Abstract
Two species of velvety tree ants, Liometopum luctuosum Wheeler, and Liometopum occidentale Emery (Hymenoptera: Formicidae), are commonly found in the western Unites States from Washington to southern California. L. luctuosum is restricted to coniferous forests in the mountains in the southern range, whereas L. occidentale is found in the lowlands. The survivorship of workers of both species exposed to several temperatures and relative humidity (RH) was determined. As temperature increased, survival of both species decreased. As the RH increased, survival of both species increased. However, L. luctuosum had higher overall survival in all treatment groups. The cuticular permeability (CP) and the rates of body water loss for each species were determined. Both species had similar CPs. Increased physiological tolerances of L. luctuosum may be an explanation for its broader distribution.