Winter is the biggest challenge for British butterflies. Most species tackle it in their vulnerable caterpillar form, burrowing into leaf litter, while others such as the purple emperor gamble by lying on an exposed branch with only camouflage for protection.

Five of our 59 species hibernate as adult butterflies, beneath evergreen leaves or in the modern equivalent of a cave: the garden shed.

In one shed in St Albans, the butterfly enthusiast Malcolm Hull is conducting an illuminating experiment, by each week counting his hibernating peacocks and small tortoiseshells.

His careful observations are revealing new facts. Hibernating butterflies particularly appreciate his brick shed (he regularly has more than 30 each winter) because it is consistently cool. Each butterfly seeks out the darkest corners. They prefer to hibernate together – safety in numbers – but each year spiders devour some. Many take “day trips” out on sunny winter days before returning to hibernate.

Most significantly, Hull has recorded the small tortoiseshell entering hibernation much earlier than the books say – often in mid-July, before Butterfly Conservation’s Big Butterfly Count. This earlier hibernation may be one cause of the once-common small tortoiseshell’s drastic decline in southern England. Is global heating causing it to hibernate before we can count it?





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