"What happens to butterflies in autumn? I have a pair of tortoiseshells which I attempt to feed on tissue moistened with Lucozade, indoors, (hopefully the glucose gives them energy!) Can they survive the winter?"
We were sent this question by Chris, a concerned reader, and thought that there might be other people who would be interested in the answer.
Different species of butterflies have different strategies to survive our cold winters. Some will hibernate in a sheltered place such as a shed or garage. It needs to be cold enough that they don’t mistakenly wake up thinking it is spring, but warm enough that their bodies will not actually freeze. Sometimes they will accidentally find their way into a house, but winter heating will disrupt their hibernation so they should be gently moved outside or into a shed. These include Peacock, Red Admiral, Small Tortoiseshell and Comma (usually the larger species).
Some species are migratory and fly over the channel from Europe in the spring and breed in the UK over the summer. Their offspring will then usually make the return journey as it gets colder in the autumn. Most notable of these is the Painted Lady.
Those that cannot survive as an adult, either by hibernating or migrating, must time their lifecycle so that a different developmental stage has the job of getting through the winter. Most often this will be the pupa (or chrysalis) as this offers the most protection, either stuck to a sheltered part of a structure (fencepost, shed, windowsill), in dense vegetation or buried underground or in the leaf litter. Some, like the Brown Hairstreak, lay eggs on branches in the autumn that will hatch out in spring when the leaves are available for their caterpillars to eat, but a few caterpillars, such as the Fox Moth, will remain active all autumn and winter, feeding on evergreen plants such as brambles.
You can find out more on Butterfly Conservation's hibernation blog post