During such periods of abundance they invade fields and devastate grain, forage crops, vineyards, and young orchards. In places they sometimes actually destroy entire crops and force settlers to abandon their locations. In winter they swarm about haystacks and destroy many tons of hay. Depredations of this character were committed by them on a considerable scale during 1916 in parts of Oregon, Idaho, and Utah. During the early development of the San Joaquin Valley, California, jack rabbits became such an intolerable pest that great community drives were organized. Large woven wire corrals with wing fences leading away several miles from the entrance were built on the open plains. The occasions of the drives were made public holidays through all the surrounding region, and people gathered sometimes to the number of from 5,000 to 8,000. A great line of beaters was formed, miles in length, and the jack rabbits were driven between wing fences into corrals. Four such drives in Fresno County in the spring of 1892 resulted in the destruction of 40,000 jack rabbits, one drive netting more than 20,000 animals. At this time the level floor of the San Joaquin Valley was crossed by numberless well-worn rabbit trails six or eight inches broad and one or two inches deep, extending in long straight lines sometimes for miles. On approaching a patch of large weeds one often saw twenty or thirty jack rabbits dash out and, after hopping away a short distance, sit with upstanding ears to look curiously at the intruder. It is a general rule that when any species of animal becomes extremely numerous it loses its ordinary wariness and, conversely, when its numbers are materially reduced its wariness is greatly increased. The periods of abundance of jack rabbits usually extend through several years until, at the height of their increase, a contagious malady suddenly sweeps them away almost to the point of extinction, as in the case of the varying hare. A period of years follows during which their numbers are slowly recovered. Jack rabbits are specially adapted for life on great plains, where speed and the ability to subsist on almost any form of vegetation are prime qualities. They are as grotesquely characteristic of the Western States as the kangaroos were of Australia, and have entered largely into the literature of the region they occupy. =THE VARYING HARES= (=Lepus americanus= and its relatives) (_For illustration, see page 507_) The varying hares, white rabbits, or snowshoe rabbits, as they are known, form a small group of closely related species and geographic races of hares peculiar to northern North America. They sometimes attain a weight of five pounds and are about half the size of the arctic hares, which they resemble in form, except that they are more heavily built and have proportionately shorter legs and larger hind feet.