Abstract
The polymorphic two-spot ladybird, Adalia bipunctata, shows clinal variation in the frequency with which melanic and non-melanic morphs occur. Here we show that the clines in melanism in The Netherlands have changed over the past two decades: they have become shallower. This change has coincided with an increase in local ambient spring temperatures at most meteorological stations close to the sampling sites. The potential contribution of thermal melanism to the change in the shape of the clines is discussed.