observed hanging from the tree-branches, apparently without a trace of
the odd-looking creatures that hung them there the autumn before. If a
number of these bags are gathered and cut open at this time, many of
them will be discovered to be empty, but the greater portion will be
found partly full of yellow eggs. Those which do not contain eggs are
male bags, and the empty chrysalis of the male will be found protruding
from the lower extremity. Upon close examination these eggs will be
observed to be obovate in form, soft and opaque, about one-twentieth of
an inch in length, and surrounded by more or less fawn-colored silky
down. If left to themselves, they hatch sometime in May, or early in
June.
The young which come from these eggs are of a brown color, very active
in their movements, and begin at once to make for themselves coverings
of silk, to which they fasten bits of the leaves of the tree on which
they are feeding, forming small cones that are closely adherent to
the leaf-surfaces. As the larvæ grow, they augment the size of their
enclosures or bags from the bottom, until they become so large and
heavy that they hang instead of remaining upright, as they did at first.
By the end of July the caterpillars become fully grown. They are now
exceedingly restless, and may be seen wandering from branch to branch
by means of their true legs which are projected from the mouths of
their baskets, to which they keep firm hold, or suspended from a branch
of a tree by a long silken thread of their own manufacture. When very
abundant, as they were in certain localities during the season just
ended, they become a great nuisance, as one can hardly walk beneath the
trees without being inconvenienced by a dozen or more dangling into his
face.
Removed from the case at this stage of existence and closely examined,
that portion of the body which has been covered by the bag will be
seen to be soft, and of a dull brownish color, inclining to red at the
sides, while the three anterior segments, which are exposed when the
insect is feeding or travelling, will be found to be horny and mottled
with black and white. The pro-legs on the middle and hinder segments,
which are soft and fleshy, will show themselves fringed with numerous
hooks, by which the larva is enabled to cling to the silken lining of
its bag and drag it along wherever it goes. The external surface of the
bag is rough and irregular, often presenting a beautiful ruffle-like
appearance, which is due to the projecting portions of the stems and
leaves which are woven into it. During their growing-period these
caterpillars are slow travellers, seldom leaving the tree on which they
were hatched. When about to change into chrysalids, they fasten their
bags securely to the twigs on which they happen to be, and then undergo
their change, the male chrysalis being very much smaller than the
female, hardly one-third its size.
When we examine the cases of the Basket-worm, hardly any two will be
seen to be alike in their ornamentation. So completely is the outside
covered, when made upon the arbor-vitæ, which seems to be a favorite
food-plant of the species, that the silken envelope is concealed from
view. The bits of twigs and leaves are probably protective, and yet one
would think that the extremely tough case which covers the caterpillar
would be quite sufficient to protect it against all assaults of foes
and stress of weather. Nevertheless, this leafy coat of mail, which
sometimes wholly covers the sac, must certainly add very much to the
protective value of the covering. The caterpillar has a soft, hairless
body, and is thus more exposed than many of its neighbors, and nature,
it would seem, has favored it far above all of its fellows.
How the worm manages to trim its coat in this manner must seem, to the
uninitiated in such matters, wholly inexplicable. To enable the reader
to understand the manner of operation, it will be necessary first to
explain its mode of feeding. The larva has perfect control of its own
movements, notwithstanding the fact that it carries its house upon its
back. It can thus thrust its body out of the sac-mouth until nearly the
whole of it is exposed, and twist and bend itself in every direction.
Specimens have been met with that had dropped from the trees hanging
by a thread and squirming, bending and snapping their bodies in the
most grotesque ways, while the case spun around like an old-fashioned
distaff. Now, when the caterpillar wants to feed it stretches its head
and neck out of the case and moves them about until a satisfactory
place has been secured, which it clasps with its true legs, three pairs
of hard, conical organs armed with sharp claws, and pulls up its body
and commences to spin. The spinning-organs are near the mouth, and
after several movements of the head, as though smearing the liquid
viscid silk upon the leaf, the head is drawn back, drawing out with it
a short thread. A similar movement is then made against one side of
the mouth of the sac, the process being repeated several times until
a stout stay-line is spun by which the larva hangs securely. Now the
creature is ready to feed. The behavior, however, varies a great deal.
In feeding upon the white pine it secures itself to one leaf by its
stay-line, while it reaches to an adjoining leaf which it bites off,
and sitting erect, as it were, in its house, comfortably chews off the
end which is continually shored upward by the first and second pairs of
true legs that stand out free and untrammelled above the sac.
[Illustration: HOUSE-BUILDER MOTH.
Young in House, Winged Male, Young Suspended and Bag-like Female in
Longitudinally-Split Cocoon.]
But more frequently the worm feeds without separating the leaf from the
point of suspension. By making itself fast to the under part of the
leaf it is thus enabled to reach the edge, which it gnaws round and
round until it has completed its destruction.
So securely does the caterpillar hold on to its house, that one would
suppose that its body was lashed to the inside. But no, its body is
unhampered, for it can turn itself easily around in its case, and go
out at either end, although the head is generally directed upward.
It clings to the inside with the hooks upon its hinder feet, and so
tenaciously, too, that the writer has never been able to pull one
out, being checked by the fear of tearing the creature in two. And
now to the mode of attaching the leaf-cuttings to the case. This
is always done at or near the mouth of the sac. The Ephemeraform
larva is a growing creature, unlike the moth itself, which emerges
a perfect insect of full growth. It commences life as a small worm,
eats small quantities, and, as may be observed, down towards the
foot of the case sews on very small tags. But after it has fastened
on these pieces to the mouth, it grows itself, and so also does the
case, which it continually stretches and enlarges. Hence the mouth of
the case is continually changing, moving upward as the worm feeds,
so that the pieces sewed upon the cap of the case thus appear, in an
adult caterpillar, precisely as they are seen scattered along the
outside from top to bottom. And now, as to how the pieces are put into
the case, I shall endeavor to explain. That the worm cuts purposely
through the twig which it needs for the case, I feel certain. Of course
the outer or detached part drops down. But, while eating, the worm
frequently, quite constantly, indeed, spreads its viscid silk along the
leaf and so keeps it attached on both sides to the upper rim of the
sac, or to its own mouth-parts, and thus the tip of the twig or leaf,
instead of falling to the ground when it is severed from the stem,
simply drops alongside of the case, to which it is held by the slight
filament that attaches it to the sac, or, as happens in many instances,
remains attached to the caterpillar’s spinneret. In either case the
leaf, twig or stem remains, and, after being drawn up, adjusted and
tightened by the worm, adheres tightly. As the creature is forever
moving its spinning-tubes around the top of the sac, these fastenings
are being continually strengthened, and thus one piece after another is
added, and so the basket grows.
While the case of the Basket-worm, and even that part of its body
which it chooses to expose to view, are known to the casual observer,
yet but few persons have ever seen the mature insect. The female moth
is wingless, and never leaves the bag, but makes her way to its lower
orifice, and there awaits the attendance of the male. She is not only
without wings, but is devoid of legs also, being, in short, nothing
more than a yellowish bag of eggs with a ring of soft, pale-brown,
silky hair near the tail. The male, on the other hand, has transparent
wings and a black body, and is very active on the wing during the
warmer portions of the day. After pairing the female deposits her
eggs, intermingled with fawn-colored down, within the empty pupa-case,
and when this task is completed works her way out of the case, drops
exhausted to the ground and dies.
Though a Southern rather than a Northern insect, yet it is found as far
north as New Jersey and New York, and occasionally in Massachusetts.
It is extremely local in character, abounding in one particular
neighborhood and totally unknown a few miles away. Where they occur in
abundance they often almost entirely defoliate the trees they attack,
but this can be easily prevented by gathering the cases containing
the eggs for the next brood during the winter and destroying them.
Hand-picking the cases with the worms in them, where their ravages
are confined to small trees and shrubbery, will also help to hold
them in check. Nature has provided two species of ichneumon for their
destruction. One of them, _Cryptus inquisitor_, is about two-fifths of
an inch in length, and the other, _Hemiteles thyridopteryx_, is nearly
one-third of an inch. Five or six of this latter species will sometimes
occupy the body of a single caterpillar, and after destroying their
victim spin for themselves tough, white, silken cocoons within the bag.
HONEY-PRODUCING CATERPILLARS.
Late in June, growing abundantly in the edges of woods throughout this
region, may be seen the _Cimicifuga racemosa_ of botanists, popularly
called Rattleweed, or Black Snakeroot. It sends up a stalk, sometimes
branching, four or five feet, terminating in a spike or spikes, six to
ten inches long, of round, greenish-white buds, which stand upon short
stems, and are arranged in rows about the stalk, diminishing in size
till they reach the pointed top. The lower buds, when they are about
the size of an ordinary pea, open first, and the flowering proceeds
by degrees up the spike, so that buds are to be met with throughout a
period of from four to six weeks. The flowers emit an intensely sweet
odor, which renders them attractive to butterflies and bees.
But should you examine these buds with care, you will find a number
of small caterpillars, the larva of the beautiful Azure Butterfly,
called _Lycæna pseudargiolus_, feeding thereon. During its younger
stages it is white, and so near the color of these buds that it is
well protected, and very difficult to find. Later on, it may be white
or greenish, and often diversified with a few black or brown patches,
irregularly diffused over the surface.
When mature the larva is one-half of an inch in length, and, like all
Lycænid larvæ, is onisciform, or shaped like the little pill-bug, so
common under stones and logs. The head is very small, and is placed
on the end of a long, green neck, which at the junction is of the
thickness of the head, but gradually enlarges, and seems to be fixed at
the hinder part of the second segment, the latter being hollowed out
so as to form for it a sheath. In the final larval stages this segment
is elevated, transversely compressed, and inclines forward, thereby
shielding the head as the larva moves about. When quiescent the neck
and head are wholly retracted, and as the former, when fully extended,
is very much longer than the depth of the second segment, it must
possess considerable elasticity.
The larva feeds on the heart of the bud, and to reach this cuts away
the surface on one side till an opening is made sufficiently large to
admit its head; and as it feeds the second segment is firmly pressed
against the bud so as to permit the utmost elongation of the neck. Thus
it is enabled to eat out the contents of the bud, and only desists
when there remains but the empty shell. When so engaged the anterior
segments are curved up and the others rest upon the stalk of the plant,
but very small larvæ repose wholly in the bud. Not a single instance
has been observed where an open flower has been attacked, but the
destruction of buds is very extensive.
But now comes the most remarkable part of the larval history of
Pseudargiolus. The whole upper part of the larva is covered with small,
glassy, star-shaped processes, scarcely raised above the surrounding
surface, from the centre of which spring short, filamentous bodies,
bristling with feathery-looking tentacles, which the caterpillar has
the power of protruding at will. It throws them out like the tentacles
of Papilio or the horns of snails. More singular still is an opening
upon the eleventh segment, placed transversely and surrounded by a
raised cushion, about which the granulations that cover the body of the
caterpillar are particularly dense. From the middle of this opening,
which is shaped like a button-hole, issues, at the caterpillar’s will,
a sort of transparent, hemispherical vesicle, from which is emitted a
good-sized drop of fluid, which the animal is capable of reproducing
when absorbed.
[Illustration: PSEUDARGIOLUS BUTTERFLY.
Larva Feeding on Bud of Black Snakeroot, and Guarded by Ants.]
Four species of ants may be seen attending, not the small larvæ,
but those that have attained the nearly mature condition. They are
invariably found on or near the larva. Their actions, as they run
over the body, caressing with antennæ, evidently persuading the larva
to emit a drop of the fluid, are alike curious and interesting. Most
of this caressing is done about the anterior segments, and while the
ants are thus occupied, or rather, while they are absent from the last
segments, the tubes of the twelfth seem expanded to their full extent,
and so remain, without retracting or throbbing, until the ants come
hurrying along with great excitement and set foot or antenna directly
on or close by the tubes, when they are instantly withdrawn. The ants
pay no heed to the tubes. They seek for nothing from them, and expect
nothing. But they turn at once to the eleventh, caress the back of that
segment, and, putting their mouths to its opening, exhibit an eager
desire and expectancy. Suddenly a dull green, fleshy, mammilloid organ
protrudes, and from the summit of which comes a tiny drop of clear
green fluid, which the ants, some two or three perhaps standing about
it, lap greedily up. As the drop disappears, this organ sinks in at
the apex, and is so withdrawn. The ants then run about, some in quest
of other larvæ upon the same stem, some with no definite object, but
presently return and pursue the caressings as before. The intervals
between the appearance of the globule vary with the condition of the
larva. Where exhaustion by long-continued solicitings occurs, some
minutes elapse before renewal is effected, the tubes in the meantime
remaining concealed. Fresh larvæ, however, require little or no urging,
and globule follows globule, as many as six emissions in seventy-five
seconds, without even a retracting of the organ. Often the presence
of the ant, when the larva is aware of it, evokes, all unsought, the
sugary fluid.
Ordinarily the tubes expand when the ants are absent from the last
segments, and are certainly withdrawn when they come near. These tubes,
from all appearances, serve as signals to the ants. When the latter
discover them expanded, they know that a refection is ready, and rush
to the opening in the eleventh segment where it is to be found. The
tubes certainly serve no other purpose. No visible duct appears in the
dome of the tube when largely magnified, and the ants seek nothing
from it or the twelfth segment. They cannot be used to intimidate,
or to frighten away enemies, for in the younger stages, when the
larvæ have the most to dread, neither the tube nor the organ in the
eleventh segment is available. The outward openings, and the orifice
in the eleventh segment, exist in the youngest larval stages, but
are functionless until the larva has nearly attained maturity. Ants
seldom attempt to caress or solicit young larvæ, but pass them by with
indifference, seemingly knowing that they cannot emit the secretion.
When an ant approaches one of these immature larvæ, the larva manifests
considerable annoyance, throwing up the hinder segments, as though the
ant was an enemy which it was desirous to get rid of. If the tubes
could now be thrust out, the ant would be attracted, rather than
repelled.
But when the period arrives that the tubes are free, and the secretion
is ready to be ejected, which is perhaps just after the third
skin-moulting, and it cannot be earlier, the larva grows now quiet and
submissive, inviting the attentions of the ants, and rewarding their
antennal caresses.
Four species of parasites affect these larvæ. Two are dipterous. These,
which are of the size of the common house-fly, deposit their eggs,
during the second larval stage, on the back, and near the junction of
the second and third segments. In process of time the grubs hatch and
eat their way into the larva, to emerge when the latter has become
fully grown, thus destroying its life. Another of these enemies is a
minute hymenopterous insect, whose egg is placed in the very young
larva, probably in the first stage of its life. The grub, in this case,
eats its way out of the half-grown larva, spins a silken cocoon, from
which in a few days issues the newly-matured parasite. The destruction
of larvæ by these, and very likely by other similar parasites, is
doubtless immense. But no parasite attacks, it does seem, the mature
larva, for, if it did, the grub of the former would live within and
destroy the chrysalis, and instead of a butterfly emerging therefrom
would come forth the parasite. Multitudes of chrysalids of other
species of butterflies are thus destroyed, but Pseudargiolus, at this
stage, appears to enjoy a singular immunity from enemies.
Why this species, and doubtless many others of its family, are thus
favored, will soon be apparent. Ants may be seen wherever these larvæ
may be found, ever ready to receive the honeyed secretion when it
pleases the little creatures to eject it, but all the while exercising
the closest vigilance lest some wary ichneumon may come along and deal
a thrust of its ovipositor, which means misery and ultimate death to
their helpless friends. So intent is the larva, with its head buried
in the flower, upon its feeding, and so quietly and stealthily does
the ichneumon approach its intended victim, that hardly a single
individual would be left to tell the story of its existence were it
not for the ants. The larvæ know their protectors, it would seem from
their actions, and are able and willing to reward their services. The
advantage is mutual, and the association friendly. No compelling by
rough means on the one part is noticeable, and no reluctant yielding
on the other. All demonstrations made by the ants are of the most
gentle character. They caress, entreat, and as they drink in the sweet
fluid, lifting their heads to prolong the swallowing, they manifest to
the utmost their satisfaction and delight. It is amusing to see them
lick away the last trace, caressing the back of the segment with their
antennæ as they do so, as though they were coaxing for a little more.
In Pseudargiolus the tubes are white, cylindrical, nearly equal in
size, rounded at summit, and studded with little tuberculations
from which arise the tentacles. These last are tapering, armed with
small spurs set in whorls, and stand out straight, making a white
hemispherical dome over the cylinder, but none of them fall below the
plane of the base of the dome, nor do they ever hang limp or lie across
the dome, as is the case in a European species. When the tube comes up
the rays rise in a close pencil, and take position as the dome expands;
but, on the contrary, when the tube is withdrawn, the top of the dome
sinks first, the rays coming together in pencil again.
[Illustration: VIOLACEA BUTTERFLY.
Larva, Protected by Ants, Feeding on Flower-buds of Dogwood.]
_Lycæna pseudargiolus_ is subject to great variation, and occurs under
many forms, most of which having been regarded as distinct species. In
the early spring Violacea appears, and is characterized by dimorphism
in the female, some of that sex being blue, others black. This form,
which may be called the winter form, deposits its eggs in the clusters
of flower-buds of the Dogwood, the young larvæ obtaining their first
food by boring into the buds, but later on eating their way into
the ovaries. The flies that come from these larvæ late in May are
Pseudargiolus, which, as stated before, lays its eggs on _Cimicifuga
racemosa_, most of the resulting butterflies over-wintering to produce
Violacea. A small percentage of the May chrysalids give butterflies as
late as September, which are smaller than the parent-form, and also
differ therefrom in the more decided character of the marginal crescent
discal spots on the under side of the wings. There does not seem to be
any regular second summer brood, that is, there are but two regular
annual broods, the Violacea of March and the Pseudargiolus of May, the
individuals happening to emerge in July, August and September being
irregular visitants, for which the name of Neglecta has been given. The
females of the last form lay their eggs upon _Actinomeris squarrosa_,
and the chrysalids, thence resulting, give Violacea the next spring.
Larvæ feeding on Dogwood vary much in color from those that feed on the
Black Snakeroot, few being white in the last stages, but nearly all
dull-crimson or green, or a mingling of the two. Nevertheless, a small
percentage of the larvæ on _Cimicifuga racemosa_ are also green or
crimson, though the most of them white. Ants do not seem to visit the
larvæ on the Dogwood, and on being introduced to them in confinement
treat them with indifference. On rare occasions tubes have been
discovered in the eleventh segment, fully expanded, and accompanied by
a pulsating movement, but no teasing or irritating availed to make them
appear. Even severe pressure applied to the sides of the segment failed
to force out any fluid. As with the fall food-plant, _Actinomeris
squarrosa_, the Dogwood is neither sweet nor juicy, and it is possible
that the larvæ feeding on these plants do not secrete the fluid.
Eggs of this polymorphic species are round, flat at base, the top
flattened and depressed, and have a diameter of one-fiftieth of an
inch. Their ground-color is a delicate green, the entire surface being
covered with a white lace-work, the meshes of which being mostly
lozenge-shaped, with a short rounded process at each angle. In from
four to eight days the egg hatches into a larva, which is scarcely
one-twenty-fifth of an inch long, and whose upper side is rounded,
the under being flat. On each side of the dorsal line is a row of
white clubbed hairs, with similar ones at the base and in front of the
second joint, making a fringe around the body. The head is very small,
obovoid, retractile and black; the legs retractile, and the color a
greenish-white or brownish-yellow.