This would seem like constant activity, too strenuous even for the constitution of an army ant. Actually the individual workers probably get plenty of rest. Each colony is divided into two units—the raiders and those that constitute the structural unit. The walls of the “headquarters” are made up of the bodies of the latter. These “living brick” do nothing throughout the day. They may be asleep. When the raiders return at dusk the structural unit breaks up and the members lead the migration to a new bivouac. The erstwhile raiders follow leisurely in the rear and in turn become the structural unit when a stopping place is selected. When to rest? When to raid? There apparently is an irresistible war rhythm, like the rhythm of the tides, in the basic constitution of these ants. Some have postulated the same sort of thing, on a lesser scale, in man who goes to war every so often but camouflages the war tide with economic or political explanations. These ants are remarkable not only as warriors but as architects. They build complex, air-conditioned, hanging houses out of thousands of their own suspended bodies. Within these structures the queen is sheltered, eggs laid, young hatched and reared. Much of the time the “houses” are constructed anew each night. This home-building behavior is unique in nature, as Dr. T. C. Schneirla of the American Museum of Natural History has pointed out: “Without any active excavating and without any manipulating of fallen materials, colonies of these species form a domicile with their own bodies. A typical bivouac is a cylindrical mass hanging from the underside of some projecting surface to the ground. In addition to the sides or under-surface of logs, other typical places are the spaces between gut tressed tree roots, masses of brush, undercut banks of stream beds, or the overhanging edge of a rock. “The characteristic ability to cluster their bodies, as well as the manner of clustering, depends first of all upon an anatomical characteristic—the opposed, recurved hooks on the terminal tarsal segments of the workers’ legs. The first ants to settle in a new place catch into a rough or soft surface by means of the tarsal hooks, or rather are pushed into this anchored position as newcomers run upon them as they stand and stretch them out in a hanging position. In fact, the hooks are really anchored by the added weight of others that have crawled down over the body of the first ant, fixing it in place and soon immobilizing it.