THE CETONIA-LARVA





The Scolia's feeding-period lasts, on the average, for a dozen days or so.

By then the victuals are no more than a crumpled bag, a skin emptied of the

last scrap of nutriment. A little earlier, the russet-yellow tint announces

the extinction of the last spark of life in the creature that is being

devoured. The empty skin is pushed back to make space; the dining-room, a

shapeless cavity with crumbling walls, is tidied up a little; and the

Scolia-grub sets to work on its cocoon without further delay.



The first courses form a general scaffolding, which finds a support here

and there on the earthen walls, and consist of a rough, blood-red fabric.

When the larva is merely laid, as required by my investigations, in a

hollow made with the finger-tip in the bed of mould, it is not able to spin

its cocoon, for want of a ceiling to which to fasten the upper threads of

its network. To weave its cocoon, every spinning larva is compelled to

isolate itself in a hammock slung in an open-work enclosure, which enables

it to distribute its thread uniformly in all directions. If there be no

ceiling, the upper part of the cocoon cannot be fashioned, because the

worker lacks the necessary points of support. Under these conditions my

Scolia-grubs contrive at most to upholster their little pit with a thick

down of reddish silk. Discouraged by futile endeavours, some of them die.

It is as if they had been killed by the silk which they omit to disgorge

because they are unable to make the right use of it. This, if we were not

watchful, would be a very frequent cause of failure in our attempts at

artificial rearing. But, once the danger has been perceived, the remedy is

simple. I make a ceiling over the cavity by laying a short strip of paper

above it. If I want to see how matters are progressing, I bend the strip

into a semicircle, into a half-cylinder with open ends. Those who wish to

play the breeder for themselves will be able to profit by these little

practical details.



In twenty-four hours the cocoon is finished; at least, it no longer allows

us to see the grub, which is doubtless making the walls of its dwelling

still thicker. At first the cocoon is a vivid red; later it changes to a

light chestnut-brown. Its form is that of an ellipsoid, with a major axis

26 millimetres in length, while the minor axis measures 11 millimetres.

(1.014 x .429 inch.--Translator's Note.) These dimensions, which

incidentally are inclined to vary slightly, are those of the female

cocoons. In the other sex they are smaller and may measure as little as 17

millimetres in length by 7 millimetres in width. (.663 x .273 inch.--

Translator's Note.)



The two ends of the ellipsoid have the same form, so much so that it is

only thanks to an individual peculiarity, independent of the shape, that we

can tell the cephalic from the anal extremity. The cephalic pole is

flexible and yields to the pressure of my tweezers; the anal pole is hard

and unyielding. The wrapper is double, as in the cocoons of the Sphex. (Cf.

"The Hunting Wasps": chapters 4 to 10 et passim.--Translator's Note.) The

outer envelope, consisting of pure silk, is thin, flexible and offers

little resistance. It is closely superimposed upon the inner envelope and

is easily separated from it everywhere, except at the anal end, where it

adheres to the second envelope. The adhesion of the two wrappers at one end

and the non-adhesion at the other are the cause of the differences which

the tweezers reveal when pinching the two ends of the cocoon.



The inner envelope is firm, elastic, rigid and, to a certain point,

brittle. I do not hesitate to look upon it as consisting of a silken tissue

which the larva, towards the end of its task, has steeped thoroughly in a

sort of varnish prepared not by the silk-glands but by the stomach. The

cocoons of the Sphex have already shown us a similar varnish. This product

of the chylific ventricle is chestnut-brown. It is this which, saturating

the thickness of the tissue, effaces the bright red of the beginning and

replaces it by a brown tint. It is this again which, disgorged more

profusely at the lower end of the cocoon, glues the two wrappers together

at that point.



The perfect insect is hatched at the beginning of July. The emergence takes

place without any violent effraction, without any ragged rents. A clean,

circular fissure appears at some distance from the top; and the cephalic

end is detached all of a piece, as a loose lid might be. It is as though

the recluse had only to raise a cover by butting it with her head, so exact

is the line of division, at least as regards the inner envelope, the

stronger and more important of the two. As for the outer wrapper, its lack

of resistance enables it to yield without difficulty when the other gives

way.



I cannot quite make out by what knack the Wasp contrives to detach the cap

of the inner shell with such accuracy. Is it the art practised by the

tailor when cutting his stuff, with mandibles taking the place of scissors?

I hardly venture to admit as much: the tissue is so tough and the circle of

division so precise. The mandibles are not sharp enough to cut without

leaving a ragged edge; and then what geometrical certainty they would need

for an operation so perfect that it might well have been performed with the

compasses!



I suspect therefore that the Scolia first fashions the outer sac in

accordance with the usual method, that is, by distributing the silk

uniformly, without any special preparation of one part of the wall more

than of another, and that it afterwards changes its method of weaving in

order to attend to the main work, the inner shell. In this it apparently

imitates the Bembex (Cf. "The Hunting Wasps": chapters 14 to 16.--

Translator's Note.), which weaves a sort of eel-trap, whose ample mesh

allows it to gather grains of sand outside and encrust them one by one in

the silky network, and completes the performance with a cap fitting the

entrance to the trap. This provides a circular line of least resistance,

along which the casket breaks open afterwards. If the Scolia really works

in the same manner, everything is explained: the eel-trap, while still

open, enables it to soak with varnish both the inside and the outside of

the inner shell, which has to acquire the consistency of parchment; lastly,

the cap which completes and closes the structure leaves for the future a

circular line capable of splitting easily and neatly.



This is enough on the subject of the Scolia-grub. Let us go back to its

provender, of whose remarkable structure we as yet know nothing. In order

that it may be consumed with the delicate anatomical discretion imposed by

the necessity of having fresh food to the last, the Cetonia-grub must be

plunged into a state of absolute immobility: any twitchings on its part--as

the experiments which I have undertaken go to prove--would discourage our

nibbling larva and impede the work of carving, which has to be effected

with so much circumspection. It is not enough for the victim to be unable

to move from place to place beneath the soil: in addition to this, the

contractible power in its sturdy muscular organism must be suppressed.



In its normal state, this larva, at the very least disturbance, curls

itself up, almost as the Hedgehog does; and the two halves of the ventral

surface are laid one against the other. You are quite surprised at the

strength which the creature displays in keeping itself thus contracted. If

you try to unroll it, your fingers encounter a resistance far greater than

the size of the animal would have caused you to suspect. To overcome the

resistance of this sort of spring coiled upon itself, you have to force it,

so much so that you are afraid, if you persist, of seeing the indomitable

spiral suddenly burst and shoot forth its entrails.



A similar muscular energy is found in the larvae of the Oryctes (Also known

as the Rhinoceros Beetle.--Translator's Note.), the Anoxia (A Beetle akin

to the Cockchafer.--Translator's Note.), the Cockchafer. Weighed down by a

heavy belly and living underground, where they feed either on leaf-mould or

on roots, these larvae all possess the vigorous constitution needed to drag

their corpulence through a resisting medium. All of them also roll

themselves into a hook which is not straightened without an effort.



Now what would become of the egg and the new-born grub of the Scoliae,

fixed under the belly, at the centre of the Cetonia's spiral, or inside the

hook of the Oryctes or the Anoxia? They would be crushed between the jaws

of the living vice. It is essential that the arc should slacken and the

hook unbend, without the least possibility of their returning to a state of

tension. Indeed, the well-being of the Scoliae demands something more:

those powerful bodies must not retain even the power to quiver, lest they

derange a method of feeding which has to be conducted with the greatest

caution.



The Cetonia-grub to which the Two-banded Scolia's egg is fastened fulfils

the required conditions admirably. It is lying on its back, in the midst of

the mould, with its belly fully extended. Long accustomed though I be to

this spectacle of victims paralysed by the sting of the Hunting Wasp, I

cannot suppress my astonishment at the profound immobility of the prey

before my eyes. In the other victims with flexible skins, Caterpillars,

Crickets, Mantes, Ephippigers, I perceived at least some pulsations of the

abdomen, a few feeble contortions under the stimulus of a needle. There is

nothing of the sort here, nothing but absolute inertia, except in the head,

where I see, from time to time, the mouth-parts open and close, the palpi

give a tremor, the short antennae sway to and fro. A prick with the point

of a needle causes no contraction, no matter what the spot pricked. Though

I stab it through and through, the creature does not stir, be it ever so

little. A corpse is not more inert. Never, since my remotest

investigations, have I witnessed so profound a paralysis. I have seen many

wonders due to the surgical talent of the Wasp; but to-day's marvel

surpasses them all.



I am doubly surprised when I consider the unfavourable conditions under

which the Scolia operates. The other paralysers work in the open air, in

the full light of day. There is nothing to hinder them. They enjoy full

liberty of action in seizing the prey, holding it in position and

sacrificing it; they are able to see the victim and to parry its means of

defence, to avoid its spears, its pincers. The spot or spots to be attained

are within their reach; they drive the dagger in without let or hindrance.



What difficulties, on the other hand, await the Scolia! She hunts

underground, in the blackest darkness. Her movements are laboured and

uncertain, owing to the mould, which is continually giving way all round

her; she cannot keep her eyes on the terrible mandibles, which are capable

of cutting her body in two with a single bite. Moreover, the Cetonia-grub,

perceiving that the enemy is approaching, assumes its defensive posture,

rolls itself up and makes a shield for its only vulnerable part, the

ventral surface, with its convex back. No, it cannot be an easy operation

to subdue the powerful larva in its underground retreat and to stab with

the precision which immediate paralysis requires.



We wish that we might witness the struggle between the two adversaries and

see at first hand what happens, but we cannot hope to succeed. It all takes

place in the mysterious darkness of the soil; in broad daylight, the attack

would not be delivered, for the victim must remain where it is and then and

there receive the egg, which is unable to thrive and develop except under

the warm cover of vegetable mould. If direct observation is impracticable,

we can at least foresee the main outlines of the drama by allowing

ourselves to be guided by the warlike manoeuvres of other burrowers.



I picture things thus: digging and rummaging through the heap of mould,

guided perhaps by that singular sensibility of the antennae which enables

the Hairy Ammophila to discover the Grey Worm (The caterpillar of the

Turnip Moth. Cf. "The Hunting Wasps": chapters 18 to 20.--Translator's

Note.) underground, the Scolia ends by finding a Cetonia-larva, a good

plump one, in the pink of condition, having reached its full growth, just

what the grub which is to feed on it requires. Forthwith, the assaulted

victim, contracting desperately, rolls itself into a ball. The other seizes

it by the skin of the neck. To unroll it is impossible to the insect, for I

myself have some trouble in doing so. One single point is accessible to the

sting: the under part of the head, or rather of the first segments, which

are placed outside the coil, so that the grub's hard cranium makes a

rampart for the hinder extremity, which is less well defended. Here the

Wasp's sting enters and here only can it enter, within a narrowly

circumscribed area. One stab only of the lancet is given at this point, one

only because there is no room for more; and this is enough: the larva is

absolutely paralysed.



The nervous functions are abolished instantly; the muscular contractions

cease; and the animal uncoils like a broken spring. Henceforth motionless,

it lies on its back, its ventral surface fully exposed from end to end. On

the median line of this surface, towards the rear, near the brown patch due

to the alimentary broth contained in the intestine, the Scolia lays her egg

and without more ado, leaves everything lying on the actual spot where the

murder was committed, in order to go in search of another victim.



This is how the deed must be done: the results prove it emphatically. But

then the Cetonia-grub must possess a very exceptional structure in its

nervous organization. The larva's violent contraction leaves but a single

point of attack open to the sting, the under part of the neck, which is

doubtless uncovered when the victim tries to defend itself with its

mandibles; and yet a stab in this one point produces the most thorough

paralysis that I have ever seen. It is the general rule that larvae possess

a centre of innervation for each segment. This is so in particular with the

Grey Worm, the sacrificial victim of the Hairy Ammophila. The Wasp is

acquainted with this anatomical secret: she stabs the caterpillar again and

again, from end to end, segment by segment, ganglion by ganglion. With such

an organization the Cetonia-grub, unconquerably coiled upon itself would

defy the paralyser's surgical skill.



If the first ganglion were wounded, the others would remain uninjured; and

the powerful body, actuated by these last, would lose none of its powers of

contraction. Woe then to the egg, to the young grub held fast in its

embrace! And how insurmountable would be the difficulties if the Scolia,

working in the profound darkness amid the crumbling soil and confronted by

a terrible pair of mandibles, had to stab each segment in turn with her

sting, with the certainty of method displayed by the Ammophila! The

delicate operation is possible in the open air, where nothing stands in the

way, in broad daylight, where the sight guides the scalpel, and with a

patient which can always be released if it becomes dangerous. But in the

dark, underground, amidst the ruins of a ceiling which crumbles in

consequence of the conflict and at close quarters with an opponent greatly

her superior in strength, how is the Scolia to guide her sting with the

accuracy that is essential if the stabs are to be repeated?



So profound a paralysis; the difficulty of vivisection underground; the

desperate coiling of the victim: all these things tell me that the Cetonia-

grub, as regards its nervous system, must possess a structure peculiar to

itself. The whole of the ganglia must be concentrated in a limited area in

the first segments, almost under the neck. I see this as clearly as though

it had been revealed to me by a post-mortem dissection.



Never was anatomical forecast more fully confirmed by direct examination.

After forty-eight hours in benzine, which dissolves the fat and renders the

nervous system more plainly visible, the Cetonia-grub is subjected to

dissection. Those of my readers who are familiar with these investigations

will understand my delight. What a clever school is the Scolia's! It is

just as I thought! Admirable! The thoracic and abdominal ganglia are

gathered into a single nervous mass, situated within the quadrilateral

bounded by the four hinder legs, which legs are very near the head. It is a

tiny, dull-white cylinder, about three millimetres long by half a

millimetre wide. (.117 x .019 inch.--Translator's Note.) This is the organ

which the Scolia's sting must attack in order to secure the paralysis of

the whole body, excepting the head, which is provided with special ganglia.

>From it run numbers of filaments which actuate the feet and the powerful

muscular layer which is the creature's essential motor organ. When examined

merely through the pocket-lens, this cylinder appears to be slightly

furrowed transversely, a proof of its complex structure. Under the

microscope, it is seen to be formed by the close juxtaposition, the

welding, end to end, of the ganglia, which can be distinguished one from

the other by a slight intermediate groove. The bulkiest are the first, the

fourth and the tenth, or last; these are all very nearly of equal size. The

rest are barely half or even a third as large as those mentioned.



The Interrupted Scolia experiences the same hunting and surgical

difficulties when she attacks, in the crumbling, sandy soil, the larvae of

the Shaggy Anoxia or of the Morning Anoxia, according to the district; and

these difficulties, if they are to be overcome, demand in the victim a

concentrated nervous system, like the Cetonia's. Such is my logical

conviction before making my examination; such also is the result of direct

observation. When subjected to the scalpel, the larva of the Morning Anoxia

shows me its centres of innervation for the thorax and the abdomen,

gathered into a short cylinder, which, placed very far forward, almost

immediately after the head, does not run back beyond the level of the

second pair of legs. The vulnerable point is thus easily accessible to the

sting, despite the creature's posture of defence, in which it contracts and

coils up. In this cylinder I recognize eleven ganglia, one more than in the

Cetonia. The first three, or thoracic, ganglia are plainly distinguishable

from one another, although they are set very close together; the rest are

all in contact. The largest are the three thoracic ganglia and the

eleventh.



After ascertaining these facts, I remembered Swammerdam's investigations

into the grub of the Monoceros, our Oryctes nasicornis. (Jan Swammerdam

(1637-1680), the Dutch naturalist and anatomist.--Translator's Note.) I

chanced to possess an abridgement of the "Biblia naturae," the masterly

work of the father of insect anatomy. I consulted the venerable volume. It

informed me that the learned Dutchman had been struck, long before I was,

by an anatomical peculiarity similar to that which the larvae of the

Cetoniae and Anoxiae had shown me in their nerve-centres. Having observed

in the Silk-worm a nervous system formed of ganglia distinct one from the

other, he was quite surprised to find that, in the grub of the Oryctes, the

same system was concentrated into a short chain of ganglia in

juxtaposition. His was the surprise of the anatomist who, studying the

organ qua organ, sees for the first time an unusual conformation. Mine was

of a different nature: I was amazed to see the precision with which the

paralysis of the victim sacrificed by the Scolia, a paralysis so profound

in spite of the difficulties of an underground operation, had guided my

forecast as to structure when, anticipating the dissection, I declared in

favour of an exceptional concentration of the nervous system. Physiology

perceived what anatomy had not yet revealed, at all events to my eyes, for

since then, on dipping into my books, I have learnt that these anatomical

peculiarities, which were then so new to me, are now within the domain of

current science. We know that, in the Scarabaeidae, both the larva and the

perfect insect are endowed with a concentrated nervous system.



The Garden Scolia attacks Oryctes nasicornis; the Two-banded Scolia the

Cetonia; the Interrupted Scolia the Anoxia. All three operate below ground,

under the most unfavourable conditions; and all three have for their victim

a larva of one of the Scarabaeidae, which, thanks to the exceptional

arrangement of its nerve-centres, lends itself, alone of all larvae, to the

Wasp's successful enterprises. In the presence of this underground game, so

greatly varied in size and shape and yet so judiciously selected to

facilitate paralysis, I do not hesitate to generalize and I accept, as the

ration of the other Scoliae, larvae of Lamellicorns whose species will be

determined by future observation. Perhaps one of them will be found to give

chase to the terrible enemy of my crops, the voracious White Worm, the grub

of the Cockchafer; perhaps the Hemorrhoidal Scolia, rivalling in size the

Garden Scolia and like her, no doubt, requiring a copious diet, will be

entered in the insects' "Who's Who" as the destroyer of the Pine-chafer,

that magnificent Beetle, flecked with white upon a black or brown ground,

who of an evening, during the summer solstice, browses on the foliage of

the fir-trees. Though unable to speak with certainty or precision, I am

inclined to look upon these devourers of Scarabaeus-grubs as valiant

agricultural auxiliaries.



The Cetonia-larva has figured hitherto only in its quality of a paralysed

victim. We will now consider it in its normal state. With its convex back

and its almost flat ventral surface, the creature is like a semi-cylinder

in shape, fuller in the hinder portion. On the back, each of the segments,

except the last, or anal, segment, puckers into three thick pads, bristling

with stiff, tawny hairs. The anal segment, much wider than the rest, is

rounded at the end and coloured a deep brown by the contents of the

intestine, which show through the translucent skin; it bristles with hairs

like the other segments, but is level, without pads. On the ventral

surface, the segments have no creases; and the hairs, though abundant, are

rather less so than on the back. The legs, which are quite well-formed, are

short and feeble in comparison with the animal's size. The head has a

strong, horny cap for a cranium. The mandibles are powerful, with bevelled

tips and three or four teeth on the edge of the bevel.



Its mode of locomotion marks it as an idiosyncratic, exceptional, fantastic

creature, having no fellow, that I know of, in the insect world. Though

endowed with legs--a trifle short, it is true, but after all as good as

those of a host of other larvae--it never uses them for walking. It

progresses on its back, always on its back, never otherwise. By means of

wriggling movements and the purchase afforded by the dorsal bristles, it

makes its way belly upwards, with its legs kicking the empty air. The

spectator to whom these topsy-turvy gymnastics are a novelty thinks at

first that the creature must have had a fright of some sort and that it is

struggling as best it can in the face of danger. He puts it back on its

belly; he lays it on its side. Nothing is of any use; it obstinately turns

over and resumes its dorsal progress. That is its manner of travelling over

a flat surface; it has no other.



This reversal of the usual mode of walking is so peculiar to the Cetonia-

larva that it is enough in itself to reveal the grub's identity to the

least expert eyes. Dig into the vegetable mould formed by the decayed wood

in the hollow trunks of old willow-trees, search at the foot of rotten

stumps or in heaps of compost; and, if you come upon a plumpish grub moving

along on its back, there is no room for doubt: your discovery is a Cetonia-

larva.



This topsy-turvy progress is fairly swift and is not less in speed to that

of an equally fat grub travelling on its legs. It would even be greater on

a polished surface, where walking on foot is hampered by incessant slips,

whereas the numerous hairs of the dorsal pads find the necessary support by

multiplying the points of contact. On polished wood, on a sheet of paper

and even on a strip of glass, I see my grubs moving from point to point

with the same ease as on a surface of garden mould. In the space of one

minute, on the wood of my table, they cover a distance of eight inches. The

pace is no swifter on a horizontal bed of sifted mould. A strip of glass

reduces the distance covered by one half. The slippery surface only half

paralyses this strange method of locomotion.



We will now place side by side with the Cetonia-grub the larva of the

Morning Anoxia, the prey of the Interrupted Scolia. It is very like the

larva of the Common Cockchafer. It is a fat, pot-bellied grub, with a

thick, red cap on its head and armed with strong, black mandibles, which

are powerful implements for digging and cutting through roots. The legs are

sturdy and end in a hooked nail. The creature has a long, heavy, brown

paunch. When placed on the table, it lies on its side; it struggles without

being able to advance or even to remain on its belly or back. In its usual

posture it is curled up into a narrow hook. I have never seen it straighten

itself completely; the bulky abdomen prevents it. When placed on a surface

of moist sand, the ventripotent creature is no better able to shift its

position: curved into a fish-hook, it lies on its side.



To dig into the earth and bury itself, it uses the fore-edge of its head, a

sort of weeding-hoe with the two mandibles for points. The legs take part

in this work, but far less effectually. In this way it contrives to dig

itself a shallow pit. Then, bracing itself against the wall of the pit,

with the aid of wriggling movements which are favoured by the short, stiff

hairs bristling all over its body, the grub changes its position and

plunges into the sand, but still with difficulty.



Apart from a few details, which are of no importance here, we may repeat

this sketch of the Anoxia-grub and we shall have, if the size be at least

quadrupled, a picture of the larva of Oryctes nasicornis, the monstrous

prey of the Garden Scolia. Its general appearance is the same: there is the

same exaggeration of the belly; the same hook-like curve; the same

incapacity for standing on its legs. And as much may be said of the larva

of Scarabaeus pentodon, a fellow-boarder of the Oryctes and the Cetonia.





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