Recent warm days bring to an end one of the best years for butterflies in Britain for some time. But though an inspiration to poets and philosophers, their abundance belies a deeper uncertainty about our changing climate I  often wonder if the imagination of our ancestors was more fertile than our own. For past inhabitants of Britain, butterflies were the bright, dancing souls of the dead come back to accompany us through the warmth of summer days and to reassure us that all is well beyond the earth.They flit through our lives like confetti on the breeze, and the American poet Robert Frost described them as “Flowers that fly and all but sing”. Come the short, cold days of winter, as nature itself looks inwards and quietens, they return to their mysterious, dark tombs. By