Conserving our butterflies and caterpillars at home

by Dr Rosalind King

During lockdown, spending time in my small garden was an essential part of my daily routine. I valued the time to slow down and really appreciate creation as flowers opened, birds fed their young and butterflies flitted around the early blossom. The wildlife I enjoyed watching has inspired me to continue taking time over autumn and winter to ensure my garden continues to provide food and shelter for all that I saw, including butterflies.

There are only 59 species of butterfly in the UK¹, but what do they do in winter, and where do they go? Each butterfly species tackles the problems of a long, cold, wet, winter differently, so it can be tricky to ensure all requirements are met. Butterflies face new issues in a changing climate, with milder, stormier and damper winters, making it an equally challenging time for adult butterflies emerging to find that their main food plants have already flowered or have not yet started to flower.

The most common way for butterflies to survive winter is as caterpillars, with thirty-one species choosing this strategy¹. As vegetation dies off in autumn, the caterpillars will find a dry pile of leaves to hide under for the winter. It may seem like a long way to crawl to find a safe hiding place, but with over 4000 muscles, compared to our 629, they are quite capable of hunting out the safest of overwintering spaces⁴.

Despite their delicate appearance, five British butterfly species survive the winter as adults. Peacock and red admiral butterflies, for example, shelter inside the roofs of cool garages or sheds in winter, and brimstone butterflies shelter in thick vegetation such as ivy. 

Adult brimstones awaken as the weather warms up ready to fill up on dandelion, knapweed, cowslip and bluebell nectar before laying their eggs. These hatched eggs can be spotted on buckthorn and alder buckthorn shrubs² as indistinct, green caterpillars between May and mid-June. Ensuring a good supply of bluebell and teasel for the adults emerging in August, plus dense areas of buckthorn scrub for caterpillar food and ivy for adult winter shelter, will help this vivid yellow butterfly continue to be a delightful early spring sighting. 

Eleven butterfly species spend their winter as pupae¹ including the Larger white. From experience, you can avoid your vegetable patch crops being entirely eaten by leaving the stalk and leaves behind of the harvested cauliflower and cabbages and relocating any caterpillars from your broccoli. This way you can still have your crop and eat it, whilst ensuring the garden is full of butterflies next year! These caterpillars have mostly pupated by September and will overwinter as such, hanging from sheds, fences or walls, safe in the knowledge that the accumulation of cabbage compounds will make them unpalatable to many potential predators.

Although not every caterpillar turns into a butterfly (many turn into moths), all are an important part of the diversity of creation. Sadly, butterflies are in decline. The Butterfly Conservation Trusts report a 76% drop in abundance or occurrence since 1976^5,6. Planting butterfly-friendly nectar plants in our gardens may be helping as recent trends show this decline is slowing. With careful planning, and a willingness to sacrifice some traditional garden aesthetics, we can help protect the whole life-cycle of the butterfly and ensure that butterflies will continue to enchant us with their beauty each year.

How can you help?

Plant It: The Woodland Trust⁹ has some helpful guides on species associated with woodlands, with a list of adult and young food plants to consider planting in your garden to encourage specific butterflies. For example, stinging nettle isn’t an obvious garden plant, but it’s a key food plant for caterpillars of small tortoiseshell, red admiral, peacock, comma and painted lady. If you can, set aside an area to be left wild to nettles, or encourage your local council to leave a section of the park for nettles so these butterflies have plenty of food for their caterpillars.

Leave It: With so many butterflies surviving the winter as caterpillars and pupa¹, garden-tidying risks halting the life cycle. Leave sections of garden wild over winter, and if you must tidy, try to do so carefully, relocating any caterpillars or pupa that you find. Be careful and use gloves, as some caterpillars have irritant hairs. These yet-to-be butterflies can also provide food for other garden favourites such as hedgehog and birds during the winter when food is scarce, so it is well worth leaving some unmanaged areas of your garden for wildlife… and it means less work for you!

Record It: The Butterfly Conservation website² can help you identify butterflies you’ve seen. You can join in next July with The Big Butterfly Count⁷ or submit records now on the iRecord app⁸. 

About the Author: Dr Rosalind King has had a life-long interest in all things wild. Her early days were spent observing caterpillars in her English and South African garden, which led to an Ecology degree from Lancaster University and a Ph.D. in Restoration Ecology from Liverpool University. Based in North West England, she actively manages her garden for wildlife, undertakes conservation activities in her local woods and enjoys a varied career as a Consultant Ecologist helping bats, badgers, newts and other creatures stay safe.

References

1.  UK Butterflies https://www.ukbutterflies.co.uk/species_phenologies.php

2. Butterfly Conservation https://butterfly-conservation.org/uk-butterflies/a-to-z

4. World Atlas https://www.worldatlas.com/articles/10-interesting-facts-about-caterpillars.html

5. United Kingdom Butterfly Monitoring Scheme https://www.ukbms.org/

6. Butterfly Conservation https://butterfly-conservation.org/butterflies/the-state-of-britains-butterflies

7. The Big Butterfly Count  https://bigbutterflycount.butterfly-conservation.org

8. Biological Records Centre https://www.brc.ac.uk/irecord/

9. Woodland Trust  https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/animals/butterflies