Insect life: Souvenirs of a naturalist

by Jean-Henri Fabre

THE BEMBEX

Not far from Avignon, on the right bank of the Rhône opposite the mouth of the Durance, is one of my favourite points for the observations about to be recorded. It is the Bois des Issarts. Let no one deceive himself as to the value of the word “bois”—wood, which usually gives the idea of a soil carpeted with fresh moss and the shade of lofty trees, through whose foliage filters a subdued light. Scorching plains, where the cicada grinds out its song under pale olives, know nothing of such delicious retreats full of shade and coolness.

The Bois des Issarts is composed of thin and scattered groups of ilex, which hardly lessen the force of the sun’s rays. When I established myself during the dog days in July and August, I used to settle myself at some spot in the wood favourable for observations. I took refuge under a great umbrella, which later lent me most unexpected aid of another kind, very valuable too, as my story will show in good time. If I had neglected to equip myself with this article, embarrassing enough in a long walk, the only way to avoid sunstroke was to lie at full length [[220]]behind some heap of sand, and when my temporal arteries beat intolerably, the last resource was to shelter my head at the mouth of a rabbit hole. Such are the means of getting cool in the Bois des Issarts.

The soil, unoccupied by any woody vegetation, is almost bare and composed of a fine, arid, very light sand, heaped by the wind in little hillocks where the stems and roots of the ilex hinder its blowing about. The slope of such hillocks is generally very smooth, from the extreme lightness of the material, which runs down into the least depression, thus restoring the regularity of the surface. It is enough to thrust a finger into the sand, and then to withdraw it in order immediately to cause a downfall, which fills up the cavity and re-establishes the former state of things without leaving any trace. But at a certain depth, varying according to the more or less recent date of the last rains, the sand retains a dampness which keeps it stable, and lends a consistency allowing of slight excavations without roof and walls falling in. A burning sun, a radiant blue sky, sand slopes yielding without the least difficulty to the strokes of the Hymenopteron’s rake, abundant game for the larvæ, a peaceful site rarely troubled by the foot of the passer-by,—all unite here in this paradise of the Bembex. Let us see the industrious insect at work.

If the reader will come under my umbrella, or profit by my rabbit burrow, this is the sight which will meet him towards the end of July. A Bembex (B. rostrata) arrives of a sudden and alights without hesitation or investigation at a spot which, as far as I see, differs in nothing from the rest of the [[221]]sandy surface. With her front tarsi, which, armed with stiff rows of hairs, suggest at once broom, brush, and rake, she begins to dig a subterranean dwelling, standing on her four hind feet, the two last slightly apart, while the front ones alternately scratch and sweep the loose sand. The precision and rapidity of the action could not be greater were the circular movement of the tarsi worked by a spring. The sand, shot backward under the creature, clears the arch of its hind legs, trickling like a liquid in a continuous thread, describing a parabola and falling some eight inches away. This dusty jet, constantly fed for five or ten minutes, is enough to show with what dizzy rapidity the tools are used. I could quote no second example of equal swiftness, which yet in no way detracts from the elegance and free movements of the insect as it advances and retires, now on one side, now on another, without allowing the parabola of sand to stop.

The soil hollowed is of the lightest kind. As the Hymenopteron excavates, the sand near falls and fills the cavity. In the landslip are mingled little bits of wood, decayed leaf-stalks, and grains of gravel larger than the rest. The Bembex picks these up in her mandibles, and, moving backward, carries them to a distance, returning to sweep again, but always lightly, without attempting to penetrate into the earth. What is the object in this surface labour? It would be impossible to learn from a first glance, but after spending many days with my dear Hymenoptera, and grouping together the scattered results of my observations, I think I divine the motive of these proceedings. [[222]]

The nest is certainly there—underground, at the depth of a few inches: in a little cell, dug in cool firm sand, is an egg, perhaps a larva, which the mother feeds daily with flies, the invariable food of Bembex larvæ. She must be able at any moment to penetrate to this nest, carrying on the wing, between her feet, the nursling’s daily ration, just as a bird of prey arrives at its eyrie carrying game for its brood in its claw. But while the bird returns to a nest on some inaccessible shelf of rock, without any difficulty beyond the weight of its prey, the Bembex must undertake each time the hard work of mining, opening afresh a gallery blocked and closed by ever-sliding sand in proportion as she proceeds. The only stable part of this underground abode is the spacious cell inhabited by the larva amid the remains of a fortnight’s feast; the narrow vestibule entered by the mother to go down to the cell, or come forth for the chase, gives way each time, at all events at the upper end, built in dry sand, rendered even looser by her constant goings and comings. Thus at each entrance or exit the Hymenopteron must clear out a passage. The exit offers no difficulties, even should the sand have the same consistency as when first stirred; the insect’s movements are free; it is safe under cover, can take its time and use tarsi and mandibles at its leisure. Going in is another matter. The Bembex is embarrassed by her prey, pressed to her body by her feet, so that there is no free use of the mining tools. What is more serious is that impudent parasites—veritable bandits in ambush—are crouching here and there about the burrow watching her difficult [[223]]entrance to hurriedly drop their egg on the game just as it disappears into the gallery. If they succeed, the son of the house, the Hymenopteron’s nursling, will perish, starved by greedy guests.

The Bembex seems aware of this danger, and arranges so as to enter quickly, without serious obstacles, so that the sand blocking the door should yield to a mere push from her head, aided by a rapid sweep of the forelegs. To this end she, so to say, sifts the materials round her abode. In leisure moments, when the sun shines and the larva has its food, and does not need her care, the mother rakes before her door, and puts on one side all the tiny bits of wood, of over-large gravel or leaves, which might get on her path and bar the passage at the perilous moment of return. The Bembex which we saw so hard at work was busy sifting so as to make access to her abode easier; the materials of the vestibule are examined, minutely sorted, and cleared of every encumbrance. Who can tell whether the rapid labour and joyous activity of the insect do not express in their own way her maternal satisfaction and happiness in caring for the roof of the cell which has received the precious trust of the egg? As the Bembex confines herself to exterior household cares without seeking to penetrate the sand, everything must be in order within, and there is nothing pressing to do. We may wait, but for the time the insect will teach us nothing more. Let us therefore examine the underground dwelling.

By lightly scratching the bank with the blade of a knife just where the Bembex was oftenest seen, one soon discovers the entrance hall, which, blocked [[224]]as it is for part of its length, is none the less recognisable by the special look of the materials moved about. This passage, a finger’s-breadth in size, rectilinear or winding, longer or shorter, according to the nature of the ground, measures eight to twelve inches. It leads to a single chamber, hollowed in damp sand, with walls undaubed with mortar, which might prevent landslips and lend polish to the rough surface. Enough if the ceiling lasts while the larva is being fed up. Future falling-in matters little when the larva is enclosed in its stout cocoon—a kind of strong box, which we shall see in process of construction. In workmanship the cell is as rustic as possible, being merely a rude excavation with no well-determined form, low roofed, and of a size which might hold two or three nests.

Within lies one head of game—one only—quite small and quite insufficient for the voracious nursling for whom it is destined. It is a golden green-fly, Lucilia Cæsar, a dweller in tainted meat, and is quite motionless. Is it really dead or only paralysed? This will be cleared up later. Just now let us observe the cylindrical egg upon its side, white, slightly curved, and a couple of millimetres in length. It is a Bembex egg. As we have foreseen from the mother’s behaviour, there is no pressing household business; the egg is laid and a first ration provided for the needs of the feeble larva, which ought to hatch in twenty-four hours. For some time the Bembex need not re-enter her hole, confining herself to keeping a good lookout in the neighbourhood, or possibly making new burrows and laying there egg after egg, always in a separate cell. [[225]]