Members of the large genus Hylaeus are typically small to medium-sized bees with black, relatively hairless bodies and most species have characteristic white, cream or yellow marks on the face and thorax. For this reason, they are sometimes referred to as ‘masked bees’. They are also referred to as ’lodger bees’ as females seek out existing hollows in which to construct their nests. Vacated borer holes in tree trunks and dead branches, hollow pithy stems and the vacated burrows of other bees or wasps are commonly used. A few species utilize the vacated nests of potter wasps. Nail holes and other man-made hollows can also suit their purposes.