We examined the influence of weather factors, including temperature, humidity and sunlight, on the diurnal flight activity of Ichneumonidae (Insecta, Hymenoptera) in an oak wood in Cabaneros National Park (Spain) in June, when the annual flight activity reaches its maximum. Ichneumonidae flight activity peaked at temperatures of around 25.6-27°C, which is reached in late morning to midday and in the evening (20.00-21.00 h). The evening peak in activity was greater. Males were more active in the morning, whereas females were more active in the afternoon. Relative humidity is closely related to air temperature but showed little correspondence with flight activity. Illuminance did not explain diurnal flight activity, other than dictating diurnal or nocturnal habits of Ichneumonidae. © 2009 Taylor & Francis.