The Turkestan cockroach, Blatta lateralis (Walker), has become an important invasive species throughout the southwestern United States and has been reported in the southern United States. It is rapidly replacing the oriental cockroach, Blatta orientalis (L.), in urban areas of the southwestern United States as the most important peri-domestic species. They typically inhabit in-ground containers such as water meter, irrigation, and electrical boxes, raises of concrete, cracks and crevices, and hollow block walls. On occasion, they will invade dwellings. At 26.7°C, male and female nymphs developed into adults in an average of 222 and 224 d, respectively. Both males and females had five nymphal instars. Adult females deposited up to 25 oothecae. The oothecae averaged 16.8 eggs and 13.9 nymphs emerged per egg capsule, resulting in an 82.7% hatch rate. Adults lived for at least 612 d.Twoparameters that might contribute to the success of Turkestan cockroaches compared with oriental cockroaches are that the developmental period of the nymphs of Turkestan cockroaches are shorter and adult female Turkestan cockroaches produce considerably more oothecae than do oriental cockroaches. These may explain the observations by Pest Management Professionals that Turkestan cockroaches are displacing oriental cockroaches in outdoor habitats throughout the southwestern United States.