[To face p. 58.
CERCERIS FERRERI AND ITS PREY, THE WEEVIL;
Rhynchites betulæ on birch leaves, showing two leaves rolled up by the weevil
After all that has been so admirably said by Léon Dufour on the long and marvellous preservation of the insects destined as food for the carnivorous larvæ, it is needless to say that the weevils which I dug up, as well as those taken from between the feet of their murderer, were perfectly fresh, though permanently motionless. Freshness of colour, suppleness of the membranes and smallest articulations, normal condition of the viscera, all combine to make one doubt whether the inert body under one’s eyes can really be a corpse, all the more that even under the magnifying glass it is impossible to perceive the smallest wound; and in spite of one’s self one expects every moment to see the insect move and walk. Yet more, in weather so hot that insects which had died naturally would in a few hours have become dried up and crumbly, or again in damp weather which would with equal rapidity have made them decay and grow mouldy. I have kept specimens in glass tubes or cones of paper over a month with no precautions, and wonderful [[59]]to say, after all this length of time, the intestines were as fresh as ever, and I found dissection as easy as if the creatures were alive. No, in presence of such facts one cannot talk of an antiseptic, and believe in real death; life is still there—life latent and passive—vegetative life. It alone, struggling successfully for a time against the destructive invasion of chemical forces, can thus preserve the organism from decomposition. Life is still there, but without motion, and we have under our eyes such a marvel as chloroform or ether might produce—a marvel caused by the mysterious laws of the nervous system.
The functions of this vegetative life are slackened and troubled no doubt, but still they are feebly exercised. I have the proof of this in that action of the viscera which takes place normally and at intervals in the weevils during the first week of that deep slumber, which will never be broken, and yet which is not death. It only ceases when the intestine is empty, as is shown by autopsy. But the faint rays of life which the creature manifests do not stop there; and though sensation appears annihilated for ever, I have succeeded in reawakening some vestige of them. Having placed weevils, recently exhumed and absolutely motionless, in a bottle with sawdust moistened with benzine, I was not a little surprised to see a quarter of an hour later moving antennæ and feet. For a moment I thought I could recall them to life. Vain hope! these movements, last trace of a sensitiveness about to cease, soon stopped, and could not be excited a second time. I have repeated this experiment from [[60]]some hours to several days after the murder, and always with the same success; only movement is tardy in appearing in proportion as the date of the victim’s death is distant. The movements are always from the forepart backward. First, the antennæ move, then the front tarsi tremble and share in the oscillations; next, the second pair do the same; and finally, the third. Once movement is excited, all these members oscillate without any order until all become again motionless, as they do sooner or later. Unless death has been quite recent, movement does not go beyond the tarsi, and the legs remain motionless.
Ten days after the murder I could not obtain the least sign of irritability by the proceeding described, and I had recourse to the Voltaic battery. This is more effective, and provokes muscular contractions where the vapour of benzine fails. One or two elements of Bunsen suffice, which are armed with the rheophores of slender needles. Plunging the point of the one under the furthest ring of the abdomen, and the point of the other under the neck, you obtain each time that the current is established, not only the quivering of the tarsi, but a strong flexion of the feet, which fold themselves under the body, and relax when the current is interrupted. These movements, very energetic during the first days, gradually lose intensity, and after a certain time appear no more. On the tenth day I have still been able to obtain visible motions, but on the fifteenth the pile was unable to provoke them, notwithstanding the suppleness of the limbs and freshness of the viscera. I have submitted also [[61]]to the action of the pile Coleoptera really dead, Blaps, Saperda, Lamia, asphyxiated by benzine or sulphureous gas, and two hours later it was impossible to provoke the movements obtained so easily from weevils lying already for several days in the singular state, intermediate between life and death, into which their redoubtable enemy plunges them.
All these facts contradict the supposition of an animal completely dead, and the hypothesis of a real corpse rendered incorruptible by some antiseptic liquid. One can only explain them by admitting that the animal is struck in the principle of its movements, and that sensitiveness, suddenly benumbed, dies slowly out, while the more tenacious, vegetative functions die yet more slowly and preserve the intestines during the time necessary for the larva.
The most important detail to show was how the murder is committed. Evidently, the chief part must be played by the poisoned dart of the Cerceris. But where and how does it penetrate the body of the weevil, covered with a hard cuirass, with pieces so closely joined? Even under the magnifying glass nothing told where the sting entered. Direct examination, therefore, was required to discover the murderous ways of the Cerceris—a problem before whose difficulties Léon Dufour had already recoiled, and the solution of which seemed to me for a time impossible. I tried, however, and had the satisfaction of succeeding, though not without some groping about.
When they fly from their holes to the chase, the Cerceris go here and there, sometimes on one [[62]]side, sometimes on the other, and return from all directions, loaded with prey, so that they must seek it on all sides; but as they barely take ten minutes between going and returning, the space worked over could not be very great, especially considering the time necessary to discover the prey, to attack and render it an inert mass. I, therefore, set myself to examine all the adjacent ground with close attention, hoping to discover some Cerceris on the hunt. One afternoon devoted to this weary work convinced me of the uselessness of my researches, and of the little chance I had of surprising any of the few Cerceris, scattered here and there, and soon lost to view by their rapid flight; above all, in difficult ground, planted with olives, I gave up the attempt. But by carrying live weevils to the neighbourhood of the nests might I not tempt the Cerceris by a prey found without trouble, and so observe the drama? The notion seemed good, and the very next day I set out to find live Cleonus ophthalmicus. Vineyards, wheat-fields, and crops of lucerne, and heaps of stones did I visit and examine one and all, and after two days of close search I possessed—dare I own it?—three weevils! bare, dusty, maimed of antennæ or tarsi, shabby old creatures which, perhaps, the Cerceris would not touch! Since the day of that fevered search, when, for a weevil’s sake, I bathed myself in perspiration during my wild expedition, many a year has passed, and yet, in spite of almost daily entomological researches, I am still ignorant of the life and habits of this Cleonus, which I met here and there, straying on the edge of paths. Wonderful powers of instinct! [[63]]in the same spots, and in a fraction of time, one Hymenopteron would have found hundreds of these insects which man cannot find, and found them fresh and shining, no doubt just emerged from the cocoon!
No matter; let us experiment with my wretched victim. A Cerceris has just gone into her gallery with her prey; before she comes out for a new expedition I place a weevil a few inches from her hole. The weevil moves about; when it strays too far I bring it back to its place. At last the Cerceris shows her wide face at the mouth of her hole; my heart beats fast. She walks for a few minutes near her dwelling, sees the weevil, brushes against it, turns, passes several times over its back, and flies off without even honouring my captive with a bite—my captive which cost me so much labour! I was confounded—knocked over. New attempts at other holes, new disappointments. Decidedly these dainty hunters will have none of the game which I offer them. Perhaps they find it too old, too tasteless; perhaps, in handling it, I communicated some smell to it which displeases them. Foreign contact disgusts these connoisseurs.