Transactions of the Society for British Entomology

2. D ’ Sc. 78.7^

• El O f\ f)V

*• •-* * \f~\ • » T.

VOL. 16

I

MAY H 197 J

HARVARD

university

TRANSACTIONS

OF THE

SOCI ETY FOR BRITISH
ENTOMOLOGY

World List abbreviation: Trans. Soc. Brit. Ent.

PART 6

CONTENTS.

Greenslade, P. J. M.

On the Ecology of some British Carabid Beetles with special

Reference to Life Histories

Date of Publication, April 1965

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of Entomology, University Museum, Oxford

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TRANSACTIONS OF THE SOCIETY
FOR BRITISH ENTOMOLOGY

VOL. 16

APRIL 1965

PART VI

( )n the Ecology of some British Carabid Beetles
with special Reference to Life Histories

By P. J. M. Gueenslade

(Dept, of Agriculture, Honiara, British Solomon Islands

Protectorate)

This account is based on work carried out at the Imperial
College Field Station, Silwood Park, Berkshire, from 1958 to 1901
(in which certain aspects of the bionomics of 26 Carabid species
were studied), supplemented by information on life histories made
available to me from the theses of Dawson and Tipton, which
are not readily accessible. Dawson (1957) studied small Fenland
Pterostichus and Agonum species, and Tipton (1960), at Reading,
worked on 22 Carabidae, of which six were not studied at Silwood.
Gilbert’s (1956, 1958) accounts of the life histories of Nebrici and
Calathus species in North Wales are also summarised in the present
survey. A total of 43 species are considered and this includes the
majority of the commonest Carabidae of lowland Britain.

Outside the British Isles, Larsson (1939) described the life
histories of Danish Carabidae, and his account was amplified for
the rest of Scandinavia by Lindroth (1945-49). Geiler (1956-57)
gives information on a number of German species. However, for
any Carabid species these accounts are not necessarily applicable
in Britain as there is evidence that life histories and other
features show geographical variation within a species.

Larsson and Lindroth divide Carabidae into those which
breed in the spring, have summer larvae and overwinter as adults,
and those which spend the summer as adults, breed in the autumn
and overwinter as larvae. This classification is used here.

In addition to the account of the life history, the habitat and,
where known, daily activity cycle of each species are given in the
following systematic account. They are subsequently discussed
in relation to life history.

Methods

At Silwood Park, Carabidae were studied mainly by pitfall
trapping. The life history accounts are based on records of adult
abundance in traps and the occurrence of callows, combined
where possible with records of copulation, the incidence of larvae
and records of the overwintering stage; in some cases gonad dis¬
sections are made. Very similar methods were used by Tipton.
Many Carabidae have resting periods in the adult state, and ideally
pitfall trapping should be combined with some type of direct

150

| April

1 — [ — i — i — i — i — i — i — i — i — i — i — r

NDJFMAMTTASO
1558 l *5}

CARABUS NEMORALIS
CPROBLEHATICUS

C. VIOLA LACEUS

CXCHRUi CARABOIDES
LEISTUS FERRUCINEUS

NEBRIA

BREVICOLLIS

NOTiOPHILUS

substriatus

N. RUFIPES

N. BIGUTtATUS
LORICERA PILICORNI5

BEMBI&ION LAMPROS
hARPALUS AFFINIS

H. RUFIPES

1965]

151

AMAR A COMMUNIS

A LUNICOLUS

STOMIS PUMICATUS

PTCROSTICHU S
CAERUIESCENS

P. NICER.

P. MELANAMUS

ABAX

PAPALIELEPIPEDUS

CALATHU5 FUSCIPES

C. MEIANOCE PHALU5

C.PICEUS

SYNUCHU5 NIVALIS

ACONUM DORSALE

Fig. 1. — Fortnightly catches of Carabidae in 23 traps, on the Imperial
College Field Station, 1958-1959: catches expressed as 10 x mean
catch per day, except N. brevicollis where the actual mean daily
catch is shown.

152 | April

sampling to reveal inactive populations, as in Gilbert’s (1956) and
Dawson’s work. However, many species are not amenable to such
sampling. For example, Nebria brevicollis is seasonally one of
the most abundant British Carabidae, and at times occurs in
highly aggregated populations which may maintain the same
pattern for long periods, but even so at Silwood the mean density
within a natural population rarely exceeded one per square yard
(Greenslade 1961). Twenty- three pitfall traps were visited as far
as possible daily from October 1958 to November 1959, and from
March to November 1960. To illustrate annual cycles of adult
abundance the 1958-59 catches are shown in figure 1. In addition,
up to 100 other traps were in operation, from time to time being
visited at daily, or less frequent but regular, intervals. Details
of the catches of these traps are recorded elsewhere (Greenslade
1961). The traps consisted of one pound jam-jars sunk in the
ground, with a circle of radius of about one foot around each
cleared of litter and vegetation.

Traps were situated in beecliwood, bracken, grass heath and
arable land. Two main groups of Carabidae were distinguished,
those of woodland (beechwood and bracken), and grassland (arable
and heath) (Greenslade 1963a). Of the species occurring in wood¬
land 15 out of a total of 23 were studied, and in grassland 17 out
of 54. Of these, six species were common to both habitats.

Greenslade (1963b) described three types of daily activity cycle
in Carabidae, nocturnal, diurnal and plastic. The last include
species whose patterns of activity vary from day to day according
to weather, and also some which show geographical variation
apparently in response to climate.

The life history accounts below are those described at the
Imperial College Field Station unless explicit reference is made to
other authorities.

Systematic Account of Life Histories

Carabus nemoralis Mull, (figure 1). Only small numbers of
adults were trapped, but they occurred from February until
November with a main peak in May and a subsidiary one in
October. Larvae were taken in June. Van der Drift (1951)
records two adult maxima also in Holland. Delkeskamp (1930)
describes a cycle in Germany in which reproduction takes place
early in the year followed by May- July aestivation by the spring
adults, which show some autumn activity. Young imagines appear
from July onwards and some may be mated in the autumn. The
Silwood observations are in agreement with this cycle. Hikimiuk
(1948) gives a similar account of the life history of this species
near Moscow. In this case the active population of newly
emerged adults in the autumn averaged only 70%, over four
years, of the spring breeding population; this suggests that some
adults are not active until the year following that in which they
were larvae. In Sweden Lindroth’s figures show a main peak in
June, numbers falling in July with a slight increase in August.

153

1965]

At Silwood C. nem oralis occurred in grassland, although in
Russia, Hikimiuk records it as a forest species. Observations on
activity rhythms show this to be a nocturnal species in Britain,
as it is in Germany (Kirchner, 1960), and Russia (Hikimiuk,
1948). Krumbiegel (1932), however, describes it as nocturnal in
North and East Europe and diurnal in the South.

C. problematicus Hbst. (figure 1). Adults occurred from April
to November with a peak in September and rather low catches
in July and August; larvae were recorded in April. This is a
predominantly larval overwintering species, although hibernating
adults have been found at Silwood and elsewhere. The life history
lias been described by van der Drift (1951): adults emerge in
May and June, aestivate during the following two months and
reappear to breed in the autumn. In south Sweden Lindroth
records a single adult peak in July.

This is a woodland species but is characteristic of bracken and
scrub on the edge of woodland rather than litter under intense
shade within it. It is nocturnal.

C. violaceus L. (figure 1). Adults were trapped from June to
September with a maximum in July, the earliest capture being
in May. Larvae were abundant in traps in late September and
October. Tipton recorded a June- July maximum. This agrees
with van der Drift’s (1951) account in Holland where it is a larval
overwintering species. The first few adults to appear in the early
summer are females which have survived the winter, followed by
the males. Later in the summer comes major emergence of the
generation which hibernated as larvae; breeding takes place in
the autumn. In Denmark the maximum occurs in June and July,
and in Sweden from June to August.

At Silwood this was found to be a widely distributed, noc-
tumally active species, occurring in woodland, arable land and
grass heath.

Cychrus caraboides (L.) (figure 1). Adults occurred at Sil¬
wood from June to September; no larvae were found. Tipton’s
records are similar. According to Lindroth this species over¬
winters as the larva, adults emerging and breeding from mid¬
summer. It is a nocturnal, woodland species.

Leistus fei'ruyincus (L.) (figure 1). The majority of catches of
this species were made in the autumn from late August into
December, although some adults, many of them callows, were
trapped in May and June. Larvae were taken in January and
February. The life history appears to be similar to that of Nebria
brericollis with a late spring adult emergence, summer diapause,
a main period of breeding in the autumn and larval overwintering.
Lindroth found a single June maximum in Sweden, while in Den¬
mark I^arsson recorded two peaks, one in June and one in Sep¬
tember.

L. ferruyineus is a woodland species occurring in the same
habitats as C. problematicus, that is on the edge of canopied areas
or in open woodland, rather than litter.

154

[April

Nebria brevicollis (F.) (figure 1). The life history has been
described in Britain by Gilbert. (1956), and Williams (1959b). It
breeds in the autumn and overwinters as the larva. Newly
emerged adults appear from May to June, show some early sum¬
mer activity, but diapause until the main period of reproductive
activity which lasts from September until November.

At Silwood the life history was similar and is briefly
summarised. Adults were trapped in the largest numbers in
October and towards the end of the period mating occurred.
First instar larvae appeared in laboratory cultures in November,
and occurred in the field until April; later instars were found in
traps and litter throughout the winter months and in early spring.
In 1959 the first callow was recorded on 13th April and the rate
of emergence is shown in table 1. About 20 days was required
for newly emerged individuals to attain mature colouring and a
hard integument on the dorsal surface. In the autumns of 1958-
1960 occasional N. brevicollis were found which showed signs of
immaturity on the under-side. They were probably late emerging
or developing individuals from the spring and did not occur in
sufficient numbers to invalidate the concept of spring emergence,
summer diapause and autumn activity.

Table 1

Percentage of callow Nebria brevicollis adults in pitfall traps —

April-June 1959

Trapping

Total Number of

Number of

Percentage

Period

Nebria

Callows

Callow

April

23-26

15

0

0

yy

27-30

32

1

31

May

1-4

29

19

65-5

yy

5-8

57

37

64-9

yy

9-11

36

21

58-3

yy

12-15

86

32

37-6

yy

16-19

28

9

321

yy

20-23

56

20

35-7

yy

24-27

18

4

22-2

yy

28-31

43

2

4-7

June

1-4

73

5

6-8

»>

5-8

75

2

2-7

**

9-11

47

0

0

Totals

594

152

At Silwood the spring catches were always lower than the
autumn, but Williams (1959b) found that at Reading in one season
spring catches were higher than those of the ensuing autumn. He
cited Lindroth (1945) as giving a bimodal curve for the occurrence
of N. brevicollis adults in Sweden with the spring numbers greater
than those of the autumn. In Denmark he quotes Larsson as
describing a single peak. However, for Britain at least such
records must be exceptional. Tipton concluded that all new
adults left the pupal cell in spring but were active for only a short

155

1965]

period, hence catches are generally lower than in the autumn. The
same conclusion was reached from a population study at Silwood
(Greenslade, 1961).

Tipton also found, again in agreement with Silwood observa¬
tions, that some breeding continued throughout the winter. In
connection with this the role of diapause in regulating the life
history is discussed later.

Tipton found similar numbers of each sex in traps during the
spring emergence, and a ratio of two males to one female in the
autumn. At Silwood where allowance was made for disturbance
activity due to the marking and recapture method used (Green¬
slade, 1961), it was found that male locomotor activity exceeded
that of the females in the ratio 1-5: 1 in the autumn, and that
the absolute jxjpulations of each sex were equal; thus the males
are relatively more active in the breeding season.

Although populations extend into other habitats, N. brevicollis
is essentially an inhabitant of woodland litter, and is nocturnal.

According to Gilbert (1958) the life history of Nebria salina
Fairmaire & Laboulbene, is essentially the same as that of N.
brevicollis.

Notiophilu8 substriatus Waterh. (figure 1). Although catches
of adults were low, they suggest a life history similar to those of
Xotioj>hilus biguttatus and X. rufipes. There were no captures
between July and September; the maximum occurred in .Tune
and there was some activity as early as February and as late as
November. No larvae were found.

The cycle of this species is not described by Lindroth, but
Larsson (1939) and Davies (1959) record it as overwintering as
the larva, while it was considered by Williams (1959) to be a
summer-larva species. The present observations tend to support
the latter, although numbers are very small. Tischler (1955)
mentions that some small diurnal Carabid species are bivoltine
and N. substriatus may l>e one of these.

N. substriatus is diurnal, and was found in woodland and
grassland.

Notiojriiilus bigut tat us (F.) (figure 1). Adults were most
frequent in traps from April to early August with a peak in May
and June; they were also taken in January and February, and
a number were caught in September and October. Larvae
occurred in the summer months, and in a collection from Silwood
larvae were distributed as follows: May (1), June (1), July (7),
August (6), September (1).

Overwintering is in the adult state with breeding in the sum¬
mer months; the minor peak of catches in the autumn is therefore
due to the generation of newly emerged adults. This agrees with
Lindroth's account of the life history.

This species is a diurnal inhabitant of woodland litter.

.V. rufipes Curt, (figure 1). The life history is the same as that
of .V. biguttatus, there being early summer and autumn peaks of
adult activity. Although no larvae were found at Silwood low

156

[April

catches of adults in August and September suggest that this is the
larval period. Similarly captures in February imply that N.
mfipes is an adult overwintering species. This again agrees with
Lindrotli and Davies (1959), and Williams (1959b) records it as
breeding in the summer months.

At Silwood in 1959 and 1960 the late summer disappearance
of the adults occurred a month later in N. mfipes than in N.
higuttatus ; this is probably not a real difference as in Scandinavia.
Lindrotli records a June adult maximum in N. higuttatus and
Larsson a May maximum for N. rufipes.

It is a diurnal woodland species, and of the Carabidae con¬
sidered here is the one most narrowly restricted to litter.

Loricera pilicomis Latr. (figure 1). Adults were trapped from
February to August with a maximum in April and May. Larvae
were recorded from May to July. Tipton found an April maximum,
a midsummer decline and a slight increase in the autumn.
Similarly Larsson recorded April-May and July-August maxima.
However, in Sweden, Lindrotli describes the species as overwinter¬
ing as the adult with a single peak of activity. In central Germany
Geiler (1960) records a single peak from May to July. In Britain
the life history would seem to consist of overwintering by adults
which breed in the following spring. Some of these adults may
survive through the summer. Newly emerged imagines show some
activity in the autumn.

Loricera was found to be diurnal at Silwood, but Kirchner
(1960) records nocturnal activity in western Germany. This
species occurs in a wide range of habitats (at Silwood in beech-
wood, alder carr, and on arable land), and it is possible that the
daily time of activity varies with microclimates of different
habitats.

Clivina fossor (L.). This species was studied by Tipton who
describes it as overwintering as the adult, and breeding in the
spring with maximum catches in April and May. It has been
taken at Silwood and elsewhere in pasture and on the edge of
woodland. It is most probably nocturnal.

Bembidion lampros (Hbst.) (figure 1). Adults were trapped
from February to October, the maximum numbers being taken
in the period May to July. Overwintering adults were found but
no larvae. According to Lindrotli it overwinters as the adult
with summer larvae; he recorded an adult maximum in Sweden
in June.

It is a diurnal species typical of arable fields, but is also com¬
mon in grassland.

Harpalus af finis (Sclirank) (figure 1). Adults occurred in pit-
falls from April until November with a maximum betwTeen May
and August, when callows were frequent. Larvae which can
almost certainly be assigned to this species were found from June
to October. According to Briggs (1957) the life history is similar
to that of H. rufipes which follows. It should be noted that in
Czechoslovakia, Skuhravy’s (1959) results suggest that H. af finis

shows u June maximum, a decline in July and August and slight
increase in October, while in //. rufipcs a simple August maximum
occurred.

At Silwood //. afjinis occurred most abundantly on arable
land, but was also common in grass heath. It was found to be
nocturnal under experimental conditions, but diurnal activity was
frequently observed in the field. Here it is defined as plastic in
its daily activity.

//. rufijfcs (Deg.) (figure 1). Adults were trapped from March
to October with large numbers from June to August when callows
were common; larvae were recorded from August to November.
Briggs (1957) has described the life history of this species in some
detail. Lggs are laid from mid-July until late September; some
of the resulting larvae are adults by the autumn, but do not
breed until the following summer. The majority overwinter as
larvae and produce callow adults early in the year. Briggs (1961)
compared pitfall catches and populations shown by direct
sampling in this species. Absolute numbers were highest in June
and July although pitfall catches were greatest before and after
this period in May and in late July and August. The early peak
in catches can be attributed to activity by overwintering adults,
and the later catch maximum to adults which had emerged earlier
that summer. Rather high total numbers and low catches in
early June suggest that the newly emerged generation shows less
activity when callow than when mature.

Both this and the preceding species are clearly autumn
breeders and larval overwinterers, but there is room for further
observation on the amount of adult overwintering which occurs.

II. rujipcs is essentially an arable land species and is nocturnal.

Amaru plebeja (Gyll.). Tipton found a May maximum with
some catches in September. In Denmark and Sweden single
maxima in, respectively, June- July, and June, are recorded. It
overwinters as the adult and breeds in the spring. A grassland
species, it is normally diurnal but may be plastic in its daily
activity.

Amaru communis (Pz.) (figure 1). Adults were trapped from
March to July with a peak in late May and early June; callows
were active in September. Large numbers of Amara larvae were
taken but it is not possible to determine their identity further than
the sub-genus. Lindroth considers it is an adult overwintering
sjiecies with a summer larval period, and this evidently applies at
Silwood. In Sweden, however, a single peak in May and June is
described with no autumn increase in activity.

This species was typical of grass heath, being absent from
woodland habitats and infrequent on arable land. It is plastic in
its daily time of activity.

A. lunicollis Schdt. (figure 1). The life history is very similar
to that of A. connuunis ; the main period of adult activity is in
July, numbers in traps are low in August and callows were taken
in September. Again this is an adult overwintering species differ-

158 ' [April

ing from A. communis only in having an adult maximum later by
approximately one month.

In habitat and activity time this species is the same as A.
communis.

Stomis pumicatus (Pz.) (figure 1). Adults were trapped from
April until July, the greatest numbers occurring in May and June;
occasional catches were made in September. No larvae or callows
were found. According to Larsson it overwinters as the adult,
breeding early in the year and therefore autumn catches are
probably of newly emerged adults.

It is a woodland species especially of bracken and open wood¬
land, and is nocturnal.

Pterostichus cupreus (L.). This species was studied by Tipton
who recorded March-April, and October maxima in pitfalls. In
Denmark a May maximum is found with a small increase in Sep¬
tember; in Sweden only a May peak occurs. In Britain this is
evidently an adult overwintering species breeding in the spring,
at least some of the new adult generation being active in the
autumn.

P. cupreus is a diurnally active inhabitant of grassland.

P. caerulescens (L.) (figure 1). This species was considered in
detail by Tipton. At Silwood it was present in traps from
February to November, the greatest numbers occurring between
May and July, when copulation was recorded. Callows occurred
and there was a second peak of catches in the autumn, which in
1960 exceeded the earlier maximum. No larvae were taken but
overwintering adults were found. From this it would appear
that like P. cupreus this is a spring breeder with winter adults,
and a larval period lasting from May-June until August-September.
Tipton’s account is in agreement with this. Lindroth recorded a
single May-June maximum in Sweden, and Larsson in Denmark
a main May peak with a smaller one in August.

Tipton found that the fat body of the adult increased during
the six weeks or so of post-emergence activity, in the autumn,
but the gonads did not mature until the spring. Experiment-
showed that this was not due to low winter temperatures, and it
was suggested that some physiological mechanism was responsible.

P. vemalis (Pz.). This species was studied by both Tipton
and Dawson whose accounts are combined here. It overwinters
as the adult and breeds in the spring. Adults show maximum
activity early in the year between April and June when eggs are
laid. Newly emerged callows are active in the autumn from
September onwards before retiring to hibernation sites. In Den¬
mark there are April and September maxima and in Sweden a
simple June maximum.

P. vemalis is found in fens, carr and badly drained grassland,
and is most probably nocturnal.

P. niger (Schall.) (figure 1). Adults were trapped from April
until October with a maximum in August during which copula¬
tion was observed. No larvae or callows were found at Silwood

but overwintering adults of botli sexes were recorded. Van der
Drift (1951) mentions callows in July in Holland, while Lindroth
records a June adult maximum in Sweden. In Denmark, Larsson
obtained larvae throughout the year, most commonly in Novem¬
ber, and an August adult maximum with callows in June and
July. These observations suggest that it is an autumn breeding
species with winter larvae, although from the extent of adult
overwintering in Britain and Larsson’s larval records it seems
that either individuals may breed in two seasons, or those emerg¬
ing late in one season do not breed until the next.

This is a widespread species occurring in woodland and grass¬
land, but less frequently on arable land. It is nocturnal.

P. mclanurius (Ill.) (figure 1). This species was trapped from
February to October, being commonest between June and
August; larvae were recorded in January and October. The life
history is described by Briggs (1957): the eggs are laid in August
and September, and larvae are present until April. Pupae occur
in May and the new generation of imagines appears in June.
Although primarily a larval overwintering species, some adults
may hibernate. This observation was also made by both Larsson
and Lindroth, and gonad dissections by Tipton suggested that
some individuals may breed in a second season.

It is a nocturnal species of grassland and arable fields.

P. nigrita (F.). The following is Tipton's account. It over¬
winters as the adult with March-April and October maxima. In
Denmark there are April-May, and August-October maxima, and
in Sweden a single May- June peak.

This species is nocturnal and occurs in damp places.

P. minor Gyll. The account of the life history' of this and the
two following species is due to Dawson. The cycle is similar to
that of P. vernalis. The overwintering stage is the adult and
larvae occur in July and August; breeding activity takes place
from April to July, and newlv emerged adults are active from
August to November.

It is an inhabitant of damp and often shady places and is
most probably nocturnal.

P. strenuus (Pz.) and P. diligens Sturm. In both these species
the life history is basically the same as in P. vernalis and P. minor,
with overwintering adults, spring breeding, and summer larvae.
Adults are active from April onwards, but the two species differ
in that the new generation of P. diligens adults is active as early
as July, while in P. strenuus they do not appear until August.

Both are species of damp places, and although the daily time
of activity is not known, they are probably nocturnal.

P. madid us (F.). Pitfall catches of adults in 1958-59 are
shown in figure 2: they were present almost throughout the year
with a well-marked peak during July and August, when copula¬
tion was frequent. Catches fell during the winter, reaching a
minimum in February and March.

•r

1(50

[ April

COPULATION

LAKVAE

CALLOWS

n — I — I — I — I I I I I I I I
N D 7 F MAMTTASO

1958 1959

Fig. 2. — Life history of Pterostichus madidus showing mean daily catches
of adults in 23 traps on the Imperial College Field Station, 1958-59,
and the incidence of copulation, larvae and callows.

CATCH PER. DAY (2) TRAPS) SEX RATIO (MANY TRAPS)

1965]

161

Fig. 3. — Pterostichus rrmdidus: changes in the sex ratio, 1960.

162

[April

Larvae of this species were found only infrequently in traps,
but they were recorded in soil and litter from September until
June. In P. madidus the adults are inactive until the integument
has acquired the mature black colour and newly emerged
individuals could be recognised only occasionally by the flexibility
of the elytra; they were recorded in this condition in June, July
and early August.

From these observations it appears that the main period of
activity occurs in July and August when the eggs are laid; the
species overwinters in the larval state and new adults emerge in
the following summer.

In 1960 changes in the sex ratio were determined in those
P. madidus taken in a large number of pitfalls as shown in figure
3, also included are the mean daily catches of male and female
P. madidus in the 23 traps. From the figure it is evident that
males emerge from May onwards, reaching a maximum in July
and August; after this the majority die, a few surviving into the
autumn. (Collecting reveals occasional winter females but rarely
males). A number of females overwinter in the adult state, re¬
appearing in May and June; the new generation emerges at the
same time as the males and hence the double peak in female
catch.

Samples of females were taken from traps at irregular intervals
from June to early November 1960 and the ovaries were dissected
after preservation in 70% alcohol. The length of the right ovary
was measured to 0*5 mm., and the condition was assessed as:

Immature — less than 4 mm. in length, individual ova indistinguish¬
able to the naked eye.

Mature — more than 4 mm. in length, individual ova distinct, the
largest usually not less than 2 mm. in length.

Spent — eggs laid, as shown by the presence of corpora lutea, the
oviducts being expanded but empty, or having collapsed
or disintegrated.

In early June it was possible to distinguish between those
females which had laid in the previous season, and immature in¬
dividuals which had not. Unfortunately, it was not possible to
recognise any females which had reached maturity in a second
season, as the egg masses filled the oviducts.

Results are shown in figure 4 as fortnightly means. No samples
were taken in the first half of September.

In agreement with the suggestion of a main breeding season
in July and August the percentage of reproductively immature
females was high in June falling steadily until October, while the
percentage of spent females rose. In the autumn there was an
increase in the proportion of immature individuals so that the
population entering the winter consisted of 25% immature and
75% spent individuals. During the winter of 1958-59 occasional
pitfall catches of P. madidus females were made suggesting that
there was no diapause and activity was limited only by weather.

MATURITY OF OVARIES MEAN OVARY

% LENGTH (MM.)

5

Fig. 4. — Pterostichus madidus : condition of the ovaries in 134 females
dissected in 1960; above, average ovary length; below, the percentage
composition of the population on different occasions in terms of the
state of maturity of the ovaries.

164

[April

Thus the fall in catch between autumn and spring (from a maxi¬
mum of 2-5 /day in October 1958 to 0-5/ day in March 1959, and
0-5 / day in October 1959 to 0 / day in March 1960) implies mortality
in the winter months. In early May 1960 the relative proportions
of immature and spent individuals in the population was in the
ratio 78% : 22%, and in February 1961 69% : 31%. In both cases
this is an inversion of the ratio of autumn 1960. Callows were not
observed until June and therefore it is concluded that the majority
of the females forming the May peak had overwintered from the
previous season. The spring reversal of the immature / spent ratio
suggests that most of the winter mortality fell on spent individuals
which had laid eggs in July and August, while immature females
survived to lay early in the summer following emergence.

The proportion of mature females rose rapidly in June, falling
slightly in July, and rising again in August before declining to
zero in the autumn. This June- July peak was followed a month
later by an increase in the proportion in which eggs had been laid ;
this also fell slightly before rising to a maximum in the autumn.
This is in agreement with early oviposition by females surviving
the winter, in that there is in June and early July a trend towards
the parous state due to egg-laying by overwintering females which
was temporarily reversed later in July and in early August as the
new generation of immature females emerged. In addition, the
mean ovary length reached a peak in June- July falling as eggs
were laid, and rising in July- August as the emergent generation
matured.

These observations confirm the suggestion that females
emerging late in the summer overwinter as adults and breed early
in the following season. In this work no male reproductive organs
were examined as no significant number of males appear to over¬
winter; there is a single peak of numbers and activity and it is
concluded that the cycle is far simpler than in the female where
at any one time a sample will show gonads covering a wide range
of maturity.

Tipton’s (1960) dissections of a small number of adult P.
madidus of both sexes suggested that for the main summer
emergence the gonads mature more rapidly in the males than in
the females. If this normally occurs it will allow early fertilisa¬
tion of overwintering females by the first males to appear.

P. madidus is widely distributed in woodland and grassland
but is most frequent in the latter. It is plastic in its daily activity
rhythm tending to be diurnal in grassland, and nocturnal in wood¬
land (Williams, 1959b, Greenslade, 1963b).

Abax parallelepipedus (Pill. & Mitt.) (figure 1). At Silwood
active adults first appeared in March, becoming abundant in May
after which catches fluctuated about the same level, apart from
a slight increase in July and early August; at the end of August
numbers declined rapidly although occasional individuals were
trapped up to mid-November. Copulation was frequent during
the summer maximum. Overwintering adults of both sexes were
found under logs and in litter.

165

1965]

The sex ratio in traps in two week periods in 1960 are shown
in table 2.

Table 2

Sex ratio of A box parallelepipedus in traps, 1960 (%)

Month May

No. of Abax examined 61 62

No. 86 35

% 59 56

June

July

Aug.

Sept

Oct.

75

68

127

151

105 98

45 11

5

12

42

39

75

92

60 44

22 4

2

4

56

57

59

61

57 45

49 36

40

33

No callows were seen. Larvae occurred throughout the year,
being most abundant in traps in September and October.

The life history has also been investigated by van der Drift.
In his account adults were first active in early May with no initial
dominance of female activity. This agrees with table 2 and is in
contrast with P. madid us. Eggs are laid in the summer and
autumn, and the presence of females with mature ovaries in May
led van der Drift to conclude that some emerge in the autumn
and do not lay eggs until the following season; thus old females
reproduce in the spring and summer, and young in the summer
and autumn. He recorded larvae from October until May.

At Silwood a high percentatge of males in traps in May, and
recorded male overwintering suggest that in this species, unlike
P. madid us, it is not only in late emerging females that reproduc¬
tion may lx* delayed until the following season.

Abax parallelejyipedus is a woodland species most frequent in
bracken and scrub rather than bare litter. It is nocturnal.

Calathus fuscipes (Gz.) (figure 1) and C. erratus Sahl. Adults
of C. fuscipes were trapped most commonly at Silwood from July
to October, although occasional specimens were taken throughout
the year. The life histories of this species and C. erratus are
described by Gilbert (1956) in North Wales, and are apparently
similar. The account summarised here applies specifically to
C. errattis.

Larvae overwinter and breeding takes place in the following
summer. Callows appear in May and June with maximum
adult activity in July and August. Egg laying begins in July and
may continue until the end of October. The winter is spent in
the third larval instar. A state of pre-pupal torpor was recorded
in larvae, being entered from January to April. In both species
some adults may breed in two seasons.

C. fuscipes is a nocturnal grassland species. Gilbert's observa¬
tions suggest that C. erratus is also nocturnal. Both species occur
in the same type of habitat, but Lindroth (1945) suggests that C.
erratus requires a soil with a higher calcium content.

C. melanocephalus (L.) (figure 1) and C. ynollis (Marsh.). At
Silwood the life history of C. melanocephalus was found to be very
broadly the same as that of C. fuscipes. C. melanocephalus and
C. mollis were also investigated by Gilbert who found them to be
similar, but showed that there were some differences between the
preceding pair. Again his account is cited.

166

[April

The adult maximum occurs in September and October and
larvae overwinter. In all four species pupation occurs in April
and early May, but the two species pairs differ in the time by
which the gonads are mature. In C. erratics and C. fuscipes
adults are all mature by August, while in the other two species
complete maturity is not reached until September.

In C. mollis and in C. melanocephalus all larval instars were
present during the winter. In C. mollis there is evidence that
individuals may breed in two seasons.

C. melanocephalus is a nocturnal species of grassland, although
it occurs in a variety of habitats from sand dunes to conditions
which are almost montane. C. mollis , also nocturnal, is restricted
to sandy habitats.

C. piceus (Marsh.) (figure 1). Adults were trapped from April
until December and in large numbers from May to the end of
August with a maximum just before the autumn decline. No
larvae or callows were found. According to Larsson it is a larval
overwintering species and in Denmark has an August-September
maximum.

C. piceus occurs in the same woodland litter habitats as Nehria
hrevicollis ; it is nocturnal.

Syyiuchus nivalis (Pz.) (figure 1). In July 1959 this species
was abundant in traps although in 1960 only two individuals
were found. A larva was taken (25/10/60) which may belong
to this species. Lindroth (1956a) has described the life history in
Sweden where it shows a July adult maximum, overwintering as
the larva.

Synuchus occurred in the edge of woodland, in bracken and
scrub, and in grassland. It is nocturnal.

Agonum muelleri (Herbst). Tipton found this species to be a
spring breeder with overwintering adults ; maxima occur in May,
and August-September.

It has a wide habitat range occurring in damp places but also
in arable fields on very dry, sandy soil. Overwintering adults are
common under bark and in other refuges in woodland. It is
plastic in its daily activity.

Agonum dorsale (Pont.) (figure 1). This species occurred in
traps from March to October with a maximum in May and an¬
other smaller one in the autumn ; adults were found under
stones and logs in the winter months. Callows occurred in
August and September. Dicker (1951) has recorded oviposition
by this species on the under-side of strawberry leaves from May
to July; ova required 7-10 days incubation, and in one observa¬
tion the imago emerged exactly four weeks after the hatching of
the larva. This is therefore an adult overwintering species and a
summer breeder. Lindroth’s figures for South Sweden show a
June maximum and a slight increase in numbers in September.
Geiler (1960) recorded July maxima in traps in central Germany.

167

1965]

A grass and arable land species particularly common in
calcareous localities; daily activity is plastic.

Agonum viduum (Pz.), A. obscurum (Hbst.), A. fidiginosum
(Pz.), and A. thoreyi Dej. These four species were studied by
Dawson. They occur in damp habitats and their daily rhythms
of activity are undescribed. All overwinter as adults, breeding in
the summer. They differ mainly in the timing of the adult
maxima.

Adults of A. obscurum occur throughout the summer; breeding
last from June until August, and callows emerge from September
until the end of November.

A. jidiginosum adults breed earlier in the year in May and
June, and callows appear from August onwards.

A. thoreyi resembles A. obscurum, breeding in June and July.

A. viduum breeds from Mav to July, but callows onlv emerge
from mid-June until the end of September.

Discussion

Classification of Life History types

The systematic account shows that the distinction between
adult and larval overwintering species holds good for almost all
the Carabidae included. The only real exceptions are the larval
overwintering Harpalus rufipcs and Abax parallelepipedus in
which a degree of adult overwintering occurs. In both cases this
appears to be due to some adults breeding early in the summer.
The resulting callows are active in the autumn of the same year
and overwinter as adults. To a much lesser extent this also
occurs in other larval overwintering species, for example Ptero-
stichus madidus. In addition, in many of these species some
adults which have bred survive to enter the winter and may
breed again in the following season. However, the initial division
on the bases of the main overwintering stage remains valid, but
there are differences between species within these two life history
groups.

In the larval overwintering species, apart from variation in
the extent to which winter adults occur, there is an obvious
division between those species with two annual maxima, Carabus
problcmaticus, Leistus ferrugmeus , and Nebria brevicollis, and the
remainder with one maximum. Similarly among the adult over¬
wintering species some habitually show a bimodal curve of an¬
nual adult activity, for example Carabus nemoralis, Pterostichus
cupreus, P. vernalis and Agonum fuliginosum ; others, for example
Notiophilus species and Bembidion lampros tend to occur as
adults throughout the summer with only a slight autumn increase
in catches to indicate the emergence of young imagines. How¬
ever, there is a complete range between these extremes, and also
the amount of autumn activity may vary from year to year.

The catches of adult overwintering species in certain traps at
Silwood in 1959 and 1960 are shown in Table 3.

168

[April

Table 3

Catches of adult overwintering

species,

1959-60

1959

1960

Total catch

156

126

Catch from August onwards

5

35

Early Summer catch

151

91

In the species concerned, the autumn emergence occurred in
August and September and catches from then onwards can be
subtracted from the annual total ; the remaining catches are those
made during the breeding maximum. This shows that there was
relatively very much more autumn activity in 1960 than in the
previous year.

The Carabidae studied at Silwood Park fell into several groups
according to the time of maximum annual adult activity. In
figure 5, records from pitfall traps are summarised, showing the

LORICERA PIUCOMMIS
ACOMUM DORSAIE
NOTIOPHILUS 0 SPP)

CARA&US NCMORAUS
NE&NA BREVlCOtUS (SPRING)
AMARA COMMUNIS
PTEROSTICHUS CAERUIESCCMS
STOMIS PUMICATUS
BEMBIDION L AMIPROS
AMARA LUN1COLLIS
HARPALUS AFPINIS
CARA&US VIOLACEUS
CyCHRuS CARABOIDES
SYNUCHUS NIVALIS
PTEROSTICHUS MtA&IDUS

P. MELANARIUS
HARPALUS RUFlPES
CALATHUS PlCEUS
ARAX PARALLELEf IPEDU*
PTEROSTICHUS NIGER
CALATHUS FUSCIPES
C. MELANOCEPHALUS
CARA&US PROBLEMATICUS
NEBRIA RREVICOLUS (AUTUMN)
LEI ST US FERRUGINEUS

Fig. 5. — Annual distribution of locomotor activity in Carabidae from pit-
fall catches; horizontal lines : periods when species were frequent
in traps; blocks : months of maximum catches.

FACIES

i n m

— I — I — I — I — I — 1 — I — 1 — I — I — I —

7 FMAMTJASOND

month of maximum frequency for each species, and, also, on the
basis of the experience of three years' trapping, the period in
which more than occasional individuals occurred. In those
species with two maxima, the one immediately following emer¬
gence is only shown for N . brevicollis.

The maxima show a succession through the year but three
seasonal facies can be distinguished.

I. March-June: — Loiiccru pilicornis, Agonum do sale, Carabus

nemoralis, Amara communis, Notiophilus 3 spp., Stomis
pumicatus, Nebria brevicollis (spring emergence), Bem-
bidion latnpros, Pterostichus caerulescens.

II. July and August: — Amara lunicollis, Harpalus rufipes , II.

af finis, Carabus violaccus , Synuchus nivalis, Pterostichus
melanarius, Calathus piceus , Abax parallelepiped us,
Pterostichus niger, Cychrus caraboides, Pterostichus
madidus.

III. September and October: — Calathus fuscipes, C. melanoce-

phalus, Carabus problenuiticus, Nebria brevicollis (autumn
breeding season), Leistus ferrugineus.

The more abundant species, especially N. brevicollis and P.
madidus, tend to be trapped throughout the year, and conversely
the occurrence of less common species show’s more restriction to
limited periods; therefore the latter may be most conveniently
used to define the three facies.

The period March to June was characterised by the trapping
of Stomis and Amara communis, and newly-emerged N. brevicollis
are also abundant. As A. communis declined, A. lunicollis ap¬
peared in numbers and defined the beginning of the next facies
lasting through July and August. This can be rather narrow ly
described by the maximum activity of Carabus violaceus, Cychrus
and Synuchus. and also by the peak activity of P. ituididus. As
mature A. lunicollis disappeared from traps in late August there
was a rise in the catches of Calathus fuscipes and C. mclanoce-
phalus, indicating the replacement of the summer by the autumn
facies. Typical of the latter are breeding N. brevicollis and L.
ferrugineus.

The true maxima of spring facies species occur from late April
until June, and extension of this period back to the beginning of
March is due to the fact that the majority of the spring species
overwinter as adults, and may appear in numbers, presumably
as temperature permits, from the end of February onwards.

During November and December the only adult Carabidae
commonly trapped were either survivors of the summer and
autumn facies, P. madidus, N. brevicollis, L. ferrugineus, and the
two autumn Calathus species, and newly emerged summer-larvae
species, P. caerulescens and Notiophilus species; of these nine
Carabidae five (55%) overwinter as larvae. In .January and
February Nebria and P. madidus still occurred, with the adult
overwintering species Loricera, C. nemoralis, Notiophilus species,

170' | April

B. lanipros and P. caerulescens ; of these, two out of nine species
(22%) overwinter as larvae.

The percentage of larval overwintering species in each facies
may also be compared (table 4).

Table 4

Incidence of larval overwintering species in seasonal facies

Facies

No. spp.

No. larval over¬
wintering spp.

% larval
overwintering

I Spring

11

1

9

II Summer

11

10

91

III Autumn

5

5

100

From November to February the species were selected by their
relative abundance in traps within a given period, and the per¬
centage figures are not strictly comparable with those for March
to October where species are placed in a facies, according to their
maxima when the whole year is considered. However, during the
period March to October there is an obvious replacement of
adult overwintering species which are active early in the spring,
by larval overwintering species which, by the end of June, become
the most numerous. In agreement with this, the November to
February figures show a reversal of the trend with the autumn
emergence of adults of spring-breeding species, which by January
and February predominate.

Carabidae and the microclimate

The basis of the argument outlined here is that in the areas
and habitats considered and within normal climatic limits, both
high temperatures and high humidities are favourable to
Carabidae. Mellanby (1939, 1940, 1958), Williams (1940), Falconer
(1945), Nicholson (1934), Wigglesworth (1953), Collioun (1960)
and others show that activity and rates of development in insects
increase with increase in temperature. This is not a simple
relationship as there are conditioning effects. That locomotor
activity in Carabidae varies with temperature has been demon¬
strated from pitfall captures by Briggs (1961) and Greenslade
(1961). Williams and Osman (1960) suggest that in Northern
Europe temperatures rarely even reach the optimum for insect
species.

Tipton (1960) and Kless (1961) showed that many Carabidae
require a high humidity, by relating the habitats of certain species
to the humidities they preferred and tolerated; Hamilton (1917)
and Kern (1912) noted that Carabid larvae were more susceptible
to desiccation than the adults.

The temperature and humidity of the Carabid environment
commonly vary inversely, so that to enjoy a high value of one a
low value of the other must be endured. The profound effect of
low winter temperatures on the annual cycles of insects in Northern
Europe shows that temperature is generally the most important.

1 965 1

171

Thus for those sjx*cies which can endure low humidity, habitats
with higher temperatures are the most favourable.

A comparison of woodland and grassland shows the differences
in temperature and humidity between sheltered and open
habitats.

Observations recorded by Geiger (1959), MacFadyen (1957)
and others demonstrate that a cover of vegetation lowers mean
temperatures at ground level and reduces and retards the daily
and seasonal fluctuation, in comparison with more open habitats.
On the Imperial College Field Station in August 1960 it was found
that in woodland and grassland the minimum temperatures
reached at the soil surface were the same but maximum tempera¬
tures in the latter were 5-7 °C. higher than in woodland. In grass¬
land the maximum was reached between noon and 4 p.m. (G.M.T.)
but in woodland not until some six hours later. Similar tempera¬
ture differences were noted by Tischler in a comparison of heavy
and light soils (1955). In some types of habitat, however, high
temperatures and humidities are associated, especially where
stones or other cover under which humidity is high, are scattered
on bare ground. Here large concentrations of Carabidae, both
individuals and species, have been recorded (Greenslade, 1963c).

The Carabidae studied at the Imperial College Field Station
were divided among woodland (litter and bracken), grassland
(arable and grass heath), and widely distributed species (Green¬
slade, 1963a). These habitats were part of the temporal vegeta¬
tion succession: — Bare ground-* Weed cover * Grass heath-*
Scrub-* Oakwood-* Beechwood. Here arable land stands for
the initial stages and bracken for scrub as it is typical of this
stage. Tischler (1955) considered that in some cases soil type was
more important than the vegetation cover in determining Carabid
distributions, but in this case where all stages of the succession
occurred on the same soil type this does not apply. Williams
(1959a) suggested that the richness of the edaphic fauna was
governed by litter development. Again this does not agree with
the Carabidae of the habitats investigated at Silwood Park. A
total of 16 species were described as woodland, and 49 as grass¬
land species, while seven were generally distributed. Thus the
richest Carabid fauna was found where litter development was
least. Therefore it was concluded that microclimates associated
with different types of vegetation were the most important factor
determining the occurrence of Carabidae.

Habitat and Activity

The relationship between different habitats, that is their
microclimate properties, and daily and annual cycles of activity
in Carabidae can be examined. If locomotor activity in Carabids
is governed mainly by temperature it is evident that open habi¬
tats will favour diurnal activity, and sheltered ones nocturnal.
In those species which are limited by humidity, activity in open
habitats will tend to be restricted to the night. In agreement

172

[April

with this, Williams (1959a) found more diurnal activity in
Carabidae in open scrub than in closed canopy woodland. Simi¬
larly Tischler (1955) recorded more diurnalism on sandy than on
heavy soils; it was also noted that on the former nocturnal
activity was greatly reduced on cold nights. This can be further
illustrated by the Silwood results. The life histories and habitats
of species and their activity cycles are shown in Table 5, which
summarises the systematic account. In the 26 species included
there is relatively more diurnal activity in the species from grass¬
land habitats than those from woodland, for those which are
plastic will tend to be diurnal in grassland and nocturnal in wood¬
land, as in Pterostichus madidus (Williams 1959b, Greenslade
1963b). If the widespread species are added to both major habitat
groups, the distribution of activity times in the species from each
is: — woodland, 12 nocturnal and 3 diurnal species, and grassland,
8 nocturnal and 9 diurnal. It must be pointed out that the
species studied at Silwood Park represented neither complete nor

Table 5

Summary of habitat, activity and life history of Carabid species

Daily

Annual

Overwintering

Species

Habitat

Activity

Activity

stage

Notiophilus rufipes

D

S

a

Calathus piceus

N

M

1

Nebria brevicollis

L

N

A

1

Cychrus caraboides

N

M

1

Notiophilus biguttatus

D

S

a

Abax parallelepipedus

N

M

1

Carabus problematicus

B

N

A

1

Leistus ferrugineus

N

A

1

Stomis pumicatus

N

M

a

Pterostichus niger

N

M

1

Carabus violaceus

N

M

1

Synuchus nivalis

N

M

1

Loricera pilicornis

W

P

S

a

Notiophilus substriatus

D

S

a

Pterostichus madidus

P

M

1

Carabus nemoralis

N

S

a

Amara communis

P

s

a

A. lunicollis

H

P

M

a

Calathus fuscipes

N

A

•' 1

C. melanocephalus

N

A

1

Harpalus rufipes

N

M

1

H. affinis

P

M

1

Pterostichus caerulescens

D

S

a

Bembidion lampros

A

D

S

a

Pterostichus melanarius

N

M

1

Agonum dorsale

P

S

a

I L —

Litter

N = Nocturnal

S = Spring

a = adult

Woodland B =

lw=

Bracken

P = Plastic

M = Summer

1 = larva

= Widespread

D = Diurnal

A — Autumn

Grassland IH =

Heath

l A = Arable

173

1965]

random samples of the species present in each habitat. However,
there were 16 woodland species of which nine were studied, while
in the grassland habitats there were 49 species of which 1 1 are
included here. Of the other grassland species Amaro plebeja and
Ptero8tichu8 cuprcus are mentioned in the systematic account and
are diurnal as is Asaphidion flavipes (L.), another grassland
species (Greenslade 1963b). Also in grassland in the area studied,
IS species of Amara occurred; many of these possessed a brassy
metallic integument, and Tischler (1955) noted that this was
associated with diurnalisra.

Habitat and overwintering can also be related. Of the wood¬
land species, one-third (3/9) overwintering as adults and the
number of species belonging to the spring, summer and
autumn facies are respectively 2:4:3. In contrast, more than
half the grassland species overwinter as adults (6/11) and the
spring, summer, autumn proportions are 5:4:2. Table 5 also
shows a close relation between overwintering stage and activity
times; diurnalism, adult overwintering and activity early in the
year tend to be associated, and conversely, late summer and
nocturnal activity and winter larvae.

As the species studied were not necessarily representative of
the Carabid fauna of the different habitats one cannot relate the
number of species of various activity types directly to habitat.
Hut in any species the daily time of activity is often associated
with a characteristic annual periodicity. As there is indepen¬
dent evidence that the woodland type of microclimate is associa¬
ted with nocturnalism, and the grassland with diurnalism, one
can conclude that in woodland habitats, nocturnalism, winter
larvae, and late summer activity predominate, while in grassland
there is more diurnalism, activity earlier in the year, and adult
overwintering.

Geograpli teal variation

It has been suggested that in South East England Carabid

habitats and activity cycles are related. In a species any of these

characteristics may vary geographically, especially life history,

and this can be attributed to climate. The obvious differences

in a North-South direction are higher mean temperatures and

longer summers in the South, and Tipton (1960) compares

monthly mean temperatures at Greenwich, Copenhagen and

Uppsala. In each, July means lie between 17 and 18 C., while

the January temperatures are Greenwich 4-4 °C., Copenhagen 0-8

C., anti Uppsala — 2*8 C., the March means are respectively 6-2

C., 2-3 CC., and 1-3 °C. The East-West trend is from an Eastern

Continental climate with a great difference between winter and

summer temperatures, to an Atlantic one with milder winters. In

this direction the annual differences are similar to the daily ones

*■

when woodland and grassland are compared. In woodland, cor¬
responding to an Atlantic climate, the amplitude of fluctuation
is least and humidities are higher.

174

[April

For life histories the Atlantic-Continental transition is from
a large proportion of larval overwintering species in the West to
adult overwintering in the East. This was pointed out by
Lindroth (1945) who cited as an example Calatlius melanocephalus
which overwinters as the larva in Britain but as the adult further
East in Europe. Here the predominance of winter larvae in an
Atlantic climate can be equated with their frequency in woodland.
In other species the life history shows no East- West change but
different habitats are occupied. Thus Carabus nem oralis has the
same annual cycle in Britain and Russia, but in the former occurs
in open habitats and in Russia in forest (Hikimiuk, 1948). On
the other hand Loricera pilicomis and Pterostichus madidus which
are nocturnal in open habitats in Germany (Kirchner, 1960) are
diurnal in the same type of habitat in England. It can be sug¬
gested that diurnalism and the occupation of open habitats, with
the advantage of higher temperatures and hence also higher levels
of activity, are permitted by higher humidities in Atlantic Britain.

In a North- South direction the situation is simpler, at least so
far as Scandinavia and Southern Britain are concerned (further
South in Europe information on life histories is scanty). In Eng¬
land spring breeding occurs earlier, and breeding continues later
into the autumn, and this can be related to temperature. The
shorter Northern summer also leads to the double maxima of
adult activity found in many English Carabids, contracting to a
single maximum in Sweden, to which two generations contribute.
The situation in Denmark is usually intermediate. Larval over¬
wintering species in which two maxima become one further North
are Carabus problematicus, Leistus ferrugineus and Nebria
brevicollis ; adult overwinterers include Loricera pilicomis, Amur a
communis, Pterostichus cupreus, P. caerulescens, P. vernalis and
P. nigrita.

Regulation of Life Histones

Very little work has been carried out on the regulation of
annual cycles in Carabidae or on the importance of diapause, but
some observations are made here and preliminary conclusions
drawn from them.

Some Carabid species show distinct and restricted annual peaks
of adult activity, examples being Pterostichus madidus and Nebria
brevicollis, while other species such as Abax parallelepipedus are
active throughout the warmer months of the year. Figure 5 sug¬
gests that the timing of the period of adult activity may be critical
in avoiding competition between adults of Carabid species in any
habitat. For example, Amara lunicollis and A. communis are
closely allied species with similar habits, but their adult activity
maxima do not coincide. Similarly the large black Pterostichine
species considered here form a series, in the order P. madidus,
P. melanarius, P. niger, A. parallelepipedus, of increasing adult
overwintering, and decreasing restriction of the period of the
adult maximum. In P. madidus the amount of adult overwinter-

175

1965]

ing is least and there is a pronounced July- August adult peak,
while in Abax there is extensive overwintering by adults of both
sexes and relatively little variation in abundance between late
spring and autumn. These species are all of the same order of
size, and are mainly adult-overwintering and nocturnal, and there
is also considerable overlap in their food and habitats; the regula¬
tion of the life historv is one wav in which they differ.

W W v

The timing of the annual cycles may also be important for
other reasons. It may ensure that resistant stages are present at
unfavourable periods of the year for there is evidence that
dormant arthropods possess greater ability to withstand desicca¬
tion than active stages (Birch and Andrewartha, 1942). On the
other hand Lindroth (1956b) has pointed out the necessity for
the synchronisation of the annual cycle; should the breeding
activity of all or part of a population become out of phase with
the normal seasonal rhythm there is an increased probability of
its members being wiped out by unfavourable climatic conditions.
Lees (1955) has suggested that diapause should be regarded
primarily as a timing mechanism to regulate the life cycle, either
to synchronise adult emergence, or, as Andrewartha (1952) has
emphasised, to ensure that active stages are present when food
supplies or physical conditions are suitable. Nebria brevicollis
is the most thoroughly studied British Carabid and has a distinct
adult summer diapause, and possible selective advantages associ¬
ated with this can be considered.

First there is the possibility that in Britain the adult diapause
in July and August is a device to survive low humidities in the
summer months; the species’ nocturnal woodland habits together
with Tipton’s (1960) work on its humidity relations, show that
it is susceptible to desiccation. However, the 30 year averages of
rainfall, temperature and humidity at Kew give no support to
this; July and August show both higher temperatures and rain¬
fall than either June or September and there is no fall in humidity
during the hotter months. However, this factor may be important
further South in Europe. It is more probable that the summer
diapause delays breeding until the autumn when some environ¬
mental factor, perhaps humidity becomes suitable for the larvae,
as Tipton showed that they are more susceptible to desiccation
than the adults.

In addition, diapause may correlate activity in N. brevicollis
and the availability of food. Lees (1955) cites a number of cases
of phytophagous arthropods in which diapause is governed by
factors similar to those which govern the growth of the food plant,
thus maintaining some relation between the development of the
animal and its food supply. It is difficult to relate diapause and
food in N. brevicollis as it is a general predator on Collembola and
other artliropods inhabiting litter (Davies, 1959). However, Evans
(1955) gives a figure of spring and autumn peaks roughly co¬
inciding with those of the Carabid, in the numbers of Acarina and
Collembola under spruce.

176

[April

Finally the diapause may synchronise breeding activity within
populations. Davies (1955) and Williams (1959) found that in N.
brevicollis breeding may extend throughout the winter; the
maximum numbers of first instar larvae were recorded in mid-
November, both by Williams and at the Imperial College Field
Station, and the peak of spring emergence occurs approximately
six months later. Occasional first instar larvae are found until
the beginning of April and if they survive the summer the latest
larvae may be expected to reach the adult state at least a month
before the onset of the main breeding activity in October. In this
way the summer period of adult diapause may ensure that all in¬
dividuals reach a similar state of sexual maturity by the beginning
of the breeding season. More important than this, it will inhibit
spring breeding by the first adult Neb rici to appear, and thus
prevent the establishment of two genetically isolated elements of
the same spatial population. Lindroth (1956b) suggested that
diapause had a similar synchronising effect in Pterostichus
melanarius. Here, there is an autumn and winter diapause in the
second larval instar which all individuals entered even though
external conditions were varied. Thus larvae which may have
hatched over a considerable period in the summer will all enter
the winter in the same stage. After winter inhibition due to cold,
development will be resumed in the spring by a larval population
all in the same instar, so ensuring some synchronisation of adult
emergence.

On the evidence available it is concluded that in Britain the
diapause in N. brevicollis is best regarded not as a device to enable
adults to survive a summer desiccation risk, but as having the
effect of synchronising breeding activity, and ensuring that larvae
appear when conditions are most suitable for them.

Although in most insects which have been investigated long
day length is associated with growth and reproduction, de Wilde
(1962) records some short day species, and noted that they tended
to be autumn breeding. A number of instances are also cited in
short day insects in which diapause is promoted by high tempera¬
tures. Therefore, it is possible that in Nebria brevicollis the
summer diapause may be a response to increasing temperatures,
while breeding is stimulated by short day length in the autumn.

Acknowledgments

I should like to thank Professor O. W. Richards for permission
to carry out the field studies described here in the Department
of Zoology, Imperial College, and the University authorities at
Cambridge for permission to quote from Dr. Dawson’s thesis. The
work was supervised by Dr. T. R. E. Soutliwood to whom I am
very grateful for advice and criticism throughout.

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