PROVISION FOR REARING THE YOUNG.
THE PRESERVATION OF THE INDIVIDUAL AND THE PRESERVATION OF THE
SPECIES--FOODS MANUFACTURED BY THE PARENTS FOR THEIR
YOUNG--SPECIES WHICH OBTAIN FOR THEIR LARVAE FOODS
MANUFACTURED BY OTHERS--CARCASSES OF ANIMALS STORED
UP--PROVISION OF PARALYSED LIVING ANIMALS--THE CAUSE OF THE
PARALYSIS--THE SURENESS OF INSTINCT--SIMILAR CASES IN WHICH
THE SPECIFIC INSTINCT IS LESS POWERFUL AND INDIVIDUAL
INITIATIVE GREATER--GENERA LESS SKILFUL IN THE ART OF
PARALYSING VICTIMS.
_The preservation of the individual and the preservation of the
species._--In the previous chapter we have seen animals preparing for
the future, and amassing materials for their own subsistence. In other
cases these provisions are destined to feed the young. It is the same
industry, sometimes exercised for the preservation of the individual,
sometimes for the perpetuation of the race. We must expect to find
acts of the last kind more instinctive and less reflective than those
of the first, and this agrees well with what we know of natural
selection. If we now see living beings display so many resources and
calculate with such certainty all that will favour the healthy
development of their descendants, we must not necessarily conclude
that the species possess these instincts from the beginning. They are
not to be regarded as mechanisms artfully wound up and functioning
since the appearance of life on the earth with the same inevitable
regularity. The qualities which we find in them were weak at first;
they have developed in the course of ages, and have finally, by
heredity, been impressed upon the creatures to manifest themselves by
necessary acts from which there is no longer any escape. There is no
need for surprise if we meet to-day, I do not say among all, but among
a very large number of animals, this foresight for offspring in a
well-marked form. It is easy to understand that the species that first
acquired and fixed an instinct propitious to the increase of the race
has rapidly prospered, stifling beneath its extension those that are
less favoured from this point of view, which is of capital importance
in a struggle for a place beneath the sun. At the present day if the
struggle of animal life offers few facts of lack of foresight for the
rearing of young, it is because this defect has killed the races who
were subject to it; they have disappeared, or have only been saved by
qualities of another order.
For the rest, if it is difficult to reconstitute except in imagination
the different stages through which, in time, and in a determined
species, acts at first imperfect, but designed, have become perfect
and instinctive, we can at least find in space different degrees of
the same instinct in allied genera which lead us by a succession of
transitions from mechanical action to reflective action.
As I cannot quote all the facts showing this care for the future, I
will select a few. It must be said at first that a considerable number
of animals show nothing of the kind. Let us leave aside all the
inferior beings to speak of those among whom we may expect some degree
of method. Crustacea, fish, Batrachians, and many others lay their
eggs, are contented to conceal them a little so that they may not
become a too easy prey, and are altogether indifferent as to what may
happen afterwards. As soon as they come out, the young obtain their
own food from day to day; myriads are destroyed, and if the races
remain so strong numerically it is because they are saved by the
innumerable quantity of eggs produced by a single female. If it were
not for this prodigious fecundity these species would have
disappeared. Birds make no provision for their young; but, on the
other hand, as long as the latter are weak and unable to obtain their
own prey, the parents feed them every day by hunting both for
themselves and the brood.
I will not insist on those beings who, like mammals, produce
physiological reserves, not for their own use, but for the profit of
their young. The females of these animals elaborate materials from
their own organism and store them up in the form of milk to nourish
the young. This fact is related to foresight, with a view to
offspring, exactly in the same way as the Honey Ants show a
transformation of foresight for the individual. In both cases industry
is replaced by the function of a specially adapted organ.
_Foods manufactured by the parents for the young._--It is especially
insects with whose industries we are here concerned, and they are more
or less instinctive in various cases. Every one knows how the
Hymenoptera prepare honey from the pollen of flowers, to some extent
for themselves, but especially in order that their young may at the
moment of appearance possess a food which will enable them to undergo
their first metamorphosis sheltered from the inclemencies outside.
These foods are enclosed with great art, according to the species,
either in skilfully-constructed cells of wax, as by Bees, or in nests
of paper or cardboard which the Wasps fabricate, or again in huts
built of earth in the manner of the _Chalicodoma_.
_Species which obtain for their larvae foods manufactured by
others._--Other insects have not this taste for lengthy labours, and
do not know how to execute them; but they do not intend that their
young shall be the victims of maternal lack of skill, and they display
marvellous resources to enable them to profit by the foresight of
others.
[Illustration: FIG. 15.]
The _Sitaris muralis_, a beetle whose customs have been described by
Fabre in a remarkable manner,[71] may be counted among the cleverest
in assuring to its larvae the goods of others. It puts them in a
position to profit by it, and when they are installed they know
sufficiently well what to do. The species has so long perpetuated
itself by this process that it has become, both in mother and
offspring, highly automatic. It is a hymenopterous insect which this
family, whose first vital manifestation is theft, thus levies a
contribution on. It is called the _Anthophora pilifera_, and during
the fine weather it makes a collection of honey intended to be
absorbed by its own larvae, if it had not the misfortune to be watched
by one of these intriguing Coleoptera. Wherever in Provence there is a
perpendicular wall, natural or artificial, a little cliff, a sloping
ditch, or the wall of one of those caves which the people of the
country use for putting their tools in, the _Anthophora_ hollows out
galleries, at the bottom of which he builds a certain number of
chambers. He fills each of them with honey, places in it an egg which
floats in the midst of this little lake of nectar, and closes it all
up. The _Sitaris_ covets this honey to nourish its offspring, and the
chamber to shelter it. After having discovered one of the galleries of
which I have spoken, the female _Sitaris_ comes about the beginning of
September to lay her eggs, which are numerous, being not generally
fewer than two thousand. In the following month the larvae appear; they
are black, and swarm in a little heap mixed up with the remains of
egg-shells. They vegetate in this condition for a long time, and may
still be found there in May. At this period they have become more
active, and, in order to complete their development, are thinking of
profiting by their favourable situation near the entrance to a gallery
of the Hymenoptera; when a male _Anthophora_ comes within reach, two
or three of them catch hold of him and climb on to his thorax. They
maintain themselves there by clinging to the hairs. At the moment of
fertilisation the male, thus burdened, comes in contact with the
female; the coleopterous larvae then pass on to her, so that, according
to Fabre's expression, the meeting of the sexes brings death and life
to the eggs at the same time. Henceforth fixed on this laying insect,
the little _Sitaris_ remain quiet, and have only to wait; their future
is assured. The _Anthophora_ has made her chambers, and with the
greatest care has filled each of them with honey. Then in the midst
she deposits an egg, which remains floating on the surface like a
little boat; when her task is accomplished, the mother passes to a new
cell to confide to it another of her descendants. During this time the
parasite larva hastily descends the abdominal hairs and allows itself
to fall on the egg of the _Anthophora_, to be then borne upon it as
upon a raft; its fall must take place at the precise instant which
will enable it to embark without falling into the honey, in which just
now it would be glued fast, and perish. This series of circumstances
results only in the introduction of a single _Sitaris_ into a chamber;
the moment which must be profited by is too short for many of them to
seize. If the female _Anthophora_ carries others hidden in her hairs,
they are obliged to await a new hatching to let themselves glide off.
Thus enclosed with the egg of the _Anthophora_ and its provision of
honey, the larva has no other rival to fear, and may alone utilise the
whole store. This parasitism has to such an extent become a habit with
the species, that the larva's organisation has become modified by it.
At the moment when it falls into the cell it cannot feed on honey. It
is indispensable for its development that it should first devour the
egg on which it floats; it can at this period be nourished by no other
food. In acting in this way it also frees itself from a voracious
being who would require much food. This first repast lasts about eight
days, at the end of which it undergoes a moult, takes another form,
and begins to float on the honey, gradually devouring it, for at this
stage it becomes able to assimilate honey. Slowly its development is
completed, with extremely interesting details with which we need not
now concern ourselves. The larva of _Sitaris_ is then in conditions
exceptionally favourable for growth; but, in spite of appearances,
there is no reason for admiring the marvellous foresight and
extraordinary sureness of instinct; nearly everything depends on a
fortuitous circumstance, a chance. This becomes very evident if we
study another related beetle; it is called the _Sitaris colletis_, and
lives at the expense of the hymenopterous _Colletes_, as its relative
at the expense of the _Anthophora_. But these two species of the same
genus are very unequally aided by chance. The one whose history we
have just traced attaches itself to an insect whose egg floats above a
store of honey; the second chooses a victim who attaches its egg to
the walls of a chamber. (Fig. 15.) This almost insignificant
difference has a considerable influence on the parasite's evolution.
In the first case it is alone, and may develop with certainty; in the
second, on the contrary, several _Sitaris_ penetrate the chamber and
climb up to attack the egg, which in this case also must be their
first food. This rivalry causes a struggle to the death. If one of the
larvae is notably more vigorous than its rivals, it may free itself
from them and survive. Let us consider the fate in store for the two
species. The first is much more favoured, since a happy chance permits
each germ to produce an individual; in the second, each individual
which completes its evolution deprives several of its brothers of
life. And even this only happens in the most favourable cases, for it
may be that not one _Sitaris_ in the chamber may reach the adult
state. If the first arrival begins to absorb the egg of the
_Colletes_, a second hungry one may kill it in the midst of its repast
and take its place. But the conqueror finds the provisions already
reduced and insufficient to enable it to reach the moulting stage, at
the end of which it could profit by the honey. Ill-nourished and
weakened, it cannot support this crisis, and its corpse falls beside
that of its fellow whom it had sacrificed. Three or four parasites may
thus succeed to the same feast, and the victory of the last is useless
to him. His first struggle for life and his first triumph are followed
by irreparable defeat. These two examples show very well how a slight
difference may favour a species, and how a happy quality is capable of
being perpetuated by heredity, since by its very nature it is destined
to be extended to more numerous beings.
[71] "Hypermetamorphoses et Moeurs des Meloides," _Ann. Sc.
Nat._, iv. Serie, t. 7, 1857, p. 299; also "Nouvelles
observations sur l'hypermetamorphose et les Moeurs des
Meloides," _ibid._, t. 9, 1858, p. 265.
[Illustration: FIG. 16.]
_Carcasses of animals stored up._--These insects lay up for their
offspring stores manufactured by themselves or by others. The class we
are now about to consider makes provision of animals either dead or in
a torpid condition, with more or less art and more or less sure
instinct. Most people have seen the _Necrophorus_ or Burying Beetle
working in fields or gardens. These are large Coleoptera who feed on
abandoned carrion; everything is good to them--bodies of small
mammals, birds, or frogs; they are very easy to please, and as long as
the beast is dead that is all they require. When they have found such
remains, and consider only how to satisfy their hunger, they do not
take much trouble, and gnaw the prey on the spot where they have found
it. They are not alone at the feast, and in spite of their diligence
numerous rivals come up to dispute it; it is necessary to share with a
great number of noisy and voracious flies and insects. In the adult
state they come out well from this competition; but as good parents
they wish to save their larvae from it, as in a feeble condition these
might suffer severely. They desire to lay up a carcass for their young
alone, and with this object they bury it in the earth. The eggs also
which will thus develop in the soil have more chance of escaping
destruction by various insectivorous animals. If these diggers find a
rat (Fig. 16) or a dead bird, three or four unite their efforts, glide
beneath it, and dig with immense activity, kicking away with their
hind legs the earth withdrawn from the hole. They do not pause, and
their work soon perceptibly advances. The rat gradually sinks in the
pit as it grows deeper. When they have the good fortune to find the
earth soft they can sink the prey in less than two hours to a depth of
thirty centimetres. At this level they stop, and throw back into the
hole the earth they have dug out, carefully smoothing the hillock
which covers the grave. Thus stored up, the carcass is ready to
receive the _Necrophorus_ eggs. The females enter the soil and lay on
the buried mammal; then they retire, satisfied to leave their little
ones, when they appear, face to face with such abundant nourishment.
When they emerge from the envelope the young larvae find themselves in
the presence of this stored food, which has been softened by
putrefaction and rendered more easy of digestion. If the treasure has
not fallen on a spot easy to dig, the _Necrophorus_ quickly recognise
the fact, and do not waste time in useless labour. Endowed with
considerable strength relatively to their size, three or four of them
creep beneath the prey, and co-ordinating their efforts they transport
it several metres off to a spot which they know by experience to be
suitable for their labours. It may happen that soft earth is too far
away, and transport becoming too difficult a task, they renounce it.
But as good food should never be wasted, they utilise it by feeding
themselves, awaiting a more manageable god-send for their offspring.
Many observers have studied these beetles, and all are surprised at
their sagacity, and the way in which their various operations are
adapted to circumstances; genuine reflection governs their acts, which
are always combined to produce a definite effect.
_Provision of paralysed living animals._--It is unnecessary to say how
much better it would be for the young larva to have at its disposal
instead of a carcass a living animal, but paralysed and rendered
motionless by some method. It is difficult to believe the thing
possible, yet nothing is better established. There is a hymenopterous
relative of the Wasp called the _Sphex_. Instead of laying up honey
they store animal provisions for their larvae. Fabre has studied one of
them, the _Sphex flavipennis_.[72] It is in September that this wasp
lays her eggs; during this month to shelter her little ones she
hollows out a dozen burrows and provisions them. She has then to
devote about three days' work to each of them, for there is much to
do, as may be imagined. For each of these hiding-places the _Sphex_
first pierces a horizontal gallery about two or three inches long;
then she bends it obliquely so that it penetrates deeply into the
earth, and it is again continued in this direction for about three
inches. At the end of this passage three or four chambers are made,
usually three; each of these is meant to receive one egg. The insect
interrupts its mining task, not forming the three chambers
consecutively; when the first is completed she provisions it--we shall
soon see in what manner--and lays an egg there; then she blocks it up,
suppressing all communication between this cell and the gallery; this
done she bores a second passage, provisions it, and lays another egg,
closes up the orifice, and proceeds to prepare the third. This work is
pushed on with great activity, and when completed the _Sphex_ entirely
fills up the subterranean passage, and completely isolates the hope of
the race at a depth sufficient to shelter it well. A last precaution
is taken: before leaving, the rubbish in front of the obstructed
opening is cleared away, and every trace of the operation disappears.
The nest is then definitely abandoned, and another one prepared.
[72] "Etude sur l'instinct et les metamorphoses des
Sphegiens," _Ann. Sci. Nat._, 1856.
The chambers in which the larvae are enclosed--hastily made with little
care, and with rough unsmoothed walls--are not very solid, and could
not last long without slipping; but as they only have to last for a
single season they possess sufficient resistance for the insect's
purpose. The larva also knows very well how to protect itself against
the roughness of the walls, and overlays them with a silky secretion
produced by its glands.
We have now to consider the nature of the provisions placed by the
_Sphex_ near the egg. Each cell must contain four crickets. That is
the amount of food necessary for a larva during its evolution, and
these insects are in fact large enough to supply a considerable amount
of nourishment. When the _Sphex_ interrupts digging operations it is
to fly on a hunting expedition. It soon returns with a cricket it has
seized, holding it by one antenna which it turns round in its jaws. It
is a heavy burden for the slender _Sphex_ to bear. Sometimes on foot,
dragging its burden after it, sometimes flying, and carrying the
suspended cricket always in a passive condition, the burrow is
gradually reached, not without difficulty. In spite of appearances,
the cricket is not dead; it cannot move, but if kept for several days
it will not putrefy, and its joints remain supple. It is simply the
victim of a general paralysis.
_The cause of the paralysis._--It was evidently of the greatest
interest to know how the _Sphex_ contrived this capture, and what
method it used to suppress the movements of the prey. In order to
obtain the solution of this problem, Fabre during a long period
accumulated experiments and observations, and at last discovered in
every detail how the thing was done. In order to compel the _Sphex_ to
act in his presence, he placed himself in front of the orifice of a
gallery in which the insect was working; he soon saw it returning with
a paralysed cricket. Arrived at the burrow, the insect placed the prey
on the ground for a moment and disappeared in the passage to see that
everything was in order, and that no damage had taken place since its
departure. Everything was going well, and it reappeared, took up its
burden, and again entered the subterranean passage, drawing the victim
along. It brought it into the chamber for which it was destined,
placing it on its back, the head down and the feet towards the door.
Then it set out hunting again until it had ranged four crickets side
by side. Before attempting a decisive experiment, the observer felt
his way. At the moment when the _Sphex_ was buried in the earth
examining the chamber, Fabre withdrew the prey a short distance and
awaited events. Having made the domiciliary visit, the _Sphex_ then
went straight to the place where it had left its insect, but could not
find it. It was naturally very perplexed, and examined the
neighbourhood with extreme agitation, not knowing what had happened,
and evidently regarding the whole affair as very extraordinary; at
last it found the victim it was seeking. The cricket still preserved
the same immobility; its executioner seized it by an antenna and drew
it anew to the entrance of the hole. In the interior of the
subterranean domain everything is in good order; the insect had just
assured itself of the fact, and we should expect to see it enter with
its prey; not at all, it entered alone, and only decided to introduce
the prey after it had made a fresh inspection. This fact is
surprising, and it is still more surprising that if the practical joke
of removing the cricket is repeated several times in succession, the
_Sphex_ drags it anew every time to the entrance of the burrow and
first descends alone; forty times over this experiment succeeded
without the insect deciding to renounce the habitual manoeuvre. Fabre
insists on this fact, and rightly, for nothing should be neglected; he
makes it a text to show how automatic instinct is, and how the acts
which proceed from it are invariably regulated so as to succeed one
another always in the same order. In their nature these acts are quite
indistinguishable from intelligent acts; only the creature is not
capable of modifying them to bring them into harmony with unforeseen
circumstances. All this is correct, but where it becomes excessive is
in endowing animals alone with instinct and separating them from this
point of view from Man. It is incontestable that the custom of
visiting the burrow before introducing a victim into it has become so
imperious in the _Sphex_ that it cannot be broken, even when it is of
no use. It is a mechanical instinct. But we may see an exactly
parallel manifestation of human intelligence. In face of danger man
utters cries of distress; they are heard and assistance comes. But
these appeals are not intelligent and appropriate to the end; they are
instinctive. Place the same individual in a situation where he knows
very well that his voice cannot be heard; this will not hinder him
from reproducing the same acts if he finds himself in the presence of
danger. It is thus that the _Sphex_ proceeds, guided by instincts, and
it is no reason for despising it. And even in the course of this
little experiment the insect gives proof of judgment. When it finds
its cricket, it is perfectly aware that it is the same cricket which
it brought, that there is no life in it, and that there is no need to
re-commence the struggle; it sees too that it is not an ordinary
corpse liable to putrefaction, but the very same cricket, and it does
not hesitate to utilise it at once.
These habits being ascertained, Fabre proceeded to find out how the
paralysis is produced. He awaited near a burrow the _Sphex's_ arrival,
dragging a victim by an antenna, and while the insect was occupied in
the subterranean survey he substituted a living cricket for that which
the _Sphex_ had left, expecting to find it on the spot where it had
been placed. On emerging it perceives the cricket scampering away; not
a moment was to be lost, and without reflection it leapt on the
refractory victim. A lively struggle followed, a duel to the death
among the blades of grass; it was a truly dramatic spectacle, the
agile assailant whirling around the Cricket, who kicked violently with
his hind legs. If a blow were to reach the _Sphex_ it would be
disembowelled; but it avoids the blows skilfully without ceasing its
own violent attack. At last the combat ends; the cricket is brought to
earth, turned on to its back, and maintained in this position by the
_Sphex_. Still on its guard, the latter seizes in its jaws one of the
filaments which terminate the abdomen of the vanquished, placing its
legs on the belly; with the two posterior legs it holds the head
turned back so as to stretch the under side of the neck. The cricket
is unable to move and the conqueror's sting wanders over the horny
carapace seeking a joint, feeling for a soft place in which it can
enter to give the finishing stroke. The dart at last reaches, between
the head and the neck, the spot where the hard portions articulate,
leaving between them a space without covering. The joint in the armour
is found. The _Sphex's_ abdomen is agitated convulsively; the sting
penetrates the skin, piercing a ganglion situated just beneath this
point; the venom spreads and acts on the nervous cells, which can no
longer convey messages to the muscles. That is not all; the sting
wanders over the cricket's belly, this time seeking the joint between
the neck and the thorax; it finds it, and is again thrust in with
fury; a second ganglion of the nervous chain is thus perforated and
poisoned. After these two wounds the victim is completely paralysed.
As already mentioned, several facts enable us to recognise that the
Cricket is by no means dead. It is simply incapable of movement, as
would happen after an injection of curare. This poison kills a
superior animal, for it hinders the muscular movements of the chest
and diaphragm, necessary to respiration; but if a frog, which can
breathe through its skin, is thus acted on it comes to life again at
the end of twenty-four or forty-eight hours if the dose has not been
too strong. The cricket is in a similar condition; it neither eats nor
breathes; being incapable also of movement, there is no vital
expenditure; it remains in a sort of torpor, or latent life, awaiting
the tragic fate that is reserved for it. When it has been deposited in
the little mortuary chamber the _Sphex_ lays an egg on its thorax. The
larva will soon come out to penetrate the body of the prey by
enlarging the hole left by the sting. It thus finds for its first
meals a food which unites the flavour of living flesh with the
immobility of death. Nothing can be more convenient. When the first
body is eaten it proceeds to the second, and thus devours successively
the four victims stored up by maternal foresight.
In order not to interrupt the description and interfere with the
succession of the acts, I have passed without remark the experiment in
which Fabre substituted a living animal for the _Sphex's_ already
paralysed captive. It seems to me, however, that in this circumstance
the insect showed judgment, and knew how to act in accordance with new
requirements. It was evidently the first time in insect memory in
which so surprising a phenomenon had been seen as a victim at the last
moment again taking the field. We cannot make instinct intervene here.
If the _Sphex's_ acts are so automatic as we are sometimes led to
believe, in accordance with facts which are perfectly accurate, we
ought always to observe the following succession of acts: first,
hollowing of the burrow; second, the chase; third, the blows of the
dart; fourth, the different manoeuvres for placing the victim in the
sarcophagus. Now in the present case the insect had accomplished the
first three series of actions, and had even begun the fourth; it ought
next to drag the cricket into the burrow without listening to the
recriminations which the latter had no business to make, since it was
to be regarded as having received the two routine doses of poison. But
the _Sphex_ sees its victim come to life, understands this fact, and
without seeking to fathom the cause judges that a new struggle and new
blows of the sting are necessary; he understands that it is necessary
to begin afresh, since the usual result has not been attained. He is
then capable of reflection, and the series of acts which he
accomplishes are not ordained with such inflexibility that it is
impossible for him to modify them in order to conform them to varying
circumstances.
The _Sphex occitanica_ acts in the same manner as its relative in this
complicated art of laying up provisions for the family. The
differences are only in detail. Instead of hollowing the burrow first
and then setting out on the chase to fill it, it does not devote
itself to the labour of digging until a successful expedition has
already assured the victim. (Fig. 17.) Instead of attacking crickets
it seeks a larger orthopterous insect, the _Ephippigera_. The struggle
is no doubt more difficult, but the result is proportionately greater,
and the pursuit does not need to be so often renewed; a single captive
is sufficient for its larva.[73]
[73] For some remarks on the action of the _Sphex_, and for
Darwin's opinion on the matter, see Romanes' _Mental
Evolution in Animals_, pp. 299-303.
[Illustration: FIG. 17.]
_The sureness of instinct._--It is not doubtful that a sure inherited
instinct conducts the _Sphex_ to prick its victim in the situation of
the nervous ganglia, which will be wounded in the act. It may be said
that the lesion results from the position in which the hymenopterous
insect maintains its victim; for the sting is on the median line, and
can only penetrate at the soft points; the two points attacked are
then rigorously determined by physical circumstances. But these
arguments have no bearing if we consider the method of procedure
adopted by the _Ammophila_,[74] a hymenopterous insect related to the
preceding, which paralyses caterpillars. It is free in this case to
insert its sting at any portion of the body; yet it knows how to turn
over and arrange the captive so that the dart shall penetrate both
times at two points where ganglia will be poisoned and immobility
without death be induced. It must then be agreed that there is here an
instinct much too sure to be called mechanical; but these facts, which
considered alone seem simply marvellous, become much less so, and lend
themselves to evolutionary interpretation, when it is recognised that
they are related by insensible degrees to other facts of the same
order, much more intelligent and at the same time less sure.
[74] Paul Marchal, "Observations sur _l'Ammophila affinis_,"
_Arch. de Zool. exp. et gener._, ii. Serie, t. x., 1892.
_Similar cases in which the specific instinct is less powerful and
individual initiative greater._--Here is, for instance, the case of
the _Chlorion_, where each animal possesses more considerable
initiative.[75] It attacks the Cockroach. These insects are of an
extremely varied size, according to age, and as they are also very
agile the _Chlorion_ is not certain of being always able to obtain
victims of the same dimension. The orifice of its burrow, which it
hollows in walls between the crevices of the stones, is calculated on
the average size of its victims. It has also the habit of paralysing
the cockroach by stinging it on the nervous chain. These preliminary
operations do not impede it, but it is embarrassed when it wishes to
introduce through the entrance of its gallery an insect which is too
large. It pulls at first as much as it can, but seeing the failure of
its efforts it does not persevere in this attempt, and comes out to
survey the situation. Decidedly the victim is too large and cannot
pass through. The _Chlorion_ begins by cutting off the elytra, which
maintain it rigid and prevent it from being compressed. This done, it
harnesses itself anew and re-commences its efforts. But this is not
sufficient, and the victim still resists. The insect returns, and
again examines the situation. Now it is a leg which is placed
cross-ways and opposes the introduction of the body; strong diseases
need strong remedies, and our _Chlorion_ sets itself to amputate this
encumbering appendage. It triumphs at last; the cockroach yields to
its efforts, and little by little penetrates the hole. As may be seen,
the labour is laborious and painful, and may present itself beneath
various aspects which call for a certain ingenuity on the part of the
animal.
[75] Reaumur, _Memoires pour servir a l'histoire des
Insectes_, Paris, 1742, t. vi., pp. 282-284.
Up to recent years the _Cerceris_ was considered to act with as much
certainty as the _Sphex_, and to obey an infallible instinct which
always guided it for the best in the interests of its offspring. The
insects it attacks belong to the genus _Buprestis_. It consumes them
in considerable numbers. Its manner of action, as described by Leon
Dufour,[76] much resembles that of the _Sphex_, and it would be
superfluous to describe it. The only fact which I wish to mention, and
which has been put out of doubt by the illustrious naturalist, is
this: the _Buprestis_ are paralysed, not dead; all the joints of the
antennae and legs remain flexible and the intestines in good condition.
He was able to dissect some which had been in a state of lethargy for
at least a week or a fortnight, although, under normal conditions,
these insects in summer decay rapidly, and after forty-eight hours
cannot be used for anatomical purposes. Another observer, Paul
Marchal, took up this question afresh, and the results which he
obtained seemed to indicate an instinct much less firm than earlier
studies tended to show.[77]
[76] "Histoire des _Cerceris_," _Ann. Sc. Nat._, ii. Serie,
t. xv., 1841, pp. 353-370.
[77] _Arch. de Zool. exp._, 1887.
_Genera less skilful in the art of paralysing victims._--These
researches show us that in the _Cerceris_ instinct is still subject to
defect. In some neighbouring genera we can seize it, as it were, in
process of formation. The way in which the _Bembex_, or Sand Wasp,
provisions burrows by maternal foresight is much less mechanical than
that of the _Sphex_. It is again Fabre who has described with most
care the customs of this hymenopterous insect.[78] It hollows out for
each egg a chamber communicating with the air by a gallery, and
performs this work with little care and very roughly. Less skilful
than the others, it does not amass at once all the provisions which
its larvae will need during the period of evolution. When the offspring
has absorbed the last prey brought, it is necessary to bring a new
victim. This insect is scarcely more advanced than birds, who feed
their young from day to day. And it is a great labour to re-open every
time the gallery which leads to the nursery; on all these visits, in
fact, the _Bembex_ fills it up on leaving, and causes the
disappearance of all revealing traces. It is obliged to take so much
trouble, because it has not inherited from its ancestors the receipt
for the paralysing sting; it throws itself without care on its victim,
delivers a few chance blows, and kills it. Necessarily it cannot,
under these conditions, lay up provisions for the future; they would
corrupt, and the larvae would not be benefited; hence the obligation of
frequently returning to the nest, and of a perpetual hunt to feed
descendants whom nature has gifted with an excellent appetite.
According to the age of the offspring, the mother chooses prey of
different sizes; at first she brings small Diptera; then, when it has
grown, she captures for it large blow-flies, and lastly gadflies.[79]
It will be seen, then, that if we suppose the instinct of the _Sphex_
to be slowly developed by being derived from a sting given at random,
we make a supposition which is quite admissible and rests on
ascertained facts. However this may be, the _Bembex_, returning to its
burrow, is able to find it again with marvellous certainty, in spite
of the care taken to hide it by removing every trace that might reveal
its existence. It is guided by an extraordinary topographic instinct,
which men not only do not possess, but cannot even understand the
nature of.
[78] _Souvenirs entomologiques_, 1879, pp. 225 _et seq._
[79] A Wasp found in La Plata, the _Monedula punctata_, as
described by Hudson (_Naturalist in La Plata_, pp. 162-164),
is an adroit fly-catcher, and thus supplies her grub with
fresh food, carefully covering the mouth of the hole with
loose earth after each visit; as many as six or seven
freshly-killed insects may be found for the use of one grub.
It would appear that certain Hymenoptera, fearing to kill their victim
with the sting, and not knowing the art of skilful lesions, attempt to
immobilise them by wounds of another sort. This is the case with the
_Pompilius_, according to Goureau,[80] who has studied it. This insect
nourishes its larvae with spiders; it seems certain that in most cases
the spider is not pricked. Victims who have been taken from the
interior of provision burrows can live for a long time in spite of
their wounds; they cannot, therefore, have received venom by
inoculation. The author already quoted believes that the Pompilius
seizes its captive by the pedicle which unites the abdomen to the
cephalothorax, and that it triturates this point between its jaws.
From this either death or temporary immobility may follow. The
_Pompilius_ also makes up for its relative ignorance by considerable
ingenuity. Thus sometimes, when it fears a return to life of the
victim destined for its larvae, it cuts off the legs while it is still
passive. Goureau has found in the nest of this insect living spiders
with their legs cut off.
[80] "Observations pour servir a l'histoire de quelques
Insectes," _Ann. Soc. entomol. de France_, t. 8, 1839, p. 541.