An experiment at Estación de Biología Chamela in western México addressed the consequences of social behavior on growth and survival of Hylesia lineata Druce caterpillars. Three of the primary hosts (Casearia corymbosa HBK, Thouinia paucidentata Radlk., and Erythroxylum havanense Jacq.) were used as experimental plants. Because caterpillars usually build shelters with leaves from their hosts, it was suspected that differences in leaf size, leaf form, and branching pattern among hosts could promote contrasting effects on larval performance. In addition, H. lineata caterpillar colonies usually are formed of dozens to hundreds of individuals, suggesting strong differences in larval performance because of group size and social interactions. During a period of 21 days, accumulation of larval biomass was greater on C. corymbosa than on T. paucidentata or E. havanense. Group size had a strong effect on growth of H. lineata larvae. Caterpillars accumulated more biomass when kept in larger groups than in small groups but the pattern was reversed as caterpillars grew older, apparently as a consequence of an increasing demand for food. This outcome was similar across hosts. Survival of larvae did not seem to be affected by either host or group size, suggesting that within the range of larval group sizes examined (46–233) the per-capita predation risk was constant, probably because of a large array of anti-predator traits that caterpillars display, and thus also balanced for host-related differences in the risk of predation.