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The Forest Tent Caterpillar

SECOND REPORT

BY CLARENCE M. >VEEI)

NEW HAMPSIIIKK C()LLK(iE
AGRICULTURxVL EXPERIMENT STATION

DUKHA:\r

Bulletin 75

flay, 1900

Fig. T)-j. — Distribution of Forest Tent Caterpillar in New Hampshire, 1899.

Circles, caterpillars present ; circles with dot, rather destructive ; circles with

cross, very destructive.

THE FORHST TENT CATERPILLAR

BY CLARENCE M. WEED

'1 lie outbreak of the Forest Tent
Caterpillar in New Hampshire in
1899 was more widespread and seri-
ous than durino^ any previous year
of which we have record. A very
great amount of damage was done to
maple sugar orchards, shade trees,
and apple orchards, as well as to
the general forest growth ; and eggs
were laid for a 1900 brood of worms,
which, in many localities, at least,
threatens to be equally destructive.
The present bulletin is issued to
furnish the people of the state with the latest available infor-
mation regarding the pest, both as to its habits and life his-
tory, and as to the means of combating it. In the bulletin I
have embodied the results of the observations made last sea-
son by myself and my assistant, Mr. W. F. Fiske, as well as
several valuable observations kindly communicated to me by
Miss Caroline G. Soule, who studied the insect at Brandon,
Vermont, and the notes of more than one hundred correspond-
ents who kindly replied to a circular letter I sent out. A few
of the paragraphs are reprinted without important change from
Bulletin 64, issued a year ago.

FiG.3S.-Cocoon in Barberry Leaves.

DISTRIBUTION IN 1 899

The localities in which these caterpillars were destructive
last season are indicated in the map on the inside front cover
of this bulletin. The circles with a cross inside indicate places

no

THE FOREST TENT CATERPILLAR

of very serious damage ; those with a dot inside, less serious
damage, and the simple circles, places where the insects were
numerous enough to be noticed by our correspondents, but
were not very destructive. It is likely that many of these
latter places will have the insects in greater numbers this
season.

An interesting fact brought out by the preparation of this
map is that the insects seem to follow rivers closely in their
spread from one locality to another. The injury has been most
severe along the Connecticut river, where the insects first
appeared in destructive numbers about four years ago.

THE LIFE HISTORY OF THE INSECT

These Forest Tent Caterpillars pass the winter within the
eggshell, the eggs being attached to the twigs in cylindrical
rings, more or less covered with a grayish varnish. In spring,
when the leaves of the trees begin to unfold, the young cater-
pillars gnaw through the eggshells and come forth. They are

then tiny creatures,
scarcely one tenth of
an inch long, show-
ing under a lens that
the blackish body is
thickly covered with
rather long brown-
ish, or grayish, hairs.
The tiny caterpillars
feed upon the ten-
der leaves of the
twig near where the
egg-mass was placed.
In about two weeks
each increases in
size to such extent
that the skin in
which it came from
the egg is too small

Fig, 39.— Cast skins of Forest Tent Caterpiliars. ^^^ ^^- '^^^^ ^^^^

r--

■■- ■■■ "' ^■■..-■A ...l "" ^ . ;■- v<<v;;- --.- '. . -;

, >?,r

•

■^

X

'^-p^'

v^

. 0^

■:*

„,

Fig. 40. — -A mass of Caterpillars on the trunk of a crab-apple tree.
(Photographed by Dr. F W. Russell )

112

THE FOREST TENT CATERPILLAR

then splits open along the back, and the caterpillar crawls out,
clad in a new skin that had gradually been forming beneath
the old one. This skin-shedding process is called moulting:
it is the general way in which insects provide for increase in
size. Some of the cast skins are shown in Fig. 39.

Wherever they go, these little larvas spin a silken thread
which marks their pathway, although the thread is so slender
that a single one is generally to be seen only through a lens,
but in places where the larvae congregate to rest when not feed-
ing, a habit that they have, it becomes quite noticeable. It is
especially so after moulting, for then one can often find on the
end of a forked twig such a miniature tent as is represented in
the picture on the title page of this bulletin, the cast skins
being intermingled with the silken threads.

Soon after the first moult the caterpillars begin feeding

again, eating, of course,
more and more of the foli-
age as they become larger.
A week or so later they
again moult, a process which
is repeated twice, thereaf-
ter, at similar intervals. At
the time of the later moults,
the caterpillars are in the
habit of congregating upon
the trunks or larger limbs
of the tree, often not far
from the ground. Beneath
the mass of larvae there is
an inconspicuous web, in
which the feet are more or
less entangled. The ap-
pearance of the caterpillars
at such times is well shown
in the photograph repro-
duced in Fig. 40. At the
end of about five weeks from the time of hatching from the
egg, the Forest Tent Caterpillars become full grown in this,

Fig. 41. — Cocoons in Apple Leaves.

THE LIFE HISTORY OF THE INSECT

IJ3

their larval state.
They are now ready
to enter upon the next
stage of their exist-
ence, that of the pupa,
or chrysalis. This is
a quiet stage, in which
the insect takes no
food, and is unable
to move about, and
it needs to protect
itself from its various
enemies. Conse-
quently, each cater-
pillar spins from cer-
tain silk glands in

the mouth a shroud F'G. 42.— Cocoon in Currant Leaves.

of silken threads, sur-
rounding itself by an oval cocoon composed of several layers
of silk, the outer ones much looser than the inner, with

the hairs of the
caterpillar inter-
mingled with
the silk on the
inside layers.
When this co-
coon is first
spun it is white,
but the caterpil-
lar soon colors
it yellow with
an excretion
from the body.
The caterpillars
generally prefer
some sort of
frame-work to

Fig. 43.-Cocoon on Fringe-tree. ^'^'^^ their CO-

114

THE FOREST TENT CATERPILLAR

coons upon. They commonly choose the leaves of trees for
this purpose. Sometimes a single large leaf will be used, its
edges being folded over, as in the case of the cocoons in
apple and currant leaves, shown in Figs. 41, 42 and 48,
while, at others, several smaller leaves may be deftly drawn
together, as in the barberry leaf cocoon shown in Fig,
38. If the insect happens to be in a pine tree it will utilize
the pine needles for this purpose, and even such delicate
structures as the panicles of the smoke bush or fringe tree
may serve the purpose. (Fig. 43.) Where the caterpillars are
numerous, the foliage of the trees is almost wholly webbed up
when the cocoons are made, giving the trees a strange, bunchy
appearance. Many of the caterpillars, however, leave the
trees, and seek shelter in other situations, such as crevices in
the rough bark, beneath boards or stones upon the ground,
in the crannies of a fence, along the clapboards or beneath
the gables of buildings.

Wherever the cocoon is spun the caterpillar inside of it soon
changes to a pupa or chrysalis — an oval brown object without

a

b

Fig. 44. — Moths of Forest Tent Caterpillar; a, male; b^ female. Natural size.

legs or wings, able to move only by a feeble wriggle of its body.
In this condition it takes no food, but its tissues undergo such
remarkable changes that about ten or twelve days after the
cocoon is made, a buff-brown moth emerges from the chrysalis
and makes its way through one end of the cocoon. This is
the adult form of the Forest Tent Caterpillar. The male moths
are slightly smaller than the females, as may be seen from
Figs. 44 <i and b, the first of which represents the male and the
second the female, both natural size.

The moths generally make their appearance the latter part

THE LIFE HISTORY OF THE INSECT i i r

of June. Soon afterwards the females deposit their eggs in
masses of about two hundred, each upon the twigs. The
moths, having completed the cycle of life, die soon after the
eggs are laid.

The eggs thus deposited early in July are to remain un-
hatched until the following spring. The actual formation of
the tiny caterpillars from the contents of the egg takes place,
however, within a few weeks after they are laid. The minute
but fully-formed caterpillars may be found within the egg
shells, by a careful examination, any time between September
and the following April. The caterpillars remain during this
long period quietly confined within their narrow houses, but
when the warmth of the spring sunshine penetrates their
abodes, they eat off the tops of the agg shells, and come out
ready to break their long fast upon the tender foliage of the
opening buds.

As a result of much patient watching, Mr. Fiske was fortu-
nate enough to observe one of the moths depositing her eggs.
He has recorded his observations in his notes as follows:

On the afternoon of June 27, three pairs of freshly-emerged Clisiocampa
disstria moths were found in the breeding cages mating, and two of them
placed, without separating, under a bell jar with some green twigs of apple.
At 8 p. m. one pair had separated, and the female was very active, buzzing
around the interior of the bell jar. Fifteen minutes later she had taken
notice of the apple twigs, and was more slowly crawling over them. By
9 o'clock she had selected a site for an egg ring, and had just begun its
deposition. About a dozen eggs were laid at this time, in the form of a
right triangle, one side forming what was to be one edge of the future egg
ring. On what would correspond to the hypothenuse of this triangle she
was now busy depositing more eggs, making each row longer and increas-
ing consequently the width of the future band, still keeping the general
form of the egg mass the same. The placing of the first egg in each row
is accomplished with some difficulty, and is also a matter of some delicacy,
for if it is not placed correctly, the whole band may suffer; but after this is
done, the remainder are easily fixed in their proper positions, the abdomen,
which is stretched nearly to its limit, so moving that each egg slips into tlie
space between the end egg on the row under construction, and the corre-
sponding egg in the row just completed. The eggs are laid at intervals of
about half a minute, and after each is deposited there is a second's
pause, followed by a little pile of bubbles of creamy whiteness, which rise
around it and help to form the tough, protecting winter coat. It is very
difficult to get a good view of the operation at close hand, on account of

Il6 THE FOREST TENT CATERPILLAR

the position in which the wings of the moth are held, drooping and well
covering the abdomen, and it cannot be stated with certainty whether the
egg itself is deposited just before or just after the extrusion of the froth.

The width of the band being decided upon, the rows are made of uniform
length thereafter and the girdle begins to take form. In the case under
observation, as the moth was undersized the band was a narrow one, and
the number of eggs in each row was about seven. When the band was
nearly completed, after about an hour's work, the moth was disturbed,
arid for the remaining distance the rows were anything but regular.
Whether as a result of this break or otherwise, there were a lot of eggs left
over after the ends of the band were united, and these were deposited
slowly and irregularly, with much preliminary feeling about on the lower
edge of the band. This part of the operation required above an hour, or as
long for the placing of a few dozen eggs as it did for the construction of
the girdle proper. The whole time, from the first observation until the egg
mass was finally left, was about two and a half hours. The moth did not
long survive the completion of the ring, but within a few hours, before it
had been a whole day in its perfected form, it died.

A condition that has been repeatedly noticed during the
last three years seems to indicate that in general the instinct
of the moth teaches it to deposit eggs only on trees bearing
leaves at the time the eggs are laid. When a maple orchard
is defoliated one year, it is likely to escape the next year^
unless it is invaded by caterpillars hatched on the surrounding
trees. The moths that develop on such a lot of defoliated
trees apparently fly to the surrounding trees that still bear
leaves before depositing their eggs. Of course this habit is
of advantage to the insect, for the chances of a sufficient food
supply for the caterpillars are greatly increased by it. In
some cases, however, the explanation is that the caterpillars
completed the defoliation of the trees before they were full
grown, and then migrated to new feeding grounds.

THE POPULAR NAME OF THE INSECT

There has been considerable discussion of late among ento-
mologists as to the best popular name for this insect. As was
said in my former bulletin, "its common name, Forest Tent
Caterpillar, is not very satisfactory, because, first, the insects
are as likely to be found in apple orchards as in forests ; and,
second, they do not make tents in the complete sense that the

THE POPULAR NAME OF THE INSECT

117

Fig. 45. — Caterpillars feeding upon Elm Leaves.

nearly-related American Tent Caterpillar does." Wirious sub-
stitutes for this name have been recently proposed, none of
which, however, seem to me sufficiently satisfactory to warrant
a change. Mr. M. V. Slingerland of New York has proposed
that the insect be called the Forest Tentless Caterpillar, but
the objections to this are, first, that it is not absolutely a tent-
less caterpillar, many of the caterpillars making in early life
miniature tents, like the one shown on the title page of this
bulletin ; and, second, as Dr. L. O. Howard has pointed out,
there are a great many other tentless caterpillars that feed
upon forest trees.

Il8 THE FOREST TENT CATERPILLAR

DESCRIPTION OF THE LIFE STAGES

^^^.— The egg mass of this Forest Caterpillar is in the form
of a belt encircling the smaller twigs of the various food-plants.
Its general shape is represented in Fig. 46, the length of the
belt varying from one fourth to one half of an inch ; the diame-
ter is usually one fourth of an inch.
The belt terminates abruptly at each
end, although it is not as a rule
squared off. The outside of the belt
consists of a glistening, varnish-like,
brownish or lead-gray material, which
covers the eggs. When the eggs are
first laid, and for some months after-
ward, this covering remains entire,
but as the winter passes it becomes
more and more broken, so that by
spring it generally has a rather rag-
ged appearance. By removing the
covering the eggs will be found be-

FiG. 46. — Eo;^ Masses. .1 *.-„-ju -j ^ ' i.^.

^ '"' neath, restmg side by side at right

angles to the supporting twig. Each egg is a trifle longer than
wide, and is covered with a reticulated network of the same
varnish-like material that conceals the mass as a whole; this
network serves to attach the eggs to the twig and to each other.
The eggs are of a dull gray color, showing white in some places.
When the caterpillars hatch they gnaw off a circular cap on
the upper end of the egg, and come out through the hole
thus made. Each egg is about one twentieth of an inch long.
The number of eggs in one belt varies from less than 150 to
more than 225, the average being nearly 200. When the in-
sects are so abundant that there is a partial exhaustion of the
food supply of the caterpillars, the normal number of eggs are
not laid, the egg rings being much smaller than usual.

Larva. — The full-grown Forest Caterpillar is about two inches
long and about one fourth of an inch thick. In shape it is
cylindrical, with six jointed legs arranged in pairs directly
back of the head, eight thick prolegs along the middle, and

DESCRIPTION OF THE LIFE STAGES

I in

two prolegs at the head end of the body. The head is dark
bluish, and the body in general has a bluish appearance, more
or less modified by the longitudinal series of marks and stripes.
Along the middle of the back there is a series of whitish or
cream-colored marks of the shape shown in I'lg. 47 a. Along

a

Fig. 47. — Forest Tent Caterpillar ; a, markings on one ring of the back ; b, markings

on one ring of the side.

the upper part of each side there is a broad blue stripe, bordered
above and below by a narrow, irregular, yellowish-white line.
On the lower surface the color is bluish black. The whole
body is sparsely clothed with rather short hairs.

Cocoon. — When the cocoon is not made within a leaf the loose
outer silk varies greatly in the area occupied. An average
size would be about one and three-fourths inch long by one
inch wide. The inner firmer part of the cocoon is generally a
little less than one and one-fourth inch long by one-half inch
wide. The inner cocoon is colored yellow by the material
voided by the caterpillars just before pupation, but the outer
fluffy silk is generally white, because it is not reached by the
yellow liquid. As already stated in a previous paragraph,
when the cocoon is made within a leaf its outer appearance
varies greatly, according to the material employed.

Pupa. — The pup^ is the dull brown, mummy-like object to
be found within the cocoon. It has neither legs nor wings,
and is unable to move otherwise than by a wriggling motion
of its body. The pupa that is to develop into a female moth

I20 THE FOREST TENT CATERPILLAR

is larger than that of the male. The sizes are approximately
as follows : Male, length three-fourth inch, width five-sixteenth
inch; female, length nine-tenth inch, width three-eighth inch.
The pupa is commonly more or less covered with the light
yellow powder which gives the cocoon its yellow color.

Moth. — The male moth (Fig. 44 a) is considerably smaller than
the female (Fig. 44/-'). The former has a wing expanse of one
and one-fourth inches, while the latter expands one and one-
half inches. Both are light buff-brown, the color of the male
being considerably deeper than that of the female. Along the
middle of the front wings there is an oblique darker band, as
shown in the figures. The feelers or antennae of both sexes
are feathery, but those of the male are much broader as well
as somewhat longer.

BIRD ENEMIES OF THE CATERPILLARS

In Bulletin 64 mention was made of many sorts of birds
that feed upon these insects. During last season these, feath-
ered allies continued their good work. Under date of June 26,
Miss Soule wrote from Brandon, Vt, : "I am almost sure that
the caterpillar has drawn the birds here, for in four summers
I have never seen nearly so many as this year, though I
have been observing birds for years. Too much cannot be
said for the birds. The orioles and the redwinged blackbirds
especially are stripping the trees of pupae. Yesterday I saw
orioles at work on a beech and an oak that had been badly
eaten at the top, and I pulled down some of the branches and
examined each of-the many cocoons. Every one had the neat
slit these birds make, and every pupa was gone. The baby
orioles all learn to do this as soon as they can fly from one
twig to another." A little later cedar birds were seen flocking
to the trees, opening cocoons and devouring the pupas. On
July 8, Miss Soule wrote : " The number of birds is really
amazing, and the thorough work they do is delightful." Re-
garding the birds that eat the moths, the same keen observer,
in an admirable article in the Sp7'mgfteld Republican^ said :
" Many cocoons gave the moths in July, and these little brown
moths could be seen in great numbers flying about the maple.

BIRD ENEMIES OF THE CATERPILLARS

12 I

•elm, apple, pear, ash, and other trees, laying their eggs near
the tips of the twigs, — flying by daylight. Then the birds had
another feast. Vireos of four kinds, fly-catchers of three kinds,
both cuckoos, robins, rose-breasted grosbeaks, tanagers, cedar-
birds, cat-birds, orioles, redwinged blackbirds, martins, and
sparrows fed on the moths as they had done on the pup;i,' and
larvae. Chipping sj^arrows became expert 'lofty tumblers' in

Fig. 48. — Apple Leaves, partially eaten ; one showing cDcoon.

their zigzag pursuit of the flying moths, and even the English
sparrows had a brief season of usefulness, for they really ate
some of these moths, though they would not touch either pupaj
or larvae."

The Baltimore orioles were among the most elTicient ene-
mies of the caterpillars, destroying them in great numbers for
their own food as well as to feed their young. These orioles
are exceedingly useful birds, as they generally feed freely upon

122

THE FOREST TENT CATERPILLAR

Fig. 49. — Baltimore Oriole attacking nest of American 'J er.t Caterpillar.

hairy caterpillars, being among the most destructive enemies
of the common American Tent Caterpillar. (Fig. 49.) They
should be encoura2:ed to nest and remain about the farm and

garden.

INSECT PARASITES

The most numerous parasites of these caterpillars were the
small two-winged flies called Tachina flies. At least three
species ^ of these friendly insects were destroying the hosts of
caterpillars. One of these flies is represented somewhat mag-

1 The three species were kindly determined by tlie Entomological Division of the
U. S. Department of Agriculture as Tachina imlla Walk., Exorista ftitilis O. S.,
Front'nia frenchli Will.

INSECT PARASITES

123

b a

Tacliinid Parasite of Forest Tent
Caterpillar : a, fly ; b, puparium.

Fig. 50,

nified in Fig. 50^?. It looks much like a common house-Hy,
and is of about the same size. This Hy deposits a whitish egg
upon the skin of the caterpillar, generally after it is more than
half-grown. The ^g^ soon develops into a tiny grub that bur-
rows through the egg-shell
and the skin of the cater-
pillar into the inside of the
body. There it remains,
absorbing the tissues of its
host, and gradually increas-
ing in size. In due time it
becomes fully developed in
this grub state, and breaks through the skin of the caterpillar.
It is then a good-sized, white, oval, footless grub. The cater-
pillar has generally spun its cocoon before the parasite comes
from its body, so that the parasite finds itself inside the cocoon
when it gets outside the caterpillar. The grubs of two species
of these Tachinid parasites work their way through the cocoon
and drop to the ground, while the other seems to remain in the
cocoon.

The parasitic larvae have now to enter upon the quiet pupa
stage. For this purpose the outer skin turns brown, and
becomes hard, forming a protective covering for the insect
inside. This is called ihe ptcparhnn (Fig. 50 b). Within this
covering the insect changes to a pupa, to change again about
two weeks later into an adult fly.

These parasites were very abundant last season, and are,
doubtless, one of the most efficient checks upon the caterpil-
lars. In some localities they seem to have nearly brought the
outbreak to an end, and it is probable that they will do still
more good this year. A correspondent at Campton, N. H.,
writes that in June great numbers of strange flies were seen in
the woods and pastures. They were probably these tachinids.

The Ichneumon flies of the genus Pimpla^ also did good ser-
vice in destroying the caterpillars. The adult is a four-winged
fly that deposits eggs in the caterpillars or newly-formed chrysa-

-^ Pimpla conquisitor yN2iS the most abundant species; a few P. />eda/is were also
reared.

124

THE FOREST TENT CATERPILLAR

Us after the cocoons, are spun. The method of egg-laying is
shown in Fig. 51. The eggs hatch into minute grubs that

develop at the expense of the
chyrsalis, finally eating up near-
ly all their substance. About
two weeks from the time the
eggs are laid the parasitic lar-
vae change to pupae, and very
soon afterwards again change
to adults.

Two other small parasites
of the Chalcid family were
also reared, although they
were not at all abundant. One
of these was the species called
by entomologists Diglochia
o7nnivo?'i^s, while the other has
not been determined. We

^:i

Fig. 51. — Ichneumon fly depositing an
egg within cocoon. (Slightly magnified.)

have also reared one species of parasite from the eggs of the
Forest Tent Caterpillars.

BACTERL-VL DISEASES

It is a well-known fact that seasons of dry weather are favora-
ble to the development of insects injurious to plant life. This
is especially true of caterpillars, and so the extraordinary dry-
ness of the spring and summer of 1899 was very favorable to
the increase of the Forest Tent Caterpillars. Their various
bird and insect enemies did good service in destroying them,
but the bacterial diseases that are likely to affect such insects
during wet seasons did them little harm. The recent outbreak
of the common American Tent Caterpillar was brought to an
end two years ago chiefly through the agency of such a dis-
ease, the wet weather being favorable to it.

These bacterial and fungus diseases have been present, to
a limited extent, among these caterpillars, both last year and
the year before. Should next June be a very wet month,
these diseases would probably do much to check the outbreak.

SUCCESSFUL REMEDIAL MEASURES 125

USELESS REMEDIAL MEASURES

As is always the case when a little-known insect becomes
destructively abundant, a great many useless remedies for
these caterpillars have been proposed. One of the most fool-
ish of these is the insertion of sulphur in the trees in holes
bored by an auger — a time honored fake that has, at various
times, been proposed for all the ills that trees are heir to.
Kerosene has also been applied to bands around the trees,
greatly to the injury of the latter, as the kerosene soaks into
the sapwood and kills the tree. The authorities of one \'er-
mont town "sprayed many trees with a mixture of kerosene,
Paris green, and soapsuds, which burned the leaves very badly
and seemed to injure the trees." Such measures are usually
the result of ignorance.

SUCCESSFUL REMEDIAL MEASURES

In Bulletin 64 I printed a summary of the remedial meas-
ures, which, after a careful study of the insect, seemed likely
to be useful. As I then wrote, the practical value of most of
these measures depends largely upon the conditions under
which they are to be applied. A suggestion that is easily
applicable to a few small trees in an apple orchard may be
wholly inapplicable to the larger trees in a woodland. The
abundance of the caterpillars, the nature and number of the
trees infested, the season of the year, and the means at hand
are all to be taken into consideration.

In the paragraphs below I have revised these directions by
incorporating the knowledge which the past season's experi-
ence with the pest has given, from our own observations as
well as from those of the various correspondents who replied
to the circulars sent out.

Egg destruction. — There seems to me no reason for modify-
ing the statements made under this heading in Bulletin 64,
except to emphasize the fact that this method is not at all
practical in cases of serious infestation. On a bright day,
when the trees are bare of leaves, egg-masses may be easily
seen. The cutting off and burning of these masses is often

126 THE FOREST TENT CATERPILLAR

practicable in a young apple-orchard, although it is generally
considered impracticable in orchards of large trees. It gener-
ally would be out of the question in woodlands, of course,
although in case of a few ornamental maples or other trees on
the home grounds such egg-collecting might well be worth
while. The gathering may be done by sending a sharp-eyed
boy into the trees to cut or rub off the glistening masses, or by
means of a pruning hook or a pair of long-handled pruning
shears. The belts of eggs should be burned after they are
gathered. When the insects are abundant these e^g masses
are so thick that to cut them off one must cut off nearly all
the twigs — a ruinous proceeding. In such cases it is better
to spray with arsenate of lead.

Killing the young caterpillars. — On small trees, where the
caterpillars are easily reached, something may be accomplished
by swabbing the colonies of young larvae when at rest by
means of a bunch of cotton waste, old rags, or something simi-
lar. In rainy weather one is more likely to find the larvae
massed together during the day than in bright weather.

Use of water. — One of the easiest ways of knocking the
caterpillars off the trees is by the use of a forcible stream of
water from a hydrant or good force pump. In Hanover the
town authorities used streams from the hydrants with an eleven-
sixteenth-inch nozzle from the fire service to good effect in
clearing the caterpillars from the magnificent elms of that
beautiful village, and the same method has been successfully
used in various other places. Of course the caterpillars that
fall to the ground are to be destroyed, or at least prevented
from again ascending the trees. The Hanover authorities
washed the trees from two to four times. The trees were
banded, so that those caterpillars which were not crushed on
the ground immediately after falling were prevented from
ascending the trees, and destroyed when they congregated on
the bark below the bands. It would be well worth while to
try this washing method in early spring, just after the cater-
pillars hatch and before the leaves expand.

Spray i?ig tvith poisons. — The season's experience has
shown that spraying with arsenical poisons is a practical and

SUCCESSFUL REMEDIAL MEASURES 12J

effective remedy against these caterpillars, especially in apple
orchards and on comparatively small shade trees. On larger
trees it is simply a question of reaching the foliage with the
spray. The chief drawback in the use of Paris green — the
commonest of these insecticides — is the danger of scorching
the foliage. In this respect the arsenate of lead is much safer,
as it does not injure the foliage at all. When Bulletin 64 was
published this substance was not upon the market, and conse-
quently had to be prepared by the user. It is now obtainable,
however, from Wm. H. Swift & Co., 75 Broad street, Boston,
Mass., who manufacture it in quantity, and offer it for sale
in wooden packages at from fifteen to eighteen cents per
pound. It is also for sale by the Bowker Chemical Com-
pany, 43 Chatham St., Boston, Mass. This is cheaper than
Paris green at the prices the latter has recently sold for.
The arsenate of lead is said to remain on the tree longer than
Paris green. It is a white powder and a deadly poison, so
that great care should be taken not to leave it around where
it might be mistaken for something else, or where it might be
reached by children or stock. Spraying with arsenical mix-
tures is most effective when it is done before the caterpillars
are one-fourth grown. It should certainly be done before they
are half grown. Later than this it is comparatively ineffec-
tive.

Bandi7ig to prei'ent invasion. — In case of an un infested
apple orchard in the vicinity of an infested woodland, it will
be advisable to band the apple trees with cotton or raupenleim
before the caterpillars are half grown, to prevent invasion
from them. The same advice would hold in the case of other
uninfested trees in the vicinity of those infested.

Banding the tree-trunks. — The remedial measure that has
been most generally employed is that of banding the trees
with some substance to prevent the ascent of the caterpillars.
It has already been pointed out that a large proportion of the
caterpillars drop off the trees from one cause or another, and
have in consequence to ascend the same or neighboring trees
in order to reach the leaves. The placing of some substance
around the trunk to prevent the upward progress of the insects

128 THE FOREST TENT CATERPILLAR

causes them to congregate below the band, ^where they are
easily reached and destroyed. The commonest material em-
ployed for this purpose seems to have been ordinary cotton
batting, tied around the trunk of the tree. This is cheap, and
answers the purpose very well. Various mechanical barriers
have also been employed with more or less success, such as
bands of hemp, tin, and tarred paper. In some cases corre-
spondents reported that tar or kerosene was poured upon the
cotton. The use of kerosene in this way is not to be com-
mended, because of the danger that it may kill young and
thin-barked trees by being absorbed through the outer bark
to the sapwood beneath.

Another sort of these barriers is found in the various viscid
substances with which the trees have been banded. These prevent
the progress of the caterpillars either by killing them through
contact as they attempt to cross, or by smearing their legs in
such a way that they turn around as soon as they come upon
it. The materials of this sort that have been used most are
lai;d, cottolene, sticky fly-paper, printers' ink, tar, and " rau-
penleim," or caterpillar lime. In many places rancid lard or
cottolene was used in considerable quantities, being smeared
around the trunk of the tree in a band about six to ten inches
wide. While this substance does not penetrate through the
outer bark of large elm trees, it should be understood that
there is danger in its use upon young, smooth-barked trees, on
account of the probability that the oil will penetrate to the
sapwood. Printers' ink seems to answer very well, as does
the sticky fly-paper until it is injured by rains. The raupen-
leim, or German caterpillar lime, recommended in my first
bulletin on this insect, has been tried in several localities, and
has given very satisfactory results. A material similar to
raupenleim is now offered by the Bowker Chemical Company,
Boston, Mass., under the name "Bodlime." It should be re-
moved from the tree after danger from insects is past.

On the whole, cotton seems to be the most advisable material
to use for banding the trees. It is not expensive ; every one can
get it; it can be applied to all sorts and sizes of trees with
little trouble, and with no danger to the tree. In case the:

SUCCESSFUL REMEDIAL MEASURES I 29

caterpillars are very abundant, two bands might be used, one
a foot or two above the other. It is simply to be tied around
the trunk of the tree with a stout string. If frequent rains
render the outside compact and useless, it can easily be taken
off and reversed, or a little new cotton added to it.

KilUng the caterpillars. — Of course the caterpillars that con-
gregate below the bands are to be destroyed. The simplest
way to do this is by the use of a stiff broom. This or some
similar method is also to be used whenever the caterpillars
appear upon the tree trunk in sufficient numbers.

After the caterpillars are half grown, they commonly come
down to the lower branches or the trunk to undergo the
moulting process. To this end they gather in great masses
on the bark, where they may be destroyed as suggested, or by
collecting the caterpillars in pails containing a little kerosene
and water. Vast numbers of the caterpillars have been de-
stroyed in these ways in New Hampshire during the last two
years.

Jarring and banding. — It has already be^n stated that these
caterpillars drop downward when disturbed, breaking the fall
by means of a thread spun from the mouth ; although when
young and suddenly jarred apparently the thread may not be
used. This habit leads to the suggestion that by a combina-
tion of jarring and banding much injury may be prevented, at
least in the apple orchard and on the home grounds, and
especially on small trees. After the trees infested have been
banded, a boy with a padded mallet maybe sent into them
with instructions to jar the limbs on which the caterpillars are
working, beginning at the top. This should be done when
the caterpillars are feeding upon the leaves, as they are then
much more easily disturbed than when they are at rest. Of
course it is not to be expected that going over once will wholly
rid the tree, but by tw^o or three repetitions of the jarring most
of the caterpillars should be removed. A sheet of cloth may
be spread beneath the tree to catch the caterpillars as they
fall, or a light roller might be run over the ground to crush
them. Those which escape destruction will congregate in
masses upon the trunk, below the bands, where they may be

130 THE FOREST TENT CATERPILLAR

destroyed by use of a stiff broom or by various other methods^
The earlier this is done after the larvae are all hatched the less
will be the injury to the foliage.

The masses of caterpillars below the bands are sometimes
killed by pouring on kerosene. If this method is employed,
great care should be taken not to add enough to saturate the
bark. Many trees have been killed by carelessness in such
use of kerosene.

Collecting cocoons. — A large proportion of the cocoons are
commonly spun where they can be reached. The destruction
of these will lessen the number of moths that lay eggs for the
next season's brood of caterpillars, although it will also lead
to the destruction of large numbers of parasites.

This collecting of the cocoons has been done extensively in
certain towns. In Hanover and Claremont the selectmen
offered a reward of five cents per hundred cocoons, and in
the former town 80,000 cocoons were collected and destroyed.
The poster gotten out by the Claremont authorities is repro-
duced on the opposite page.

The chief objection to this method is that it leads to the
destruction of large numbers of parasites. The proportion of
parasites to moths is likely to vary considerably in different
localities. Our observations indicate that at Claremont, last
season (1899), about 30 per cent, of the pupa^ were para-
sitized, while at Brandon, Vt., more than 40 per cent, were
parasitized. Now these parasites are Nature's means of
checking the outbreaks of this Forest Caterpillar, and it seems
unfortunate that in destroying our foes we should also destroy
our friends. It must be borne in mind, however, that any
parasite found in these cocoons will not take effect upon next
year's brood of caterpillars until they have completed their
growth and done the damage, so that as regards the next sea-
son alone it is better to destroy the pupae, even if some of the
parasites are destroyed at the same time.

A simple method, however, may be adopted by which the
moths may be destroyed and most of the parasites saved to
continue their good work. It was first suggested to me by
Mr. Fiske. Select a piece of shaded grassland, which is not

"ON*

CATERPILLARS!!

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The Selectmen of Claremont will pay
Five Cents a Quart for this year's Co-
coons of the Forest Tent Caterpillar,
gathered in Claremont, during the next
ten days.

Cocoons must be delivered at the
Selectmen's Room, Town Hall, between
the hours of 5 and 6 in the afternoon
of any week day during said time

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iTKniHffiiin'?w»Tiniw»MiHW»''ii'nffmitiiw>'wmni'im'i"iiiintTT»ifWiwm"fffT">www

There is the utmost need that the pubhc should
awake to the danger that threatens the trees from
this pest. The destruction of woodland and of shade
trees seems imminent unless some way of killing the
caterpillars is devised. At the present time this year's
caterpillars are beginnm^ to go into cocoons. They
remain in this state about ten days, when a moth is
hatched from the cocoon. This moth lays from 200
to 300 eggs, each of which becomes a caterpillar to
ravage the trees next summer.

Let all good citizens understand that each cocoon is
a source of very great injury: and that every cocoon
destroyed will aid in the preservation of trees which
cannot b)e spared.

Let young and old join in the work of gathering co-
coons. It is for the direct benefit of the town that
this should be done.

A, C. STONE, I Selectmen

C. A. FISHER, of

W. T. FREEMAN. ) Claremont.

Claremont, N. H., June 20, 1899.

Facsimile of hand-bill offering bounty for cocoons.

132 THE FOREST TENT CATERPILLAR

much tramped upon by people or animals, scatter over this
the cocoons as they are collected, not making the layer more
than an inch deep; leave the cocoons in this position until

•

the moths begin to emerge ; then rake the cocoons up and
burn them. During the week or ten days that the cocoons
remain here most of the parasites will have left them and
found shelter in the turf, where they will complete their devel-
opment. By keeping two or three hundred cocoons in a box
under observation, the time when the first moths come out can
be readily determined.

^UnMIt

B