Females of Pepsis cerberus from Big Bend National Park (BBNP) selectively hunt Aphonopelma steindachneri (Araneae: Theraphosidae) as their host. Mean body length and head capsule width for males and females of P. cerberus was 18.9 and 21.9 mm, respectively. Mean number of eggs in ovarioles ranged from 6 - 26 (mean: 13.8). There are 5 larval instars. Under laboratory conditions (22 deg C, 60-70% RH) 1st-instar larvae emerged within 3 - 4 days after oviposition. Time required from oviposition to cocoon formation ranged from 19-22 days. Pupal stage duration was 14-18 days. Peak activity period for adults was between 1000 - 1359 hr CST.