Page:Popular Science Monthly Volume 11.djvu/56

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46
THE POPULAR SCIENCE MONTHLY.

to affect the conclusion. The former nest contains about two hundred, the second about four hundred individuals; but as they are somewhat torpid, and there are no larvæ to be fed, much food is not required. In each case only two or three individuals came out for food, each about twice a day, though some days they did not come out at all. Thinking that possibly these specimens were unusually voracious, or in some other way abnormal, I imprisoned the foragers belonging to one of the nests. The following day two others came out for food, and continued coming for several days. I then imprisoned them also, when two others came out—showing, I think, that the community requires food, and that it was the functions of certain individuals to obtain it.

One of the most interesting problems about ants is, of course, to determine the amount of their intelligence. In order to test this, it seemed to me that one way would be to ascertain some object which they would clearly desire, and then to interpose some obstacle which a little ingenuity would enable them to overcome. With this object in view, I placed food in a porcelain cup on a slip of glass surrounded by water, but accessible to the ants by a bridge, consisting of a strip of paper two-thirds of an inch long and one-third wide. Having then put a F. nigra from one of my nests to this food, she began carrying it off, and by degrees a number of friends came to help her. I then, when about twenty-five ants were so engaged, moved the little paper bridge slightly, so as to leave a chasm just so wide that the ants could not reach across. They came to the edge and tried hard to get over, but it did not occur to them to push the paper bridge, though the distance was only about one-third of an inch, and they might easily have done so. After trying for about a quarter of an hour they gave up the attempt, and returned home. This I repeated several times. Then, thinking that paper was a substance to which they were not accustomed, I tried the same with a bit of straw one inch long and one-eighth of an inch wide. The result was the same. I repeated this twice. Again I placed particles of food close to and directly over the nest, but connected with it only by a passage several feet in length. Under these circumstances it would be obviously a saving of time and labor to drop the food on to the nest, or at any rate to spring down with it, so as to save one journey. But, though I have frequently tried the experiment, my ants never adopted either of these courses. I arranged matters so that the glass on which the food was placed was only raised one third of an inch above the nest. The ants tried to reach down, and the distance was so small that occasionally, if another ant passed underneath just as one was reaching down, the upper one could step on to its back, and so descend; but this only happened accidentally, and they did not think of throwing the particles down, nor, which surprised me very much, would they jump down themselves.