Chelostoma

Chelostoma are small-sized, slim, and elongated megachilid bees. They can be found across many different habitats in the Northern Hemisphere. Both sexes tend to have an overall dark coloration and a sparse pilosity. Females have very distinctive mouth parts, often with hair-fringed mandibles that leave the base of the labrum exposed even when closed. Like other megachilids, they have a ventral scopa. Males are similar in appearance to females, but hairier and sometimes with a different eye color. The males of several species also have a small, hard ventral projection or bump and an abdomen that terminates in a pair of lobes of variable shape. Nests are commonly built in pre-existing cavities in dead wood and inside hollow plant stems. However, some species will also inhabit insect hotels and human-made structures in urban environments. Brood cell partitions and the terminal plug of the nests are made using a mineral mortar made of small soil particles mixed with salivary secretions and nectar. Most species are specialized foragers.