Males of the tropical saturniid Automeris phrynon Druce (=A. orneatus Druce) (Lepidoptera: Hemileucinae) captured in the Atlantic lowland rainforest at Finca La Selva, Costa Rica, fly during late morning hours to caged females that are presumably emitting pheromones. This report adds to the relatively few known examples of tropical saturniid species which exhibit diurnal activity, even though numerous extratropical saturniids are known to be day-flying. Larvae of this species are brightly colored, urticating, and gregarious during the early instar stages. In captivity, male larvae feed for approximately two months before pupating, and eclose in 20 to 30 days. The period from egg hatching to eclosion is 1-5 weeks longer for females. In captivity, female moths lay 200-400 eggs over a 4-5 day period during early evening hours