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CHAPTER VI.

RECOGNITION OF FRIENDS.

IT has been already shown that with ants, as with bees, while the utmost harmony reigns between those belonging to the same community, all others are enemies. I have already given ample proof that a strange ant is never tolerated in a community. This of course

implies that all the bees or ants of a community have the power of recognising one another, a most surprising fact, when we consider the shortness of their life and their immense numbers. It is calculated that in a single hive there may be as many as 50,000 bees, and in the case of ants the numbers are still greater. In the large communities of Formica pratensis it is probable that there may be as many as from 400,000 to 500,000 ants, and in other cases even these large numbers are exceeded.

If, however, a stranger is put among the ants of another nest, she is at once attacked. On this point I have satisfied myself, as will be seen in the following pages, that the statements of Huber and others are perfectly correct. If, for instance, I introduced a stranger into one of my nests, say of Formica fusca or

Lasius niger, she was at once attacked. One ant would seize her by an antenna, another by a leg, and she was either dragged out of the nest or killed.

Moreover, we have not only to deal with the fact that ants know all their comrades, but that they recognise them even after a lengthened separation.

Huber mentions that some ants which he had kept in captivity having accidentally escaped, 'met and recognised their former companions, fell to mutual caresses with their antennæ, took them up by their mandibles, and led them to their own nests; they came presently in a crowd to seek the fugitives under and about the artificial ant-hill, and even ventured to reach the bell-glass, where they effected a complete desertion by carrying away successively all the ants they found there. In a few days the ruche was depopulated. These ants had remained four months without any communication.' This interesting statement has been very naturally copied by succeeding writers. See, for instance, Kirby and Spence's 'Introduction to Entomology,' vol. ii. p. 66, and Newport, 'Trans. of the Entomological Society of London,' vol. ii. p. 239.

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Forel, indeed, regards the movements observed by Huber as having indicated fear and surprise rather than affection; though he is quite disposed to believe, from his own observations, that ants would recognise one another after a separation of several months.

Huber, p. 172.

The observation recorded by Huber was made casually, and he did not take any steps to test it by subsequent experiments. The fact, however, is of so much importance that I determined to make further observations on the subject. In the first place, I may repeat that I have satisfied myself by many experiments, that ants from one community introduced into another, always be it understood of the same species,―are attacked, and either driven out or killed. It follows, therefore, that as within the nest the most complete harmony prevails-indeed, I have never seen a quarrel between sister ants-they must by some means recognise one another.

When we consider their immense numbers this is sufficiently surprising; but that they should recognise one another, as stated by Huber, after a separation of months, is still more astonishing.

I determined therefore to repeat and extend his observations.

Accordingly, on August 20, 1875, I divided a colony of Myrmica ruginodis, so that one half were in one nest, A, and the other half in another, B, and were kept entirely apart.

On October 3, I put into nest B a stranger and an old companion from nest A. They were marked with a spot of colour. One of them immediately flew at the stranger; of the friend they took no notice.

October 18.-At 10 A.M. I put in a stranger and a

friend from nest A. In the evening the former was killed, the latter was quite at home.

October 19.-I put one in a small bottle with a friend from nest A. They did not show any enmity. I then put in a stranger; and one of them immediately began to fight with her.

October 24.-I again put into the nest a stranger and a friend. The former was attacked, but not the latter. The following day I found the former almost dead, while the friend was all right.

October 31.-I again put a stranger and a friend into the nest. The former was at once attacked; in this case the friend also was, for a moment, seized by the leg, but at once released again. On the following morning the stranger was dead, the friend was all right.

November 7.-Again I put in a stranger and a friend. The former was soon attacked and eventually driven out; of the latter they did not seem to me to take any particular notice. I could see no signs of welcome, no gathering round a returned friend; but, on the other hand, she was not attacked.

Again, I separated one of my colonies of Formica fusca into two halves on August 4, 1875, and kept them entirely apart. From time to time I put specimens from the one half back into the other. The details of this experiment will be found in the Appendix. At first the friends were always amicably received, but after some months' separation they were occasionally

attacked, as if some of the ants, perhaps the young ones, did not recognise them. Still they were never killed, or driven out of the nest, so that evidently when a mistake was made, it was soon recognised. No one who saw the different manner in which these ants and strangers were treated, could have the slightest doubt that the former were recognised as friends and the latter as enemies. The last three were put back on May 14, 1877, that is to say, after a separation of a year and nine months, and yet they were amicably received, and evidently recognised as friends!

These observations were all made on Formica fusca, and it is of course possible that other species would behave in a different manner.

Indeed, in this respect Lasius flavus offers a surprising contrast to F. fusca. I was anxious to see whether the colonies of this species, which are very numerous round my house, were in friendly relations with one another. With this view, I kept a nest of L. flavus for a day or two without food, and then gave them some honey, to which they soon found their way in numbers. I then put in the midst of them an ant of the same species from a neighbouring nest; the others did not attack, but, on the contrary, cleaned her -though, from the attention she excited and the numerous communications which took place between her and them, I am satisfied that they knew she was not one of themselves. After a few minutes she accompanied some of the returning ants to the nest. They