Injection of ammonia always stops motion at once in Buprestids, Weevils, and Scarabæus, but it is not always possible to put the creature into the state just described. If the wound be too deep, or the little drop instilled be too strong, at the end of two or three days the victim really dies, and after two or three days there is but a decaying body. If, on the contrary, the prick be too slight, it recovers the power of motion, at least partially, after being inanimate for more or less time. The Cerceris herself may operate clumsily, just like man, for I have seen this kind of resurrection in a victim struck by the dart of a Hymenopteron. Sphex flavipennis, whose history will presently occupy us, heaps in her dens young crickets struck by her venomed lancet. From one of her holes I have taken three poor crickets whose extreme flabbiness would, in any other circumstances, have denoted death. But here, again, death was only apparent. Placed in a bottle, these crickets kept quite fresh but motionless for nearly three weeks, after which two grew mouldy, while the third came partly to life—that is to say, it regained motion of the antennæ, mouth-parts, and, which is more remarkable, of the first two pairs of feet. If even the skill of the Hymenopteron sometimes fails to benumb a victim for good and all, can one expect constant success with the rough experiments of man? [[78]]
In Coleoptera of the second category—those where the ganglia of the thorax are distant one from another—the effect of ammonia is quite different. Those which show themselves least vulnerable are the Caraboidea. A puncture which would instantly have annihilated motion in the large Scarabæus sacer, in the middle size Caraboidea only causes violent, disordered convulsions. By degrees the creature quiets down, and after some hours’ rest resumes its habitual movements as if nothing had happened to it. If the experiment be repeated on it twice, thrice, even four times, the results are the same, until the wound becomes too serious, and it dies outright, as is proved by the drying up and putrefaction which soon follow.
The Melasomes and the Longicorns are more sensitive to the action of ammonia. The injection of a small corrosive drop quickly renders them motionless, and after some twitching they seem dead. But the paralysis which would have persisted in Weevils, Scarabids, and Buprestids is but momentary. Before long motion reappears as energetic as before. It is only when the dose of ammonia is of a certain strength that movement does not reappear. But then the creature is really dead, and putrefaction rapidly comes on. It is then impossible to cause complete and persistent paralysis in Coleoptera with ganglia far apart by the means so efficacious in those with ganglia near together. At the utmost one can only obtain momentary paralysis, which passes quickly away. The demonstration is decisive. Cerceris which prey on Coleoptera conform in their [[79]]choice to what the most learned physiology and finest anatomy alone can teach. It would be vain to endeavour to see nothing here but chance agreement; it is not chance which explains such harmony. [[80]]
VI
THE YELLOW-WINGED SPHEX
In their impenetrable coat of mail the Coleoptera offer but one vulnerable point to their dart-bearing foe. This defect in the cuirass is known to the assassin, and the poisoned sting is there inserted, striking at one blow the three centres of motion, the Weevil and Buprestid, which alone have a nervous organisation sufficiently centralised, being selected. But what happens when the insect wears no armour and is soft-skinned, so that the Hymenopteron can pierce it anywhere that the chances of the struggle may direct? Is there then a choice as to where the blow is given? Like the assassin who strikes at the heart to shorten the dangerous struggles of his victim, does the Sphex follow the tactics of the Cerceris, and strike by preference at the motor ganglia? If so, what happens when these are distant from one another, acting so independently that paralysis of one does not affect the others? These questions will be answered by the history of an insect which hunts field crickets, Sphex flavipennis.
It is towards the end of July that this Sphex [[81]]tears open the cocoon which until then has protected it, and flies away from its subterranean cradle. During the whole of August one constantly sees it seeking drops of honey on the spiny heads of Eryngium campestre, the commonest of such robust plants as brave the dog days. But this careless life is brief, for in the earliest days of September the Sphex has begun the hard existence of miner and hunter. It is usually on some small flat spot on banks along a road that the dwelling is established, only there must be two indispensable conditions—a sandy soil easy to work, and sun. Beyond this no precaution is taken to shelter the domicile against autumn rain and winter frost. A horizontal position, unsheltered, beaten by rain and wind, suit the Sphex perfectly, so long as it is exposed to the sun. But when the work is half-way through, if heavy rain should come, it is sad to see next day galleries in course of construction choked with sand and finally abandoned.
Rarely does the Sphex work in solitude; it is in small bands of ten, twenty, or more excavators that the claim selected is worked. One must have spent some days watching one of these colonies in order to form any idea of the restless activity, the feverish haste, the abrupt movements, of these hard-working miners. They rapidly attack the ground with the rakes of their forefeet, canis instar, as Linnæus says. A puppy does not show more energy in scratching up the ground in play. At the same time each labourer hums a joyous song—shrill, high-pitched, interrupted at short intervals, and modulated by vibrations of wings and thorax. One [[82]]would think they were a troop of merry comrades, stimulating one another to work by a cadenced rhythm. Meanwhile, the sand flies, falling in fine dust on their quivering wings, and the heavier gravel, pulled out bit by bit, rolls far away. If a bit resist too much, the insect goes at it with a high note, reminding one of the cry with which a woodcutter accompanies the stroke of his axe. Under the redoubled efforts of tarsi and mandibles the cavity is already sketched out, and the Sphex can already dart into it. Then comes a lively interchange of forward movements to detach material, and of backward to brush out fragments. In this hurried coming and going the Sphex does not so much walk as dart forward, as though impelled by a spring. With panting abdomen, antennæ vibrating, the whole body moved by a strong thrill, she springs forward and is out of sight. You still hear the unwearied hum underground, and one sees from time to time hind legs pushing backward a wave of sand to the mouth of the burrow. From time to time labour underground is interrupted either that the Sphex may dust herself in the sunlight, and get rid of grains of dust which insinuate themselves into delicate joints and hamper the liberty of her movements, or that she make a reconnaissance in the neighbourhood. Notwithstanding these short interruptions, in a few hours the gallery is hollowed out and the Sphex appears on her threshold, to voice her triumph, and give the last touch to her labours by effacing some inequality, or carrying away some particles of earth, the objection to which only the eye of a Sphex could perceive. [[83]]
Of the many tribes of Sphegidæ visited by me, there is one of which I retain a specially lively recollection, on account of its singular installation upon the edge of a high road, where were little heaps of mud thrown up from side ditches by the cantonnier’s shovel. One, well sun-dried, had a conical shape like a sugar-loaf over fifteen inches high. The situation pleased the Sphegidæ, who had established a more populous community than I have ever again met with. From base to summit the cone of dried mud was pierced with burrows, giving it the appearance of a huge sponge. In every story was feverish animation, and a busy coming and going which brought to mind the scene in some great workshop when orders are pressing. Crickets were being dragged by the antennæ up the slopes of the conical city; there was storing of provisions in the larders of the cells; dust was pouring from galleries in process of construction; at intervals the grimy faces of the miners appeared at mouths of passages—there was a constant going and coming. Now and then, in a short interval of leisure, a Sphex ascended the top of the cone, perhaps to take a general and well-satisfied view from this belvedere. What a tempting sight!—one to make me long to carry away the entire city with its inhabitants. It was useless to try; the mass was too heavy. One cannot take up a village by the roots to plant it elsewhere.