Field studies were conducted on a population of the spider wasp, Pepsis cerberus from Big Bend National Park (Brewster Co., TX). Females utilize the theraphosid spider Aphonopelma steindachneri as the host for their larvae. Female wasps are larger than males. Clutch size ranged from 5 - 26 eggs / female (mean: 11.82). There are 5 larval instars; the amount of time required from oviposition to the onset of pupation was 19 - 22 days. The pupal stage required 8 - 10 days. Wasp larvae initially feed on the cuticular lamellae and underlying connective tissues of the host, and then proceed to the longitudinal muscles of the abdomen, medial region of the midgut, ovaries and testes, book lungs, and finally the heart and neural tissues. Over 60% of females searched for hosts between 1000 - 1359 hr (CST). The species of plants whose flowers provide nectar for adult wasps, as well as the ethogram for hunting in females, will be discussed.