Butterfly experts are cautiously optimistic that if Britain has a similar summer this year, some of the most threatened species could make a significant recovery after populations plummeted in recent years because of bad weather, habitat loss and intensive farming. Continuous or heavy rain makes its hard for butterflies to survive because the temperature is usually too low for them to fly. The wood white is Britain's smallest butterfly and its numbers have fallen by 96 per cent since the Seventies. But last year suggested increases of 600 per cent, with the most sightings in Herefordshire, Buckinghamshire and across Ireland. The marsh fritillary, which has also been in decline, increased by 134 per cent and the Adonis blue by 74 per cent.