Steven Cheshire's British Butterflies
British Butterflies: Education: Butterflies in Winter

As global warming begins to have an effect on our wildlife, it appears that our butterflies are also responding to increases in average winter temperatures. During recent winters several species, namely Red Admiral, Painted Lady, Peacock, Small Tortoiseshell, Speckled Wood, Brimstone and Clouded Yellow have been regularly reported on sunny days mid winter days even at ambient temperatures of less than 10 degrees celsius.

Some species of butterfly hibernate as adults during the cold winter months while other survive the winter as eggs (ova), larvae (caterpillars) or chrysalis (pupae). If butterflies emerge early from hibernation, they may die especially if it goes cold again, especially if they have been unable to locate a suitable sheltered place to go back into hibernation.

Butterflies encountered during this time are often discovered hibernating in sheds, outhouses, farmyard buildings and structures such as bird hides on nature reserves. Butterflies also hibernate in natural hollows in trees, caves, rock crevices, in stone walls and other spaces which are protected from the worst of the British weather.

A Peacock found hibernating in the roof of a bird watching hide, despite the cob webs, it has found a safe place to see out the winter.Above: A Peacock found hibernating in the roof of a bird watching hide, despite the cob webs, it has found a safe place to see out the winter. During the winter, butterflies need to stay cold but dry in order to hibernate successfully. Warm snaps may wake them up but this could be fatal... become too warm and active and the butterfly risks wasting energy and unable to find another suitable sheltered spot when the weather goes bad again. Get wet or hibernate somewhere damp and the butterfly risks fatal fungal infections.

Most butterflies will not become active or wake from hibernation until the first warm days of spring, usually in early March when the first flowers appear, especially catkins which are a vital food source for butterflies so early in the year. However, a sudden increase in temperature may cause it to become active.

A butterfly (Small Tortoiseshell) causes a brief interruption to the early stages of Ronnie O'Sullivan and Stuart Bingham's first-round match at the UK Championship in Telford in December 2010.Above: A butterfly (Small Tortoiseshell) causes a brief interruption to the early stages of Ronnie O'Sullivan and Stuart Bingham's first-round match at the UK Championship in Telford in December 2010 live on the BBC. If you do find a butterfly outside in winter and it appears motionless but is in a dry sheltered place, its best to leave it where it is.

What is hibernation?
Hibernation usually takes place during the coldest months of the year. Creatures such as butterflies hibernate because of a lack of food and warmth. By staying dormant, they use very little energy.

Some species of butterfly hibernate as adult butterflies, including the Brimstone, Peacock, Small Tortoiseshell and Red Admiral, while other species survive the winter as eggs, caterpillars or chrysalis.

What do I do if I find a hibernating butterfly?
During the winter months, you may chance upon a hibernating butterfly in your home. If the butterfly is not moving, it is recommended that you leave it and the room alone until early March/April.

However, during warm spells, sunny days or after turning on your central heating, a hibernating butterfly may become active. Unless it is warm and sunny outside, it is recommended that you do not release the butterfly into the wild. Releasing the butterfly into the cold weather would almost certainly kill it as it may be unable to find another suitable place to hibernate before it gets dark.

What to do?
Use an old shoe box which has a narrow slot cut into one side. The slot should be about 1cm wide by 5cm tall, also punch some more holes in the box for ventilation. Put the butterfly in the box and place the box in a cool place away from direct sunshine. Make sure the box cannot get wet and have the slot pointing towards the brightest part of the garden. The butterfly will probably stay in the box for the winter but if it does warm it will find its way out of the box via the slot on its own.

When to release?
If you have placed the box in an outhouse, shed or garage, make sure you check on the butterfly during early February and March. If there are any signs of activity or if the butterfly has moved during this time, place the box outside in a sheltered spot.

Surviving the winter
Be prepared for your butterfly not to survive the winter. Many individuals will die in the wild either through cold, starvation (if they did not feed enough during the autumn to store energy to last it through hibernation) or die of fungal infections, especially if they have hibernated in a location where its constantly damp. Also birds and other predators will happily eat a hibernating butterfly if they can find them.

A Peacock butterfly basking in winter sunshine... after a heavy snowfall.
Above: A Peacock butterfly basking in winter sunshine... after a heavy snowfall.