The operating method is of the simplest. It is a question of taking a needle, or, better and more convenient, the point of a fine steel nib, and introducing a tiny drop of some corrosive fluid into the thoracic motor centres, by pricking the insect slightly at the junction of the [[52]]prothorax, behind the first pair of feet. The fluid which I employ is ammonia; but obviously any other liquid as powerful in its action would produce the same results. The nib being charged with ammonia as it might be with a very small drop of ink, I give the prick. The effects obtained differ enormously, according to whether we experiment upon species whose thoracic ganglia are close together or upon species in which those same ganglia are far apart. In the first class, my experiments were made on Dung-beetles: the Sacred Scarab[5] and the Wide-necked Scarab; on Buprestes: the Bronze Buprestis; lastly, on Weevils, in particular on the Cleonus hunted by the heroine of this essay. In the second class, I experimented on Ground-beetles: Carabi, Procrustes, Chlænii, Sphodri, Nebriæ; on Longicornes: Saperdæ and Lamiæ; on Melasoma-beetles: Cellar-beetles, Scauri, Asidæ.
In the Scarabæi, the Buprestes and the Weevils the effect is instantaneous: all movement ceases suddenly, without convulsions, so soon as the fatal drop has touched the nerve-centres. The Cerceris’ own sting produces no [[53]]more speedy annihilation. There is nothing more striking than this immediate immobility provoked in a powerful Sacred Beetle.
But this is not the only resemblance between the effects produced by the Wasp’s sting and those resulting from the nib poisoned with ammonia. The Scarabs, Buprestes and Beetles artificially stung, notwithstanding their complete immobility, preserve for three weeks, a month or even two the perfect flexibility of all their joints and the normal freshness of their internal organs. Evacuation takes place with them during the first days as in the normal state; and movements can be induced by the electric battery. In a word, they behave exactly like the Beetles immolated by the Cerceris; there is absolute identity between the state into which the kidnapper puts her victims and that which we produce at will by injuring the thoracic nerve-centres with ammonia. Now, as it is impossible to attribute the perfect preservation of the insect for so long a period to the tiny drop injected, we must reject altogether any notion of an antiseptic fluid and admit that, despite its perfect immobility, the insect is not really dead, that it still retains a glimmer of life, which for some time to come keeps the organs in their normal condition of freshness, but gradually fades out, until at last [[54]]it leaves them the prey of corruption. Besides, in some cases, the ammonia does not produce complete annihilation of movement except in the insect’s legs; and then, as the deleterious action of the liquid has doubtless not extended far enough, the antennæ preserve a remnant of mobility and we see the insect, even more than a month after the inoculation, draw them back quickly at the least touch: a convincing proof that life has not entirely deserted the inanimate body. This movement of the antennæ is also not uncommon in the Weevils wounded by the Cerceris.
In every case the injection of ammonia at once stops all movement in Scarabs, Weevils and Buprestes; but we do not always succeed in reducing the insect to the condition just described. If the wound be too deep, if the drop administered be too strong, the victim really dies; and, in two or three days’ time, we have nothing but a putrid body before us. If the prick, on the other hand, be too slight, the insect, after a longer or shorter period of deep torpor, comes to itself and at least partially recovers its power of motion. The assailant herself may sometimes operate clumsily, just like man, for I have noticed this sort of resurrection in a victim stung by the dart of a Digger-wasp. The Yellow-winged Sphex, whose [[55]]story will shortly occupy our attention, stacks her lairs with young Crickets first pricked with her poisoned lancet. I have extracted from one of those lairs three poor Crickets whose extreme limpness would, in any other circumstances, have denoted death. But here again death was only apparent. Placed in a flask, these Crickets kept in very good condition, perfectly motionless all the time, for nearly three weeks. In the end, two went mouldy, and the third partly revived, that is to say, he recovered the power of motion in his antennæ, in his mouth-parts and, what is more remarkable, in his first two pair of legs. If the Wasp’s skill sometimes fails to benumb the victim permanently, one can hardly expect invariable success from man’s rough experiments.
In the Beetles of the second class, that is to say, those whose thoracic ganglia are some distance apart, the effect of the ammonia is quite different. The least vulnerable are the Ground-beetles. A puncture which would have produced instant annihilation of movement in a large Sacred Beetle produces nothing but violent and disordered convulsions in the medium-sized Ground-beetles, be they Chlænius, Nebria or Calathus. Little by little the insect quiets down and, after a few hours’ rest, its usual movements are resumed as though it had [[56]]met with no accident whatever. If we repeat the experiment on the same specimen, twice, thrice, or four times over, the results remain the same, until the wound becomes too serious and the insect actually dies, as is proved by its desiccation and putrefaction, which follows soon after.
The Melasoma-beetles and Longicornes are more sensitive to the action of the ammonia. The injection of the corrosive drop pretty quickly renders them motionless; and, after a few convulsions, the insect seems dead. But this paralysis, which would have persisted in the Dung-beetles, the Weevils and the Buprestes, is only temporary here: within a day, motion is once more apparent, as energetic as ever. It is only when the dose of ammonia is of a certain strength that the movements fail to reappear; but then the insect is dead, quite dead, for it soon begins to decay. It is impossible, therefore, to produce complete and persistent paralysis in Beetles that have their ganglia far apart by the same measures which proved so efficacious in Beetles with ganglia close together: the utmost that we can obtain is a temporary paralysis whose effects pass off within a day.
The demonstration is conclusive; the Cerceres that prey on Beetles conform in their selection to what could be taught only by the [[57]]most learned physiologists and the finest anatomists. One would vainly strive to see no more in this than casual coincidences: it is not in chance that we shall find the key to such harmonies as these. [[58]]
[1] Marie Jean Pierre Flourens (1794–1867), the celebrated French physiologist, appointed perpetual secretary of the Academy of Science in 1833 and a member of the French Academy.—Translator’s Note. [↑]
[2] François Magendie (1783–1855), professor of anatomy in the Collège de France, noted for his experiments on the physiology of the nerves.—Translator’s Note. [↑]