Insects have their own version of hibernation, known as diapause. It’s basically like they push pause on their lifecycle, shutting down until conditions improve and they can become active again. They can do this at different stages – some might see out the winter as adults, pupae, larvae or even eggs.

Different butterflies (and moths!) have different winter survival strategies. Most shut down for the season, entering diapause as either an egg, a caterpillar, a pupa or an adult. Remarkably, painted ladies avoid the winter altogether by migrating south in autumn!

Larvae

Most of the UK’s butterflies and moths spend the winter in their larval form, as caterpillars. Some will just huddle down in leaf litter or clumps of grass below their favourite food plant. Others might create their own shelter to give them a little more protection. Large skipper caterpillars use silk to spin grass blades together, forming a tube they can hide in. Marsh fritillary caterpillars spend the winter together in a communal web.

Some species have much more elaborate plans. Blue butterflies have complex relationships with ants and the large blue is no exception. When caterpillars first hatch in summer they feed on leaves, but as they grow their tastes change. They drop to the floor and produce a sugary liquid that attracts ants. Then they mimic an ant larva, tricking the ants into carrying the caterpillar down into their nest. Once inside, they feed on ant grubs until they’re fully grown. This is where they’ll spend the winter, deep inside an ant nest. They’ll pupate in spring and the adult will crawl back outside.

Pupae

The second most popular choice is to spend the winter as a pupa, wrapped in a protective chrysalis. The caterpillars will fatten up in spring or summer, find a place to pupate and then stay there over winter. In most cases, the transformation from caterpillar to butterfly is put on pause over winter. It will resume in spring, so the adult can emerge.

Pupae are often stuck to plant stems or hidden in leaf litter. One of the pupae you’re most likely to see is that of the large white. They can sometimes be found on the outer walls of houses, if you have a garden with plenty of food for the caterpillars. They’re wonderfully angular, alien-looking structures covered in spots and speckles.

Eggs

Some butterflies spend the winter inside their egg, waiting for warmer weather to hatch. One example is the rare black hairstreak. The adults fly for a very short time around June, when females lay eggs on blackthorn twigs. The larva develops inside the egg and is fully formed by winter. But since the twigs are bare in winter, it doesn’t emerge. Instead, it enters diapause, emerging in spring when there are tasty buds and leaves to eat.

Brown hairstreaks also spend the winter as eggs on blackthorn trees, but their larvae only partially develop inside before entering diapause. They spend the winter dormant and their development resumes in spring.

Adults

A small number of butterflies spend the winter in their flying form. They’ll find a sheltered spot to tuck themselves away and shut down for the season. Though, on sunny days, the warmer temperatures might cause them to stir and venture out.

Hiding spots can include caves, tree cavities, dense evergreens like ivy, or even sheds and garages. Their dark underwings help them blend in with their surroundings. Occasionally, butterflies find their way into houses and mistake them for the perfect place to spend the winter. As the weather cools, they enter their hibernation-like state. But the problem comes when our heating goes on, warming them up and causing them to become active. 

Peacock, small tortoiseshell, comma, red admiral and brimstone butterflies all spend the winter as an adult.

What to do if you find a butterfly in your house in winter

Our winter is typically too cold for butterflies to stay active, so they spend the coldest months in a dormant state - technically insects don't hibernate, but it's a very similar process. Most pass the winter as caterpillars, a chrysalis or an egg, but a few species spend the winter as adult butterflies. The two you're most likely to find inside your house are the small tortoiseshell and the peacock.

They come inside in late summer or early autumn, find a cool part of the house and enter their dormant state. Later in winter, when your central heating comes on and the house gets warmer, they wake up and become active again.

What should I do with it?

If it's still winter, conditions outside are likely to be too cold for a butterfly to survive and find food. They might find a cooler spot in the house to roost and settle again, such as a loft or cellar, but if they are very active you may need to lend them a hand.

Carefully catch the butterfly and place it in a cardboard box, then leave it somewhere cool for a half an hour or so, giving it chance to settle down. Then you can relocate it somewhere cooler - the inside of a shed, garage or outhouse is perfect. Just make sure the butterfly has an escape route for when spring arrives.

If you have nowhere suitable for a butterfly to spend the rest of the winter, try to keep it in a relatively cool spot until the weather improves. Release it on a warm and dry day and it can fly away and find another suitable roosting place.