Science in the Park: How do Butterflies Survive Winter?

Overwintering butterfly (© Sebastian Knight/Shutterstock)

Butterfly's survival strategies

The life cycle of a butterfly involves four stages: from egg, to caterpillar, to pupa (or chrysalis), to adult. During the winter, a butterfly goes into a dormant state which is sort of like hibernation, although insects do not truly hibernate the way animals do. A butterfly will enter the hibernation state regardless of the stage of the life cycle it is in, whether it is already a fully grown butterfly, in egg form (an ovum), larvae (a caterpillar) or a chrysalis (a pupa).

 Butterfly pupa in dormant stage (©dov makabaw sundry/Alamy Stock Photo)

Britain has 58 species of butterfly, and 9 of these species spend winter as an egg, 32 spend it as a caterpillar, 11 as a pupa, and 6 as adults. The timing of their wake from hibernation is very important – when the butterfly wakes it needs to have access to the right plants. For example, most caterpillars can only consume a small range of plants, so they need to emerge when these plants are around for them to feed on.

Butterflies need to stay cold and dry while hibernating. Butterflies that are disturbed during hibernation are likely to wake early and die, especially if they have to use energy to find another suitable sheltered place to hibernate. Left undisturbed, most butterflies hibernate until the first warm days of spring, usually around the beginning of March.

 Where to find dormant butterflies

 Butterfly hibernating on wooden pallet (©iStockphoto/GettyImages)

If you’re keen to find dormant butterflies this winter, good places to look are in sheds, farmyard buildings and sheltered structures like bird houses. Butterflies can also be found hibernating in natural hollows in trees, log piles, rock crevices, stone walls and other outdoor spaces.

You can also take a trip to the park with a torch and switch it on in a poorly-lit area. You should find yourself surrounded by some very hardy moths, which have their main period of adult activity in wintertime. These include the winter moth, December moth, and spring usher in the UK. (Shhh... don’t wake them!)

Butterflies in your house this winter?

Eggs, larvae and pupae are usually well hidden over winter, but sometimes people do find the chrysalis of the large white butterfly attached to a wall in their house. The small tortoiseshell and peacock also sometimes decide to overwinter in our homes during late summer/early autumn, when it is still warm outside and they are looking for sheltered conditions.

If you find a dormant butterfly in your house, which is likely to be heated on cold days, you need to relocate it to a cold area outdoors. 

Butterflies and climate change

Climate change is a problem for hibernating butterflies because unusually high temperatures in winter can wake them up too soon. During recent winters, several species have been spotted active: the red admiral, painted lady, peacock, small tortoiseshell, speckled wood, brimstone and clouded yellow. If you do come across an active butterfly in winter, release it outdoors on a warm day so it can find somewhere else to hibernate.