The influence of temperature and photoperiod on reproduction of the predatorHemerobius pacificusBanks was studied in the laboratory. Short photoperiods (8–12 h) and a relatively low temperature (18.3°C) were found to be favorable for mating, fecundity, fertility and longevity. A life table is presented for these conditions. The adults lived a mean of 72 days (maximum 147 days). They deposited a mean of 715 eggs/♀ (maximum 2554 eggs); fertility was 92.0% until a week before death. The mean generation time was 6.1 weeks.Reproduction occurred at temperatures as low as 4.4°C. Mating and fecundity decreased at a constant temperature of 23.9°C, even under a short photoperiod. Estival diapause, which would protect this predator from hot summer climates could not be induced. It is concluded thatH. pacificusis adapted to areas of California which have mild winter climates.