The water strider, Gerris paludum insularis (Motschulsky), was reared in a growth cabinet at seven constant temperatures from 10 to 40°C under a 16:8 (L:D) photoperiod. There were highly significant differences among development times for all temperature regimes and the immature stages. Eggs failed to hatch at 10 and 40°C. The lower developmental temperature threshold was estimated to be 11.0°C and the upper, 35.6°C. Total development required 500 Celsius degree-days (DD) above threshold. The optimal temperatures for development and survival were 25 and 30°C, respectively. The presence or absence of this species in its normal range of distribution and habitats may be a useful indicator of thermal pollution.