Meadow mice inhabit practically the whole of the Northern Hemisphere-- America, north of the Tropics; all of Europe, except Ireland; and Asia, except the southern part. In North America there are few wide areas except arid deserts free from meadow mice, and in most of the United States they have at times been numerous and harmful. The animals are very prolific, breeding several times a season and producing litters of from 6 to 10. Under favoring circumstances, not well understood, they sometimes produce abnormally and become a menace to all growing crops. Plagues of meadow mice have often been mentioned in the history of the Old World, and even within the United States many instances are recorded of their extraordinary abundance with accompanying destruction of vegetation. The runs of meadow mice are mainly on the surface of the ground under grass, leaves, weeds, brush, boards, snow, or other sheltering litter. They are hollowed out by the animals' claws, and worn hard and smooth by being frequently traversed. They are extensive, much branched, and may readily be found by parting the grass or removing the litter. The runs lead to shallow burrows where large nests of dead grass furnish winter retreats for the mice. Summer nests are large balls of the same material hidden in the grass and often elevated on small hummocks in the meadows and marshes where the animals abound. The young are brought forth in either underground or surface nests. Meadow mice are injurious to most crops. They destroy grass in meadows and pastures; cut down grain, clover, and alfalfa; eat grain left standing in shocks; injure seeds, bulbs, flowers, and garden vegetables; and are especially harmful to trees and shrubbery. The extent of their depredations is usually in proportion to their numbers. Thus, in the lower Humboldt Valley, Nevada, during two winters (1906-8) these mice were abnormally abundant, and totally ruined the alfalfa, destroying both stems and roots on about 18,000 acres and entailing a loss estimated at fully $250,000. When present even in ordinary numbers meadow mice cause serious injury to orchards and nurseries. Their attacks on trees are often made in winter under cover of snow, but they may occur at any season under shelter of growing vegetation or dry litter. The animals have been known almost totally to destroy large nurseries of young apple trees. It was stated that during the winter of 1901-2 nurserymen near Rochester, N. Y., sustained losses from these mice amounting to fully $100,000.