The nests of some species of Formica are six feet in diameter and contain many thousand individuals. Ants also build nests of clay or mud and inhabit hollow trees. Ants in Europe build true mounds, sometimes three feet high, but in North America they are mostly subterranean, though in Wisconsin one ant (F. obscuripes) erects a true mound about 20 inches high.
Formica sanguinea is one of our most abundant species, making hillocks of sand or clay, according to the nature of the ground.
From the formicary walks and underground galleries radiate in a labyrinth in all directions; and deep down, where the soil is perpetually moist, the galleries descend to a relatively greater depth than in Europe. Packard has found a variety of this species in Labrador, where it is common. It does not throw up hillocks, but tunnels in the earth. The nest of (Ecophylla smaragdina is formed by drawing together a number of green leaves, which are united with a fine web. Some nests are a foot in diameter. This species swarms in hilly for ests in New Guinea. Its sting is not very se vere.
It is in argillaceous countries especially that the CEcodomas build their enormous for micaries, so that one perceives them from afar by the projection which they form above the level of the soil, as well as by the absence of vegetation in their immediate neighborhood, These nests occupy a surface of many square metres and their depth varies from one to two metres. Very many openings, of a diameter of about one to three inches, are contrived from the exterior and conduct to the inner cavities which serve as storehouses for the eggs and larva. The central part of the nest forms a sort of funnel, designed for the drain age of water, from which, in a country where the rains are often abundant, they could hardly escape without being entirely submerged if the did not provide some outlet for it.
The ant)) myth has been ex ploded by Wheeler, who shows that these ants do not plant grass seeds or "ant-rice' for a harvest. It is probable that Lincecum's error was due to the fact that the sprouted seeds stored up and then cast away as inedible take root and thus form a partial circle of tall grass around the nest.
Mushroom Gardens.— Moller has de scribed what he calls "mushroom gardens" made by several South American species of Attu. The ants cut and bring the large pieces of leaves into their cellars, then cut them into smaller fragments and finally comminute these still further till they form a flocculent greenish-brown pulp. This pulp is heaped up and soon becomes invaded by the mycelium of a fungus (Rozites gongylophora). The mycelium is kept aseptically clean— that is, free from all other species of fungi and even from bacteria — and induced to grow in an abnormal way by bringing forth minute swell ings which constitute the only food of the ant colony. Moller likens these swellings to the
kohlrabi of the German kitchen gardens.
Forel has studied the habits of two other species (Alta cephalotes and A. sexclens) in Colombia, in relation to this process Of col lecting and comminuting the leaves and in cultivating the mushroom. He has found that the largest workers (soldiers) triturate the leaves and defend the nest. They draw blood when they fight. The indigenes are said to use these insects for closing wounds. They in duce them to bite the two lips of the wound and thereupon sever the bodies from the heads, which then serve as a suture. The medium sized workers cut the leaves from the trees, while in the nest the workers of the minim caste are forever clipping the threads of the mycelium of the Rozites, which then develops the kohlrabi on which the ants feed.
Wheeler excavated a large nest of leaf cutting ants (Attu fervent) in a piece 'of • wood land in Texas. The large burrows, nearly an inch in diameter, were found' to extend down to a depth of from three to five feet, and open into large chambers, of which were fully 10 inches across and- five to eight inches high. A of these chambers were traversed by the roots of a large cedar, in the- shade of which the ants had dug their formicary. Mushroom gardens were found heaped upon the floor,. or, more rarely, enveloping, as aerial or Mangling') gardens, the roots that extended across the chambers. .
The shape of a mushroom garden is that of a discoidal sponge. On its upper surface the ants0..e up the -flocculent vegetable &brig, thrm in all directions with fungus hynhse, in the form of thin, vertical, anastomosmg plates, so that as much surface as possible is exposed to the atmosphere of -the chamber. This at mosphere must contain a great amount of car+ bon-dioxide and a very small amount of oxy gen. The ants leave several tubular or funnel shaped openings, varying in diameter, and ex tending down into some -chambers excavated in the base of the vegetable mass. In these chain+ hers lives the huge queen of the colony (an insect nearly an inch long), the newly-fledged males and virgin queens, together with the lar vae, pupa: and attendant ants. The whole mush: room garden swarms with workers representing all the different castes -so. characteristic of the genus Alto. The big-headed soldiers stalk about slowly over the surface of the comb, descending from time to time into the -interior, as if to make sure that the great 'family is properly • at tending to its multifarious occupations, while thousands of minims keep moving about through the meshes of the mycelium, weeding the garden.