Herein we investigate the behavior and anatomy of all larval instars of the cleptoparasitic bee, Coelioxys (Cyrtocoelioxys) chichimeca Cresson. The species is found in Central America with its host, Centris (Heterocentris) bicornuta Mocsáry, one of the cavity-nesting members of the genus. The egg/mature oocyte of C. chichimeca, unusually small (like known eggs of other Coelioxys), is described, as is egg placement in the wall of the brood chamber. The anatomy and behavior of each of the five larval instars is described. The first instar develops within the egg chorion, from which the second instar emerges. The second and third instars apparently normally remain attached by their posterior ends either to the egg chorion or to the place where the egg had been attached to the cell wall. The second instar possesses an array of large spines on the outer surface of each mandible thought to rupture the thick chorion, thus allowing eclosion. Both second and third instars have modified head capsules and mandibles enabling them to attack host immatures. Both instars possess an extremely large pair of spiracles on the eighth abdominal segment and lesser-enlarged spiracles on the two preceding abdominal segments as well as enlarged internal lateral tracheal trunks. These modifications are likely related to the need for the larva to acquire air from the substrate while the body is submerged in nectar. Fourth and fifth instars, no longer attached to the substrate, assume the morphological attributes and behavior of normal provisions-consuming megachilid larvae. The last larval instar defecates and afterwards spins a cocoon bearing a conspicuous nipple. A male pupa is also illustrated and described.