Doing our bit for butterflies

Beautiful butterflies feature Organic Way Summer 2023

Our latest annual butterfly survey has revealed the devastating impact of last year’s summer heatwave on UK butterfly populations. Liz Potter explains what’s at stake and what we can do about it

There are few sights more stirring than Lepidoptera on the wing. But, like the songflight of a skylark at dawn or the snuffling of a hedgehog at dusk, a butterfly fluttering by is fast becoming a reminder of summers past. Last year’s drought has not helped matters.

A 2022 report on The State of the UK’s Butterflies revealed that 80% of butterflies have declined in abundance and/or distribution since the 1970s. This is hugely alarming, especially given their role as an indicator species for insects more generally: their short life cycle meaning they react quickly to environmental changes. Now, the UK Butterfly Monitoring Survey (UKBMS) for 2022 shows that last year’s soaring summer temperatures (reaching a British record of 40.3°C in July) has brought yet more bad news.

“Butterfly populations naturally bounce around a lot and zig-zag from year to year,” says Dr Richard Fox, Head of Science for Butterfly Conservation. “It’s only by comparing each species against our survey data – which stretches back to 1976 – that concerning factors have emerged. The second generations of common species such as the small tortoiseshell, peacock, green-veined white, brimstone, small white and small copper fell off a cliff from August-September. We’re certain that’s due to the drought. The other element is that for those butterflies that only produce one generation a year, we haven’t seen the full effect of the drought yet, so this could just be the tip of an iceberg.”

Eco benefits

Besides their beauty, Britain’s 57 resident butterfly species (and two migrant species) bring numerous ecological benefits to our gardens. They’re not only considered a flagship indicator for overall environmental health, they also play a key role as pollinators, with specialist mouthparts (probosces) to extract nectar from some of our rarest wildflowers. In addition, bats and birds, particularly blue tits, predate their caterpillars to feed their young, while parasitic flies and wasps consider them a tasty host to consume from the inside out.

In turn, butterflies are famously fussy about where they lay their eggs: caterpillars of the orange-tip butterfly for instance depend on cuckooflower (Cardamine pratensis) and garlic mustard (Alliaria petiolata), while the rare Duke of Burgundy butterfly depends on cowslips and primroses (Pimula spp.). This dependence on drought-sensitive plants makes their caterpillars incredibly vulnerable.

“Generally speaking, hot sunny weather is a boon for butterflies – they love it,” says Richard. “They’re cold-blooded creatures that need the warmth of the sun in order to function. The real problem is drought, which kills the plants that those new eggs are developing on, so that when the caterpillars hatch, the plant has shrivelled away to nothing, and there’s no back up.”

Species that depend on grasses as a foodplant are a particular worry. “There’s a whole bunch of butterflies whose caterpillars feed on long-growing grasses on road verges, field margins and meadows,” says Richard. “The ringlet seems to favour damper grassland, and the more common gatekeeper, meadow brown and large skipper all have a single generation each year, so we won’t see the full impact of the drought until this June, July and August.”

Though relatively common, the small tortoiseshell is already in massive long-term decline. “They’ve suffered their fourth worst year since monitoring began,” says Richard. “They did badly in all parts of the UK apart from Northern Ireland, suffering an 80% decrease since 1976, so we only have one-fifth of them left now. Anything that further reduces the population is not good news.”

Surveys tracking butterfly recovery following droughts in 1976 and 1995 paint a bleak picture. “To this day 1977 remains the worst year on record for butterflies in the UK,” says Richard. “Many of the threatened species never regained their populations – not solely because of the drought; subsequent decades of habitat destruction have meant that many of the places they used to live are now intensively managed fields or have become housing estates.”

A substantial drought in 1995 brought further catastrophe. “Large white abundance in the UK dropped by 66%; small whites were down 56%; ringlets down 51%; green-veined whites down 41%; speckled wood down 41%. It took a number of years for those populations to recover. The worry now is that climate change will bring more frequent drought: forecasts suggest they could happen every six years. And if that comes to pass, none of those butterfly species will be able to bounce back.”

What we can do

Larger populations of butterflies will be more resilient in the face of drought so it’s important that we all do our bit to support them. At a community level, our gardens can provide important ‘stepping stones’ between nature reserves and other wild areas.

Firstly, it’s helpful to create shade. “A study on the ringlet butterfly in 1995 saw that populations in woodland survived the drought better,” says Richard. “So, plant trees, large shrubs and more hedging, which will also extend the life of caterpillar foodplants in drought.”

Then, let some of your grass grow long. “Don’t do it just for No Mow May, but all year round. You don’t have to abandon your whole garden – just a strip next to the fence will make a difference for wildlife. The speckled wood is very much at home in urban areas, so a patch of long grass could be life-saving for them.

“I generally don’t recommend growing nettles for butterflies in gardens,” says Richard. “The small tortoiseshell and peacock butterflies are nettle specialists that need large patches of them in full sun and will ignore the scraggy patch behind your shed.”

Planting nectar-rich flowers is less important than creating pesticide-free habitat. “We need to contribute to the national population of butterflies – not just by creating a ‘motorway service station’ of fast food from a buddleia bush,” says Richard. “Though it’s fine and lovely to see butterflies coming in for the nectar, we all need to think about creating some habitat for caterpillars as well. If you create the habitat, they will come, and they will benefit.”

Caterpillar foodplants

• Red admiral: mainly common nettle (Urtica dioica)
• Peacock: mainly common nettle (Urtica dioica)
• Brimstone: buckthorn (Rhamnus cathartica); alder buckthorn (Frangula alnus)
• Painted lady: thistles (Cirsium spp. and Carduus spp.); mallows (Malva spp.); common nettle (Urtica dioica), viper’s-bugloss (Echium vulgare)
• Comma: common nettle (Urtica dioica); hop (Humulus lupulus); elm (Ulmus spp.)
• Green-veined white: many plants including garlic mustard (Alliaria petiolata); cuckooflower (Cardamine pratensis); hedge mustard (Sisymbrium officinale); watercress (Rorippa nasturtium-aquaticum); charlock (Sinapis arvensis); large bittercress (C. amara); wild cabbage (Brassica oleracea); wild radish (Raphanus raphanistrum); nasturtium (Tropaeolum majus)
• Small tortoiseshell: mainly common nettle (Urtica dioica)
• Small white: mainly cultivated cabbage, Brussels sprouts, broccoli etc (Brassica oleracea); nasturtium (Tropaeoleum majus)
• Large white: mainly cultivated cabbage, Brussels sprouts, broccoli etc (Brassica oleracea); oil seed rape (Brassica napus); nasturtium (Tropaeolum majus); wild mignonette (Reseda lutea); sea kale (Crambe maritima)

Pollinator friendly plants for a nectar cafe
Pollinator friendly plants for a nectar cafe

This feature originally appeared in Organic Way, Summer 2023

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