Life among the ants

The works of Pliny and other ancient writers contain references to ants which collected great stores of seeds, and these accounts were quoted by numerous mediaeval authors. Modern students of ants, however, worked mostly in northern and central Europe, and as they did not find any of these harvesting ants they were rather inclined to dismiss the classic stories as fiction pure and simple, and class the seed-gathering ants with the unicorn and the mermaid.

In 1829, however, one W. H. Sykes, an Englishman located in India, reported that certain ants near his station not only collected great quantities of grass seed, but after a heavy rain could always be seen bringing their cereal out of the underground granaries to dry it in the sun. These observations went far to vindicate the ancient naturalists, and the work of J. T. Moggridge, in 1873, completed the vindication. Moggridge watched the workers bring in the seeds, bite off the germinating part to prevent the seeds from sprouting, and store them in the nests, which often contain a pint or so of grain. By examination of these hoards he identified as many as eighteen different families of plants represented in a single nest. Despite the efforts to prevent germination by biting off the radicles (a fact noted by Pliny some sixteen hundred years before) many of the seeds do sprout, and thus the harvesting ants play a part in the distribution of plants. Of this subject Moggridge says: “As the ants often travel some distance from their nest in search of food, they may certainly be said to be, in a limited sense, agents in the dispersal of seeds, for they not infrequently drop seeds by the way, which they fail to find again, and often also among the refuse matter which forms the kitchen hidden in front of their entrances, a few sound seeds are often present, and these in many instances grow up and form a little colony of strange plants. This presence of seedlings foreign to the wild grounds in which the nest is usually placed, is quite a feature where there are old established colonies of Atta barbara, where young plants of fumitory, chickweed, cranesbill, Arabis thaleana, etc., may be seen on or near the rubbish heap.... One can imagine cases in which the ants during the lapse of long periods of time might pass the seeds of plants from colony to colony, until after a journey of many stages, the descendants of the ant-borne seedlings might find themselves transported to places far removed from the original home of their immediate ancestors.”

There are many species of harvester ants in America; one of the most interesting is Solenopsis geminata, popularly known as the fire-ant because of its readiness to use its painful sting. Although the fire-ant certainly stores up seeds, often to the extent of damaging crops of soft fruits like strawberries, it will also eat insects, or almost anything else that it can get. The nests are usually found beneath flat stones, and in some localities are so common and so populous that Wheeler refers to the fire-ant as being “in possession of a large portion of the soil of the American tropics.” In Louisiana and other southern states these ants nest along the shores of lagoons and bayous; when the floods come and the nest is submerged the workers cling together in a ball as much as eight inches in diameter, with the brood in the center. This ball floats in the water, the ants constantly shifting about so that very few are drowned, and very little brood lost, until they are able to effect a landing.

The so-called Texas harvester (Pogonomyrmex molefaciens) has become famous because a man named Lincecum, about 1862, published a paper in which he claimed that this ant actually plants seeds in the ground, weeds and cultivates its fields all summer, gathers the crop, dries it in the sun, and finally stores it away in subterranian granaries. This story was accepted and promulgated by Charles Darwin, and so was believed in many quarters. It seems to rest solely upon the fact that ant-rice (Aristida) is usually found growing about the nest, although it may occur nowhere else in the immediate vicinity. “Four years of nearly continuous observation,” writes Wheeler, “enable me to suggest the probable source of Lincecum’s misconception. If the nests of this ant can be studied during the cool winter months—and this is the only time to study them leisurely, as the cold subdues the fiery stings of their inhabitants—the seeds, which the ants have garnered in many of their chambers will often be found to have sprouted. Sometimes, in fact, the chambers are literally stuffed with dense wads of seedling grasses and other plants. On sunny days the ants may often be seen removing these seeds when they have sprouted too far to be fit for food and carrying them to the refuse heap, which is always at the periphery of the crater or cleared earthen disk. Here the seeds, thus rejected as inedible, often take root and in the spring form an arc or a complete circle of growing plants around the nest. Since the Pogonomyrmex feeds largely, though by no means exclusively, on grass seeds, and since, moreover, the seeds of Aristida are a very common and favorite article of food, it is easy to see why this grass should predominate in the circle. In reality however, only a small percentage of the nests, and only those situated in grassy localities, present such circles. Now to state that molefaciens, like a provident farmer, sows this cereal and guards and weeds it for the sake of garnering its grain, is as absurd as to say that the family cook is planting and maintaining an orchard when some of the peach stones, which she has carelessly thrown into the backyard with the other kitchen refuse, chance to grow into peach trees.”

Wheeler has also observed the mating flight of the Texas harvester, and his graphic description is worth setting down in its entirety: “During three successive years (1901-1903) at Austin, Texas, the nuptial flight of molefaciens took place on one of the last days of June (28 and 29) or the first in July. On one of these occasions (July 4, 1903) the flight was of exceptional magnitude and beauty. A few days previous the country had been deluged with heavy rains, but Independence Day was clear and sunny, the mesquite trees were in full bloom and the air resounded with the hum of insects. For several days I had seen a few males and winged females stealthily creep out of the nest entrance as if for an airing, but hurry back at the slightest alarm. From 1:30 to 3 o’clock, however, on the afternoon of July 4, all the numerous colonies I could visit during a long walk west of the town, gave forth their males and females as by a common impulse. The number issuing from a single large nest was often sufficient to have filled a half liter measure. Soon every mound and disk was covered with the bright red females and darker males, intermingled with workers, many of whom kept on bringing seeds and dead insects into the nest as unconcernedly as if nothing unusual were happening. The males and females, quivering with excitement, mounted the stones or pebbles of the nest or hurriedly climbed onto the surrounding leaves and grass and rocked to and fro in the breeze. Then, raising themselves on their feet and spreading their opalescent wings, they mounted obliquely one by one into the air. I could follow them only for a distance of ten or twenty meters when their rapidly diminishing bodies melted away against the brilliant cloudless sky. Many pairs, hesitating to take flight, chased one another about on the surface of the nest. The amorous males seized many of the females before they could leave the ground. Lizards crept forth in great numbers and gulped down quantities of the fat females, while others were borne off into the air by large robber flies (Asilidae). By a little after three o’clock the males and females had left the nest and only the workers were seen pursuing the quiet routine business of bringing in seeds.”