Least weasels are characterized by the same swift alertness and boldness so marked in the larger species. In fact they are, if possible, even quicker in their movements. Once when camping in spring among scattered snowbanks on the coast of Bering Sea, I had an excellent opportunity to witness their almost incredible quickness. Early in the morning one suddenly appeared on the margin of a snowbank within a few feet, and after craning its neck one way and the other, as though to get a better view of me, it vanished, and then appeared so abruptly on a snowbank three or four yards away that it was almost impossible to follow it with the eye. It was beginning to take on its summer coat of brown and was extremely difficult to locate amid the scattered patches of snow and bare moss of the tundra. Certainly no other mammal can have such flash-like powers of movement. They feed mainly on mice, lemmings, shrews, small birds, their eggs and young, and insects. Mice furnish a large proportion of their prey and weasels have often been seen following the runways of field mice. Their small size enables them to pursue mice into their underground workings as readily as a ferret enters a rabbit burrow. They also climb trees and bushes with great agility, although nearly always seeking their victims on the ground. The mice upon which they prey are often so much larger than the weasels that they cannot be dragged into the dens. The weasels continue in full activity throughout the winter and constantly burrow into the snow in search of their prey. In the snow or in the ground the holes of this animal are about the diameter of one’s finger. In the Old World the small weasels are reported to have several litters in a season, each containing five or six young. At Point Barrow, Alaska, a female captured on June 12 still contained twelve embryos. This indicates that only one litter a year would be born there, and that _Mustela rixosa_ is more prolific than its European representative. In the more southern latitude least weasels live in forests and about farms, sheltering themselves under logs, brush piles, stone walls, and similar cover. They are always restless and filled with curiosity regarding anything of unusual appearance. When one encounters a man it shows no fear, but slyly moving from one shelter to another, now advancing and now retreating, examines the stranger carefully before going on its way. As they devote practically their entire lives to the destruction of field mice, they are valuable friends of the farmer and should have his good will and protection. Unfortunately for these weasels, no discrimination is shown between them and their larger relatives of more injurious habits.