A specimen of Polistes carnifex (i.e. the sand-wasp noticed by Mr. Bates) was hunting about for caterpillars in my garden. I found one about an inch long, and held it out towards it on the point of a stick. It seized it immediately, and commenced biting it from head to tail, soon reducing the soft body to a mass of pulp. It rolled up about one-half of it into a ball, and prepared to carry it off. Being at the time amidst a thick mass of a fine-leaved climbing plant, it proceeded, before flying away, to take note of the place where it was leaving the other half. To do this, it hovered in front of it for a few seconds, then took small circles in front of it, then larger ones round the whole plant. I thought it had gone, but it returned again, and had another look at the opening in the dense foliage down which the other half of the caterpillar lay. It then flew away, but must have left its burden for distribution with its comrades at the nest, for it returned in less than two minutes, and making one circle around the bush, descended to the opening, alighted on a leaf, and ran inside. The green remnant of the caterpillar was lying on another leaf inside, but not connected with the one on which the wasp alighted, so that in running in it missed it, and soon got hopelessly lost in the thick foliage. Coming out again, it took another circle, and pounced down on the same spot again, as soon as it came opposite to it. Three small seed-pods, which here grew close together, formed the marks that I had myself taken to note the place, and these the wasp seemed also to have taken as its guide, for it flew directly down to them, and ran inside; but the small leaf on which the fragment of caterpillar lay not being directly connected with any on the outside, it again missed it, and again got far away from the object of its search. It then flew out again, and the same process was repeated again and again. Always when in circling round it came in sight of the seed-pods down it pounced, alighted near them, and recommenced its quest on foot. I was surprised at its perseverance, and thought it would have given up the search; but not so, it returned at least half-a-dozen times, and seemed to get angry, hurrying about with buzzing wings. At last it stumbled across its prey, seized it eagerly, and as there was nothing more to come back for, flew straight off to its nest, without taking any further note of the locality. Such an action is not the result of blind instinct, but of a thinking mind; and it is wonderful to see an insect so differently constructed using a mental process similar to that of man.
Memory.
We may here first allude to an observation of Sir John Lubbock already quoted in another connexion (see [p. 147]). It is here evident that the wasp, after finding the store of honey in the room, and after finding the window closed in the 'wasp-line' direction to its nest, required three repeated lessons from Sir John before she learnt that the window on the other side of the room, and away from the direction of her nest, afforded no obstacle to her exit. Having learnt this, the fourth time she came she again flew to the closed window as before, and then, as if but dimly remembering that there was another opening somewhere that offered no such mysterious resistance to her passage, 'she took two or three turns round the room, and then flew out through the open window.' Having now taken the bearings of all the room upon her own wings, and having again found the difference between the two windows in respect of resistance, although in all other respects so much alike, the next time she came she made in the first instance as it were an experimental flight towards the closed window, but clearly had the alternative of going to the open one in her memory; for on finding the window closed as before, she did not alight, but flew straight from the closed to the open window. The same thing happened once again, but now, with the distinction between the two windows thus fully learnt, and with it the perception that in this case 'the shortest cut was the longest way round,' she never again flew to the closed window; in the forty successive visits which she paid through the remainder of that day, and the hundred visits or so which she made during the two following days, she seems to have uniformly flown to the open window.
As evidence of forgetfulness, it will be enough to refer to the case of another wasp which, under precisely similar circumstances to those just detailed, learnt her way out of the open window one day, having made fifty passages through it in five hours. Yet Sir John remarks,—
It struck me as curious that on the following day this wasp seemed by no means so sure of her way, but over and over again went to the closed window.
It is further of interest to note, as showing the similarity of the memory displayed by these insects with that of the higher animals, that there are considerable individual differences to be found in the degree of its manifestation.
In this respect they certainly differ considerably. Some of the bees which came out of the little postern door (already described) were able to find their way back after it had been shown to them a few times. Others were much more stupid; thus one bee came out on the 9th, 10th, 11th, 12th, 14th, 15th, 16th, 17th, 18th, and 19th, and came to the honey; but though I repeatedly put her back through the postern, she was never able to find her way for herself.
I often found that if bees which were brought to honey did not return at once, still they would do so a day or two afterwards. For instance, on July 11, 1874, a hot thundery day, and when the bees were much out of humour, I brought twelve bees to some honey; only one came back, and that one only twice; but on the following day several of them returned.
This latter observation is important, as proving that bees can remember for at least a whole day the locality where they have found honey only once before, and that they so far think about their past experiences as to return to that locality when foraging.