he natural history of Oncocnemis piffardi (Walker) is described and the larva and pupa are illustrated. Larvae have been field-collected as well as cultured on Spiraea latifolia (Art.) Borkh., its natural host. Elpe semiothisae (Brooks) (Tachinidae) and an apparently undescribed Mesocharus (Ichneumonidae) were reared from field-collected larvae. The Mesocharus is a hyperparasite of yet another ichneumonid.