Exmoor estate sees resurgence of rare butterfly once on the brink of extinction

Over 1,000 heath fritillaries have been recorded so far across 13 sites on the estate - a significant rise from around 600 at the same time last year, with still a few surveys to take place. Early results suggest eight sites have higher counts than 2024, and three previously unoccupied sites have been recolonised. One small site has seen a dramatic increase, from just four butterflies last year to 186 this year.

The heath fritillary was almost extinct in Britain in the early 1980s, but targeted conservation work has brought it back from the brink.

The encouraging progress on Exmoor follows years of dedicated habitat management by the National Trust and Butterfly Conservation, which has created the ideal conditions for the fritillary to thrive. These efforts include using red Devon cattle to selectively graze the area, removing bracken and cutting glades at the edge of the woodland.

An exceptionally warm and sunny spring has also prompted the heath fritillary to emerge two to three weeks earlier than usual. Staff and volunteers have adjusted their monitoring accordingly, although there is concern that climate variability could impact the butterfly’s life cycle if wet weather arrives before the flight peak.

Basil Stow, National Trust Area Ranger at Holnicote, said: “We’re really pleased to be seeing such healthy numbers of heath fritillaries at Holnicote this year – it’s a real testament to the dedication of our teams, volunteers and partners who have spent a huge amount of time since the 1980s understanding and caring for the needs of this vulnerable species.

“But the early emergence is a mixed blessing. If unsettled weather follows, it could cut short the butterfly’s flight season and disrupt its life cycle. It’s a reminder of how delicately balanced nature is and how climate extremes can threaten even our most carefully managed landscapes.”

Jenny Plackett, South West England Conservation Manager at Butterfly Conservation, said: “It’s wonderful to see such strong numbers of heath fritillary on Exmoor this year. They’ve clearly benefitted from the warm, sunny spring, emerging as adults weeks ahead of schedule. We’ve recorded butterflies at several new sites, including areas where they haven’t been seen since the 1990s. The heath fritillary is generally very sedentary, so this kind of expansion is highly unusual and suggests that recent habitat management is working. We’re hopeful these populations will establish and extend their range across the estate.”

The heath fritillary and the high brown fritillary are both among the UK’s rarest butterflies and rely on carefully managed habitats. While the high brown favours bracken-covered woodland clearings and lays its eggs on violets, the smaller heath fritillary thrives in moorland and coppiced woodland where its caterpillars feed exclusively on common cow-wheat.

In the 1980s, the heath fritillary was on the brink of extinction in the UK. Targeted conservation has since brought the species back from the edge, but it remains restricted to four core landscapes: Exmoor, the Blean Woods in Kent, the Tamar Valley in the south west, and south Essex woodlands.

Exmoor is now considered the most important stronghold for the species. The early successional habitats it depends on – dominated by bracken, heather and gorse, with plentiful cow-wheat – require ongoing, sensitive management to sustain.

Basil Stow added: “The benefit of working across such a big landscape – rather than just on our own land – means we can create more habitats, and crucially, connect them up so the butterflies can move between suitable areas. This “network effect” will make the population more resilient in the long-term, and help the species to recolonise local sites where it had once become extinct.”