They not only live everywhere in the wilderness, but are prompt to swarm about camps and other habitations, where they make free with the food supplies. Few frequenters of forest camps in the Northern States and Canada have failed to see the bright eyes of these pretty little animals peering at them from some crevice, or the mice scurrying along the log wall like little squirrels. [Illustration: FIELD, or MEADOW, MOUSE _Microtus pennsylvanicus_] [Illustration: PINE MOUSE _Pitymys pinetorum_] They are industrious workers and once in a cabin quickly locate some cozy nook in a box or other secluded place to construct a warm nest of any soft fibrous vegetable material available. This completed, they set busily at work nights to raid the food supply of the owner and hide it in suitable storage places, such as a crevice among boxes, an old shoe or a pocket in a garment hung on the wall. Their depredations usually cause so much exasperation that the camper overlooks the grace and beauty of his visitors and makes every effort to destroy them. If the occupants of such camps would keep their supplies in mouse-proof containers and would then feed their woodland friends, they would find them quickly responsive and most attractive guests. [Illustration: RED-BACKED MOUSE _Evotomys gapperi_] [Illustration: RUFOUS TREE MOUSE _Phenacomys longicaudus_] In their native haunts these mice have habits varying with varying conditions. On brushy plains they burrow in the ground, while in the woods they sometimes burrow under rocks, stumps, and logs, or live in hollows in stumps and trees. As nimble in climbing as squirrels, many live in hollow trees sometimes more than fifty feet above the ground. That our inability to see at night prevents more than an occasional glimpse at the doings of the small animals which often swarm all about us was impressed on me at one of my camps in the desert of Lower California. My blankets were spread under a small leafless tree growing near the base of a rocky ledge, in the crevices of which many relatives of the white-footed mice were living. The first morning in camp I awoke as the sky began to pale and color with the approach of day. The dry branches of the tree a few feet overhead became sharply silhouetted against the sky, revealing several of the mice running up and down them and leaping from twig to twig with all the active grace of tiny squirrels. The mice appeared to be racing about in pure playful enjoyment of the exercise, and when the light had increased sufficiently to render objects on the ground distinct they suddenly ran down the tree trunk and vanished in a crevice in the rocks. This game was repeated on several succeeding mornings and is no doubt commonly indulged in where conditions are favorable.