The Clouded Yellows - le Souci
Some butterflies were flying in the sunshine on December 9th. Particularly, a small group of Clouded Yellows exuberantly chased each other along a bank. Two wheeled as though on a mating dance and perhaps it was so. The previous night and before there had been frosts, and in some shady pockets the frost held to the fallen leaves till beyond midday. Yet the books maintain that the Clouded Yellow does not survive the winters at any stage of its life history in northern Europe.
Since several species of Clouded Yellow are found here, it is not immediately clear which species you see. There are the true Clouded Yellow, the Pale Clouded Yellow and Berger's Clouded Yellow. The third species is so similar to the second that it cannot easily be distinguished. Both are a pale yellow and the hind wing on the upper side has almost no dark border. These features separate both the latter from the true Clouded Yellow, which has strong dark brown borders to the rather bright orange colour on the upper surface. But then again, about 10% of that population are almost white, except for the borders. The food plant of all are small plants of the pea family, such as the crown vetch, melilot, clovers and lucerne. One expects to find some distinct ecological preferences, otherwise why and how are there several species? Perhaps some over winter as caterpillars and some as adults?
It is generally written that all survive the year only in the frost free parts of southern Europe and through the summer migrate through a succession of several generations to the North. Yet I read that in Britain in the 1850's "eggs are laid in May by females which have hibernated". In some years in the 19th century hundreds of adults were collected. In 1865, 972 specimens were collected (how many more got away?) between August and October in two fields of wheat stubble at Looe in Cornwall. These were certainly migrants from France. All species have been found eastwards towards Moscow. Is it really the case that all is due to migration? Perhaps my butterflies will survive till spring?