.X

s

O. punctor CKirby.)

I). K. D.VIDENSK. SEI.SK. SKR., NATURV. OG MATH. AKD., 8. R.VII. 1 [C.WESENHEHG-LUND]

TAB. XI

Aut. del.

O. prodotes (Dyar.)

I). K. D.VIDENSK. SELSK. SKH..NATURV. or, MATH. Apo.,8. R.VII. 1 [C.WESENBERG-LUND]

TAB. XII

Aut. del.

0. rusticus (Rossi.)

I). K. D.VinKNSK. SKLSK. SKH., NATI:RV. OG MATH. AFD., 8. R.VII.l [C.WESBNBERG' LUND]

TAB. XIII

0. dianiceus (H. D. K.)

I). K. D.YIDKNSK. SKI.SK. SKR., NATUKV. OG MATH. AFD., 8. H.V1I. 1 [C.WESENBERG-LuNDJ

TAB. XIV

Finlaya genicnlata (Olivier.)

I). K. D.VIDEXSK. SELSK. SKU., NATURV. OG MATH. AFO., 8. R.VII. 1 [C.WESENBBRG-LUND]

TAB. XV

Tceniorhynchus Richardi (Ficalbi) I.

I). K. D.VlDBNSK. SBLSK. SKR., NATUHV.OC, MATH. AKD., 8.R.VII. 1 [C.WESENBERG-LUND]

TAB. XVI

Twniorhyncluis Richardi (FicalbiJ II.

D. K. D.VIDENSK. SELSK. SKR., NATURV. OG MATH. AFD., 8. R.VII. 1 [C.WESBNBERQ-LUND]

TAB. XVII

Ant. del.

Theobaldia unnnlata (Schrank.)

O.K. D.VIDKNSK.SELSK.SKH., NATUHV.OG MATH. AFD., 8.R.VII. 1 [C.WESENBEKG-LUND]

TAB. XVIII

A ut. del.

Culicella morsitans (Theobald) I.

D. K. D.VIDENSK. SELSK. SKR., NATI;RV. OG MATH. AFD., 8. R.V11. 1 [C.WESENBERG-LuND]

TAB. XIX

Aut. del.

Culicella morsitans (Theobald) II.

I). K. D.VIDENSK. SELSK. SKH., NATCRV. or, MATH. AFD., 8. R.VII. 1 [C.WESENBERG-LUND]

TAB. XX

9

Aut. del.

pipiens Linnc.

I). K. D.VIDKNSK. SELSK. SKK., NATURV. on MATH. AFD., 8. R.VII. 1 [C.WESENBEKG-LUND]

TAB. XXI

C. nigrituhis Theobald.

Det Kgl. Danske Videnskabernes Selskabs Skrifter.

Naturvidenskabelig og; mathematisk Afdeling,

8<ie Rgekke.

Kr. 0re

I, 1915 — 1917 10. 75.

1. Prytz, K. og J. N. Nielsen: Undersegelser til Fremstilling af Normaler i Melersystemet, grundet

paa Sammenligning med de danske Rigsprototyper for Kilogrammet og Meteren. 1915 1. 55.

2. Rasmussen, Hans Baggesgaard: Om Bestemmelse af Nikotin i Tobak og Tobaksextrakter. Kn

kritisk Undersegelse. 1916 1. 75.

3. Christiansen, M.: Baktericr af Tyfus-Coligruppen, forekommende i Tarmen hos sunde Spjed-

kalve og ved disses Tarminfektioner. Sammenlignende Undersegelser. 1916 2. 25.

4. Juel, C.: Die elementare Ringfiache vierter Ordnung. 1916 *, (i().

5. Zeuthen, H. G.: Hvorledes Matliematiken i Tiden fra Platon til Euklid blev en rationel Viden-

skab. Avec un resume en francais. 1917 8. >

II, med 4 Tavler, 1916 — 1918 11. 50.

1. Jergensen, S. M.: Det kemiske Syrebegrebs Udviklingshistorie indtil 1830. Efterladt Manuskript,
udgivet af Ove Jergensen og S. P. L. S0rensen. 1916 8. 45.

2. Hansen-Ostenfeld, Carl: De danske Farvandes Plankton i Aarene 1898 — 1901. Phytoplankton
og Protozoer. 2 Protozoer; Organismer med usikker Stillingf Parasiter i Phytoplanktonter. Med

4 Figurgrupper og 7 Tabeller i Teksten. Avec un resumS en francais. 1916 2. 75.

3. Jensen, J. L. W. V.: Unders0gelser over en Klasse fundamentale Uligheder i de analytiske Funk-
tioners Theori. I. 1916 » 90.

4. Pedersen, P. O.: Om Poulsen-Buen og dens Teori. En Experimental undersegelse. Med 4 Tav-
ler. 1917 2. 90.

5. Juel, C.: Die gewundenen Kurven vom Maximalindex auf einer Regelflache zweiter Ordnung. 1917 » 75.

6. Warming, Eug. ; Om Jordudlebere. With a Resume in English. 1918 3. 65.

III, med 14 Kort og 12 Tavler, 1917—1919 26. 00.

1. Wesenberg-Lund, C.: Furesostudier. En bathymetrisk Undersegelse af Molleaaens Seer. Under
Medvirkning af Oberst M. J. Sand, Mag. J. Boye Petersen, Fru A. Seidelin Raunkicer og Mag. sc.
C. M. Steenberg. Med 7 bathymetriske Kort, 7 Vegetationskort, 8 Tavler og ca. 50 i Texten trykte
Figurer. Avec un resume en francais. 1917 22. >

2. Lehmann, Alfr.: Stofskifte ved sjselelig Virksomhed. With a Resume in English. 1918 3. 15.

3. Kramers, H. A.: Intensities of Spectral Lines. On the application of the Quantum Theory to
the problem of the relative intensities of the components of the fine structure and of the stark

effect of the lines of the hydrogen spectrum. With 4 plates. 1919 9. 50.

IV (under Pressen).

1. Bohr, N.: On the Quantum Theory of Line-Spectra. Part I. 1918 2. 25.

Samme. Part. II. 1918 4. 00.

V (under Pressen).

1. Bjerrum, Niels und Kirschner, Aage: Die Rhodanide des Goldes und das freie Rhodan. Mit

einem Anhang uber das Goldchlorid. 1918 , 3. 50.

2. Orla-Jensen, S.: The lactic acid Bacteria. With 51 Plates. 1919 46. 00.

VI (under Pressen).

1. Christensen, Carl: A Monograph of the genus Dryopteris. Part II. 1920 8. 25.

2. Lundblad, O.: Siisswasseracarinen aus Diinemark. Mit 12 Tafeln und 34 Figuren im Text. 1920. 18. 50.

VII (under Pressen).

1. Wesenberg-Lund, C.: Contributions to the Biology of the Danish Culicidse. With 21 Plates and

19 Figures in the text. 1920-21 29. 00.

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