MEANS OF DEFENCE OF THE LARVA.
There is, perhaps, no period in the life of an insect when it is
so much in danger of the attacks of foes, as when it is in the
larva state. Possessed, at the best, with but very feeble powers
of locomotion, in comparison with those of winged insects, it is
continually exposed to destruction on all sides, from which it has
not the power to escape. Not only do insects of various species
particularly select the larva for the object of their attacks, but
birds and other creatures are also in the lists against them. Thus
imperilled, what chance has the larva against foes so numerous, and in
a contest so unequal? It has been calculated that a pair of sparrows,
for their own consumption, and for that of their tender brood, destroy
at least three thousand caterpillars in a week! and we well know what
multitudes of larvæ fall into the clutches of the cawing rooks which
follow the tail of the plough. The winged insects are tolerably secure,
although many even of their ranks fall victims to the swift-winged
swallow and sand-martin, and to the rapid leap of the artful trout. But
the poor crawling larvæ are neither strong enough to fight, nor swift
enough to flee, and fall by thousands into the unsparing hands of their
various enemies.
[Illustration: _Leaf-rolling Larvæ._]
[Illustration: _Larva Case of Shells._]
Yet, the Creator, who has wisely appointed a large portion of their
numbers for food to many creatures, has also taken many precautions
to prevent their being entirely annihilated, as might otherwise have
been the case. These are well deserving a brief notice, previous to
our passing on to the last stage in the history of the larva. From
what has been already said about the coats of various larvæ, it may be
imagined that that must be a stout-hearted enemy which could venture
to attack some of them. The spines and hard excrescences with which
they are furnished must, undoubtedly, prove far from agreeable to the
touch of a foe; and there can be no question that this sort of armour
is, of itself, a good defence to many larvæ. Others form artificial
coverings, which are equally useful, by concealing them from the
notice of their enemies. Thus, as we have before remarked, some dwell
in tubes of leaves, hid from every eye; others encase themselves in
a shield of cemented gravel or shells, like those represented in the
cut, presenting a most grotesque appearance; others hide themselves
in variously-formed cells. Some, immediately on being touched, roll
themselves up, like hedge-hogs, into a ball, which looks like a little
globe of hairs, and is so slippery that it cannot be retained between
the fingers; others, again, when they are touched, instantly drop down,
and from their colour, resembling precisely that of the herbage into
which they have fallen, it becomes next to fruitless to search for them.
A very singular larva which, both for offence and defence, adopts
a most extraordinary procedure, must be mentioned by itself. This
larva is not unfrequently to be found in our houses, and is said to
feed upon our disgusting and annoying invaders--the bugs; but it so
completely contrives to conceal its real character, that not once in a
hundred times would it, probably, be recognised as an insect at all.
It collects together a number of particles of sand, or fragments of
wool, or silk, or earth, and with singular skill, contrives to form a
sort of coat out of these, in which it envelopes itself. Thus attired,
as may be imagined, it is not easy to discover what the object really
is, and it thus, undoubtedly, escapes the undesirable notice of any of
its enemies. But more than this: like those North American Indians,
who hunt by concealing themselves in the skins of wolves, and so
attract less attention from the herd than they would do if they were
to expose themselves in their natural aspect to view, this crafty
larva steals upon its prey in much the same manner, although it can
run with sufficient swiftness when necessary. It creeps forward with
the greatest stealth, moving only one leg at a time, and thus quite
insensibly approaches its victim, who is not at all alarmed at what
merely appears to be a lump of dust. Soon, however, it is convinced of
its fatal mistake, and discovers the terrible fact that it is in the
embrace of an unsparing devourer.
Other larvæ escape notice in a singular manner, by their close
resemblance to little pieces of stick. Thus, we are told by Messrs.
Kirby and Spence, that "there is a certain tribe of caterpillars called
surveyors (_Geometræ_), that will sometimes support themselves, for
whole hours, by means of their posterior legs, solely upon their hinder
extremity, forming an angle, of various degrees, with the branch on
which they are standing, and looking like one of its twigs. The body is
kept stiff and immovable, with the separations of the segments scarcely
visible; it terminates in a knob, the legs being applied close, so
as to resemble a bud at the end of a twig; besides which, it often
exhibits intermediate tubercles, which increase the resemblance. Its
colour, too, is usually obscure, and similar to that of the bark of a
tree: so that, doubtless, the sparrows and other birds are frequently
deceived by this manoeuvre, and thus balked of their prey. Rösel's
gardener, mistaking one of these caterpillars for a dead twig, started
back in great alarm, when, upon attempting to break it off, he found it
was a living animal."
Some, however, are actually armed, so as to offer an active resistance
to the onslaught of any enemy. Mr. Abbot has described a terrible
caterpillar, well known in certain districts in America, under the
strange title of the "Hickory-horned Devil." This creature is furnished
with seven or eight strong horn-like spines, upwards of half an inch
in length, which project from its head and anterior segments. When
threatened by danger, the caterpillar does not attempt to fly, but
lifts up its head menacingly, and shakes it about in a very fierce
manner. The negroes, in particular, are so terrified at its aspect,
that they dread it as much as the rattlesnake. But, in reality, it
is harmless; and Mr. Abbot, in order to convince the ignorant people
that such was the case, took hold of it, in their presence, without
receiving any injury. This, however, did not convince them, and they
made answer that, although it did not sting him, it would undoubtedly
sting them.
The weapon of another is thus pleasantly described by De Geer:--"In the
month of July, I found a caterpillar resting upon a small twig, which
I cut off in order to enable me to examine it more attentively. As I
was scrutinizing its appearance, I happened, accidentally, to touch its
body. Instantly there shot out, from a spot near the head, two streams
of clear fluid, which struck me on the face, and partly entered one of
my eyes, causing a very acute, but fortunately, not a very enduring
pain. My surprise at this salute prevented my taking particular notice
of the place from whence the jets proceeded. It appears probable that
this caterpillar has been thus endowed with this squirting apparatus to
enable it to defend itself against its enemies, or at least, to assist
in frightening, or perhaps in hunting, its prey. For myself, I confess,
after the reception I had met with, I felt some degree of fear at too
nearly approaching it."
[Illustration: _Squirting Larva. The Cleft and squirting Organ are
shown separately._]
On examining them carefully at another opportunity, this entomologist
found that these caterpillars were provided with a squirting apparatus,
situated in a cleft in the neck. When the creature is irritated, it
thrusts out a curious organ, divided into four branches, and drilled
with holes, like the rose of a watering-pot. From this organ shoot the
jets of fluid spoken of. After the discharge they are drawn in again,
and covered over by the closing up of the cleft. Strange to say, when
taken in-doors, the caterpillar lost the power of squirting altogether.
It appeared as if it could only do so in the open air, where a number
of insect enemies were arrayed against it. This caterpillar is commonly
known as that of the Puss-moth, and has sometimes caused the most
strange and foolish country tales by its striking appearance. It has
been described as a horrible monster, having a head like a lion, jaws
like a shark, a horn like a unicorn, and two tremendous stings in its
tail! Certainly, its appearance is not the most engaging in the world,
as may be conceived from the representation of it in the cut; and what
adds to its singularity is, that it possesses the power of lashing its
sides with its tail, so as to drive away flies. If the reader should be
fortunate enough to find one, he may have some amusement in examining
all the curious apparatus with which this rather forbidding looking
insect is supplied.
The winter draws near, and sends its foretokening cold breathings to
warn every creature, vegetable and animal, that the dark season is
arriving, when food is no longer to be obtained. What is to become
of the larva? Can it endure the penetrating tooth of frost, or the
overwhelming shower of rain? Or can it endure to be from week to week,
from month to month, without a mouthful of food? From the facts already
stated with reference to the age of larva, it is very certain that many
larvæ have to bear these trials; and some, not merely during one, but
during several winters. We must, therefore, inquire how they have been
defended, or strengthened, so as to enable them so to do.
[Illustration: _Shaggy-coated Larvæ._]
The alteration in the coats of animals during winter, or rather, just
previous to it, and the fact that animals destined to inhabit the
arctic regions are enveloped in coats of the shaggiest hair, are well
known to every person. There can be no doubt, that in many instances
in the insect world, where a larva has to be exposed to the frosts of
winter, the same provision of a hairy covering, which has been given to
them by the Creator, is intended to meet the same end, and to preserve
their soft and tender bodies from the destructive influence of extreme
cold. The following striking observation of a talented entomologist,
who has not thought it beneath him to write a most interesting book
only on the family of ants (M. Huber), shows very clearly that such
is, in fact, the intention of providing the larva with a covering of
this kind. He noticed that the larvæ of some species of ants destined
to pass through the winter, were furnished with this kind of warm
clothing, while those which were not so destined had smooth coats, that
is, even in the same species: thus proving to us, beyond a doubt, that
as the winter approached, the warm coat was put on by the larvæ. The
engraving on the last page represents some extraordinary specimens of
hairiness in caterpillars from Brazil, now in the British Museum.
A large number of larvæ become torpid during winter--they are not
dead--they are not sensibly alive--they are plunged in that long
half-death which affects not only them but also many large animals,
who retire in winter, lie down to sleep for weeks, and awake to
find the cold departing, and the spring-time nigh at hand. But the
frost sometimes proves too severe for them, and the poor insects
become sometimes congealed into solid lumps of ice! Alas! we shall
exclaim, then there is an end to their life when that takes place;
and, undoubtedly, the severity of such a degree of cold destroys large
numbers; yet, strange to say, some larvæ actually revive, even after
they have been thus frozen into hard inanimate lumps. One observer
states that he has found them in this condition; and so entirely
congealed, that they chinked like small stones when dropped into
a glass tumbler! yet they revived after careful management. In an
experiment made during Sir John Ross's voyage to the arctic regions,
upon the larvæ of a moth, they were four successive times exposed to
the intense cold of 40° below zero, and four times they revived again
on being brought into the warm atmosphere of the cabin. Experiments
have also been made by other persons with a like result. It may,
therefore, be considered certain that some larvæ will bear to be frozen
into solid masses, so that they will snap asunder like an icicle, and
yet return to life again; and even go through all their stages of
development, into the perfect insect. How remarkable a fact this is,
when we remember the deadly effect of frost upon man and the higher
animals!
Many larvæ, however, form nests of various kinds, in which they
comfortably spend the dreary days and nights of this stern season.
"With this view," write the excellent observers, Kirby and Spence,
"the larva of _Cossus ligniperda_ forms a covering of pieces of wood,
lined with fine silk; those of some other moths excavate, under a
stone, a cavity exactly the size of their bodies, to which they give
all round a coating of silk; and the larvæ of _Pieris Cratægi_ enclose
themselves, in autumn, in cases of the same material, and thus pass the
cold season, in small societies of from two to twelve, under a common
covering formed of leaves. Bonnet mentions a trait of the cleanliness
of these insects, which is almost ludicrous. He observed in one of
these nests a sort of sack, containing nothing but grains of excrement;
and a friend assured him that he had seen one of these caterpillars
partly protrude itself out of the case, the hind feet first, to eject
a similar grain; so that it would seem the society have on their
establishment a scavenger, whose business it is to sweep the streets,
and convey the rejected matters to one grand repository. This, however
singular, is rendered not improbable, from the fact that beavers dig,
in their habitations, holes solely destined for a like purpose, as do
also badgers."
A singular variety of larva-nest is mentioned by a Mexican traveller.
He says,--"After having ascended for about an hour, we came to the
region of oaks, and other majestically tall trees, the names of which I
could not learn. Suspended from their stately branches were innumerable
nests, enclosed, apparently, in white paper bags, in the manner of
bunches of grapes in England, to preserve them from birds and flies.
I had the curiosity to examine one of them, which I found to contain
numberless caterpillars. The texture is so strong that it is not easily
torn; and the interior contained a quantity of green leaves to support
the numerous progeny within."
The larvæ of some Australian insects form the most curious nests
we have ever beheld. A representation, taken from specimens in the
entomological collection at the British Museum, will show what
extraordinary structures these are. They appear like minute bundles of
faggots, and have been formed by the insect cutting short pieces of
twigs, all nearly of the same size, and then cementing them together in
the manner represented. Some of these are of a large size, as large as
a moderate-sized pear; others are smaller, and these present the most
beautifully regular appearance, consisting of a number of very small
rods, bound together in a cylindrical form, like the _fasces_ of the
Roman soldiery.
[Illustration: _Australian Larva-cases._]
In this manner larvæ pass through the winter. Without a doubt many
perish; but there remain infinite numbers at the end of this season,
which, from the depths of their cells, become sensible to the influence
of spring, so soon as the first footsteps of that season are felt upon
the earth. The larva wakens to active life once more; and with an
appetite rendered all the keener by its fast of four or five months,
it leaves its dormitory, and begins to consume whatever suitable food
may lie in its way; and so it continues, until the time of its change
approaches.