I therefore took nine females from the colony whence I had got them in the morning; three of these had been already experimented upon. Again they were conveyed in a dark box—each imprisoned in a paper twist. The starting-place was to be the neighbouring town of Carpentras, about three kilometres from the burrows. I meant to release them not amid fields as before, but in a street in the midst of a populous quarter, where the Cerceris, with their rustic habits, had assuredly never penetrated. As the hour was late I put off the experiment, and my captives spent the night in their prison cells.
The next morning, towards eight o’clock, I marked them with a double white spot on the thorax to distinguish them from those of the evening before, which had only one, and set them free successively in the middle of the street. Each mounted vertically, as if to get as soon as possible from between the houses and gain a wide horizon, then rising above the roofs, instantly and energetically turned its flight south. And it was from the south that I brought them into the town, and their burrows are south. Nine times with my nine prisoners did I obtain this striking result—that an insect quite beyond its bearings should not hesitate a moment what direction to take to regain its nest.
Some hours later I too was at the burrows. I saw several of my yesterday’s Cerceris with a white dot, but none of the last set free. Had they been [[261]]unable to find the way back? Were they out hunting, or in their galleries recovering from the excitement of such a trial? I do not know. The next morning I came again, and had the satisfaction of finding at work, as active as if nothing extraordinary had happened to them, five Cerceris with two white dots. Three kilometres of distance,—the town with its houses, roofs, and smoky chimneys—all so novel to my rustic Cerceris,—had proved no obstacle to their return home.
Taken from its brood and carried an enormous distance, the pigeon returns promptly to its dovecote. If one were to consider the length of journey in proportion to the size of the animal, how superior to the pigeon is the Cerceris carried away three kilometres and returning to its burrow! The size of the insect does not equal a cubic centimetre, while that of the pigeon must quite equal the cube of a decimetre, if it does not exceed it. The bird, a thousand times larger than the Hymenopteron, ought, in order to rival it, to find its dovecote at a distance of 3000 kilometres—thrice the greatest length of France from north to south. I do not know if a carrier-pigeon has ever shown such prowess, but wing-power and yet more lucidity of instinct cannot be measured by yards. Nor can we here consider the question of size, and one can only see in the insect a worthy rival to the bird without deciding which has the advantage.
Are the two guided by memory when placed by man beyond their bearings and carried to great distances—into regions with which they are unacquainted and in unknown directions? Is memory [[262]]as quick when, having reached a certain height at which they can in some sort take their bearings, they launch themselves with all their power of wing towards that part of the horizon where are their nests? Is it memory which traces their aerial way across regions seen for the first time? Evidently not. It is not possible to recollect the unknown. The Hymenopteron and the bird know nothing of their surroundings; nothing can have taught them the general direction which they followed when carried thither, for it was in the darkness of a closed box that the journey was made. Locality, orientation,—all is unknown, and yet they find their way. They have then as guide something better than simple memory—a special faculty, a kind of topographic consciousness of which we can form no idea, possessing nothing analogous to it.
I am now about to establish experimentally how subtle and precise is this faculty in the narrow cycle where it is applied, and also how limited and obtuse when it has to move out of habitual conditions. Such is the invariable antithesis of instinct.
A Bembex, actively engaged in feeding her larva, has left her burrow. She will return immediately with the product of the chase. The entrance is carefully stopped with sand—swept backward by the insect before departing. Nothing distinguishes it from the rest of the sandy surface. But this offers no difficulty to the Hymenopteron, who finds her doorway again with a sagacity which I have already described. Let us plan some treachery; let us perplex her by altering the state of the place. I cover the entrance with a flat stone as large as [[263]]my hand. She soon returns. The complete change made upon her threshold during her absence does not seem to cause her the slightest hesitation; at all events she alights immediately upon the stone, and tries for an instant to hollow it, not at a chance spot, but exactly over the opening of her burrow. Quickly turned aside from this attempt by the hardness of the obstacle, she traverses the stone in every direction, goes round it, slips underneath, and begins to dig in the precise direction of her dwelling.
The flat stone is too trifling an obstacle to disconcert the clever fly; let us find something better. I did not allow the Bembex to continue her excavation, which I saw would soon prove successful, and drove her far off with my handkerchief. The absence of the frightened insect for a considerable time allowed me to prepare my snares leisurely. What materials must now be employed? In these improvised experiments one must know how to turn all things to profit. Not far off on the high road is the fresh dropping of a beast of burden; here is wood for our arrow. The dropping was collected, crushed, and spread in a layer at least an inch thick on the threshold of the burrow and its surroundings over more than a quarter of a yard. Assuredly here was such a façade as never Bembex knew. Colour, the nature of the material, the effluvium,—all combined to deceive the Hymenopteron. Can she take this stretch of manure—this dung—for the front of the dwelling? She does! Here she comes; studying from above the unusual condition of the place, and settling in the middle of the layer, just opposite the entrance, routing about, making a way [[264]]through the fibrous mass, and penetrating to the sand, she promptly discovers the mouth of the passage. I stop and drive her away a second time.
Is not the precision with which the Bembex settles before her dwelling, though masked in a way so novel, a proof that sight and memory are not in such a case the only guides? What further can there be? Smell, perhaps. That is very doubtful, for the emanations from the dung could not baffle the perspicacity of the insect. Nevertheless, let us try another odour. I happen to have with me, as part of my entomological outfit, a little phial of ether. The covering of manure is swept off and replaced by a cushion of moss, not very thick, but covering a wide surface, on which I pour the contents of my phial the moment I see the Bembex coming. The over-strong emanations keep her off, but only for an instant. She alights on the moss, still reeking of ether, traverses the obstacle and penetrates to her dwelling. The etherised effluvia did not disturb her any more than did those of the manure; something surer than smell tells where her nest is.
The antennæ have been often suggested as the seat of a special sense to guide insects. I have already shown how the suppression of these organs appears to offer no obstacle to the researches of the Hymenoptera. Let us try once more in wider conditions. The Bembex is caught, its antennæ amputated to the roots, and is then released. Stung by the pain—wild with terror at being held between my fingers—the insect flies off swifter than an arrow. I had to wait a whole hour, uncertain as to its [[265]]return. However, it came, and with its invariable precision alighted quite close to its doorway, whose look I had changed for the fourth time, having covered the site with a large mosaic of pebbles the size of a nut. My work, which, compared to the Bembex, surpassed what for us are the Megalithic monuments of Brittany, or the lines of Menhirs at Carnac, was powerless to deceive the mutilated insect. Though deprived of antennæ it found the entrance in the midst of my mosaic as easily as would have done an insect under other conditions. This time I let the faithful mother go home in peace.