Hylaeus longiceps is historically known from coastal and lowland dry shrubland habitat up to 2,000 ft (610 m) in numerous locations on the islands of Maui, Lanai, Molokai, and Oahu. Perkins (1899, p. 98) noted H. longiceps was locally abundant, and probably occurred throughout much of the leeward and lowland areas on these islands. All Hylaeus bees roughly resemble small wasps in appearance; however, Hylaeus bees have plumose (branched) hairs on the body that are longest on the sides of the thorax, which readily distinguish them from wasps (Michener 2000, in litt.). Bees in the family Colletidae are also referred to as plasterer bees because they line their nests with a self-secreted, cellophane- like material. Eggs hatch and develop into larvae (immature stage) and as larvae grow, they molt through three successive stages (instars), then change into pupae (a resting form) in which they metamorphose and emerge as adults (Michener 2000, in litt.). The diet of the larval stages is unknown, although it is presumed the larvae feed on stores of pollen and nectar collected and deposited in the nest by the adult female.