Popular Science Monthly/Volume 48/April 1896/The Ways and Means of Ants
By NORMAN ROBINSON.
A FEW days since I witnessed an engineering feat on the part of a company of ants that interested me greatly. A Florida chameleon (Anolis principalis) had wandered into my laboratory and taken refuge under a newspaper which was lying in a chair. Some one had evidently occupied the chair without taking up the paper, with the result, of course, of crushing out the life, of the unfortunate little anolis. Having occasion to use the chair, I removed the paper, and discovered the flattened-out body of the little lizard, around which a company of ants were evidently holding a consultation as to the best method of utilizing the game thus accidentally provided for them.
The particular species of emmet that was thus engaged I am not able to identify. Our Florida ants have not been very carefully studied, and I think it quite possible that this is an undescribed species. Popularly he is known here as the "racehorse" ant, and the name is certainly appropriate. Of all the fast and fussy little runabouts that his omnipresent family affords, he is far and away the supreme. It would be hard to find even among the marvels of the insect kingdom any such concentrated bundle of nerves and muscles and brains. He is a little black mite of a fellow, three millimetres (about an eighth of an inch) in length, and it takes one hundred and sixty-two of him to weigh one grain. His ordinary walk is a fast trot, but when he really gets down to business even that kangaroo among insects, the flea, can not beat him in getting over the ground or being in a dozen places apparently at the same moment. Naturally he is a terrible nuisance to housekeepers; borax, corrosive sublimate, Cayenne pepper, and all the other warranted prophylactics against the plague of ants simply amuse him. Not long since I tried all the devices I had ever heard of, and which do often prove effective with other species of ants, in a vain effort to keep this active little rogue out of a new barrel of sugar. A strong solution of corrosive sublimate was poured in a circle on the floor around the barrel. He simply waited for the floor to get dry and calmly trotted over to the alluring barrel of sweets. Three hours after trying this "poison guard" I found a colony of a hundred or so comfortably regaling themselves upon the coveted treasure. Caustic potash dissolved and used in the same way served a little better purpose, but this soon solidified into a carbonate, and its usefulness was at an end. I next procured some freshly ground and pure Cayenne pepper, which some "scientific" newspaper correspondent had recommended as an infallible protection against these little pests. "They can not possibly walk over it," this sapient scientist declared. I spread it in liberal measure around the barrel, but, alas! for newspaper science; it is a positive fact that before I had finished my circling wall of Cayenne pepper these little black imps were racing over it by hundreds. I gave it up. There was nothing to do but to build a low table, put the legs in cans of kerosene oil, and keep on it the barrel of sugar and all other provisions that I wished to protect against these cunning little marauders. Since then I have had no further trouble with them, save in one or two instances where the kerosene was allowed to evaporate. So far as I know, this particular species of ant is rarely found—at least, gives no trouble—here in the country. It seems to be especially partial to "city life."
But to return to the ant conference over the dead body of the anolis. When I first saw them, a hundred or so of these little "racehorse" ants were scampering about in the most fussy and excited way. Two little fellows would meet, cross antennae, and start otf at a lightning pace, to repeat the performance with the next one they met. No doubt they had some plan and were really talking over the matter; but apparently it was just an indistinguishable jumble of black imps racing up and down without rhyme or reason. After watching for a moment this curiously involved but seemingly aimless dance, I left to attend to other matters. Returning in the course of half an hour, I saw to my surprise that the dead chameleon had apparently come to life, and was crawling over the edge of th.e chair seat. A little closer inspection, however, showed that the revival was only apparent, and that these little Sandows were actually dragging off the dead body of the anolis. This was so astonishing that I naturally gave the matter a little closer attention. It was very much as though a score of men should be caught picking up a big church and walking off with it, or half a dozen fishermen should shoulder a whale and carry it to market!
In order to estimate as nearly as possible what these ants were really doing, I placed the body of the dead lizard on the scale pan of a Becker analytical balance, and found that it weighed eight hundred and ninety-six milligrammes. Ten of the ants weighed exactly four milligrammes and a half. This, of course, gave a weight of nine twentieths of a milligramme for each ant. Thus it will be seen that these little insect Samsons were actually draging off an animal almost two thousand times as large as themselves (exactly nineteen hundred and ninety-one times)!
How did they do it? To test the matter, I placed the dead anolis back in the wooden chair seat where I first found him. Watch in hand, I awaited events. Not an ant was in sight. One minute passed, nearly two, when a solitary scout made his appearance, and, by a series of little hesitating, jerky, zigzag trots, made his way up within about an inch of the chameleon. Either by sight or smell, or in some other way, this ant evidently recognized the lost treasure. Without a second's delay he turned sharply about and ran down the chair leg and disappeared somewhere under the matting with which the floor was covered. In a little less than a minute four ants made their appearance on the scene and carefully reconnoitred the field; this time two of them came and felt the body of the anolis, executed a few little zigzag trots, touched antennæ, and started back again for the chair leg. By this time a dozen or more had climbed on to the chair seat and were running about the dead body. Any further attempt to keep watch of individual ants was of course abandoned. Most of them did not go near the object of their gathering, but simply ran back and forth over the chair bottom in seemingly the most aimless way. After ten minutes had passed, and probably a hundred more or less of the little fellows were assembled and plenty were coming, they began to gather around the body, first four or five, then ten, twenty, thirty. There appeared to be no captain or leader, and seemingly very little concert of action. Those that came up would give a little tug, and then away possibly to some other part of the body, or may be to scamper over the chair bottom among the crowd of apparent idlers. I found it very difficult to count those that were at any moment pulling or pushing—both were evidently being done as they worked from either side—but as near as I could count, forty ants were the most that at any one time were tugging at this, to them, relatively enormous load. After trying various points with very little success, they finally gathered, about thirty of them, at the tail. This they readily swung around. They had at last "got the hang of it." Perhaps I imagined it, but it seemed to me I could see the added enthusiasm with which they now tugged away at their burden. Then the tail moved faster, then the head was pulled and pushed forward; and so, by swinging first one end and then the other, the, to them, gigantic mass was moved steadily toward the edge of the chair. I think here is a clear case of thought, afterthought, contrivance, the abandonment of one plan that proved a failure and the adoption of another that proved a success. They tried at first to move the whole weight, and found it too much for them; they then tried swinging it around one end at a time, and succeeded. What human engineering skill without tools could have done better?
One curious fact that I observed was that these ants do not fancy steady work. Most of them would come up and give a little push or pull and scamper off to join the crowd that was racing about on all sides. Occasionally one would tug away for two or three seconds. This seemed about the extreme limit of their endurance. Possibly the muscular activity they exhibited was too intense for prolonged exertion.
And now let us make a little calculation as to the amount of force that each ant must have exerted. As before stated, here was a company of them dragging over a wooden chair seat a weight nineteen hundred and ninety-one times that of each individual engaged in the task! Supposing that forty ants were at one time at work (which is the largest number that I could count), and that the force exerted was evenly distributed (which in point of fact could not have been the case), each ant must have done at least one fortieth of the work. In other words, each of these tiny workmen was dragging or pushing forward nearly fifty times his own weight (exactly 49·75). A man of medium build weighs, we will say, one hundred and fifty pounds. Fifty times this is seven thousand five hundred pounds, or three tons and three quarters. So that even Sandow in relative strength is a long way inferior to these curious little "racehorse" ants.