The Hunting Wasps

by Jean-Henri Fabre

A slender waist, a slim shape; an abdomen tapering very much at the upper part and fastened to the body as though by a thread; black raiment with a red sash across the belly: there you have a summary description of these burrowers, who are akin to the Sphex in form and colouring, but differ greatly from them in habits. The Sphex hunt Orthoptera—Locusts, Grasshoppers, Crickets—while caterpillars are the quarry of the Ammophilæ. This change of prey in itself suggests new methods in the lethal tactics of instinct.

If the name did not sound so pleasant to the ear, I would willingly quarrel with the term Ammophila, which means ‘sand-lover,’ as being too exclusive and often erroneous. The real lovers of sand, of dry, dusty, streaming sand, are the Bembex, who prey on Flies; but the caterpillar-hunters, whose story I now propose to relate, have no predilection for ordinary shifting sand, and even avoid it as being liable to [[232]]landslips on the slightest provocation. Their perpendicular shaft, which has to remain open until the cell receives the provisions and an egg, requires a firmer setting if it is not to be prematurely blocked. What they want is a light soil, easily tunnelled, in which the sandy element is cemented with a little clay and lime. Edges of paths, sunny banks where the grass is rather bare: those are the favourite spots. In spring, quite early in April, we see the Hairy Ammophila (A. hirsuta) there; when September and October come, we find the Sandy Ammophila (A. sabulosa), the Silvery Ammophila (A. argentata), and the Silky Ammophila (A. holosericea). I will here condense the information which I have gathered from the four species.

In the case of all four the burrow is a vertical shaft, a sort of well, possessing at most the diameter of a thick goose-quill and a depth of about two inches. At the bottom is the cell, which is always solitary and consists of a mere widening of the entrance-shaft. It is, when all is said, a poor lodging, obtained economically, in one day’s work; the larva will find no protection there against the winter except from the four wrappers of its cocoon, copied from that of the Sphex. The Ammophila digs by herself, quietly, without hurrying, without any joyous enthusiasm. As usual, the fore-tarsi serve as [[233]]rakes and the mandibles do duty as mining-tools. When some grain of sand offers too much resistance to its removal, you hear rising from the bottom of the well, as though to give voice to the insect’s efforts, a sort of shrill grating sound produced by the quivering of the wings and of the whole body. At frequent intervals the Wasp appears in the open with a load of refuse in her teeth, some bit of gravel which she flies away with and drops at a distance of a few inches, so as not to litter the place. Of the grains extracted some appear to deserve special attention, owing to their shape and size; at least, the Ammophila does not treat them as she does the rest: instead of flying off and dropping them far from the work-yard, she removes them on foot and lays them near the well. These are picked materials, ready-made blocks of stone which will serve presently for closing the dwelling.

This outside work is performed with measured movements and solemn diligence. The insect stands high on its legs, with its abdomen stretched at the end of its long pedicle, and turns round slowly, pivoting its whole body stiffly, with the geometrical rigidity of a line revolving on itself. If it wishes to fling to a distance the rubbish which it thinks will be in the way, it does so in short silent flights, often [[234]]backwards, as though the Wasp, emerging from her well head last, avoided turning, so as to save time. It is the species carrying their abdomens on the longest stalks, such as the Sandy Ammophila and the Silky Ammophila, which mainly display this automaton-like rigidity in action. That belly swelling into a pear at the end of a thread is in fact a very delicate thing to steer: a sudden movement might warp the fine stalk. So we must walk with a sort of geometrical rigour; if we have to fly, we will do so backwards, to avoid tacking too often. On the other hand, the Hairy Ammophila, who has a short abdominal pedicle, works at her burrow with the heedless, nimble movements which we admire in most of the Digger-wasps. She has more freedom of action, because her belly does not get in her way.

The home is dug. At a later hour in the day, or even merely when the sun has left the place where the burrow has just been bored, the Ammophila invariably visits the little heap of stones placed in reserve during the excavating, with the object of choosing a bit to suit her. If there is nothing that satisfies her needs, she explores the neighbourhood and soon discovers what she wants, a small flat stone slightly larger in diameter than the mouth of her hole. She carries off this slab in her mandibles and lays it, [[235]]as a temporary door, over the opening of the burrow. To-morrow, when the weather is once more hot and the sun bathes the slopes and encourages hunting, the Wasp will know quite well how to find her home, rendered inviolable by the massive door; she will come back with a paralysed caterpillar, grasped by the skin of its neck and dragged between its captor’s legs; she will lift the slab, which nothing distinguishes from other little stones around and which she alone is able to identify; she will let down the game to the bottom of the well, lay her egg, and close the house for good by sweeping into the perpendicular shaft all the rubbish which she has kept in the vicinity.

Time after time the Sandy Ammophila and the Silvery Ammophila have shown me this temporary closing of the hole when the sun begins to go down and when the lateness of the hour compels the victualling to be put off till the morrow. When the dwelling had been sealed up by the Wasp, I too would postpone my observations till the next day, but only after first making a map of the ground, choosing my lines and landmarks and planting a few stalks as signposts to show me the way to the well when it was filled. If I did not come back very early in the morning, if I left the Wasp time to take advantage of the hours of bright [[236]]sunshine, I invariably found the burrow finally stocked with provisions and closed.

This faithfulness of memory is striking. The Wasp, delayed in her task, puts off the rest of her work to the next day. She does not spend the evening, she does not spend the night in the home which she has just dug: on the contrary, she leaves the premises altogether and goes away, after concealing the entrance with a little stone. The locality is not familiar to her; she knows it no better than any other spot, for the Ammophilæ behave like the Languedocian Sphex and lodge their families here or there, wherever they happen to roam. The Wasp was there by chance; the soil suited her; she dug her burrow; and she now goes off. Where to? Who can tell? Perhaps to the flowers not far away, where, by the last gleams of daylight, she will sip a drop of sugary liquid at the bottom of the cups, even as our miners, after toiling in their dark galleries, fly for comfort to the bottle in the evening. She goes off, to a less or greater distance, stopping at this bin and that in the flowers’ cellar. The evening, the night, the morning slip by. Still, she must return to the burrow and complete her task, she must return after the marches and countermarches of the morning hunt and the bewildering flight from flower to flower during [[237]]the libations of the evening before. That the Social Wasp should return to her nest and the Social Bee to her hive does not surprise me at all: the hive and the nest are permanent residences, the way to which becomes known by long practice; but the Ammophila has no acquaintance with the locality which could help her to return to her burrow after such a long absence. Her tunnel is at a spot which she perhaps visited yesterday for the first time and which she must find again to-morrow, when she is quite out of her bearings and moreover hampered with a heavy load of game. Nevertheless, this little feat of topographical memory is performed, sometimes with a precision that left me astounded. The Wasp would walk straight to her burrow as if she had long been using all the little paths in the neighbourhood. At other times she would wander backwards and forwards and renew her search over and over again.

If the quest is greatly prolonged, the prey, which is a troublesome burden when you are in a hurry to find your home, is laid down in some high place, on a cluster of thyme or a tuft of grass, where it will be well in sight presently, when wanted. Thus eased, the Ammophila resumes her active search. I made a pencil-sketch, as she moved about, of the tracks [[238]]followed. The result was a medley of tangled lines, with sudden bends and turns, branches in and branches out, windings and repeated intersections—in short, a regular labyrinth whose complicated maze was an ocular demonstration of the perplexity of the lost one.

When the well has been found and the slab removed, the Wasp has to come back to the caterpillar, which is not always done without some groping about, in cases where her wanderings to and fro have been very numerous. Though she left her prey easily visible, the Wasp appears to foresee the difficulty of finding it again when the moment comes to drag it home. At least, if the search is unduly prolonged, you see her suddenly interrupt her exploration of the ground and return to her caterpillar, which she feels and nibbles at for a moment, as though to make sure that it is really her own game, her property. Then she hurries back again to the field of search, which she leaves a second time, if need be, and a third, in order to inspect the prey. I am not at all sure that these repeated visits of the Wasp to the caterpillar are not a means of refreshing her memory of the place where she left it.

This is what happens in exceedingly complicated cases; but as a rule the Wasp goes back quite easily to the well dug the day before [[239]]on the spot to which chance has taken her. The vagabond’s guide is her topographical memory, whose marvellous feats I shall have to tell later. As for me, in order to return next day to the well hidden under the lid of the little flat stone, I dared not trust to my unaided memory: I needed notes, sketches, lines of latitude and longitude, landmarks—in short, all the minutiæ of geometry.