The nesting habits of many of our wild bees still remain unknown. Their importance, from an ecological as well as from an animal behavior standpoint, is great. Each species is adjusted to a set of environmental conditions which the kind and location of the nest helps to assure it. The young are protected from extremes of heat and moisture, as well as from parasites and predators by the materials composing the cell, by the manner of its construction and by the nesting site selected by the mother bee. The following account consists of brief notes on the habits of certain western species.