The diel egg-laying activity was recorded by means of an egg-laying recording apparatus. Simultaneous hourly registrations of temperature and nocturnal illumination were obtained. With few exceptions egg-laying occurred during the night. The activity was highest in the first part of the night and a bimodal distribution curve was found. Moonlight had a depressing effect; above 0.1 lux no eggs were laid. The influence of the moon was more clearly visible at high temperatures. An attempt is made to explain the biomodal distribution curve found.