What happens to butterflies in the winter?
Winter is almost upon us, and that means it’s time for most of our insects to hunker down until the spring. While the majority of the UK’s butterflies will spend the winter as caterpillars, chrysalises or even eggs, there are a few species of butterfly that can overwinter as adults. We explore some of the strategies for winging it through the winter.
Lying dormant
Unlike mammals and birds, butterflies tend to rely on external sources of heat to raise their body temperature enough to carry out their usual activities. One of the ways adult butterflies, including the Comma, Small Tortoiseshell, and Peacock, survive the colder weather, is to go into a dormant state. A little bit like hibernation, the butterflies will reduce their activity and bodily processes and effectively sleep until warmer temperatures arrive. You may come across a “sleeping” butterfly in a shed or garage where they have tucked themselves away from the elements and potential predators.
Cold weather superpower
Some butterflies will employ an extra special superpower to help them overwinter as adults. The Brimstone, Small Tortoiseshell and Peacock store glycerol in their bodily fluids, which acts a sort of antifreeze. This antifreeze, as well as the ability to get rid of water that they don’t need, allows them to avoid freezing as temperatures drop below 0°C. The ability to survive freezing temperatures is also shared by some caterpillars, such as those of the Grayling and Ringlet butterflies. However, unlike adult butterflies which avoid freezing in order to survive, these caterpillars have a way of choosing which areas of their body they want to freeze. They do this using ice-nucleating agents – molecules which act as focal points for ice formation. By putting these molecules in particular areas of the body, the caterpillars can freeze without ice crystals causing severe damage to vital internal tissues.
A winter holiday
Looking for another way to survive the winter if you’re an adult butterfly? Take a winter holiday. Some butterflies, such as the Painted Lady, seek out warmer climates during the winter and subsequent generations can then return the following year when temperatures warm up. However, some species who used not to survive in the UK in winter are now finding that they can. The Red Admiral is an example of this. Traditionally, Red Admirals were very rare here during winter – they had all migrated further south to continue their life cycles. However, as a result of climate change, nowadays Red Admirals are increasingly choosing to overwinter in the UK, sometimes in large numbers. And it doesn’t seem like the Red Admirals become dormant. Instead, they roost and shelter themselves from the worst of the weather and make use of more favourable conditions to fly, feed, mate and lay eggs.
What to do if you come across an overwintering butterfly?
If you happen across a dormant or roosting butterfly while you’re gardening or in an unheated building like your shed, the best thing you can do is to leave it. However, if the butterfly can’t stay where it is, or the butterfly is in a heated place like your house where your central heating has the potential to trick it into thinking spring has come early, you can try and relocate it to a more suitable place. Carefully coax it into a cardboard box or container and let it sit in a cool place. Once the butterfly has calmed down, you can gently encourage it onto a wall or ceiling of an unheated place, such as a shed, garage or porch – somewhere where it can escape when it reawakens in spring.
How can you help overwintering butterflies?
Whatever the size of your Wild Space, you can create winter refuges for butterflies.
Most butterflies overwintering as adults need places in which to tuck themselves away from the elements, whether they are dormant or just sheltering from the worst of the winter weather.
Have a larger garden? Create a log pile, plant a hedge, or create an Ivy wall.
Smaller space or balcony? Try including a trellis planter with a butterfly-friendly climber.
If you can, leave leaf litter in place or create a leaf pile to provide shelter for overwintering caterpillars and pupae.
And remember to follow our butterfly planting tips to provide nectar for the hungry butterflies when they wake up in the spring.