CHAPTER III.

ANTS.

WITHIN the last ten or twelve years our information on the habits and intelligence of these insects has been so considerably extended, that in here rendering a condensed epitome of our knowledge in this most interesting branch of comparative psychology, it will be found that the chapter is constituted principally of a statement of observations and experiments which have been conducted during the short period named. The observers to whom we are mainly indebted for this large increase of our knowledge are Messrs. Bates, Belt, Müller, Moggridge, Lincecum, MacCook, and Sir John Lubbock. From the fact that these naturalists conducted their observations in different parts of the world and on widely different species of ants, it is not surprising that their results should present many points of difference; for this only shows, as we might have expected, that different species of ants differ considerably in habits and intelligence. Therefore, in now drawing all these numerous observations to a focus, I shall endeavour to show clearly their points of difference as well as their points of agreement; and in order that the facts to be considered may be arranged in some kind of order, I shall deal with them under the following heads :-Powers of special sense; Sense of direction; Powers of memory; Emotions; Powers of communication; Habits general in sundry species; Habits peculiar to certain species; General intelligence of various species.

Powers of Special Sense.

Taking first the sense of sight, Sir John Lubbock maae a number of experiments on the influence of light coloured by passing through various tints of stained glass, with the

following results. The ants which he observed greatly dislike the presence of light within their nests, hurrying about in search of the darkest corners when light is admitted. The experiments showed that the dislike is much greater in the case of some colours than in that of others. Thus under a slip of red glass there were congregated on one occasion 890 ants, under green 544, under yellow 495, and under violet only 5. To our eyes the violet is as opaque as the red, more so than the green, and much more so than the yellow. Yet, as the numbers show, the ants had scarcely any tendency to congregate under it: there were nearly as many under the same area of the uncovered portion of the nest as under that shaded by the violet glass. It is curious that the coloured glasses appear to act on the ants in a graduated series, which corresponds with the order of their influence on a photographic plate. Experiments were therefore made to test whether it might not be the actinic rays that were so particularly distasteful to the ants; but with negative results. Placing violet glass above red produces the same effect as red glass alone. Obviously, therefore, the ants avoid the violet glass because they dislike the rays which it transmits, and do not prefer the other colours because they like the rays which they transmit. Sodium, barium, strontium, and lithium flames were also tried, but not with so much effect as the coloured glass.

It has just been observed that the relative dislike which Sir John Lubbock's ants showed to lights of different colours seems to be determined by the position of the colour in the spectrum-there being a regular gradation of intolerance shown from the red to the violet end. As these ants dislike light, the question suggests itself that the reason of their graduated intolerance to light of different colours may be due to their eyes not being so much affected by the rays of low as by those of high refrangibility. In this connection it would be interesting to ascertain whether ants of the genus Atta show a similarly graduated intolerance to the light in different parts of the spectrum; for both Moggridge and MacCook record of this genus that it not only does not shun the light, but seeks it—coming to

the glass sides of their artificial nests to enjoy the light of a lamp. Possibly, therefore, the scale of preference to lights of different colours would be found in this genus to be the reverse of that which Sir John Lubbock has found in the case of the British species.

As regards hearing, Sir John Lubbock found that sounds of various kinds do not produce any effect upon the insects. Tuning-forks and violin notes, shouting, whistling, &c., were all equally inefficient in producing the slightest influence upon the animals; and experiments with sensitive flames, microphone, telephone, &c., failed to yield any evidence of ants emitting sounds inaudible to human ears.

Lastly, as regards the sense of smell, Sir John Lubbock found that on bringing a camel's-hair brush steeped in various strong scents near where ants were passing, "some went on without taking any notice, but others stopped, and evidently perceiving the smell, turned back. Soon, however, they returned, and passed the scented pencil. After doing this two or three times, they generally took no further notice of the scent. This experiment left no doubt on my mind." In other cases the ants were observed to wave about and throw back their antennæ when the scented pencil was brought near.

That ants track one another by scent was long ago mentioned by Huber, and also that they depend on this sense for their power of finding supplies which have been previously found by other ants. Huber proved their power of tracking a path previously pursued by their friends, by drawing his finger across the trail, so obliterating the scent at that point, and observing that when the ants arrived at that point they became confused and ran about in various directions till they again came upon the trail on the other side of the interrupted space, when they proceeded on their way as before. The more numerous and systematic experiments of Sir John Lubbock have fully corroborated Huber's observations, so far as these points are concerned. Thus, to give only one or two of these experiments; in the accompanying woodcut (Fig. 1, A is the nest, B a board, n f g slips of paper, h and m

A

n

similar slides of glass, on one of which, h, there was placed pupa, while the other, m, was left empty. Sir John Lubbock watched two particular (marked) ants proceeding from A to h and back again, carrying the pupa on h to the nest A. Whenever an ant came out of A upon B he transposed the slips ƒ and g. Therefore at the angle below n there was a choice presented to the ant of taking the unscented pathway leading to the full glass h, or the scented pathway leading to the empty glass m. The two marked ants, knowing their way, always took the right turn at the angle; but the stranger ants, being guided only by scent, for the most part took the wrong turn at the angle, so going to the empty glass m. For out of 150 stranger ants only 21 went to h, while the remaining 129 went to m. Still the fact that all the stranger ants did not follow the erroneous scent-trail to m, may be taken to indicate that they are also assisted in finding treasure by the sense of sight, though in a lesser degree. Therefore Sir John Lubbock concludes that in finding treasure 'they are guided in some cases by sight, while in others they track one another by scent.'

h

Fig. 1.

m

As further evidence showing how much more ants depend upon scent than upon sight in finding their way, the following experiment may be quoted. In the accompanying woodcut (Fig. 2) the line marked 1, 2, 3 represents the edge of a paper bridge leading to the nest; A the top of a pencil which is standing perpendicularly upon a board, represented by the general black surface; B the top of the same pencil when moved a distance of a few inches from its first position A. On the top of this pencil were placed some pupa. Sir John Lubbock, after contriving this arrangement, marked an ant and put it upon the pupæ on the top of the pencil. After she had made two journeys carrying pupæ from the pencil to the nest (the tracks she pursued being represented by the two thick white lines), while she was in the nest he moved the pencil to its position at B. The thir

white line represents the course then pursued by the ant in its endeavours to find the pencil, which was shifted only a few inches from A to B. That is, the ants on their journey to the shifted object travelled very often back

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wards and forwards and round the spot where the coveted object first stood. Then they would retrace their steps towards the nest, wander hither and thither from side to side between the nest and the point A, and only after very repeated efforts around the original site of the larvæ reach, as it were, accidentally the object desired at B.' Therefore the ants were clearly not guided by the sight of the pencil.

The same thing is well shown by another form of experiment. Some food was placed at the point a (Figs. 3 and 4) on a board measuring 20 inches by 12 inches,