Colias croceus

Male, Switzerland, February 2007

Switzerland, February 2007. Female of the white form, helice.

Switzerland, November 2009, female helice

Switzerland, October 2009, female helice

Val d'Aran, July 2005

Another female showing the upperside - this time in Spain.

This lovely butterfly is a familiar sight in most of Europe, including the south of Britain. In most places, though, it cannot survive the winter and is present only as a migrant. For that reason its numbers vary enormously from year to year. In Switzerland, for example, it may be entirely absent some years and is abundant in others. It appears to be able to survive the winter in the Rhône Valley in favourable seasons, but certainly not every year. It survived the non-winter of 2006-7 and the winter of 2007-8 but didn't survive the very harsh winter 2008-9.

I used to believe the pictures that show pairs of butterflies with uppersides visible showed courting couples. It has recently been pointed out to me that in all cases the female is actually rejecting the male. True courtship is very brief.