Under laboratory conditions of approximately 26°C and 60% RH, the average durations of the life-history stages of Phytoseiulus macropilis (Banks) were: egg, 43 hours; larva, 13 hours; protonymph 21 hours; and deutonymph, 23 hours. The total period from egg deposition to adulthood averaged slightly more for females (101 hours) than for males (98 hours). Preoviposition and oviposition periods averaged 31 hours and 20 days, respectively, and average oviposition was 52 eggs (range, 33–75) per female. Mean adult longevity of mated individuals was 27 days for females, 30 days for males; of unmated individuals, 45 and 42 days, respectively. Females isolated from males for 40–41 days after emergence were able to mate and lay viable eggs. The ♀:♂ sex ratio ranged from 4:1 to 5:1. The food provided consisted of all stages of Tetranychus tumidus Banks. Larvae of P. macropilis did not feed, but all subsequent stages ate readily; nymphs and adults preferred eggs and larvae of the prey rather than the later stages. Deutonymphs ate more than protonymphs, but less than adults, and adult females ate more than males. Average consumption by nymphs of P. macropilis was 10 eggs, 12 larvae, 5 nymphs, or 2 adults of T. tumidus.