Independent: A Red Admiral butterfly rests among flowering snowdrops in a Dorset churchyard. It is a sight that would have been impossible just a few years ago. Until about 15 years ago, Red Admirals were summer migrants to Britain. But, with a warming climate and earlier springs, they have increasingly over-wintered in the south. This picture, taken by Dr Martin Warren, chief executive of Butterfly Conservation, is, he says, "real proof that the climate is changing". The species …