Animal Intelligence - George John Romanes

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the colony from below continued to ascend until reaching the lower bevelled edge of the shelf, at which point the more timid individuals, although unable to see the vase, somehow became aware of trouble, and turned about without further investigation, while the more daring advanced hesitatingly just to the upper edge of the shelf, when, extending their antennæ and stretching their necks, they seemed to peep cautiously over the edge until beholding their suffering companions, when they too turned and followed the others, expressing by their behaviour great excitement and terror. An hour or two later, the path or trail leading from the lower colony to the vase was almost entirely free from ants.

      I killed one or two ants on their path, striking them with my finger, but leaving no visible trace. The effect of this was that as soon as an ant ascending towards the shelf reached the spot where one had been killed, it gave signs immediately of great disturbance, and returned directly at the highest possible speed.

      A curious and invariable feature of their behaviour was that when such an ant, returning in fright, met another approaching, the two would always communicate, but each would pursue its own way, the second ant continuing its journey to the spot where the first had turned about, and then following that example.

      For some days after this there were no ants visible on the wall, either above or below the shelf.

      Then a few ants from the lower colony began to reappear, but instead of visiting the vase which had been the scene of the disaster, they avoided it altogether, and following the lower front edge of the shelf to the tumbler standing near the middle, made their attack upon that. I repeated the same experiment here with precisely the same result. Killing or maiming a few of the ants and leaving their bodies about the base of the tumbler, the others on approaching, and even before arriving at the upper surface of the shelf where their mutilated companions were visible, gave signs of intense emotion, some running away immediately, and others advancing to where they could survey the field and then hastening away precipitately.

      Occasionally an ant would advance towards the tumbler until it found itself among the dead and dying; then it seemed to lose all self-possession, running hither and thither, making wide circuits about the scene of the trouble, stopping at times and elevating the antennæ with a movement suggestive of wringing them in despair, and finally taking flight. After this another interval of several days passed, during which no ants appeared. Now, three months later, the lower colony has been entirely abandoned. Occasionally, however, especially when fresh and fragrant violets have been placed on the shelf, a few 'prospectors' descend from the upper nail-hole, rarely, almost never, approaching the vase from which they were first driven away, but seeking to satisfy their desire at the tumbler. To turn back these stragglers and keep them out of sight for a number of days, sometimes for a fortnight, it is sufficient to kill one or two ants on the trail which they follow descending the wall. This I have recently done as high up as I can reach, three or four feet above the mantel. The moment this spot is reached, an ant turns abruptly and makes for home, and in a little while there is not an ant visible on the wall.

      In a subsequent volume of 'Nature' (viii. p. 244), Mr. Darwin publishes another letter which he received from Mr. Hague upon the same subject. It seems that Mr. Moggridge suggested to Mr. Darwin that, as he and others had observed ants to be repelled by the mere scent of a finger drawn across their path, the observation of Mr. Hague might really resolve itself into a dislike on the part of the ants to cross a line over which a finger had been drawn, and have nothing to do with intelligent terror inspired by the sight of their slaughtered companions. The following is Mr. Hague's reply to Mr. Darwin's request for further experiments to test this point:—

      Acting on Mr. M——'s suggestion, I first tried making simple finger-marks on their path (the mantel is of marble), and found just the results which he describes in his note as observed by himself at Mentone, that is, no marked symptoms of fear, but a dislike to the spot, and an effort to avoid it by going around it, or by turning back and only crossing it again after an interval of time. I then killed several ants on the path, using a smooth stone or piece of ivory, instead of my finger, to crush them. In this case the ants approaching all turned back as before, and with much greater exhibition of fear than when the simple finger-mark was made. This I did repeatedly. The final result was the same as obtained last winter. They persisted in coming for a week or two, during which I continued to kill them, and then they disappeared, and we have seen none since. It would appear from this that while the taint of the hand is sufficient to turn them back, the killing of their fellows with a stone or other material produces the effect described in my first note. This was made clear to me at that time, from the behaviour of the ants the first day I killed any, for on that occasion some of them approaching the vase from below, on reaching the upper edge of the mantel, peeped over, and drew back on seeing what had happened about the vase, then turned away a little, and after a moment tried again at another and another point along the edge, with the same result in the end. Moreover, those that found themselves among the dead and dying went from one writhing ant to another in great haste and excitement, exhibiting the signs of fright which I described.

      I hardly hope that any will return again, but if they do, and give me an opportunity, I shall endeavour to act further on Mr. M——'s suggestion.

      With this quotation I shall conclude the present division of the chapter; for, looking to all the other observations previously mentioned, there can be no question concerning the general fact that ants have the power of communicating with one another. And under subsequent headings abundant additional evidence on this point will be found implicated with the other facts detailed.

       Table of Contents

      Swarming.—The precise facts with regard to the swarming of ants are not yet certainly established. As regards some of the facts, however, there is no doubt. The winged males and females first quit the nest in enormous numbers, and choose some fine afternoon in July or August for their wedding flight. The entrances to the nest are widened by the workers and increased in number, and there is a great commotion on the surface of the nest. The swarm takes place as a thick cloud of all the male and female insects, rising together to a considerable height. The flight continues for several hours, usually circling round some tree or tower, and it is during the flight that fertilisation is effected. After it is effected, the swarm returns to the ground, when the males perish, either from falling a prey, in their shelterless condition, to birds or spiders, or, on account of not being able to feed themselves, from starvation. 'The workers, or neuter ants, of their own colony have lost all interest in them from the moment of their return, and trouble themselves no more about them, for they well know that the males have now fulfilled their vocation.' The great majority of the fertilised females share the same fate as the males. But a small proportion find concealment in holes, which they either dig for themselves, or happen to find ready made, and there found a new colony. The first thing they do is to pull off their now useless wings, by scratching and twisting them, one after the other, with the clawed ends of their feet. They then lay their eggs, and become the queens of new colonies.

      Forel says that no fertilised female ever returns to her original home; but that the workers keep back a certain number of females which are fertilised before the swarming takes place; in this case the workers pull off the wings of the fertilised females. The majority of observers, however, maintain that some of the females composing the swarm return to their native home to become mothers where they had been children. Probably both statements are correct. A writer in the 'Groniger Deekblad' for June 16, 1877, observes that, looking to the injurious effects of in-breeding, the facts as related by Forel are less probable than those related by other observers, and that, if they actually occur, the females fertilised before flight are probably kept by the ants as a sort of 'reserve corps to which the workers resort only in case of need, and if they fail to secure any returning queens.'

      Nursing.—The eggs will not develop into larvæ unless nursed. The nursing is effected by licking the surface of the eggs, which under the influence of this process increase in size, or grow. In about a fortnight, during which time the workers carry the eggs from higher to lower levels of the

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