Malacosoma americanum(F.) andM. disstriaHübner were collected by black-light traps in eastern West Virginia in 1988–1990. Ten locations were sampled in 1988 and 1989 and 27 locations in 1990. Traps were operated at each location for 0.5-h intervals centered at 2100,2300,0100,0300, and 0500 hours. Factorial analyses of variance were performed on the quantity of each species collected in each time interval. Peak flight time forM. americanumoccurred at 2300 and 0100 hours whereas mostM. disstriaflew during 0300 and 0500 hours. Flight activity ofM. americanumwas unrelated to the presence ofM. disstria. However,M. disstriaflew significantly later at night, and was less abundant whenM. americanumwas present. Other research suggests that species withinMalacosomause similar sex pheromones. Separate flight activities of these species may help reduce interspecific pheromone attraction and aid the reproductive isolation of these species.