On August 15, 1955, during studies on the ecology of caterpillars on cabbage near Carp, Ontario, two species of Lepidoptera were observed in unique association. A final-instar larva of the diamondback moth, Plutella maculipennis (Curt.), bore on its third abdominal tergite an egg of the imported cabbageworm, Pieris rapae (L.) (Fig. 1). The larva appeared to he unaffected by the presence of the egg and when brought into the laboratory spun its cocoon within 24 hours. The egg remained attached to the larval skin, becoming enclosed within the cacoon, and hatched during the prepupal period. The resultant larva tried to free itself from the cocoon for several hours and eventually died.