As we huddle up inside with hot chocolates and good books many might wonder about the fortunes of some of our favourite summer icons – the butterflies.
Our butterflies can’t retreat into cosy homes (although occasionally they do sneak into ours!), so have had to evolve to survive the long winter months. The majority of the UK’s butterflies will spend the winter as caterpillars, chrysalises or even eggs, but there are a few species of butterfly that can overwinter as adults.
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 like flying, feeding and mating. 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 save their energy by reducing their activity and bodily processes and effectively sleeping 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.
It’s really important to try to not disturb the habitats they might use to shelter in, check out here for more advice.
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 like 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 embrace it. They are able to choose which areas of their body they want to freeze. They do this using ice-nucleating agents – essentially 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 again. However, some species which couldn’t previously survive in the UK in winter are now finding that they can. Species like the Red Admiral. Traditionally, Red Admirals were very rare here during winter – they all migrated further south to continue their life cycles. However, because of climate change, 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.
