The selection of plant species used by the range caterpillar,Hemileuca oliviaeCockerell, for feeding, pupation, and oviposition in the short-grass prairie habitat of Lincoln County, N.Mex., was studied in relation to the assortment of plants available in three plant communities found along a hillside. Larvae were polyphagous; feeding larvae were distributed randomly on grasses in two of the three communities, with only small departures from randomness found in the third community. Major departures from random distributions during pupation and oviposition were due to selection by larvae and adults of structures that would provide adequate physical support for these stages. Selection during pupation and oviposition did not reflect any broad taxonomic associations among the plant species, but rather certain physical attributes, such as a stiff upright habit.