The predatory behaviour of Stethorus punctillum larvae was studied on the two-spotted spider mite (Tetranychus urticae), in order to assess how it responded to temperatures and relative humidities typical of glasshouse conditions on four edible crop plant species. Locomotory activity (distance covered, time spent walking, walking speed, angular velocity, and turning rate) was recorded at 20, 25 and 30 °C and relative humidity levels of 33%, 65% and 90% RH on tomato, pepper, aubergine and cucumber and analysed using video/computer techniques. The results show that activity of S. punctillum significantly increased at higher temperatures. Host plant species also strongly influenced the performance of the predator, which was most active on pepper and tomato and least active on aubergine. Relative humidity had no significant influence.