Halictinae are a large and taxonomically diverse group of ground-nesting bees. Solitary and social members coexist in all faunal zones, and several distinct evolutionary pathways to higher social levels can be discerned among extant species. The genus Evylaeus embraces the most advanced halictine societies known. These are made up of a queen and numerous small, unmated and nonreproductive workers. A strong correlation exists between architectural complexity and the level of socialization attained in those forms, since only a structural preadaptation permits a development of large colonies possessing a division of labor and intensive brood care.