The egg of Chelostoma (Prochelostoma) philadelphi (Robertson) and its last larval instar, which had been preserved while defecating, are described and illustrated. The egg was collected from nests constructed in frass-filled burrows of the beetle Xylobiops basilaris (Say) in a dead branch of Ficus carica L. Nests consisting of a short linear arrangement of cells are described as is the provisioning behavior of the bee. Although distinguishable, the last stage larva is similar to that of another species belonging to a different subgenus of Chelostoma. The two larvae will be compared in a subsequent publication.