Let us look at the Sphex at work in flat ground, as is much more frequently the case. As soon as the burrow is hollowed out, the chase begins. Let us profit by the absence of the Hymenopteron [[84]]in search of game, and take a look at her dwelling. The spot chosen by a Sphex colony is generally horizontal, though the ground is not so level but that there are little mounds crowned by a tuft of grass or thrift, or inequalities consolidated by the slender roots of the vegetation which covers them. It is on the sides of such furrows that the Sphex places her den. For two or three inches in depth the gallery is horizontal, serving as an approach to the hidden shelter for the provender and the larvæ. In this vestibule the Sphex takes refuge in bad weather, rests there at night, and occasionally by day for a few instants, showing only her expressive face and impudent eyes. Beyond the vestibule an abrupt turn descends more or less obliquely to a depth of two or three inches more, ending in an oval cell rather larger in diameter, whose axis lies parallel with the horizontal gallery. The cell walls are not covered with any particular cement, but in spite of their bareness they have evidently been the object of most careful labour. The sand is heaped and levelled on the floor, on the ceiling, and sides, so as to do away with the risk of landslips, or any roughness which might injure the delicate skin of the larva. This cell communicates with the passage by a narrow entrance, just wide enough to allow the Sphex, burdened with prey, to enter. When this first cell is furnished with an egg and necessary provisions, the Sphex walls up the entrance, but does not yet abandon her burrow. A second cell is hollowed beside the first, and provisioned in the same manner; there is then a third made, and sometimes a fourth. Only then does the Sphex cast back into the [[85]]burrow the rubbish heaped at the entrance, completely effacing all outward trace of her work. Three cells are usually found in each burrow, rarely two, and yet more rarely four. As one learns by dissecting the insect, one may estimate the number of eggs laid at about thirty, which would make the number of burrows needed ten. Now these are hardly begun before September, and are finished before the end of the month. Consequently the Sphex cannot devote more than two or three days at most to each burrow and its stores. Evidently the active little creature has not a minute to lose, when in so short a time she has to hollow out the lair, procure a dozen crickets, sometimes brought from a distance through endless difficulties, to store them, and finally to stop up the burrow. Moreover, there are days when wind makes hunting impossible; rainy days or overcast ones suspending all work. The Sphex cannot give to her building the enduring solidity that Cerceris tuberculata gives to its deep galleries. This species transmit their solid abodes from one generation to another, each year hollowed more deeply, so that I was often bathed in perspiration when I tried to reach them, and frequently my efforts and my implements proved useless. The Sphex inherits nothing, and must herself do everything, and that rapidly. Her dwelling is but a tent, hastily erected and moved on the morrow. In compensation the larvæ, covered but by a thin layer of sand, know how to supply the shelter which their mother has not given them; they can clothe themselves with a double and triple waterproof covering, far superior to the thin cocoon of the Cerceris. [[86]]
But here comes a Sphex with noisy hum, returning from the chase. She pauses on a neighbouring bush, holding in her mandibles one of the antennæ of a big cricket, weighing far more than herself. Tired out by the weight, she rests a moment, then grasps her captive between her feet, and with a supreme effort flies right across the ravine between her and her abode. She alights heavily on the flat ground where I am watching, in the very middle of a Sphex village. The rest of the journey is made on foot, the Sphex, not in the least intimidated by my presence, comes astride her victim, holding her head proudly aloft while she drags along the cricket between her feet by one of its antennæ held in her jaws. If the soil be bare there is no difficulty, but should a network of grass spread its runners across the way, it is curious to see the astonishment of the Sphex at finding her efforts baffled by this little obstacle—curious to witness her marches and countermarches and repeated attempts until the difficulty is surmounted either by the aid of her wings or a well-planned détour. The cricket is at last conveyed to its destination and placed so that its antennæ come exactly to the mouth of the burrow. Then the Sphex abandons it and descends in haste to the bottom of the cave. A few seconds later she puts her head out with a little cry of joy. The antennæ of the cricket are within reach; she seizes them and promptly conveys it down to her den.
I still ask myself in vain why these complicated manœuvres at the moment of conveying the cricket into the burrow. Why, instead of going down [[87]]alone and returning to resume the prey left on the threshold, does not the Sphex drag it into the gallery, as she did in the open air, since the space is wide enough, or take it with her while she enters backwards? The various predatory Hymenoptera which I have been able to observe all drag their prey at once to the bottom of their cells, holding it underneath them by their mandibles and intermediary feet. Léon Dufour’s Cerceris does indeed somewhat complicate her movements, since after putting down her Buprestis for a moment at the door of her underground abode, she instantly goes backward into the gallery, seizes her victim with her mandibles and drags it down; but that is very unlike the tactics adopted in a like case by the Sphex. Why this domiciliary visit, which invariably precedes the introduction of the prey? May it not be that before descending hampered by a load, the Sphex thinks it prudent to give a look round the bottom of her dwelling to make sure that all is in order and to drive out, if necessary, some impertinent parasite which may have slipped in during her absence? Several Diptera, predatory flies, especially Tachinidæ, watch at the doors of all the hunting Hymenoptera, spying out the favourable moment to lay their eggs on other people’s game, but none penetrate into the dwelling, nor venture into the dark passages, where, if by ill-luck the owner caught them, they might have to pay dearly for their audacity. The Sphex, like others, pays her tribute to the predatory Tachinidæ, but they never enter her burrow to commit their misdeeds. Besides, have they not all the time they need to lay their eggs on the cricket? [[88]]If they look sharp, they may very well profit by the Sphex’s momentary absence from her victim to confide their posterity to it. What yet greater danger menaces the Sphex which renders this preliminary descent to the bottom of the burrow such an imperious necessity?
The one observed fact which can throw any light on the problem is this. Amid a colony of Sphegidæ in full activity, whence all other Hymenoptera are habitually excluded, I one day surprised a sportsman of a different kind, Tachytes nigra, carrying one by one, without any haste and with the greatest composure, amid the crowd where he was but an intruder, grains of sand, little bits of dry stalk, and other small materials, to stop up a burrow of the same shape and size as the neighbouring ones of the Sphegidæ. This labour was pursued too conscientiously to admit of any doubt as to the presence of the worker’s egg in the underground dwelling. A Sphex with anxious movements, apparently the legitimate owner of the burrow, never failed each time that the Tachytes entered the gallery to dart in pursuit, but emerged swiftly, as if frightened, followed by the other, who continued her task unmoved. I visited this burrow, the evident cause of strife between them, and found a cell provisioned with four crickets. Suspicion almost gave place to certainty, for this allowance far exceeded the needs of a Tachytes’ larva, which is at least one-half smaller than the Sphex. The calm insect whose care to stop up the burrow at first suggested that it was the owner was really a usurper. How comes it that the Sphex, larger and [[89]]more robust than her adversary, allows herself to be robbed with impunity, limiting herself to a fruitless pursuit, and flying like a coward when the intruder, who seems not even to perceive her, turns round to come out of the burrow? Is it with insects as with men, the first quality needed for success is audacity—audacity—audacity? Certainly the usurper had no lack of it. I can still see that Tachytes, imperturbably calm, going and coming before the meek Sphex, which stamped with impatience, but did not venture to fall upon the thief.
Let us add that in other circumstances I have repeatedly found this Hymenopteron, I suppose to be a parasite—this Tachytes nigra, dragging a cricket by one of its antennæ. Was it a prey lawfully acquired? I would fain think so, but the indecision of the insect which strayed about the ruts in the paths as if seeking a convenient burrow always left me suspicious. I have never been present when it burrowed, if indeed it ever does undertake that labour, and what is more, I have seen it abandon its game to decay, perhaps not knowing what to do with it for want of a hole where to put it. Such wastefulness seems to indicate goods ill-gotten, and I ask myself if the cricket were not stolen when the Sphex left it on her threshold? I also suspect Tachytes obsoleta, banded with white round the abdomen like Sphex albisecta, which nourishes its larvæ with crickets such as are hunted by the latter. I have never seen it digging galleries, but I have caught it dragging crickets that the Sphex would not have disdained. This similarity of food in species of different genera makes me doubtful whether the [[90]]booty were lawfully come by. Let me add, however, to atone in some measure for the injury which my suspicions may do to the character of the genus, that I have seen the perfectly lawful capture of a little cricket yet wingless by Tachytes tarsina, and have also seen it hollow cells and store them with prey bravely acquired. Thus I have only suspicions to offer as to why the Sphex persists in descending to the bottom of her hole before carrying in prey. Is there some other end besides that of dislodging a parasite which may have got in during the owner’s absence? I despair of finding out; who can interpret the thousand manœuvres of instinct? Poor human reason which cannot even explain the wisdom of a Sphex!
At all events, it is proved that these manœuvres are singularly invariable, àpropos of which I will mention an experiment which greatly interested me. At the moment when the Sphex makes her domiciliary visit, I take the cricket and put it some way off. The Sphex comes up, utters her usual cry, looks round with astonishment, and seeing the game too far off, comes out to seize and put it in the right position. Then she goes down again without the cricket. Same manœuvre on my part, same disappointment when she reappears. Again the prey is brought to the mouth of the hole, and again the Sphex goes down alone, and so on as long as my patience holds out. Forty times on end have I tried the experiment on the same individual; her persistence vanquished mine, and her tactics never varied.
Having proved the inflexible pertinacity of all [[91]]the Sphegidæ in one colony on whom I cared to experiment, I could not but perplex myself over it. “Does then the insect obey a fixed tendency which circumstances cannot modify?” I asked myself. “Are its actions all done by rule, and is it unable to acquire the least experience from its own proceedings?” Later observations modified this too absolute judgment.
The following year, at the proper time, I visited the same spot. The new generation had inherited for their burrows the place chosen by the preceding ones; it had also faithfully inherited their tactics, for the cricket experiment gave the same results. Such as were the Sphegidæ of the past year such are those of the present one, equally persistent in a fruitless attempt. My error grew confirmed until good luck brought me to another colony in a different place. I renewed my experiments. After two or three trials with the old, well-known result, the Sphex got astride of the cricket, seized its antennæ with her mandibles, and dragged it at once into the burrow. Who looked a fool then? The experimenter baffled by the clever Hymenopteron. At the other holes her neighbours, some sooner, some later, found me out, and went down with their prey instead of persisting in leaving it on the threshold to seize it later. What is the meaning of this? This colony, descended from another stock, for sons return to the spot selected by their forefathers, is cleverer than the one observed last year. Craft is inherited; there are sharper-witted tribes and duller ones, apparently according to the faculties of their forefathers. With Sphegidæ, as with us, the kind [[92]]of intellect changes with the province. Next day I tried the cricket experiment in another locality, and it invariably succeeded. I had come upon a dense-minded tribe, a true colony of Bœotians, as in my earlier observations. [[93]]