Fifty five species of butterfly are native to Britain, several of which are at the northern edge of their range and are confined to localities in southern England. Wet weather prevents butterflies from flying. The larvae of any one species generally have a specific food plant which, in about a third of butterfly species, is either a woodland tree or an associated woodland plant. Most butterflies have declined in abundance in recent decades. The decline has been most marked in woodland butterflies owing to the lack of management of broadleaf woodland, which impoverishes the herb flora through excessive shade. Sunny clearings and rides, which are very favourable, may also be absent.