cylindrical cavity of the requisite dimensions, and deposited an egg
at the bottom, they inclose along with it one or more caterpillars,
spiders, or other insects, each particular species for the most part
selecting a distinct kind, as a provision for the young one when
hatched, and sufficiently abundant to nourish it until it becomes
a pupa. Many thus furnish several cells. This process, however, is
varied by different species, some of whose operations are worthy of a
more detailed description.
One of the most early histories of the procedure of an insect of this
kind, probably the common sand-wasp (_Ammophila vulgaris_), is left us
by the excellent Ray, who observed it along with his friend Willughby.
On the 22d of June 1667, he tells us, they noticed this insect dragging
a green caterpillar thrice as big as itself, which after thus conveying
about fifteen feet, it deposited at the entrance of a hole previously
dug in the sand. Then removing a pellet of earth from its mouth, it
descended into the cavity, and, presently returning, dragged along with
it the caterpillar. After staying awhile it again ascended, then rolled
pieces of earth into the hole, at intervals scratching the dust into
it like a dog with its fore feet, and entering it as if to press down
and consolidate the mass: flying also once or twice to an adjoining
fir-tree, possibly to procure resin for agglutinating the whole. Having
filled the burrow to a level with the surrounding earth so as to
conceal the entrance, it took two fir-leaves lying at hand, and placed
them near the orifice as if to mark the place.--Such is the anecdote
left on record by our illustrious countryman, of whose accuracy of
observation there can be no doubt[661]. Who that reads it can refrain
from joining in the reflection which it calls from him, "_Quis hæc
non mihi miretur et stupeat? Quis hujusmodi opera meræ machinæ possit
attribuere_[662]_?_"
I myself, when walking with a friend some months ago, observed
nearly similar manœuvres performed by another hymenopterous insect
which may be called a spider-wasp (_Pompilus_), which attracted our
attention as it was dragging a spider to its cell. The attitude in
which it carried its prey, namely with its feet constantly upwards;
its singular mode of walking, which was backwards, except for a foot
or two when it went forwards, moving by jerks and making a sort
of pause every few steps; and the astonishing agility with which,
notwithstanding its heavy burthen, it glided over or between the
grass, weeds, and other numerous impediments in the rough path along
which it passed--together formed a spectacle which we contemplated
with admiration. The distance which we thus observed it to traverse
was not less than twenty-seven feet, and great part of its journey
had probably been performed before we saw it. Once or twice, when
we first noticed it, it laid down the spider, and making a small
circuit returned and took it up again. But for the ensuing twenty or
twenty-five feet it never stopped, but proceeded in a direct line for
its burrow with the utmost speed. When opposite the hole, which was
in a sand bank by the way side, it made a sharp turn, as evidently
aware of being in the neighbourhood of its abode, but when advanced
a little further laid down its burthen and went to reconnoitre.
At first it climbed up the bank, but, as if discovering that this
was not the direction, soon returned, and, after another survey
perceiving the hole, took up the spider and dragged it in after it.
In the two instances above given, one dead caterpillar or spider
only was deposited in each hole. But an insect described by Reaumur
under the name of the mason-wasp (_Epipone spinipes_), very common
in some parts of England, after having excavated a burrow, with an
ingenuity to which on a future occasion I shall draw your attention,
places along with its egg as food for the future young, about twelve
little green grubs without feet, which it has carefully selected full
grown and conveyed without injuring them. You will inquire, Why this
difference of procedure? With regard to the choice of a number of
small grubs rather than of one large caterpillar, what I have said
in a former letter on the subject of different species of this tribe
being appointed to prey upon and thus keep within due limits the
larvæ of different kinds of insects, will be a sufficient answer.
But one circumstance creditable to the talents of the mason-wasp as
a skilful purveyor should not be omitted, namely, that the number of
grubs laid up is not always the same, but is exactly proportioned
to their size, eleven or twelve being stored when they are small,
but only eight or nine when larger. With respect however to the
caution of the wasp in selecting full grown grubs and conveying them
uninjured to her hole, a satisfactory explanation may be given.
If those that are but partly grown were chosen, they would die in
a short time for want of food, and putrefying would destroy the
inclosed egg, or the young one which springs from it. But when larvæ
of any kind have attained their full size, and are about to pass into
the pupa state, they can exist for a long period without any further
supply. By selecting these, therefore, and placing them uninjured
in the hole, however long the interval before the egg hatches, the
disclosed larva is sure of a sufficiency of fresh and wholesome
nutriment.--To prevent the possibility of any injury to its egg from
the motions or voracity of this living prey, the wasp is careful to
pack the whole so closely, each grub being coiled above the other in
a series of rings, and to consolidate the earth so firmly above them,
that they have not the slightest power of motion[663].--Those which
select more powerful caterpillars, or revenge the injuries of their
insect brethren by devoting spiders to the destruction they have so
often caused, take care to sting them in such a manner as, without
killing them outright, will incapacitate them from doing any injury.
Zeal and activity in providing for the well-being of their future
progeny, not inferior to what are exhibited by the tribe of
Ichneumons, _Sphecina_[664], and mason-wasps, though less cruelly
exerted, are also shown by various species of wild bees, of which we
have in this country a vast number. Having first excavated a proper
cell with a dexterity and persevering labour never enough to be
admired, they next deposit in it an egg, which they cover with a mass
of pollen or honey collected with unwearied assiduity from a thousand
flowers. As soon as the grub is hatched, it finds itself enveloped in
this delicious banquet provided for it by the cares of a mother it is
doomed never to behold; and so accurately is the repast proportioned
to its appetite and its wants, that as soon as the whole is consumed
it has no longer need of food; it clothes itself in a silken cocoon,
becomes a pupa, and after a deep sleep of a few days bursts from its
cell an active bee.
No circumstance connected with the _storgé_ of insects, is more
striking than the herculean and incessant labour which it leads
them cheerfully to undergo. Some of these exertions are so
disproportionate to the size of the insect, that nothing short of
ocular conviction could attribute them to such an agent. A wild bee
or a Sphex, for instance, will dig a hole in a hard bank of earth
some inches deep and five or six times its own size, and labour
unremittingly at this arduous undertaking for several days, scarcely
allowing itself a moment for eating or repose. It will then occupy
as much time in searching for a store of food; and no sooner is this
task finished, than it will set about repeating the process, and
before it dies will have completed five or six similar cells or even
more. If you would estimate this industry at its proper value, you
should reflect what kind of exertion it would require in a man to dig
in a few days out of hard clay or sand, with no other tools than his
nails and teeth, five or six caverns twenty feet deep and four or
five wide--for such an undertaking would not be comparatively greater
than that of the insects in question.
Similar laborious exertions are not confined to the bee or Sphex
tribe. Several beetles in depositing their eggs exhibit examples of
industry equally extraordinary. The common dor or clock (_Geotrupes
stercorarius_), which may be found beneath every heap of dung, digs
a deep cylindrical hole, and, carrying down a mass of the dung to
the bottom, in it deposits its eggs. And many of the species of the
_Scarabæidæ_[665] roll together wet dung into round pellets, deposit
an egg in the midst of each, and when dry push them backwards by
their hind feet into holes of the surprising depth of three feet,
which they have previously dug for their reception, and which are
often several yards distant. Frequently the road lies across a
depression in the surface, and the pellet when nearly pushed to the
summit rolls back again. But our patient Sisyphi are not easily
discouraged. They repeat their efforts again and again, and in the
end their perseverance is rewarded by success. The attention of
these insects to their eggs is so remarkable, that it was observed
in the earliest ages, and is mentioned by ancient writers, but with
the addition of many fables, as that they were all of the male
sex, that they became young again every year, that they rolled the
pellets containing their eggs from sun-rise to sun-set every day,
for twenty-eight days without intermission[666], &c. It is one of
this tribe of beetles (_S. sacer_) whose image is so often met with
amongst the hieroglyphics of the Egyptians, with whom it was a symbol
of the world, of the sun, and of a courageous warrior. Of the world,
as P. Valerianus supposes, on account of the orbicular form of its
pellets of dung, and the notion of their being rolled from sun-rise
to sun-set; of the sun, because of the angular projections from its
head resembling rays, and the thirty joints of the six tarsi of its
feet answering to the days of the month; and of a warrior, from the
idea of manly courage being connected with its supposed birth from a
male only[667]. It was as symbolical of this last that its image was
worn upon the signets of the Roman soldiers; and as typical of the
sun, the source of fertility, it is yet, as Dr. Clarke informs us,
eaten by the women to render them prolific[668].
These beetles, however, in point of industry must yield the palm
to one (_Necrophorus Vespillo_) whose singular history was first
detailed by M. Gleditsch in _the Acts of the Berlin Society_ for
1752. He begins by informing us that he had often remarked that dead
moles when laid upon the ground, especially if upon loose earth, were
almost sure to disappear in the course of two or three days, often
of twelve hours. To ascertain the cause, he placed a mole upon one
of the beds in his garden. It had vanished by the third morning; and
on digging where it had been laid, he found it buried to the depth
of three inches, and under it four beetles which seemed to have been
the agents in this singular inhumation. Not perceiving any thing
particular in the mole, he buried it again; and on examining it at
the end of six days he found it swarming with maggots apparently the
issue of the beetles, which M. Gleditsch now naturally concluded had
buried the carcase for the food of their future young. To determine
these points more clearly, he put four of these insects into a glass
vessel half filled with earth and properly secured, and upon the
surface of the earth two frogs. In less than twelve hours one of
the frogs was interred by two of the beetles: the other two ran
about the whole day as if busied in measuring the dimensions of the
remaining corpse, which on the third day was also found buried.
He then introduced a dead linnet. A pair of the beetles were soon
engaged upon the bird. They began their operations by pushing out the
earth from under the body so as to form a cavity for its reception;
and it was curious to see the efforts which the beetles made by
dragging at the feathers of the bird from below to pull it into its
grave. The male having driven the female away continued the work
alone for five hours. He lifted up the bird, changed its place,
turned it and arranged it in the grave, and from time to time came
out of the hole, mounted upon it and trod it under foot, and then
retired below and pulled it down. At length, apparently wearied with
this uninterrupted labour, it came forth and leaned its head upon
the earth beside the bird without the smallest motion as if to rest
itself, for a full hour, when it again crept under the earth. The
next day in the morning the bird was an inch and a half under ground,
and the trench remained open the whole day, the corpse seeming as
if laid out upon a bier, surrounded with a rampart of mould. In the
evening it had sunk half an inch lower, and in another day the work
was completed and the bird covered.--M. Gleditsch continued to add
other small dead animals, which were all sooner or later buried; and
the result of his experiment was, that in fifty days four beetles had
interred in the very small space of earth allotted to them, twelve
carcases: viz. four frogs, three small birds, two fishes, one mole,
and two grasshoppers, besides the entrails of a fish, and two morsels
of the lungs of an ox. In another experiment a single beetle buried
a mole forty times its own bulk and weight in two days[669]. It is
plain that all this labour is incurred for the sake of placing in
security the future young of these industrious insects along with
a necessary provision of food. One mole would have sufficed a long
time for the repast of the beetles themselves, and they could have
more conveniently fed upon it above ground than below. But if they
had left thus exposed the carcase in which their eggs were deposited,
both would have been exposed to the imminent risk of being destroyed
at a mouthful by the first fox or kite that chanced to espy them.
At the first view I dare say you feel almost inclined to pity the
little animals doomed to exertions apparently so disproportioned
to their size. You are ready to exclaim that the pains of so short
an existence, engrossed with such arduous and incessant toil, must
far outweigh the pleasures. Yet the inference would be altogether
erroneous. What strikes us as wearisome toil, is to the little agents
delightful occupation. The kind Author of their being has associated
the performance of an essential duty with feelings evidently of the
most pleasurable description; and, like the affectionate father
whose love for his children sweetens the most painful labours, these
little insects are never more happy than when thus actively engaged.
"A bee," as Dr. Paley has well observed, "amongst the flowers in
spring, (when it is occupied without intermission in collecting
farina for its young or honey for its associates,) is one of the
cheerfullest objects that can be looked upon. Its life appears to be
all enjoyment: so busy and so pleased[670]."
Of the sources of exquisite gratification which every rural walk will
open to you, while witnessing in the animals themselves those marks of
affection for their unseen progeny of which I have endeavoured to give
you a slight sketch, it will be none of the least fertile to examine
the various and appropriate instruments with which insects have been
furnished for the effective execution of their labours. The young of
the saw-fly tribe (_Serrifera_[671]) are destined to feed upon the
leaves of rose-trees and various other plants. Upon the branches of
these the parent fly deposits her eggs in cells symmetrically arranged;
and the instrument with which she forms them is a saw, somewhat like
ours but far more ingenious and perfect, being toothed on each side,
or rather consisting of two distinct saws, with their backs (the teeth
or serratures of which are themselves often serrated, and the exterior
flat sides scored and toothed), which play alternately; and, while
their vertical effect is that of a saw, act laterally as a rasp. When
by this alternate motion the incision, or cell, is made, the two saws,
receding from each other, conduct the egg between them into it[672].
The _Cicada_, so celebrated by the poets of antiquity, which lays
its eggs in dry wood, requires a stronger instrument of a different
construction. Accordingly it is provided with an excellent double
auger, the sides of which play alternately and parallel to each other,
and bore a hole of the requisite depth in very hard substances without
ever being displaced.
The construction of the sting or ovipositor with which the different
species of Ichneumon are provided, is not less nicely adapted to its
various purposes. In those which lay their eggs in the bodies of
caterpillars that feed exposed on the leaves of plants it is short,
often in very large species not the eighth of an inch long: having
free access to their victims, a longer sting would have been useless.
But a considerable number oviposit in larvæ which lie concealed where
so short an instrument could not possibly approach them. In these,
therefore, the sting is proportionably elongated, so much so that in
some small species it is three or four times the length of the body.
Thus in _Pimpla Manifestator_, whose economy has been so pleasingly
illustrated by Mr. Marsham[673], and which attacks the larva of a
wild bee (_Chelostoma[674] maxillosa_) lying at the bottom of deep
holes in old wood, the sting is nearly two inches long[675]: and it
is not much shorter in the more minute _I. Strobilellæ_ L., which
lays its eggs in larvæ concealed in the interior of fir cones, which
without such an apparatus it would never be able to reach.
The tail of the females of many moths whose eggs require to be
protected from too severe a cold and too strong a light, is
furnished, evidently for application to this very purpose, with a
thick tuft of hair. But how shall the moth detach this non-conducting
material and arrange it upon her eggs? Her ovipositor is provided
at the end with an instrument resembling a pair of pincers, which
for this purpose are as good as hands. With these, having previously
deposited her eggs upon a leaf she pulls off her tuft of hairs, with
which she so closely envelops them as effectually to preserve them
of the required temperature: and having performed this last duty to
her progeny she expires.
The ovipositor of the capricorn beetles, an infinite host, is a
flattened retractile tube, of a hard substance, by means of which
it can introduce its eggs under the bark of timber, and so place
them where its progeny will find their appropriate food[676]. The
auger used by certain species of Œstrus, to enable them to penetrate
the hides of oxen or deer and form a nidus for their eggs, has been
before described[677].--But to enumerate all the varieties of these
instruments would be endless.
The purpose which in the insects above mentioned is answered by their
anal apparatus, is fulfilled in the numerous tribes of weevils by the
long slender snout with which their head is provided. It is with this
that _Balaninus Nucum_ pierces the shell of the nut, and the weevil
(_Calandra granaria_) the skin of the grains of wheat, in which they
respectively deposit their eggs, prudently introducing one only into
each nut or grain, which is sufficient, but not more than sufficient,
for the nourishment of the grub that will inhabit it.
II. Hitherto I have adverted to those insects only which perish
before their young come into existence, and can therefore evince
their affection for them in no other way than by placing the eggs
whence they are to spring in secure situations stored with food;
and these include by far the largest portion of the race. A very
considerable number, however, extend their cares much further: they
not only watch over their eggs after depositing them, but attend
upon their young, when excluded, with an affectionate assiduity equal
to any thing exhibited amongst the larger animals, and in the highest
degree interesting. Of this description are some solitary insects,
as several species of the Linnean genus Sphex, earwigs, field-bugs,
and spiders: and those insects which live in societies, namely, ants,
bees, wasps, and termites: the most striking traits of whose history
in these respects I shall endeavour to lay before you.
You have seen that the greater number of the _Sphecina_ after
depositing their eggs in cells stored with a supply of food,
take no further care of them. Some, however, adopt a different
procedure. One of these, called by Bonnet the _Mason-wasp_, but
different from Reaumur's, not only incloses a living caterpillar
along with its egg in the cell, which it carefully closes, but at
the expiration of a few days, when the young grub has appeared and
has consumed its provision, re-opens the nest, incloses a second
caterpillar, and again shuts the mouth: and this operation it repeats
until the young one has attained its full growth[678]. A similar
mode, according to Rolander, is followed by _Ammophila vulgaris_
as well as by the yellowish wasp of Pennsylvania, described by
Bartram in the _Philosophical Transactions_[679], and by another
related to _Mellinus arvensis_, observed by Duhamel[680]; both of
which, however, instead of caterpillars, supply their larvæ with a
periodical provision of living flies.
What a crowd of interesting reflections are these most singular
facts calculated to excite! With what foresight must the parent
insect be endowed, thus to be aware at what period her eggs will
be hatched into grubs, and how long the provision she has laid up
will suffice for their support! What an extent of judgement, thus
in the midst of various other occupations to know the precise day
when a repetition of her cares will be required! What an accuracy of
memory, to recollect with such precision the entrance to her cell,
which the most acute eye could not discover; and without compass
or direction unerringly to fly to it, often from a great distance
and after the most intricate and varied wanderings! If we refer the
whole to instinct, and to instinct doubtless it must in the main if
not wholly be referred, our admiration is not lessened. Instinct,
when simple and directed to one object, is less astonishing; but
such a complication of instincts, applied to actions so varied and
dissimilar, is beyond our conception. We can but wonder and adore!
We are indebted to De Geer for the history of a field-bug
(_Pentatoma grisea_), a species found in this country, which shows
marks of affection for her young such as I trust will lead you,
notwithstanding any repugnant association that the name may call up,
to search upon the birch tree, which it inhabits, for so interesting
an insect. The family of this field-bug consists of thirty or
forty young ones, which she conducts as a hen does her chickens.
She never leaves them; and as soon as she begins to move, all the
little ones closely follow, and whenever she stops assemble in a
cluster round her. De Geer having had occasion to cut a branch of
birch peopled with one of those families, the mother showed every
symptom of excessive uneasiness. In other circumstances such an alarm
would have caused her immediate flight; but now she never stirred
from her young, but kept beating her wings incessantly with a very
rapid motion, evidently for the purpose of protecting them from the
apprehended danger[681].--As far as our knowledge of the economy
of this tribe of insects extends, there is no other species that
manifests a similar attachment to its progeny; but such may probably
be discovered by future observers.