which comes from the chenille a brosse: out of a brood of 350 eggs,
produced by a single moth of this kind, he took 80, from which he
obtained, when they were arrived at their perfect state, 15 females;
from whence he deduces the following consequence: if 80 eggs give 15
females, the whole brood of 350 would have produced 65; these 65,
supposing them as fertile as their mother, would have produced 22,750
caterpillars, among which there would have been at least 4265 females,
who would have produced for the third generation 1,492,750 caterpillars.
This number would have been much larger, if the number of females among
those which were selected by M. Lyonet had been greater. M. de Geer
counted in the belly of a moth 480 eggs; reducing these to 400, if
supposing one-fourth only of these to be females and as fruitful as
their mother, they will give birth to 40,000 caterpillars for the second
generation; and for the third, supposing all things equal, four millions
of caterpillars. It is not surprizing, therefore, that they are found so
numerous in years that are favourable to their propagation. But the
Creator of all things has for our sakes limited this abundant
multiplication, and wisely ordained, that those species which are the
most numerous shall have the greatest number of enemies, who, though
constantly employed on the destruction of individuals, are unable to
effect that of the species; by which means an equilibrium is preserved,
and no one species preponderates. Few insects live long after their last
transformation, but their species are continued by their amazing
fecundity; their growth is completed, and their parts hardened sooner
than those of larger animals, and the duration of their existence is
proportionably limited. There are, however some species of flies which
lie in a torpid state during the winter, and revive with the returning
warmth of spring.
OF THE FOOD OF INSECTS.
There are few, if any, productions either of the animal or vegetable
kingdoms, which do not supply some kind of insect with food. They may,
therefore, be considered under two heads, those which live on
vegetables, and those which are supported by animal food; each insect
knows that which is proper to sustain its life, where to seek it, and
how to procure it. I have already observed, that several insects, when
arrived at a state of perfection, feed after their transformation upon
food totally different from that which nourished them in their larva
state.
Among those which feed on vegetables, some sink themselves in the earth,
and by destroying the roots of the plants, do considerable injuries to
our gardens. The food of others is dry and hard; they pierce the wood,
reduce it to powder, and then feed on it; some, as the cossus, attack
and destroy the trees, while the food of others more delicate is the
leaves. The leaf is eaten in a different manner by different insects;
some eat the whole substance, while others feed only on the parenchymous
parts, which are contained between its superficial membranes, forming
withinside the leaf paths and galleries. These insects are not always
content with the leaf, but attack the flower also: even this food is too
gross for many; the bee, the butterfly, the moth, as well as several
species of flies, feed only on the honey, or finer juices, which they
collect from flowers. We are continually finding the larva of some
insect in pears, plumbs, peaches, and other fruit; these unwelcome
intruders on the produce of human industry divide fruits, grain, and
corn with us, often depriving us of large quantities. There is, indeed,
no part of a plant which does not serve as food to different insects;
some have one kind of plant marked out for them to inhabit and feed on,
others have another assigned to them, on which, and no other, they will
feed; each has its appropriate food, and though the parent animal eats
not at all, or lives upon food entirely different, yet she is guided, as
has before been observed, to deposit her eggs on that peculiar shrub or
plant that will be food for her young; while some, more voracious than
the rest, feed upon all with equal avidity; but in countries less
cultivated than our own, their annoyance and devastations are terrible.
The gryllus migratorius, a few years since, poured out of Tartary in
such quantities, as to lay waste a great part of Europe, producing
almost unequalled calamities, swarming in such multitudes as to cloud
the air and cover the ground, mocking human power and craft; wherever
they settled, all verdure disappeared, and the summer fruitfulness was
turned into winter desolation; in Sweden the cattle perished with
hunger, and the men were forced to abandon their country, and fly to the
neighbouring regions.[87] The far greater part feed only, however, on
one species of plant, or at most on those which are similar to it, and
the same species may always be found on the same plant. Reaumur says,
that the caterpillar which infests and feeds upon the cabbage, destroys
in twenty-four hours more than twice its weight. If larger animals
required a proportionable quantity, the earth would not afford
sufficient nourishment for its inhabitants.
[87] Select Dissertations from the Amœnitates Academicæ, vol. I, p.
398.
A great number of insects reject vegetable, and live on animal food;
some seeking that which is beginning to putrefy, while others delight in
food entirely putrid; others again are nourished by the most filthy
puddles, and disgusting excrements; some attack and feed on man himself,
while others are nourished by his provision, his cloaths, his furniture:
some prey upon insects of another species; others, again, attack their
own, and harrass each other with perpetual carnage. Reaumur informs us,
that those insects which feed upon dead carcases never attack living
animals; the flesh-fly deposits her eggs in the bodies of dead animals,
where her progeny receive that nourishment best adapted for them; but
this fly never attempts to lay her eggs in the flesh of sound and living
animals.
Every animal has its appropriate lice, which feed on and infest it. M.
Rhedi has given an accurate account of a great number of these little
noxious creatures accompanied with figures; but, as if it were not
sufficient that these creatures should dwell and live on the external
part of the body, and suck the blood of the animal that they infest, we
find another species of insects seeking their food in the more vital
parts, and feeding on the flesh of the animal, while full of life and
health. Reaumur has given an history of a fly, oestrus bovis, the larva
of which lives upon the backs, and feeds on the flesh of young oxen and
cows, where it produces a kind of tumor. The fly lodges its eggs in the
flesh, by making a number of little wounds, in each of which it deposits
eggs, so that every wound becomes a nest, the eggs of which are hatched
by the heat of the animal. Here the larvæ find abundant food, at the
same time that they are protected from the changes of the weather; and
here they stay till they are fit for transformation. The parts they
inhabit are often easy to be discovered by a kind of lump or tumor,
which they form by their ravages; this tumor suppurates, and is filled
with matter; on this disgusting substance the larvæ feed, and their
heads are always found plunged in it.[88]
[88] The obscure and singular habitations of the British oestri are
the stomach and intestines of the horse, the frontal and maxillary
sinuses of sheep, and beneath the skin of the backs of horned cattle.
In other parts of the world they inhabit various other animals.
The larva of the oestrus bovis lives beneath the skin of horned
cattle, between it and the cellular membrane, in a proper sack or
abcess, which is rather larger than the insect, and by narrowing
upwards opens externally to the air by a small aperture. When arrived
at its full growth, it effects its escape from the abcess by pressing
against the external opening; when the opening has thus obtained the
size of a small pea, the larva writhes itself through, and falls from
the back of the animal to the ground; and, seeking a convenient
retreat, becomes a chrysalis, in which state it continues from about
the latter end of June to about the middle of August; the perfect
insect, on leaving the chrysalis, forces open a very remarkable
marginated triangular lid or operculum. The oestrus in its perfect or
fly state is the largest of the European species of this genus, and is
very beautiful. Although its effects on the cattle have been so often
remarked, yet the fly itself is rarely seen or taken, as the attempt
would be attended with considerable danger. The pain it inflicts in
depositing its egg is much more severe than in any of the other
species: when one of the cattle is attacked by this fly, it is easily
known by the extreme terror and agitation of the whole herd; the
unfortunate object of the attack runs bellowing from among them to
some distant part of the heath, or the nearest water, while the tail,
from the severity of the pain, is held with a tremulous motion
straight from the body, in the direction of the spine, and the head
and neck are also stretched out to the utmost. The rest, from fear,
generally follow to the water, and disperse to different parts of the
field. The larvæ of this insect are mostly known among the country
people by the name of wornuls, wormuls, or warbles, or more properly
bots.
The larva of the oestrus equi is very commonly found in the stomach of
horses. These larvæ attach themselves to every part of the stomach,
but are generally most numerous about the pylorus; and are sometimes
found in the intestines. They hang most commonly in clusters, being
fixed by the small end to the inner membrane of the stomach, to which
they adhere by two small hooks or tentacula. The larvæ having attained
their full growth in about a month, on dropping to the ground find
some convenient retreat, change to the chrysalis, and in about six or
seven weeks the fly appears.
The larva of the oestrus hæmorrhoidalis resembles in almost every
respect that of the oestrus equi, and occupies the same situation in
the stomach of the horse. When it is ripe, and has passed through the
intestines and the sphincter ani it assumes the chrysalis state in
about two days, and in about two months the fly appears.
The generally received opinion has been that the female fly enters the
anus of the horse to deposit its eggs, and Reaumur relates this
circumstance on the authority of Dr. Gaspari; from the account of its
getting beneath the tail, it is probable that the fly he saw was the
hippobosca equina, which frequently does this: its getting within the
rectum appears to have been additional. That a fly might deposit its
eggs on the verge of the anus is not impossible, but we know no
instance of it: the fact is, that the part chosen by the oestrus
hæmorrhoidalis for this purpose is the lips of the horse, which is
very distressing to the animal from the excessive titillation it
occasions; for he immediately after rubs his mouth against the ground,
his fore legs, or sometimes against a tree, or if two are standing
together, they often rub themselves against each other. At the sight
of this fly, the horse appears much agitated, and moves its head
backward and forward in the air to baulk its touch, and prevent its
darting on the lips; but the fly, watching for a favourable
opportunity, continues to repeat the operation; till at length, the
enraged animal endeavours to avoid it by galloping away to a distant
part of the field. If still pursued, its last resource is in the
water, where the oestrus is never observed to follow him.
The oestrus veterinus is by Linnæus called nasalis, from an idea of
its entering the nostrils of the horse to deposit its eggs, which it
could not well do without destroying its wings, and is therefore
probably as much a fable as the “mire per anum intrans” of the oestrus
hæmorrhoidalis.
The oestrus ovis is mostly found in the horns and frontal sinuses of
the sheep, though it has been remarked that the membranes lining these
cavities were hardly at all inflamed, while those of the maxillary
sinuses were highly so; from which it is suspected that they inhabit
the maxillary sinuses, and crawl, on the death of the animal, into
these situations in the horns and frontal sinuses. When the larvæ are
full-grown they fall through the nostrils, and change to the pupa
state, lying on the earth, or adhering by the side to a blade of
grass. The fly bursts the shell of the pupa in about two months.
The above concise account of the different oestri is extracted from
the excellent paper on the subject by Mr. B. Clark, F. L. S. For his
more ample description, accompanied with coloured figures of the
several British species, see Transactions of the Linnean Society, vol.
iii. page 283-329, just published. EDIT.
Neither the larva, pupa, or even the egg-state of some insects are
exempt from the attacks of others, who deposit their eggs in them;
these, after having passed through the usual transformations, become
what is termed the ichneumon fly. The following are the curious
observations of an ingenious naturalist on this fly. “As I was
observing,” says he, “one day some caterpillars which were feeding
voluptuously on a cabbage leaf, my attention was attracted to part of
the plant, about which a little fly was buzzing on its wing, as if
deliberating where to settle: I was surprized to see the herd of
caterpillars, creatures of twenty times its size, endeavouring in an
uncouth manner, by various contortions of the body to get out of its
way, and more so whenever the fly poised on the wing as if going to
drop; at length the creature made its choice, and seated itself on the
back of one of the largest and fairest of the cluster; it was in vain
the unhappy reptile endeavoured to dislodge the enemy. If the
caterpillar had shewn terror on the approach of the fly, its anguish at
intervals now seemed intolerable, and I soon found that it was in
consequence of the strokes or wounds given by the fly. At every wound
the poor caterpillar wreathed and twisted its whole frame, endeavouring
to disengage itself, by shaking off the enemy, sometimes aiming its
mouth towards the place; but it was all in vain; its little, but cruel
tormentor kept its place. When it had inflicted thirty or forty of these
wounds, it took its flight with a visible triumph; in each of these
wounds the little fly had deposited an egg. I took the caterpillar home
with me, to observe the progress of the eggs which were thus placed in
its body, taking care to give it a fresh supply of leaves from time to
time; it recovered to all appearance in a few hours from the wounds it
had received, and from that time, for the space of four or five days,
seemed to feed with its usual avidity. The eggs were all hatched into
small oblong voracious worms, which fed from the moment of their
appearance on the flesh of the caterpillar, in whose body they were
inclosed, and seemingly without wounding the organs of respiration or
digestion; and when they had arrived at their full growth, they eat
their way out of the sides of the animal, at the same time destroying
it. The caterpillar thus attacked by the larva of the ichneumon never
escapes, its destruction is infallible; but then its life is not taken
away at once; the larva, while it is feeding thereon, knows how to spare
the parts which are essential to its life, because its own is at that
time tied up in that of the caterpillar. No butterfly is produced from
it; the worms that feed on the wretched creature, are no sooner out of
its body, than every one spins its own web, and under this they pass the
state of rest necessary to introduce them to their winged form.”[89] To
treat of each species of the ichneumon would alone fill a volume;
Linnæus enumerates no less than seventy-seven of them.[90]
[89] Inspector, No. 64.
[90] “The genus of insects called ichneumon derive their support and
nourishment from other insects, some depositing their eggs in the
larva, others again in the pupa, and some even in the ovum or egg
itself, the contents of which, minute as they are, are sufficient to
support the young larvæ until their change into their pupa state. Some
deposit only one egg in a place, as the ichneumon ovulorum, and others
again a great number, as ichneumon puparum, &c. but whether the egg be
placed in the pupa, larva, or ovum, the destruction of the foster
parent is inevitable. The larvæ of large moths or butterflies that
have been wounded by an ichneumon, live and feed, though with evident
marks of disease, until those parasites are full fed, and able to
change into their second or pupa state.” See Observations on the
Œconomy of the Ichneumon Manifestator, in the Transactions of the
Linnean Society, vol. 3, p. 23 & seq. by T. Marsham, Esq. Sec. L. S.
EDIT.
Of this strange scene it is difficult for us to form a proper judgment;
we are unacquainted with the organs of the caterpillar, ignorant of the
nature of its sensations, and therefore we cannot be assured what may be
the effects of that which we see it suffer. “It is wisdom to suppose we
are ignorant, while we know the Creator cannot be cruel.” From
revelation we learn, that man is the mean through which life is conveyed
to the creatures of this lower world; that by sinking into error, and
fostering evil, he perverts his own life, and corrupts all that which
proceeds from him: so that the effects are the same on the orders
beneath him, as would arise to the world if a continual cloud was placed
between us and the sun, depriving us at once of the salutary effects of
its invigorating heat and cheering light. Hence there is in this
degraded world an obscure and melancholy shade cast over all the
beauties of creation.
Lastly, the number of insects which feed upon others, nay, some even
upon their own species, is very great: it is among these that we find
the traces of the greatest art and cunning, as well in attack as
defence; some indeed use main force alone. Most persons are acquainted
with the dexterous arts of the spider, the curious construction of the
web he spins, and the central position he takes, in order to watch more
effectually the least motion that may be communicated to its tender net.
Those who wish to pursue this subject further, will find ample
satisfaction by consulting the works of Reaumur and De Geer.
OF THE HABITATION OF INSECTS.
Insects may be divided, with respect to their habitations, into two
classes, aquatic and terrestrial.
Stagnant waters are generally filled with insects, who live therein in
different manners. These are, 1. Aquatic insects which remain always on
the superficies of the water, or which at least plunge themselves
therein but rarely. 2. Others that live only in the water, and cannot
subsist out of it. 3. Many, after having lived in the water while in the
larva and pupa state, quit it afterwards with wings, and become entirely
terrestrial. 4. Some undergo all their transformations in the water, and
then become amphibious. 5. Others again are born and grow in the water,
but undergo their pupa state on dry land, and after they are arrived at
their perfect state, live equally in air and water; and 6. There are
some who live at the same time part in the water and part on land, but
after their transformation cease to be aquatic.
Among the insects which remain on the superficies of the water, are some
spiders, which run with great address and agility, without moistening
their feet or their body; when they repose themselves, they extend their
feet as much as possible. There are also aquatic bugs, which swim, or
rather run on the water with great velocity, and by troops; another bug
walks very slowly on the water; the gyrinus moves very swiftly, and in
circles. There is a species of podura[91] which live in society, and are
often accumulated together in little black lumps. Those insects which
always live in the water are generally born with the figure which they
retain during their whole lives, as the monoculi, crabs, several kinds
of water mites, &c.
[91] De Geer Discours sur les Insectes, tom. 2, p. 103.
Those insects which, after having lived in the water, leave it when in a
winged state, are very numerous: among these we may reckon the
libellula, the ephemera, the phryganea, culices, tipulæ, and some
species of muscæ. All these, when in the larva and pupa state, live in
the water; but when they have assumed their perfect form, are entirely
terrestrial, and would perish in their former element.
The notonecta, the nepa or aquatic scorpion, &c. never quit the water
till they have passed through all their transformations, when they
become amphibious, generally quitting it in the evening.
The water-beetles, of which there are many species, remain in the water
all day, but toward evening come upon the ground and fly about, then
plunge themselves again in the water at the approach of the rising sun.
The larvæ of these insects are entirely aquatic, but when the time of
their pupa state arrives, they take to the earth, where they make a
spherical case; so that these insects are aquatic in the larva,
terrestrial in the pupa, and amphibious in the imago state.
We find an instance of an insect that lives at the same time in the
water and the air, in the singular larva described by Reaumur, Memoires
de l’Acad. in 1714, p. 203. It has the head and tail in the water, while
the rest of the body is continually kept above the surface. In order to
support itself in this singular position, it bends the body, bringing
the head near the tail, raising the rest above the water, and supporting
itself against some fixed object, as a plant, or against the borders of
the pond; or, if it be placed in a glass vessel, against the sides of
the vessel; and if the glass be inclined gently, so that the water may
nearly cover the larva, it immediately changes its position, in order
that part of the body may be kept dry.
At the baths of Abano, a small town in the Venetian state, there is a
multitude of springs, strongly impregnated with sulphur, and of a
boiling heat. In the midst of these boiling springs, within three feet
of four or five of them, there is a tepid one about blood-warm. In this
water, not only the common potamogetons and confervas, or pond-weeds and
water-mosses are found growing in an healthy state, but numbers of small
black water beetles are seen swimming about, which die on being taken
out and plunged suddenly into cold water.[92]
[92] Jones’s Physiological Disquisitions, p. 171.
Many insects that live under the surface of the earth crawl out on
certain occasions, as the julus, scolopendra, and the oniscus; they are
often also to be found under stones, or pieces of rotten wood. Some
insects remain under ground part of their life, but quit that situation
after their change; as do some caterpillars, many of the coleoptera
class, &c. There are some species of spiders, which form habitations in
sand; one of which makes a hole in the sand, lining it with a kind of
silk, to prevent its crumbling away; this spider generally keeps on the
watch near the mouth of the hole, and, if a fly approach, runs at it
with such velocity, as seldom to fail in its attempt of seizing the
little animal, which is immediately conveyed to the den of the spider.
The formica-leo, or ant-lion, also inhabits sand.[93]
[93] The art and dexterity with which the formica-leo entraps ants, as
well as other insects, merits notice; he makes a pit in fine dry sand,
shaped like a funnel or an inverted cone, at the point or reverted
apex of which he takes his station, concealing every part of his body
except the tips of his two horns; these are expanded to the two sides
of the pit. When an insect treads on the edge of this precipice, it
perhaps slides into it; if not, its steps remove a little of the sand,
which of course descends down the sides, and gives the enemy notice of
his prey. He then throws up the sand with which his head is covered,
to involve the insect, and bring it to the bottom with the returning
force of the sand: this, by repeated efforts he is sure to effect, as
all the attempts of the unfortunate victim to escape, when once within
the verge of the pit, are in vain. One species of the formica-leo
forms no pit to entrap its prey, but seizes it by main force. EDIT.
Another spider, discovered by M. l’Abbe Sauvage,[94] burrows in the
earth like a rabbit, making a hole one or two feet deep, of a regular
diameter, and sufficiently large to move itself with ease. It lines the
whole of it, either to keep the ground from tumbling in, or in order to
perceive more regularly at the bottom what happens at the mouth, at
which it forms a kind of door, made of different layers of earth,
connected together by threads and covered with a strong web of a close
texture; the threads are prolonged on one side, and fixed to the ground,
so as to form a strong joint; the door is hung in such a manner, as
always to fall by its own gravity. One of these cases or nests is in her
Majesty’s cabinet at Kew.
[94] Histoire de l’Acad. 1758, p. 26.