The biology and the life cycle of Issoria lathonia (Nymphalidae) (Linnaeus 1758) on its host plant, Viola tricolor L. (Violaceae), are described from laboratory studies. In the laboratory eggs are laid singly on the host plant leaves as well as on the surfaces of plastic screen cages. Newly hatched larvae aggregate and feed on the host plant leaves. Later instars disperse on the plant and continue to feed on leaves and flowers. Head capsule widths, and weight and size measurements show that larvae develop through 5 instars. The larvae crawl off the host plant and pupate off the host. The life cycle from egg to adult requires 23-31 d at 26 degrees C, and 16:8 (L:D) photoperiod in the laboratory. The butterfly has been reared continuously in the laboratory for about 2 years.