Social Life in the Insect World

by Jean-Henri Fabre

In possession of these data and this unexpected enlightenment I varied the experiments, but all pointed to the same conclusion. In the morning I established the female under the usual wire-gauze cover. For support I gave her a little twig of oak as before. There, motionless as if dead, she crouched for hours, half buried in the dry leaves, which would thus become impregnated with her emanations.

When the hour of the daily visits drew near I removed the twig, which was by then thoroughly saturated with the emanations, and laid it on a chair not far from the open window. On the other hand I left the female under the cover, plainly exposed on the table in the middle of the room.

The moths arrived as usual: first one, then two, then three, and presently five and six. They entered, flew out again, re-entered, mounted, descended, came and went, always in the neighbourhood of the window, not far from which was the chair on which the twig lay. None made for the large table, on which, a few steps further from the window, the female awaited them in the wire-gauze cover. They hesitated, that was plain; they were still seeking.

Finally they found. And what did they find? Simply the twig, which that morning had served the ample matron as bed. Their wings rapidly fluttering, they alighted on the foliage; they explored it over and under, probed it, raised it, and displaced it so that the twig finally fell to the floor. None the less they continued to probe between the leaves. Under the buffets and the draught of their wings and the clutches of their eager feet the little bundle of leaves ran along the floor like a scrap of paper patted by the paws of a cat.

While the twig was sliding away with its band of investigators two new arrivals appeared. The chair lay in their path. They stopped at it and searched eagerly at the very spot on which the twig had been lying. But with these, as with the others, the real object of their desires was there, close by, under a wire cover which was not even veiled. None took any note of it. On the floor, a handful of butterflies were still hustling the bunch of leaves on which the female had reposed that morning; others, on the chair, were still examining the spot where the twig had lain. The sun sank, and the hour of departure struck. Moreover, the emanations were growing feebler, were evaporating. Without more ado the visitors left. We bade them goodbye till the morrow.

The following tests showed me that the leaf-covered twig which accidentally enlightened me might be replaced by any other substance. Some time before the visitors were expected I placed the female on a bed of cloth or flannel, card or paper. I even subjected her to the rigours of a camp-bed of wood, glass, marble, and metal. All these objects, after a contact of sufficient duration, had the same attraction for the males as the female moth herself. They retained this property for a longer or shorter time, according to their nature. Cardboard, flannel, dust, sand, and porous objects retained it longest. Metals, marble, and glass, on the contrary, quickly lost their efficacy. Finally, anything on which the female had rested communicated its virtues by contact; witness the butterflies crowding on the straw-bottomed chair after the twig fell to the ground.

Using one of the most favourable materials—flannel, for example—I witnessed a curious sight. I placed a morsel of flannel on which the mother moth had been lying all the morning at the bottom of a long test-tube or narrow-necked bottle, just permitting of the passage of a male moth. The visitors entered the vessels, struggled, and did not know how to extricate themselves. I had devised a trap by means of which I could exterminate the tribe. Delivering the prisoners, and removing the flannel, which I placed in a perfectly closed box, I found that they re-entered the trap; attracted by the effluvia that the flannel had communicated to the glass.

I was now convinced. To call the moths of the countryside to the wedding-feast, to warn them at a distance and to guide them the nubile female emits an odour of extreme subtlety, imperceptible to our own olfactory sense-organs. Even with their noses touching the moth, none of my household has been able to perceive the faintest odour; not even the youngest, whose sensibility is as yet unvitiated.

This scent readily impregnates any object on which the female rests for any length of time, when this object becomes a centre of attraction as active as the moth herself until the effluvium is evaporated.