But by far the most satisfactory way of studying the ants is in their native haunts on the barrens, where I had ten nests under observation. One of these was so situated that it received the direct rays of the sun all day, and was protected from north and east winds by dense, low shrubbery. On sunny days, even with a cool wind from the north, when taking my seat in this sheltered spot, I would soon become uncomfortably warm. This hill was always active whenever I visited it, while in other localities the ants would often be all housed. Around this active nest I stuck stems of millet eighteen inches high, surmounted by the close-packed heads. The ants climbed the stems, loosened and secured the seeds, and stored them within the nest. They worked vigorously, sometimes twenty or more on one head pulling away at the seeds. In my artificial formicary they did not mount the stems, even when the heads were not more than three or four inches from the ground, but seeds that I scattered in the jar were always taken below.
I threw down a handful of apple-seeds near the entrance of the active hill on the barrens. This immediately attracted a large number of excited ants. They rushed to the seeds in a warlike attitude, and began carrying them off, depositing them two or three feet away. But as soon as the excitement caused by the sudden pouring down of the seeds had subsided, they seemed to comprehend that they had been throwing away good seeds; and now, changing their tactics, not only carried the remainder into the nest, but finally brought back and stored all those that had been thrown away.
On excavating the nests we found granaries of seed scattered irregularly throughout to the depth of twenty-two inches below the surface of the ground: some were near the surface, and a few sprouted seeds were scattered about in the mound. The mound is usually not more than four to six inches above the level of the ground.
The great majority of nests that I have found are in the low pine barrens—so low that on reaching the depth of two feet the water runs into the cavity like a spring, and stands above some of the granaries. Notwithstanding this wet locality, I found no sprouted seeds in the deeper store-rooms, but only in the warmer mound. On sunny days the larvæ are brought up into the mound and deposited in chambers near the surface, where they receive the benefit of the sun's rays. On cool, cloudy days and in the early morning I found no larvæ near the surface. If the ants are intelligent enough to treat the larvæ in this way, why should they not store seeds where they will not sprout? And when they need to sprout them in order to obtain the sugar they contain, it would take no more wisdom to treat the seed as they do the larvæ—bringing them near the surface to obtain the right degree of heat for the required result.
The little workers seem very determined not to allow any green thing to grow on their mounds. Cassia and croton and many other plants start to grow from seeds which the ants have dropped, but they are always cut down and destroyed if too near the mound, though allowed to grow at a little distance; so that a botanist would be astonished at the great variety of plants within a small area if not aware of the source from which they came. I sometimes found small shrubs of Kalmia hirsuta and Hypericums entirely dead on the mounds, the roots completely girdled in many places. It is very amusing to watch them in their efforts to destroy grass and other plants. Their determined persistence is remarkable: they cut off the tender blades and throw them away. But they do not stop here: the roots must be exterminated; so several dig around the plant, throwing the earth backward, and after making it bare they cut and girdle the roots until the plant is killed.
1. With well-formed teeth.
2. Partially developed.
3. Entirely obsolete.
MANDIBLES OF THE HARVESTING-ANT.
Early in March the ants in the jar seemed to have completed their domicile. At first, several chambers were visible through the glass, and the galleries leading to them, but gradually the light was all shut out by placing little particles of earth against the glass, thus depriving me of the opportunity of watching their movements within the nest. So I now took the jar to the barrens, and set it by the side of a nest which was about a mile distant from where most of the ants were obtained. Here I carefully broke it, and took the thin shell of glass from around the nest, which did not fall, but stood six inches in height and eighteen inches in circumference. With a large knife I removed a thin layer of earth, which revealed three admirable chambers with galleries leading from one to the other. Immediately below there were five chambers well filled with ants, and below these other chambers were scattered irregularly throughout, with only thin partitions between.
1
I use the term "soldier" for the sake of definiteness. The soldier approaches the queen in size, and in many of the specimens the head is larger than that of the queen.
2
Hymenoptera of the British Museum: Formicidæa, p. 170.