Insect life: Souvenirs of a naturalist

by Jean-Henri Fabre

A slender waist, a slim shape, an abdomen much compressed at the upper part, and seemingly attached to the body by a mere thread, a black robe with a red scarf on its under parts,—such is the description of these Fossors; like Sphegidæ in form and colouring, but very different in habits. The Sphegidæ hunt Orthoptera, crickets, ephippigers, and grasshoppers, while the Ammophila chases caterpillars. This difference of prey at once suggests new methods in the murderous tactics of instinct.

Did not the name sound pleasant to the ear, I should be inclined to quarrel with Ammophila, which means sand-lover, as being too exclusive and often erroneous. The true lovers of sand—dry, powdery, and slippery sand—are the Bembex, which prey on flies: but the caterpillar-hunters, whose history I am about to tell, have no liking for pure, loose sand, and even avoid it as being too subject to landslips which may be caused by a mere trifle. Their vertical pits, which must remain open until the cell is stored with food and an egg, require more solid [[206]]materials if they are not to be blocked prematurely. What they want is a light soil, easy to mine, where the sandy element is cemented by a little clay and lime. The edges of paths—slopes of thin grass exposed to the sun,—such are the places they favour. In spring, from the first days of April, one sees Ammophila hirsuta there; in September and October there are A. sabulosa, A. argentata, and A. holosericea. I will make an abstract of the notes furnished by these four species.

For all four the burrow is a vertical shaft, a kind of well, with at most the dimension of a large goose quill, and about two inches deep. At the bottom is a single cell, formed by a simple widening of the shaft. To sum up, it is a poor dwelling, obtained at small expense, at one sitting, affording no protection if the larva had not four wrappers in its cocoon, like the Sphex. The Ammophila excavates alone, deliberately, with no joyous ardour. As usual, the anterior tarsi do duty as rakes and the mandibles as mining tools. If some grain of sand offer too much resistance, you may hear rising from the bottom of the well a kind of shrill grinding sound, produced by the vibration of the wings and entire body as if to express the insect’s struggles. Frequently the Hymenopteron comes up with a load of refuse in its jaws, some bit of gravel which it drops as it flies some little way off, in order not to block up the place. Some appear to merit special attention by their form and size,—at least the Ammophila does not treat them like the rest, for instead of carrying them away on the wing, she goes on foot and drops them near the shaft. They [[207]]are choice material—blocks ready prepared to stop up the dwelling by and by.

[To face p. 207.

AMMOPHILA SABULOSA TAKING STONE TO COVER ITS BURROW; A. ARGENTATA MINING

This outside work is done with a self-contained air and great diligence. High on its legs, its abdomen outstretched at the end of its long petiole, it turns round and moves its whole body at once with the geometrical stiffness of a line revolving on itself. If it has to throw away to a distance the rubbish it decides to be only encumbrances, it does this with little silent flights, often backwards, as if, having come out of the shaft tail first, it thought to save time by not turning round. Species with long-stalked bodies, like A. sabulosa and A. argentata, are those that chiefly display this automaton-like rigidity. Their abdomen, enlarged to a pear-shape at the end of a thread, is very troublesome to manage; a sudden movement might injure the fine stalk, and the insect has to walk with a kind of geometrical precision, and if it flies, it goes backward to avoid tacking too often. On the other hand, A. hirsuta, which has an abdomen with a short petiole, works at its burrow with swift easy movements such as one admires in most of the miners. It can move more freely, not being embarrassed by its abdomen.

The dwelling is hollowed out. Later on, when the sun has passed from the spot where the hole is bored, the Ammophila is sure to visit the little heap of stones set aside during her burrowing, intent to choose some bit which suits her. If she can find nothing that will do she explores round about, and soon discovers what she wants—namely, a small flat stone rather larger than the mouth of her well. She carries it off in her mandibles, and for the time [[208]]being closes the shaft with it. Next day, when it is hot again, and when the sun bathes the slopes and favours the chase, she will know perfectly well how to find her home again, secured by the massive door, and she will return with a paralysed caterpillar, seized by the nape of its neck and dragged between its captor’s feet; she will lift the stone, which is just like all the others near, and the secret of which is known only to her, will carry down the prey, lay an egg, and then stop the burrow once for all by sweeping into the shaft all the rubbish kept near at hand.

Several times I have seen this temporary closing of the hole by A. sabulosa and A. argentata when the sun grew low and the late hour obliged them to wait until the next day to go out hunting. When they had put the seals on their dwellings I too waited for the morrow to continue my observations, but first I made sure of the spot by taking my bearings and sticking in some bits of wood in order to rediscover the well when closed, and always, unless I came too early, if I let the Hymenopteron profit by full sunshine, I found the burrow stored and closed for good and all.