Butterflies have poor year in 2021 – but some threatened species fare better

Cold, wet spring weather left butterflies faring poorly in 2021 – but some threatened species are doing well with conservation help, experts have said.

Results from the annual UK Butterfly Monitoring Scheme (UKBMS) show that, with a chilly April and one of the coldest, wettest Mays on record, especially in England and Wales, many common and widespread species had a poor year.

Overall it was a below-average year for UK butterflies, ranking 28th out of 46 years of the national survey, which sees sites surveyed for butterflies on a weekly basis throughout the summer, and the worst since 2017.

The green-veined white had its fourth worst year on record, and the large skipper its fifth worst, while the common blue, large white and small skipper all had a poor year.

Even some widespread species that have seen long-term increases fared badly in 2021, such as the ringlet butterfly, which recorded its lowest numbers since 2012.

Despite the adverse conditions, there were some better results for threatened species such as the heath fritillary, the survey found.

The endangered butterfly, which relies on the right woodland management for its habitat and has been the focus of long-term intensive conservation efforts in Kent, Essex and Somerset, had a good year.

It has seen populations more than double – an 112% increase – at monitored sites over the past decade.

The silver-studded blue butterfly, which is classed as vulnerable to extinction in Britain, has also benefited from conservation work on its heathland and grassland habitats and saw its best year since 1996 last year.

Its numbers have increased by 70% since the 1970s, the conservation organisations behind the survey said.

Butterfly Conservation’s associate director of recording and monitoring, Dr Richard Fox, said: “We’re delighted to be seeing some positive signs for species such as the heath fritillary, especially when the general long-term picture for UK butterflies is one of great decline.

“It reinforces the importance of managing and restoring habitat in a way that supports the survival of our butterflies.

“While the heath fritillary remains a priority for conservation, these successes demonstrate what can be achieved through dedicated long-term conservation effort.”

He added: “There are grounds for cautious optimism in the results of many other threatened species that are the focus of conservation action, especially given that 2021 wasn’t a good year for butterflies in general.”

He pointed to good years for both black and brown hairstreaks, and for the Glanville fritillary, dingy skipper, Adonis blue and chalk hill blue, all of which had numbers above their long-term averages.

But many species still show major long-term declines, such as white admirals, which recorded their third worst year since 1976 at monitored sites, with all three worst years occurring in the last decade.

Butterfly populations fluctuate naturally from year to year as a result of the weather, but long-term declines are being driven by human activity, such as land management and climate change – with conservation efforts making a real difference to local numbers, Butterfly Conservation said.

Ian Middlebrook, UKBMS programme lead, said butterflies are among the creatures most reliant on sunshine for their activity.

“It’s not just the direct impact it has on the butterflies being able to fly – there are the knock-on effects for food plants at different stages of the butterfly’s life,” he said.

He also said climate change is affecting butterflies in different ways, with some expanding their range as temperatures rise but also increasing the risk of being out of sync with food plants.

And there is significant pressure from development, the loss of key habitats, and intensification of farm management, he said.

Dr Marc Botham, butterfly ecologist at the UK Centre for Ecology and Hydrology (UK CEH), said the scheme had received 476,000 records from more than 2,900 sites, despite 2021’s challenges for data-gathering and conservation activities.

He said the records from volunteers enabled scientists to measure how butterflies are faring and assess the health of the countryside.

“The UKBMS data are vital in assessing the effectiveness of government policies and progress towards the UK’s biodiversity targets,” he added.

The scheme, led by Butterfly Conservation, UK CEH, British Trust for Ornithology and Joint Nature Conservation Committee, involves weekly counts at thousands of the same sites across the UK from April to September, targeted species surveys and counts from randomly selected sites.