Data are presented on range, density, and distribution ofHemileuca oliviaeCockerell in Chihuahua, Mexico. Populations were found near Cuauhtemoc, Anahuac, and at various locations between Chihuahua City and El Sueco, but were absent from overgrazed and agricultural lands, and grasslands in the Chihuahua Desert. Egg clusters were distributed randomly at a height of 21.2 ± 9.5 cm from the base of grass stems, primarilyBouteloua gracilis(H.B.K.) Lag. Development ofH. oliviaewas asynchronous within and between sites. Sixth instars had a clumped distribution and a maximum recorded density of 24.44 per 100 m2