Is this unknown sense localized in a particular part of the Wasp and the Bee? Is it exercised by means of a special organ? We immediately think of the antennae. The antennae are what we always fall back upon when the insect's actions are not quite clear to us; we gladly put down to them whatever is most necessary to our arguments. For that matter, I had plenty of fairly good reasons for suspecting them of containing the sense of direction. When the Hairy Ammophila (A Sand-wasp who hunts the Grey Worm, or Caterpillar of the Turnip-moth, to serve as food for her grubs. For other varieties of the Ammophila, cf. "Insect Life": chapter 15.—Translator's Note.) is searching for the Grey Worm, it is with her antennae, those tiny fingers continually fumbling at the soil, that she seems to recognize the presence of the underground prey. Could not those inquisitive filaments, which seem to guide the insect when hunting, also guide it when travelling? This remained to be seen; and I did see.
I took some Mason-bees and amputated their antennae with the scissors, as closely as I could. These maimed ones were then carried to a distance and released. They returned to the nest with as little difficulty as the others. I once experimented in the same way with the largest of our Cerceres (Cerceris tuberculata) (Another Hunting Wasp, who feeds her young on Weevils. Cf. "Insect Life": chapters 4 and 5.—Translator's Note.); and the Weevil-huntress returned to her galleries. This rids us of one hypothesis: the sense of direction is not exercised by the antennae. Then where is its seat? I do not know.
What I do know is that the Mason-bees without antennae, though they go back to the cells, do not resume work. They persist in flying in front of their masonry, they alight on the clay cup, they perch on the rim of the cell and there, seemingly pensive and forlorn, stand for a long time contemplating the work which will never be finished; they go off, they come back, they drive away any importunate neighbour, but they fetch and carry no more honey or mortar. The next day, they do not appear. Deprived of her tools, the worker loses all heart in her task. When the Mason-bee is building, the antennae are constantly feeling, fumbling and exploring, superintending, as it were, the finishing touches given to the work. They are her instruments of precision; they represent the builder's compasses, square, level and plumb-line.
Hitherto my experiments have been confined to the females, who are much more faithful to the nest by virtue of their maternal responsibilities. What would the males do if they were taken from home? I have no great confidence in these swains who, for a few days, form a tumultuous throng outside the nests, wait for the females to emerge, quarrel for their possession, amid endless brawls, and then disappear when the works are in full swing. What care they, I ask myself, about returning to the natal nest rather than settling elsewhere, provided that they find some recipient for their amatory declarations? I was mistaken: the males do return to the nest. It is true that, in view of their lack of strength, I did not subject them to a long journey: about half a mile or so. Nevertheless, this represented to them a distant expedition, an unknown country; for I do not see them go on long excursions. By day, they visit the nests or the flowers in the garden; at night, they take refuge in the old galleries or in the interstices of the stone-heaps in the harmas.
The same nests are frequented by two Osmia-bees (Osmia tricornis and Osmia Latreillii), who build their cells in the galleries left at their disposal by the Chalicodomae. The most numerous is the first, the Three-horned Osmia. It was a splendid opportunity to try and discover to what extent the sense of direction may be regarded as general in the Bees and Wasps; and I took advantage of it. Well, the Osmiae (Osmia tricornis), both male and female, can find their way back to the nest. My experiments were made very quickly, with small numbers and over short distances; but the results agreed so closely with the others that I was convinced. All told, the return to the nest, including my earlier attempts, was verified in the case of four species: the Chalicodoma of the Sheds, the Chalicodoma of the Walls, the Three-horned Osmia and the Great or Warted Cerceris (Cerceris tuberculata). ("Insect Life": chapter 19.—Translator's Note.) Shall I generalize without reserve and allow all the Hymenoptera (The Hymenoptera are an order of insects having four membranous wings and include the Bees, Wasps, Ants, Saw-flies and Ichneumon-flies.—Translator's Note.) this faculty of finding their way in unknown country? I shall do nothing of the kind; for here, to my knowledge, is a contradictory and very significant result.
Among the treasures of my harmas-laboratory, I place in the first rank an Ant-hill of Polyergus rufescens, the celebrated Red Ant, the slave-hunting Amazon. Unable to rear her family, incapable of seeking her food, of taking it even when it is within her reach, she needs servants who feed her and undertake the duties of housekeeping. The Red Ants make a practice of stealing children to wait on the community. They ransack the neighbouring Ant-hills, the home of a different species; they carry away nymphs, which soon attain maturity in the strange house and become willing and industrious servants.
When the hot weather of June and July sets in, I often see the Amazons leave their barracks of an afternoon and start on an expedition. The column measures five or six yards in length. If nothing worthy of attention be met upon the road, the ranks are fairly well maintained; but, at the first suspicion of an Ant-hill, the vanguard halts and deploys in a swarming throng, which is increased by the others as they come up hurriedly. Scouts are sent out; the Amazons recognize that they are on a wrong track; and the column forms again. It resumes its march, crosses the garden-paths, disappears from sight in the grass, reappears farther on, threads its way through the heaps of dead leaves, comes out again and continues its search. At last, a nest of Black Ants is discovered. The Red Ants hasten down to the dormitories where the nymphs lie and soon emerge with their booty. Then we have, at the gates of the underground city, a bewildering scrimmage between the defending blacks and the attacking reds. The struggle is too unequal to remain indecisive. Victory falls to the reds, who race back to their abode, each with her prize, a swaddled nymph, dangling from her mandibles. The reader who is not acquainted with these slave-raiding habits would be greatly interested in the story of the Amazons. I relinquish it, with much regret: it would take us too far from our subject, namely, the return to the nest.
The distance covered by the nymph-stealing column varies: it all depends on whether Black Ants are plentiful in the neighbourhood. At times, ten or twenty yards suffice; at others, it requires fifty, a hundred or more. I once saw the expedition go beyond the garden. The Amazons scaled the surrounding wall, which was thirteen feet high at that point, climbed over it and went on a little farther, into a cornfield. As for the route taken, this is a matter of indifference to the marching column. Bare ground, thick grass, a heap of dead leaves or stones, brickwork, a clump of shrubs: all are crossed without any marked preference for one sort of road rather than another.
What is rigidly fixed is the path home, which follows the outward track in all its windings and all its crossings, however difficult. Laden with their plunder, the Red Ants return to the nest by the same road, often an exceedingly complicated one, which the exigencies of the chase compelled them to take originally. They repass each spot which they passed at first; and this is to them a matter of such imperative necessity that no additional fatigue nor even the gravest danger can make them alter the track.
Let us suppose that they have crossed a thick heap of dead leaves, representing to them a path beset with yawning gulfs, where every moment some one falls, where many are exhausted as they struggle out of the hollows and reach the heights by means of swaying bridges, emerging at last from the labyrinth of lanes. No matter: on their return, they will not fail, though weighed down with their burden, once more to struggle through that weary maze. To avoid all this fatigue, they would have but to swerve slightly from the original path, for the good, smooth road is there, hardly a step away. This little deviation never occurs to them.