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THE METHOD OF THE AMMOPHILAE.




My readers may differ in appraising the comparative value of the trifling
discoveries which entomology owes to my labours. The geologist, the
recorder of forms, will prefer the hypermetamorphosis of the Oil-beetles
(The chapter treating of this subject has not yet been translated into
English and will appear in a later volume.--Translator's Note.), the
development of the Anthrax (Cf. "The Life of the Fly": chapter 2.--
Translator's Note.) or larval dimorphism; the embryogenist, searching into
the mysteries of the egg, will have some esteem for my enquiries into the
egg-laying habits of the Osmia (Cf. "Bramble-bees and Others": chapter 4.--
Translator's Note.) ; the philosopher, racking his brain over the nature of
instinct, will award the palm to the operations of the Hunting Wasps. I
agree with the philosopher. Without hesitation, I would abandon all the
rest of my entomological baggage for this discovery, which happens to be
the earliest in date and that of which I have the fondest memories. Nowhere
do I find a more brilliant, more lucid, more eloquent proof of the
intuitive wisdom of instinct; nowhere does the theory of evolution suffer a
more obstinate check.

Darwin, a true judge, made no mistake about it. (Charles Robert Darwin,
born the 12th of February, 1809, at Shrewsbury, died at Down, in Kent, on
the 19th of April, 1882. For an account of certain experiments which the
author conducted on his behalf, cf. "The Mason-bees": chapter 4.--
Translator's Note.) He greatly dreaded the problem of the instincts. My
first results in particular left him very anxious. If he had known the
tactics of the Hairy Ammophila, the Mantis-hunting Tachytes, the Bee-eating
Philanthus, the Calicurgi and other marauders, his anxiety, I believe,
would have ended in a frank admission that he was unable to squeeze
instinct into the mould of his formula. Alas, the philosopher of Down
quitted this world when the discussion, with experiments to support it, had
barely begun: a method superior to any argument! The little that I had
published at that time left him with still some hope of an explanation. In
his eyes, instinct was always an acquired habit. The predatory Wasps killed
their prey at first by stabbing it at random, here and there, in the
softest parts. By degrees they found the spot where the sting was most
effectual; and the habit once formed became a true instinct. Transitions
from one method of operation to the other, intermediary changes, sufficed
to bolster up these sweeping assertions. In a letter of the 16th of April,
1881, he asks G.J. Romanes to consider the problem:

"I do not know," he says "whether you will discuss in your book on the mind
of animals any of the more complex and wonderful instincts. It is
unsatisfactory work, as there can be no fossilised instincts, and the sole
guide is their state in other members of the same order, and mere
PROBABILITY.

"But if you do discuss any (and it will perhaps be expected of you), I
should think that you could not select a better case than that of the sand-
wasps which paralyse their prey as described by Fabre in his wonderful
paper in the "Anales des sciences naturelles," and since amplified in his
admirable "Souvenirs..."

I thank you, O illustrious master, for your eulogistic expressions, proving
the keen interest which you took in my studies of instinct, no ungrateful
task--far from it--when we tackle it as it should be tackled: from the
front, with the aid of facts, and not from the flank, with the aid of
arguments. Arguments are here out of place, if we wish to maintain our
position in the light. Besides, where would they lead us? To evoking the
instincts of bygone ages, which have not been preserved by fossilization?
Any such appeal to the dim and distant past is quite unnecessary, if we
wish for variations of instinct, leading by degrees, according to you, from
one instinct to another; the present world offers us plenty.

Each operator has her particular method, her particular kind of game, her
particular points of attack and tricks of fence; but in the midst of this
variety of talents we observe, immutable and predominant, the perfect
accordance of the surgery with the victim's organization and the larva's
needs. The art of one will not explain the art of another, no less exact in
the delicacy of its rules. Each operator has her own tactics, which
tolerate no apprenticeship. The Ammophila, the Scolia, the Philanthus and
the others all tell us the same thing: none can leave descendants if she be
not from the outset the skilful paralyser or slayer that she is to-day. The
"almost" is impracticable when the future of the race is at stake. What
would have become of the first-born mammal but for its perfect instinct of
suckling?

And then, to suppose the impossible: a Wasp discovers by chance the
operative method which will be the saving attribute of her race. How are we
to admit that this fortuitous act, to which the mother has vouchsafed no
more attention than to her other less fortunate attempts, could leave a
profound trace behind it and be faithfully transmitted by heredity? Is it
not going beyond reason, going beyond the little that is known to us as
certain, if we grant to atavism this strange power, of which our present
world knows no instance? There is a good deal to be said for this point of
view, my revered master! But, once more, arguments are here out of place;
there is room only for facts, of which I will resume the recital.

Hitherto I had but one means of studying the operative methods of the
spoilers: to surprise the Wasp in possession of her capture, to rob her of
her prey and immediately to give her in exchange a similar prey, but a
living one. This method of substitution is an excellent expedient. Its only
defect--a very grave one--is that it subjects observation to very uncertain
chances. There is little prospect of meeting the insect dragging its victim
along; and, in the second place, should good fortune suddenly smile upon
you, preoccupied as you are with other matters you have not the substitute
at hand. If we provide ourselves with the necessary head of game in
advance, the huntress is not there. We avoid one reef to founder on
another. Moreover, these unlooked for observations, made sometimes on the
public highway, the worst of laboratories, are only half-satisfactory. In
the case of swiftly-enacted scenes, which it is not in our power to renew
again and again until perfect conviction is reached, we always fear lest we
may not have seen accurately, may not have seen everything.

A method which could be controlled at will would offer the best guarantees,
above all if employed at home, under comfortable conditions, favourable to
precision. I wished, therefore, to see my insects at work on the actual
table at which I am writing their history. Here very few of their secrets
would escape me. This wish of mine was an old one. As a beginner, I made
some experiments under glass with the Great Cerceris (C. tuberculata) and
the Yellow-winged Sphex. Neither of them responded to my desires. The
refusal of each to attack respectively her Cleonus or her Cricket
discouraged further progress in this direction. I was wrong to abandon my
attempts so soon. Now, very long afterwards, the idea occurs to me to place
under glass the Bee-eating Philanthus, whom I sometimes surprise in the
open engaged in forcing a bee to disgorge her honey. The captive massacres
her bees in such a spirited fashion that the old hope revives stronger than
ever. I contemplate reviewing all the wielders of the stiletto and forcing
each to reveal her tactics.

I was obliged to abate these ambitions considerably. I had some successes
and many more failures. I will tell you of the former. My insect-cage is a
spacious dome of wire-gauze resting on a bed of sand. Here I keep in
reserve the captives of my hunting-expeditions. I feed them on honey,
placed in little drops on spikes of lavender, on heads of thistle, or field
eryngo, or globe-thistle, according to the season. Most of my prisoners do
well on this diet and seem scarcely affected by their internment; others
pine away and die in two or three days. These victims of despair nearly
always throw me back, because of the difficulty of obtaining the necessary
prey at short notice.

Indeed it entails no small trouble to secure in the nick of time the game
demanded by the huntress who has recently fallen a captive to my net. As
assistant-purveyors I have a few small schoolboys, who, released from the
tedium of their declensions and conjugations, set out, on leaving the
classroom, to inspect the greenswards and beat the bushes in the
neighbourhood on my behalf. The gros sou, the penny-piece, if you please,
stimulates their zeal; but with misadventurous results! What I need to-day
is Crickets. The band sallies forth and returns with not a single Cricket,
but numbers of Ephippigers, for which I asked the day before yesterday and
which I no longer need, my Languedocian Sphex being dead. General surprise
at this sudden change of market. My young scatterbrains find it hard to
understand that the beast which was so precious two days ago is now of no
value whatever. When, owing to the chances of my net, a renewed demand for
the Ephippiger sets in, then they will bring me the Cricket, the despised
Cricket.

Such a trade could never hold out if now and again my speculators were not
encouraged by some success. At the moment when urgent necessity is sending
up prices, one of them brings me a magnificent Gad-fly intended for the
Bembex. For two hours, when the sun was at its height, he kept watch on the
threshing-floor hard by, waiting for the blood-sucker, in order to catch
him on the buttocks of the Mules which trot round and round trampling the
corn. This gallant fellow shall have his gros sou and a slice of bread and
jam as well. A second, no less fortunate, has found a fat Spider, the
Epeira, for whom my Pompili are waiting. To the two sous of this fortunate
youth I add a little picture for his missal. Thus are my purveyors kept
going; and, after all, their help would be very inadequate if I did not
take upon myself the main burden of these wearisome quests.

Once in possession of the requisite prey, I transfer the huntress from my
warehouse, the wire-gauze cage, to a bell-glass varying in capacity from
one to three or four litres (1 3/4 to 5 or 7 pints.--Translator's Note.),
according to the size and habits of the combatants; I place the victim in
the arena; I expose the bell-glass to the direct rays of the sun, without
which condition the executioner as a rule declines to operate; I arm myself
with patience and await events.

We will begin with the Hairy Ammophila, my neighbour. Year after year, when
April comes, I see her in considerable numbers, very busy on the paths in
my enclosure. Until June I see her digging her burrows and searching for
the Grey Worm, to be placed in the meat-cellar. Her tactics are the most
complex that I know and more than any other deserves to be thoroughly
studied. To capture the cunning vivisector, to release her and catch her
again I find an easy matter for the best part of a month; she works outside
my door.

I have still to obtain the Grey Worm. This means a repetition of the
disappointments which I had before, when, to find a caterpillar, I was
obliged to watch the Ammophila while hunting and to be guided by her hints,
as the truffle-hunter is guided by the scent of his Dog. A patient
exploration of the harmas, one tuft of thyme after another, does not give
me a single worm. My rivals in this search are finding their game at every
moment; I cannot find it even once. Yet one more reason for bowing to the
superiority of the insect in the management of her affairs. My band of
schoolboys get to work in the surrounding fields. Nothing, always nothing!
I in my turn explore the outer world; and for ten days the pursuit of a
caterpillar torments me till I lose my power of sleep. Then, at last,
victory! At the foot of a sunny wall, under the budding rosettes of the
panicled centaury, I find a fair supply of the precious Grey Worm or its
equivalent.

Behold the worm and the Ammophila face to face beneath the bell-glass.
Usually the attack is prompt enough. The caterpillar is grabbed by the neck
with the mandibles, wide, curved pincers capable of embracing the greater
part of the living cylinder. The creature thus seized twists and turns and
sometimes, with a blow of its tail, sends the assailant rolling to a
distance. The latter is unconcerned and thrusts her sting thrice in rapid
succession into the thorax, beginning with the third segment and ending
with the first, where the weapon is driven home with greater determination
than elsewhere.

The caterpillar is then released. The Ammophila stamps on the ground; with
her quivering tarsi she taps the cardboard on which the bell-glass stands;
she lies down flat, drags herself along, gets up again, flattens herself
once more. The wings jerk convulsively. From time to time the insect places
its mandibles and forehead on the ground, then rears high upon its hind-
legs as though to turn head over heels. In all this I see a manifestation
of delight. We rub our hands when rejoicing at a success; the Ammophila is
celebrating her triumph over the monster in her own fashion. During this
fit of delirious joy, what is the wounded caterpillar doing? It can no
longer walk; but all the part behind the thorax struggles violently,
curling and uncurling when the Ammophila sets a foot upon it. The mandibles
open and shut menacingly.

SECOND ACT.--When the operation is resumed, the caterpillar is seized by
the back. From front to rear, in order, all the segments are stung on the
ventral surface, except the three operated on. All serious danger is
averted by the stabs of the first act; therefore, the Wasp is now able to
work upon her patient without the haste displayed at the outset.
Deliberately and methodically she drives in her lancet, withdraws it,
selects the spot, stabs it and begins again, passing from segment to
segment, taking care, each time, to lay hold of the back a little more to
the rear, in order to bring the segment to be paralysed within reach of the
needle. For the second time, the caterpillar is released. It is absolutely
inert, except the mandibles, which are still capable of biting.

THIRD ACT.--The Ammophila clasps the paralysed victim between her legs;
with the hooks of her mandibles she seizes the back of its neck, at the
base of the first thoracic segment. For nearly ten minutes she munches this
weak spot, which lies close to the cerebral nerve-centres. The pincers
squeeze suddenly but at intervals and methodically, as though the
manipulator wished each time to judge of the effect produced; the squeezes
are repeated until I am tired of trying to count them. When they cease, the
caterpillar's mandibles are motionless. Then comes the transportation of
the carcase, a detail which is not relevant in this place.

I have set forth the complete tragedy, as it is fairly often enacted, but
not always. The insect is not a machine, unvarying in the effect of its
mechanism; it is allowed a certain latitude, enabling it to cope with the
eventualities of the moment. Any one expecting to see the incidents of the
struggle unfolding themselves exactly as I have described will risk
disappointment. Special instances occur--they are even numerous--which are
more or less at variance with the general rule. It will be well to mention
the more important, in order to put future observers on their guard.

Not infrequently the first act, that of paralysing the thorax, is
restricted to two thrusts of the sting instead of three, or even to one,
which is then delivered in the foremost segment. This, it would seem, from
the persistency with which the Ammophila inflicts it, is the most important
prick of all. Is it unreasonable to suppose that the operator, when she
begins by pricking the thorax, intends to subdue her capture and to make it
incapable of injuring her, or even of disturbing her when the moment comes
for the delicate and protracted surgery of the second act? This idea seems
to me highly admissible; and then, instead of three dagger-thrusts, why not
two only, why not merely one, if this would suffice for the time being? The
amount of vigour displayed by the caterpillar must be taken into
consideration. Be this as it may, the segments spared in the first act are
stabbed in the second. I have sometimes even seen the three thoracic
segments stung twice over: at the beginning of the attack and again when
the Wasp returned to her vanquished prey.

The Ammophila's triumphant transports beside her wounded and writhing
victim are also subject to exceptions. Sometimes, without releasing its
prey for a moment, the insect proceeds from the thorax to the next segments
and completes its operation in a single spell. The joyous entr'acte does
not take place; the convulsive movements of the wings and the acrobatic
postures are suppressed.

The rule is paralysis of all the segments, however many, in regular order
from front to back, including even the anal segment if this boast of legs.
By a fairly frequent exception the last two or three segments are spared.
Another exception, but a very rare one, of which I have observed only a
single instance, consists in the inversion of the dagger-thrusts of the
second act, the thrusts being delivered from back to front. The caterpillar
is then seized by its hinder extremity; and the Ammophila, progressing
towards the head, stings in reverse order, passing from the succeeding to
the preceding segment, including the thorax already stabbed. This reversal
of the usual tactics I am inclined to attribute to negligence on the
insect's part. Negligence or not, the inverted method has the same final
result as the direct method: the paralysis of all the segments.

Lastly, the compression of the neck by the mandibulary pincers, the
munching of the weak spot between the base of the skull and the first
segment of the thorax, is sometimes practised and sometimes neglected. If
the caterpillar's jaws open and threaten, the Ammophila stills them by
biting the neck; if they are already growing quiescent, she refrains.
Without being indispensable, this operation is useful at the moment of
carting the prey. The caterpillar, too heavy to be carried on the wing, is
dragged, head first, between the Ammophila's legs. If the mandibles are
working, the least clumsiness may render them dangerous to the carrier, who
is exposed to their bite without any means of defence.

Moreover, once on the way, thickets of grass are traversed in which the
Grey Worm can seize a blade and offer a desperate resistance to the
traction. Nor is this all. The Ammophila does not as a rule trouble about
her burrow, or at least does not complete it, until she has caught her
caterpillar. During the mining-operations, the game is laid somewhere high
up, out of reach of the Ants, on some tuft of grass, or the twigs of a
shrub, whither the huntress, from time to time, stopping her well-sinking,
hastens to see if her quarry is still there. For her this is a means of
refreshing her memory of the spot where she has laid it, often at some
distance from the burrow, and of preventing attempts at robbery. When the
moment comes for removing the game from its hiding-place, the difficulty
would be insurmountable were the worm, gripping the shrub with all the
might of its jaws, to anchor itself there. Hence inertia of the powerful
hooks, which are the paralysed creature's sole means of resistance, becomes
essential during the carting. The Ammophila obtains it by compressing the
cerebral ganglia, by munching the neck. The inertia is temporary; it wears
off sooner or later; but by this time the carcase is in the cell and the
egg, prudently laid at a distance on the ventral surface of the worm, has
nothing to fear from the caterpillar's grapnels. No comparison is
permissible between the methodical squeezes of the Ammophila benumbing the
cephalic nerve-centres and the brutal manipulations of the Philanthus
emptying the crop of her Bee. The huntress of Grey Worms induces a
temporary torpor of the mandibles; the ravisher of Bees makes them eject
their honey. No one gifted with the least perspicacity will confound the
two operations.

For the moment we will not dwell any longer on the method of the Hairy
Ammophila; we will see instead how her kinswomen behave. After protracted
refusals the Sandy Ammophila (A. sabulosa, FAB.),on whom I experimented in
September, ended by accepting the proffered prey, a powerful caterpillar as
thick as a lead-pencil. The surgical method did not differ from that
employed by the Hairy Ammophila when operating on her Grey Worm in one
spell. All the segments, excepting the last three, were stung from front to
back, beginning with the prothorax. This single success with a simplified
method left me in ignorance of the accessory manoeuvres, which I do not
doubt must more or less closely recall those of the preceding species.

I am all the more inclined to accept these secondary manoeuvres, not as yet
recorded--the transports of triumph and the compressions of the neck--
inasmuch as I see them practised upon the Looper caterpillars, which differ
so greatly from the others in external structure, exactly as I have
described them in the case of the Grey Worm, which is of the ordinary form.
Two species, the Silky Ammophila (A. holoserica, FAB.) and Jules' Ammophila
(See in the first volume of the "Souvenirs entomologiques" what I mean by
this denomination.--Author's Note.), affect this curious prey, which moves
with the stride of a pair of compasses. The first, often renewed under
glass during the greater part of August, has always refused my offers; the
second, her contemporary, has, on the contrary, promptly accepted them.

I present Jules' Ammophila with a slender, brownish Looper which I caught
on the jasmine. The attack is not slow in coming. The caterpillar is
grabbed by the neck: lively contortions of the victim, which rolls the
aggressor over and drags her along, now uppermost, now undermost in the
struggle. First the thorax is stung, in its three rings, from back to
front. The sting lingers longest near the throat, in the first segment.
This done, the Ammophila releases her victim and proceeds to stamp her
tarsi, to polish her wings, to stretch herself. Again I observe the
acrobatic postures, the forehead touching the ground, the hinder part of
the body raised. This mimic triumph is the same as that of the huntress of
the Grey Worm. Then the Looper is once more seized. Despite its
contortions, which are not in the least abated by the three wounds in the
thorax, it is stung from front to back in each segment still unwounded, no
matter how many, whether supplied with legs or not. I expected to see the
sting refrain more or less in the long interval which separates the true
legs in front from the pro-legs at the back (Fleshy legs found on the
abdominal segments of caterpillars and certain other larvae.--Translator's
Note.): segments devoid of organs of defence or locomotion did not seem to
me to deserve conscientious surgery. I was mistaken: not a segment of the
Looper is spared, not even the last ones. It is true that these, being
eminently capable of catching hold with their false legs, would be
dangerous later were the Wasp to neglect them.

I observe, however, that the lancet works more rapidly in the second part
of the operation than in the first, either because the caterpillar, half
subjugated by the triple wound at the outset, is easier to reach with the
sting, or because the segments more remote from the head are rendered
harmless with a smaller injection of poison. Nowhere do we see repeated the
care expended upon paralysing the thorax, still less the insistent
attention to the first segment. On returning to her Looper after the
entr'acte devoted to the joys of success, the Ammophila stabs so swiftly
that, on one occasion, I saw her obliged to begin all over again. Lightly
stung along its whole length, the victim still struggles. Without
hesitation, the operator unsheathes her scalpel for the second time and
operates on the Looper afresh, with the exception of the thorax, which was
already sufficiently anaesthetized. This done, all is in order; there is no
more movement.

After the stiletto the hooks of the mandibles rarely fail to intervene.
Long and curved, they nibble at the paralysed victim's neck, sometimes from
above, sometimes from below. It is a repetition of what the Hairy Ammophila
showed us: the same sudden squeezes of the pincers, with rather long
intervals between. These intervals, these measured bites and the insect's
watchful attitude have every appearance of telling us that the operator is
noting the effect produced before giving a fresh pinch of the nippers.

It will be seen how valuable is the evidence of Jules' Ammophila: it tells
us that the immolaters of Looper caterpillars and those of ordinary
caterpillars follow precisely the same method; that victims displaying very
dissimilar external structure do not entail any modification of the
operative tactics so long as the internal organization remains the same.
The number, arrangement and degree of mutual independence of the nerve-
centres guide the sting; the anatomy of the game, rather than its form,
controls the huntress' tactics.

Let me mention, before I dismiss the subject, a superb example of this
marvellous anatomical discrimination. I once took from between the legs of
a Hairy Ammophila, which had just paralysed it, a caterpillar of Dicranura
vinula. What a strange capture compared with the ordinary caterpillar!
Bridling in thick folds beneath its pink neckerchief, its fore-part raised
in a sphinx-like attitude, its hinder-part slowly waving two long caudal
threads, the curious animal is no caterpillar to the schoolboy who brings
it to me, nor to the man who comes upon it while cutting his bundle of
osiers; but it is a caterpillar to the Ammophila, who treats it
accordingly. I explore the queer creature's segments with the point of a
needle. All are insensitive; all therefore have been stung.





Next: THE METHOD OF THE SCOLIAE

Previous: THE BEE-EATING PHILANTHUS



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