animals with their _sensations_, which has been introduced into many
definitions of this mysterious power, for two reasons. In the first
place, this definition merely sets the world upon the tortoise; for
what do we know more than before about the nature of instinct, when
we have called it, with Brown, a predisposition to certain actions
when certain sensations exist, or with Tucker have ascribed it to the
operation of the senses, or to that internal feeling called appetite?
But, secondly, this connexion of instinct with bodily sensation, though
probable enough in some instances, is by no means generally evident.
We may explain in this way the instincts connected with hunger and
the sexual passion, and some other particular facts, as the laying
of the eggs of the flesh-fly in the flowers of _Stapelia hirsuta_,
instead of in carrion their proper nidus, and of those of the common
house-fly in snuff[763] instead of dung; for in these instances the
smell seems so clearly the guide, that it even leads into error. But
what connexion between sensation and instinct do we see in the conduct
of the working-bees, which fabricate some of the cells in a comb larger
than others, expressly to contain the eggs and future grubs of drones,
though these eggs are not laid by themselves, and are still in the
ovaries of the queen? So we may plausibly enough conjecture that the
fury with which, in ordinary circumstances, at a certain period of the
year, the working-bees are inspired towards the drones, is the effect
of some disagreeable smell or emanation proceeding from them at that
particular time: but how can we explain, on similar grounds, the fact
that in a hive deprived of a queen, no massacre of the drones takes
place? Lastly, to omit here a hundred other instances, as many of them
will be subsequently adverted to, if we may with some show of reason
suppose that it is the sensation of heat which causes bees to swarm;
yet what possible conception can we form of its being bodily sensations
that lead bees to send out scouts in search of a hive suitable for the
new colony, several days _before_ swarming?
After these observations on the nature of instinct, generally, I
pass on to contrast in several particulars the instincts of insects
with those of other animals; and thus to bring together some
remarkable instances of the former which have not hitherto been laid
before you, as well as to deduce from some of those already related,
inferences to which it did not fall in with my design before to
direct your attention. This contrast may be conveniently made under
the three heads of--the exquisiteness of their instincts--their
number--and their extraordinary development.
The instincts of by far the majority of the superior animals are of
a very simple kind, only directing them to select suitable food; to
propagate their species; to defend themselves and their young from
harm; to express their sensations by various vocal modulations; and
to a few other actions which need not be particularized. Others
of the larger animals, in addition to these simpler instinctive
propensities, are gifted with more extensive powers; storing up food
for their winter consumption, and building nests or habitations for
their young, which they carefully feed and tend.
All these instincts are common to insects, a great proportion of
which are in like manner confined to these. But a very considerable
number of this class are endowed with instincts of an _exquisiteness_
to which the higher animals can lay no claim. What bird or fish, for
example, catches its prey by means of nets as artfully woven and
as admirably adapted to their purposes as any that ever fisherman
or fowler fabricated? Yet such nets are constructed by the race of
spiders. What beast of prey thinks of digging a pit-fall in the track
of the animals which serve it for food, and at the bottom of which
it conceals itself, patiently waiting until some unhappy victim
is precipitated down the sides of its cavern? Yet this is done by
the ant-lion and another insect. Or, to omit the endless instances
furnished by wasps, ants, the Termites, &c., what animals can be
adduced which, like the hive-bee associating in societies, build
regular cities composed of cells formed with geometrical precision,
divided into dwellings adapted in capacity to different orders of
the society, and storehouses for containing a supply of provision?
Even the erections of the beaver, and the pensile dwelling of the
tailor-bird, must be referred to a less elaborate instinct than that
which guides the procedures of these little insects--the complexness
and yet perfection of whose operations, when contrasted with the
insignificance of the architect, have at all times caused the
reflecting observer to be lost in astonishment.
It is, however, in the _deviations_ of the instincts of insects and
their _accommodation to circumstances_, that the exquisiteness of
these faculties is most decidedly manifested. The instincts of the
larger animals seem capable of but slight modification. They are
either exercised in their full extent or not at all. A bird, when
its nest is pulled out of a bush, though it should be laid uninjured
close by, never attempts to replace it in its situation; it contents
itself with building another. But insects in similar contingencies
often exhibit the most ingenious resources, their instincts
surprisingly accommodating themselves to the new circumstances
in which they are placed, in a manner more wonderful and
incomprehensible than the existence of the faculties themselves. Take
a honey-comb, for instance. If _every_ comb that bees fabricate were
_always_ made _precisely_ alike--with the same general form, placed
in the same position, the cells all exactly similar, or where varying
with the variations always alike;--this structure would perhaps
in reality be not more astonishing than many of a much simpler
conformation. But when we know that in nine instances out of ten the
combs in a bee-hive are thus similar in their properties, and yet
that in the tenth one shall be found of a form altogether peculiar;
placed in a different position; with cells of a different shape--and
all these variations evidently adapted to some new circumstance not
present when the other nine were constructed,--we are constrained to
admit that nothing in the instinct of other animals can be adduced,
exhibiting similar exquisiteness: just as we must confess an ordinary
loom, however ingeniously contrived, far excelled by one capable of
repairing its defects when out of order.
The examples of this variation and accommodation to circumstances among
insects are very numerous; and as presenting many interesting facts in
their history not before related, I shall not fear wearying you with a
pretty copious detail of them, beginning with the more simple.
It is the instinct of _Geotrupes vernalis_ to roll up pellets of
dung, in each of which it deposits one of its eggs; and in places
where it meets with cow- or horse-dung only, it is constantly under
the necessity of having recourse to this process. But in districts
where sheep are kept, this beetle wisely saves its labour, and
ingeniously avails itself of the pellet-shaped balls ready made to
its hands which the excrement of these animals supplies[764].
A caterpillar described by Bonnet, which from being confined in
a box was unable to obtain a supply of the bark with which its
ordinary instinct directs it to make its cocoon, substituted pieces
of paper that were given to it, tied them together with silk, and
constructed a very passable cocoon with them.--In another instance the
same naturalist having opened several cocoons of a moth (_Cucullia
Verbasci_), which are composed of a mixture of grains of earth and
silk, just after being finished; the larvæ did not repair the injury in
the same manner. Some employed both earth and silk; others contented
themselves with spinning a silken veil before the opening[765].
The larva of the cabbage-butterfly (_Pontia Brassicæ_) when about to
assume the pupa state, commonly fixes itself to the under-side of
the coping of a wall or some similar projection. But the ends of the
slender thread which serves for its girth would not adhere firmly
to stone or brick, or even wood. In such situations, therefore, it
previously covers a space of about an inch long and half an inch
broad with a web of silk, and to this extensive base its girth can be
securely fastened. That this proceeding, however, is not the result
of a blind unaccommodating instinct, seems proved by a fact which has
come under my own observation. Having fed some of these larvæ in a
box covered by a piece of muslin, they attached themselves to this
covering; but as its texture afforded a firm hold to their girth,
they span _no_ preparatory web.
_Bombus_[766] _Muscorum_ and some other species of humble-bees cover
their nests with a roof of moss. M. P. Huber having placed a nest
of the former under a bell glass, he stuffed the interstices between
its bottom and the irregular surface on which it rested, with a linen
cloth. This cloth, the bees, finding themselves in a situation where
no moss was to be had, tore thread from thread, carded it with their
feet into a felted mass, and applied it to the same purpose as moss,
for which it was nearly as well adapted.--Some other humble-bees tore
the cover of a book with which he had closed the top of the box that
contained them, and made use of the detached morsels in covering
their nest[767].
The larva of _Cossus ligniperda_, which feeds in the interior of trees,
previously to fabricating a cocoon and assuming the pupa state, forms
for the egress of the future moth a cylindrical orifice, except when it
finds a suitable hole ready made. When the moth is about to appear, the
chrysalis with its anterior end forces an opening in the cocoon. If the
orifice in the tree has been formed by itself, in which case it exactly
fits its body, it _entirely_ quits the cocoon, and pushes itself half
way out of the hole, where it remains secure from falling until the
moth is disclosed. But if the orifice, having been adopted, be larger
than it ought to have been, and thus not capable of supporting the
pupa in this position, the provident insect pushes itself only _half
way_ out of the cocoon, which thus serves for the support which in the
former case the wood itself afforded[768].
The variations in the procedures of the larva of a little
moth described by Reaumur, whose habitation has been before
noticed[769]--one of those which constantly reside in a
subcylindrical case--are still more remarkable. This little
caterpillar feeds upon the elm, the leaves of which serve it at
once for food and clothing. It eats the parenchyma or inner pulp,
burrowing between the upper and under membranes, of portions of which
cut out, and properly sewed together, it forms its case. Its usual
plan is, to insinuate itself between the epidermal membranes of the
leaf, close to one of the edges. Parallel with this it excavates a
cavity of suitable form and dimensions, gnawing the pulp even out
of every projection of the serratures, but carefully avoiding to
separate the membranes at the very edge, which with a wise saving of
labour it intends should form one of the seams of its coat; and as
the little miner is not embarrassed with the removal of the excavated
materials, which it swallows as it proceeds, a cavity sufficiently
large is but the work of a few hours. It then lines it with silk, at
the same time pushing it into a more cylindrical shape; and lastly,
cutting it off at the two ends and inner side, it sews up the latter
with such nicety that the suture is scarcely discoverable; and is
now provided with a case or coat exactly fitting its body, open at
the two ends, by one of which it feeds and by the other discharges
its excrement, having on one side a nicely-joined seam, and the
other--that which is commonly applied to its back--composed of the
natural marginal junction of the membranes of the leaf.
Such are the ordinary operations of this insect, which, when it is
considered that the case is rather fusiform than cylindrical; that
the end through which it eats is circular, and the other curiously
three-cornered like a cocked-hat; and that consequently its cloth
requires to be very irregularly and artfully cut, to be accommodated
to such a figure--it must be admitted, are the result of an instinct
of no very simple kind. Complicated, however, as these manœuvres
seem, our ingenious workman is not confined to them. By way of
putting its resources to the test, Reaumur cut off the serrated edge
from the nearly-finished coat of one of them, and exposed the little
occupant to the day. He expected that it would have quitted its
mutilated garment and commenced another; and so it certainly would,
had it been guided by an invariable instinct. But he calculated
erroneously. Like one of its brother tailors of the biped race, it
knew how "to cut its coat according to its cloth," and immediately
setting about repairing the injury sewed up the rent. Nor was this
all. The scissors having cut off one of the projections intended to
enter into the construction of the triangular end of its case, it
entirely changed the original plan, and made that end the head which
had been first designed for the tail.
On another occasion Reaumur observed one of these larvæ to cut out
its coat from the very centre of a leaf, where it is obvious a series
of operations wholly different must be adopted, the two membranes
composing it necessarily requiring to be cut and sewed on _two_
sides instead of on one only. But what was most striking in this new
procedure was the alteration which the caterpillar made in the period
of sewing up its garment. When these larvæ cut out their case from
the edge of a leaf, they seem aware that, if they were to detach it
entirely from the inner side before the process of sewing, lining,
&c., is completed, having no support on the exterior edge, it would
be liable to fall down; at the same time they could not sew together
the membranes composing it at the _inner_ side, without cutting them
in part from the leaf. While, therefore, they divide the major part
of their inner side from the leaf, they artfully leave them attached
to it by one of the large nerves at each end: and these supports they
do not cut asunder until the intermediate space has been sewed up,
and they are ready to step, with their house on their back, upon the
_terra firma_ of the disk of the leaf. In this instance, therefore,
the larvæ do not wholly separate their case from the leaf, until it is
sewed. But when the same larvæ cut out their materials from the middle
of the leaf, where, though completely cut round, they are retained in
their situation secure from all danger of falling by the serratures of
the incisions made by the jaws of the larvæ, these little tailors vary
their mode, and _entirely_ detach the pieces from the surrounding leaf,
before they proceed to set a stitch into them[770].
In the preceding instances the variation of instinct takes place
in the same individual, but Bonnet mentions a very curious fact in
which it occurs in different generations of the same species. There
are annually, he informs us, two generations of the Angoumois moth,
an insect which has been before mentioned[771], as destructive to
wheat: the first appear in May and June, and lay their eggs upon
the ears of wheat in the fields; the second appear at the end of
the summer or in autumn, and these lay their eggs upon wheat in the
granaries. These last pass the winter in the state of larvæ, from
which proceeds the first generation of moths. But what is extremely
singular as a variation of instinct, those moths which are disclosed
in _May_ and _June_ in the granaries, quit them with a rapid flight
at sun-set, and betake themselves to the yet unreaped fields, where
they lay their eggs; while the moths which are disclosed in the
granaries after harvest, stay there, and never attempt to go out, but
lay their eggs upon the stored wheat[772].--This is as extraordinary
and inexplicable as if a litter of rabbits produced in spring were
impelled by instinct to eat vegetables, while another produced in
autumn should be as irresistibly directed to choose flesh.
It is, however, into the history of the hive-bee that we must look
for the most striking examples of variation of instinct; and here, as
in every thing relating to this insect, the work of the elder Huber
is an unfailing source of the most novel and interesting facts.
It is the ordinary instinct of bees to lay the foundation of
their combs at the top of the hive, building them perpendicularly
_downwards_; and they pursue this plan so constantly, that you might
examine a thousand (probably ten thousand) hives, without finding any
material deviation from it. Yet Huber in the course of his experiments
forced them to build their combs perpendicularly upward[773]; and, what
seems even more remarkable, in an horizontal direction[774].
The combs of bees are always at an uniform distance from each
other, namely about one third of an inch, which is just wide
enough to allow them to pass easily and have access to the young
brood. On the approach of winter, when their honey-cells are not
sufficient in number to contain all the stock, they _elongate_ them
considerably, and thus increase their capacity. By this extension
the intervals between the combs are unavoidably contracted; but in
winter well-stored magazines are essential, while from their state of
comparative inactivity spacious communications are less necessary.
On the return of spring, however, when the cells are wanted for the
reception of eggs, the bees contract the elongated cells to their
former dimensions, and thus re-establish the just distances between
the combs which the care of their brood requires[775]. But this is
not all. Not only do they elongate the cells of the old combs when
there is an extraordinary harvest of honey, but they actually give to
the new cells which they construct on this emergency a much greater
_diameter_ as well as a greater depth[776].
The queen-bee in ordinary circumstances places each egg in the
centre of the pyramidal bottom of the cell, where it remains fixed
by its natural gluten: but in an experiment of Huber, one whose
fecundation had been retarded, had the first segments of her abdomen
so swelled that she was unable to reach the bottom of the cells. She
therefore attached her eggs (which were those of males) to their
lower side, two lines from the mouth. As the larvæ always pass that
state in the place where they are deposited, those hatched from the
eggs in question remained in the situation assigned them. But the
working-bees, as if aware that in these circumstances the cells would
be too short to contain the larvæ when fully grown, _added to their
length_, even before the eggs were hatched[777].
Bees close up the cells of the grubs, previously to their
transformation, with a cover or lid of wax: and in hanging its abode
with a silken tapestry before it assumes the pupa state, the grub
requires that the cell should not be too short for its movements.
Bonnet having placed a swarm in a very flat glass hive, the bees
constructed one of the combs parallel to one of the principal sides,
where it was so straight that they could not give to the cells their
ordinary depth. The queen, however, laid eggs in them, and the
workers daily nourished the grubs, and closed the cells at the period
of transformation. A few days afterwards he was surprised to perceive
in the lids, holes more or less large, out of which the grubs partly
projected, the cells having been too short to admit of their usual
movements. He was curious to know how the bees would proceed. He
expected that they would pull all the grubs out of the cells, as they
commonly do when great disorders in the combs take place. But he did
not sufficiently give credit to the resources of their instinct. They
did not displace a single grub--they left them in their cells: but
as they saw that these cells were not deep enough, they closed them
afresh with lids much more convex them ordinary, so as to give to
them a sufficient depth; and from that time no more holes were made
in the lids.
The working bees, in closing up the cells containing larvæ, invariably
give a convex lid to the large cells of drones, and one nearly flat
to the smaller cells of workers: but in an experiment instituted by
Huber to ascertain the influence of the size of the cells on that of
the included larvæ, he transferred the larvæ of workers to the cells
of drones. What was the result? Did the bees still continue blindly to
exercise their ordinary instinct? On the contrary, they now placed a
nearly _flat_ lid upon these large cells, as if well aware of their
being occupied by a different race of inhabitants[778].
On some occasions bees, in consequence of Huber's arrangements in
the interior of their habitations, have begun to build a comb nearer
to the adjoining one than the usual interval; but they soon appeared
to perceive their error, and corrected it by giving to the comb a
gradual curvature, so as to resume the ordinary distance[779].
In another instance, in which various irregularities had taken place
in the form of the combs, the bees, in prolonging one of them, had,
contrary to their usual custom, begun two separate and distant
continuations, which in approaching instead of joining would have
interfered with each other, had not the bees, apparently foreseeing the
difficulty, gradually bent their edges so as to make them join with
such exactness that they could afterwards continue them conjointly[780].
In constructing their combs, bees, as you have been before told, in
my letter on the habitations of insects, form the first range of
cells--that by which the comb is attached to the top of the hive--of
a different shape from the rest. Each cell instead of being hexagonal
is pentagonal, having the fifth broadest side fixed to the top of
the hive, whence the comb is much more securely cemented to that
part, than if the first range of cells had been of the ordinary
construction. For some time after their fabrication, the combs remain
in this state; but at a certain period the bees attack the first
range of cells as if in fury, gnaw away the sides without touching
the lozenge-shaped bottoms; and having mixed the wax with propolis,
they form a cement well known to the ancients under the names of
_Mitys_, _Commosis_ and _Pissoceros_, which they substitute in the
place of the removed sides of the cells, forming of it thick and
massive walls and heavy and shapeless pillars, which they introduce
between the comb and the top of the hive so as to agglutinate them
firmly together. Huber, who first in modern times witnessed this
remarkable modification of the architecture of bees, observed, that
not only are they careful not to touch the bottoms of the cells, but
that they do not remove at once the cells on both sides of the comb,
which in that case might fall down; but they work alternately, first
on one side and then on the other, replacing the demolished cells as
they proceed, with mitys, which firmly fixes the comb to its support.
The object of this substitution of mitys for wax seems clear. While
the combs are new and only partially filled with honey, the first
range of cells, originally established as the base and the guide for
the pyramidal bottoms of the subsequent ones, serves as a sufficient
support for them. But when they contain a store of several pounds,
the bees seem to foresee the danger of such a weight proving too
heavy for the thin waxen walls by which the combs are suspended, and
providently hasten to substitute for them thicker walls, and pillars
of a more compact and viscid material.