In Minnesota, there are twelve described species within the genus Coelioxys. Bees in this genus are cleptoparasitic (cuckoo bees), and their hosts are bees in the genus Megachile. Coelioxys are present in their host's habitat, visiting flowers near host nests. Like other cuckoo bees, females will perch on an object or vegetation establishing a vantage point from which they can monitor the host nest(s). When the host leaves to collect provisions or nesting materials, Coelioxys females enter the nest. Using the sharp point on the end of their abdomen, they pierce a hole in the brood cell leaf (or petal) lining, then lay an egg concealed in the nest materials. The first instar larva develops large sickle-like mandibles that are used to destroy the host egg (or larva). It then develops within the brood cell, feeding on the pollen provisions provided by the host bee. The larvae sheds the large mandibles after the first instar stage. Their hosts, bees in the genus Megachile, either nest aboveground in cavities or belowground, often under an object such as a flat rock.

Coelioxys are dark gray or black bees with white hair bands on the abdomen. They have hairs on their compound eyes and often red legs; some species have red markings on their abdomen. Females have a sharp point on the end of their abdomen, and males have multiple tooth-like prongs on the end of their abdomen. Bees in this genus range in length from 5 to 17 mm (0.2 to 0.7 inches).