Where do butterflies spend the winter?

In the UK the winter can last several months. That is more than long enough for us humans to endure, but what about butterflies? Beautiful, yet considered to be ethereal summer sprites and often perceived of as fragile creatures.

Well it might surprise a few people to learn that butterflies are both tough and ingenious in their approaches to surviving the winter. Different species overwinter as various stages of their respective life cycles.

Out of 57 species that are regular residents all year:

• 31 spend winter as a caterpillar
• 11 as a chrysalis
• 9 as an egg
• 5 as adults
• 1 “uniquely in the UK” as either caterpillar or chrysalis – the Speckled Wood

Note: A full list of species can be found at the end of this post

Lets take one example, the Purple Emperor. It spends winter as a young caterpillar, almost motionless on a forked twig or close to a leaf bud of a Sallow tree, trying its best to stay hidden from those that might eat it! It mimics the appearance of its home exceedingly well and it takes people with a trained eye or very hungry birds to find them! But just pause to think how well adapted and tough this creature is, to sit out all that winter has to throw at it and then just carry on noshing away on the Sallow once spring returns.

A trio of Purple Hairstreak eggs on Oak buds.

The Purple Hairstreak has a different strategy. It spends winter as an egg, tucked up at the base of Oak leaf buds. Here they are reasonably safe, though there is always the threat of parasitisation by microscopic wasps and flies to worry about! A lot of books purport these eggs to be laid singly, but my own studies have shown that this is not always so. I have often found them in pairs, trebles and even groups of five. One would think that in general a single egg had more chance of survival as it is less noticeable, though perhaps in groups one or more egg may benefit from being “lost” in the crowd when parasites or other predators visit?

The statistics show that most species spend winter as a caterpillar. They are then a useful way of highlighting how important our grassland and meadow habitats are to butterflies, as a large proportion of those 31 species are reliant on grasses or other plants in meadow type habitats. That is why, when managing them, it is so important to leave some areas uncut over winter, as that is where so many of these caterpillars are trying to survive.

Orange-tip over-wintering as a chrysalis (this one is about to hatch and is a male).