The life histories of Tetranychus urticae Koch, T. pacijicus McGregor and T. turkestani (Ugarov and Nikolski) (Acarina: Tetranychidae) were studied at 5 constant temperatures ranging from 15.5° to 29.4°C on cotton cotyledons. Average developmental times of al! 3 species were similar. These ranged from 25 .8 to 29.0 days at 15.5°C and from 6.1 to 6.7 days at 29.4°C for females. Males required slightly less time. Total progeny at 23.8°C was 84.6, 103.3, and 78.9 eggs/female for T. turkestani, T. urticae and T. pacijicus, respectively, and at 29.4°C was 73.5, 64.3 and 68.3 eggs/females for T. turkestani, T. urticae and T. pacijicus, respectively. The percentage of female offspring was 74 OJo for T. urticae, 55 OJo for T. turkestani and 57 OJo for T. pacijicus. Average female adult longevity at 23.8°C was 12.46, 14.71 and 12.71 days for T. turkestani, T. urticae, and T. pacijicus, respectively, and at 29.4°C was 8.79, 9.71, and 8.91 days for T. turkestani, T. urticae and T. pacijicus, respectively. Life tables were constructed from survivorship and fecundity data.· collected at 23.8 and 29.4°C. The intrinsic rate of increase for the 3 tetranychids ranged from 0.204 to 0.219 at 23.8°C and from 0.293 to 0.295 at 29.4°C. The results of this study are compared with other investigations of the same species.