INSECTS
cavity in the earth, perhaps two by three feet in diameter and a foot beneath the surface, walled with a thick cement lining; but from this chamber there may extend tunnels upward to the surface, or horizontally to other smaller chambers located at a distance from the central one. The termites that live in these nests subsist principally upon home-grown food, and it is in the great vaulted central chamber that they raise the staple article of their diet. The cavity is filled almost entirely with a porous, spongy mass of living fungus. The fungi as we ordinarily see them are the toadstools and mushrooms, but these fungus forms are merely the fruiting bodies sent up from a part of the plant concealed beneath the ground or in the dead wood; and this hidden part has the form of a network of fine, branching threads, called a mycelium. The mycelium lives on decaying wood, and it is the mycelial part of the fungus that the termites cultivate. They feed on small spore-bearing stalks that sprout from the threads of the mycelium. The substratum of the termite fungus beds is generally made of pellets of partly digested wood pulp.
The nests that termites erect above the ground include the most remarkable architectural structures produced by insects. They are found in South America, Australia, and particularly in Africa. In size they vary from mere turrets a few inches high to great edifices six, twelve, or even twenty feet in altitude. Some are simple mounds (Fig. 86 A), or mere hillocks; others have the form of towers, obelisks, and pyramids (B); still others look like fantastic cathedrals with buttressed walls and tapering spires (Fig. 87); while lastly, the strangest of all resemble huge toadstools with thick cylindrical stalks and broad-brimmed caps (Fig. 86 C). Many of the termites that build mound nests are also fungus-growing species, and one chamber or several chambers in the nest are given over to the fungus culture.
Termite nests built in trees are usually outlying retreats
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