One last remark. We know how furiously Hymenoptera armed with a sting used only for defence rush at the bold man who disturbs their nest, and punish his temerity. Those on the contrary whose sting is used only for hunting are very pacific, as if they guessed how important for their family is the little poison drop in their vase. That droplet is the safeguard of their race—I might really say their means of subsistence; therefore they use it economically, in the serious business of the chase, with no parade of vengeful courage. I was not once punished by a sting when I established myself amid colonies of our various predatory Hymenoptera, whose nests I overturned, carrying off larvæ and provisions. To induce the creature to use its weapon, one must lay hold of it, and even then the skin is not always pierced, unless one puts within reach a part more delicate than the fingers, such as the wrist. [[101]]
VIII
LARVA AND NYMPH
The egg of Sphex flavipennis is white, elongated, and cylindrical, slightly curved, and measuring three to four millimetres in length. Instead of being laid fortuitously on any part of the victim, it is invariably placed on one spot, across the cricket’s breast—a little on one side, between the first and second pairs of feet. The eggs of the white bordered, and of the Languedocian Sphex occupy a like position—the first on the breast of a cricket, the second on that of an ephippiger. This chosen spot must possess some highly important peculiarity for the security of the young larva, as I have never known it vary.
Hatching takes place at the end of two or three days. A most delicate covering splits, and one sees a feeble maggot, transparent as crystal, somewhat attenuated and even compressed in front, slightly swelled out behind, and adorned on either side by a narrow white band formed by the chief trachea. The feeble creature occupies the same position as the egg; its head is, as it were, engrafted on the same spot where the front end of the egg was fixed, and the remainder of its body rests on the victim without [[102]]adhering to it. Its transparency allows us readily to perceive rapid fluctuations within its body, undulations following one another with mathematical regularity, and which, beginning in the middle of the body, are impelled, some forward and some backward. These are due to the digestive canal, which imbibes long draughts of the juices drawn from the sides of the victim.
Let us pause a moment before a spectacle so calculated to arrest attention. The prey is laid on its back, motionless. In the cell of Sphex flavipennis it is a cricket, or three or four, piled up; in that of the Languedocian Sphex there is a single victim, but proportionately large, a plump-bodied ephippiger. The grub is a lost grub if torn from the spot whence it draws nourishment. Should it fall, all is over, for weak as it is, and without means of locomotion, how would it again find the spot where it should quench its thirst? The merest trifle would enable the victim to get rid of the animalcule gnawing at its entrails, yet the gigantic prey gives itself up without the least sign of protestation. I am well aware that it is paralysed, and has lost the use of its feet from the sting of its assassin, but at this early stage it preserves more or less power of movement and sensation in parts unaffected by the dart. The abdomen palpitates, the mandibles open and shut, the abdominal styles and the antennæ oscillate. What would happen if the grub fixed on one of the spots yet sensitive near the mandibles, or even on the stomach, which, being tenderer and more succulent, would naturally suggest itself as fittest for the first mouthfuls of the feeble grub? Bitten on the quick parts, [[103]]cicada, cricket, and ephippiger would display at least some shuddering of the skin, which would detach and throw off the minute larva, for which probably all would be over, since it would risk falling into the formidable, pincer-like jaws.
But there is a part of the body where no such peril is to be feared—the thorax wounded by the sting. There and there only can the experimenter on a recent victim dig down the point of a needle—nay, pierce through and through without evoking any sign of pain. And there the egg is invariably laid—there the young larva always attacks its prey. Gnawed where pain is no longer felt, the cricket does not stir. Later, when the wound has reached a sensitive spot, it will move of course as much as it can; but then it is too late—its torpor will be too deep, and besides, its enemy will have gained strength. That is why the egg is always laid on the same spot, near the wounds caused by the sting on the thorax, not in the middle, where the skin might be too thick for the new-born grub, but on one side—toward the junction of the feet, where the skin is much thinner. What a judicious choice! what reasoning on the part of the mother when, underground, in complete darkness, she perceives and utilises the one suitable spot for her egg!
I have brought up Sphex larvæ by giving them successively crickets taken from cells, and have thus been able, day by day, to follow the rapid progress of my nurslings. The first cricket—that on which the egg is laid—is attacked, as I have already said, toward the point where the dart first struck—between the first and second pairs of legs. At the end of a [[104]]few days the young larva has hollowed a hole big enough for half its body in the victim’s breast. One may then sometimes see the cricket, bitten to the quick, vainly move its antennæ and abdominal styles, open and close its empty jaws, and even move a foot, but the larva is safe and searches its vitals with impunity. What an awful nightmare for the paralysed cricket! This first ration is consumed in six or seven days; nothing is left but the outer integument, whose every portion remains in place. The larva, whose length is then twelve millimetres, comes out of the body of the cricket through the hole it had made in the thorax. During this operation it moults, and the skin remains caught in the opening. It rests, and then begins on a second ration. Being stronger it has nothing to fear from the feeble movements of the cricket, whose daily increasing torpor has extinguished the last shred of resistance, more than a week having passed since it was wounded; so it is attacked with no precautions, and usually at the stomach, where the juices are richest. Soon comes the turn of the third cricket, then that of the fourth, which is consumed in ten hours. Of these three victims there remains only the horny integument, whose various portions are dismembered one by one and carefully emptied. If a fifth ration be offered, the larva disdains or hardly touches it, not from moderation, but from an imperious necessity.
It should be observed that up to now the larva has ejected no excrement, and that its intestine, in which four crickets have been engulfed, is distended to bursting. Thus, a new ration cannot tempt its [[105]]gluttony, and henceforward it only thinks about making a silken dwelling. Its repast has lasted from ten to twelve days without a pause. Its length now measures from twenty-five to thirty millimetres, and its greatest width from five to six. Its usual shape, somewhat enlarged behind and narrowed in front, agrees with that general in larvæ of Hymenoptera. It has fourteen segments, including the head, which is very small, with weak mandibles seemingly incapable of the part just played by them. Of these fourteen segments the intermediary ones are provided with stigmata. Its livery is yellowish-white, with countless chalky white dots.