What do butterflies do in winter?
Butterfly species occurring in the UK have evolved various strategies for dealing with our climate.
The adults of some species die after breeding, and the species survives the winter in the egg, larva (caterpillar) or pupa (chrysalis) stage.
Of the 58 species of butterfly that occur in the UK, 32 spend the winter as a caterpillar, 11 as a chrysalis and 9 as an egg. The speckled wood is unique as it can overwinter at either the larva or pupa stage.
Other species spend the winter in their adult (butterfly) form here in the UK, such as the peacock and small tortoiseshell which can often be found overwintering in garages and lofts, or even bedrooms. They spend the winter in a dormant state, not technically hibernating, and may become active on warmer days.
The reason for these different strategies is not simply that some species deal better with the cold as an egg and some cope better as a chrysalis. It is actually because the lifecycle has to synchronise with the availability of specific food plants for the caterpillar, as well as trying to reduce competition from other species. Most species rely on a small number of larval food plants, sometimes only one species. If the caterpillars of two butterfly species rely on one plant species, it makes sense for the caterpillars to emerge at different times of year to reduce competition for this food.
Some migrant species, such as the painted lady, may complete another migration, flying to warmer climates to enable them to feed in winter.
One species that typically migrates to the UK from North Africa and continental Europe, and dies after breeding, is the red admiral. The young butterflies which emerge then make a southward migration back to warmer climates. In recent years, this species has begun spending winter in the UK in its adult form, becoming inactive in cold weather but not entering the same state of dormancy as other species. This overwintering behaviour may be a sign of climate change leading to changes in migration.
An overwintering red admiral