Diel patterns of activity of Thymelicus lineola adults (Lepidoptera: Hesperiidae) in relation to weather *

ABSTRACT. 1. Daily patterns of activity, thoracic temperature ( T th ) and thermoregulatory behaviour in relation to environmental conditions were studied in the European skipper Thymelicus lineola (Ochsenheimer) adults. 2. Daily activity was limited mainly by T th , which in turn was dependent on air temperature ( T a ) and sunlight. However, when light intensity fell to < 100 W m −2 , skippers also became inactive. 3. T th was sometimes as much as 12°C above T a , and this was most pronounced under cool conditions when basking activity predominated. 4. Black globe temperature ( T bg ) which, in the absence of wind, is influenced by both T a , and radiant heat load in a manner similar to a basking butterfly, was used to approximate the maximum T th attained by T.lineola through basking. 5. Both males and females basked at T bg >20°C, and if this temperature was not attained, skippers remained inactive. As T bg increased, basking activity declined more rapidly in males than in females. Basking bouts were also shorter in males. 6. Males also flew, fed and courted females at T bg >20°C, while females only fed and flew at T bg >22°C. The percentage of both sexes feeding and flying, and courting in the case of males, were positively correlated with T bg . 7. In warm weather, males divided their time equally between flying and feeding, while females spent the majority of their time feeding. Feeding bouts were shorter and flying bouts were longer in males than in females. Flight duration in males was positively correlated with T bg . 8. Skippers avoided, and, consequently laid fewer eggs in, shady areas. 9. Sexual differences in activity patterns in relation to weather reflect differences in the reproductive requirements of the two sexes.