Hungry and hairy Hungarian hogs help save UK's most endangered butterfly

Since 1978, this pretty orange insect with black chequered wings has declined by 65% in population and 87% in distribution across the UK. It is now found in just three locations in England, one of which is the sun-bathed Heddon Valley near Barnstaple.

The south-facing bracken-covered slopes offer ideal breeding conditions for the High Brown but high-growing trees and shrubs quickly take over the habitat.

The Hungarian breed shaggy swine and English Longhorn cattle owned by the National Trust act as living lawnmowers, chomping down the aggressive growth to create space for the tiny, delicate Common Dog-violets which are the High Brown caterpillars' sole food plant.

Butterfly Conservation Project Officer Ellie Wyatt said: "This is an incredibly exciting project and working with the National Trust is very rewarding. The trust have been working with the pigs for a couple of years and noticed how their rootling actions benefited the soil and encouraged violets to germinate, so it's great to continue this work to help save the High Brown Fritillary.

"The Longhorn cattle are also gorgeous and look majestic in the landscape and I'm looking forward to seeing the trails they and the pigs make through the bracken and seeing if violets spring up in these paths. From the pigs to the pollarding woodland work, it’s an innovative project to be part of and I feel honoured to be working with so many passionate people to help this rare butterfly."

The High Brown Fritillary has a wing span up to 67mm - among the biggest in the UK. Its distinctive caterpillars, covered in spikes, are perfectly camouflaged in dry brown leaf litter in April and May, while the showy adults appear in June and July and drink nectar from thistles and bramble flowers.

The species was once widespread across England and Wales, but has suffered dramatic decline since the 1960s, largely due to destruction of its habitat for development and changes in land management practices.

Butterfly Conservation secured a £228,000 Species Recovery Grant from Natural England last year, to which it and the National Trust added £12,000 each. The Trust is also providing the livestock from a nearby site.

They are putting up fencing around three fields to target the hungry herbivores in specific areas and Ellie has been working with volunteers to clear other scrub plants like the thorny gorse that could take over the habitat.

The team are even painstakingly collecting the tiny seeds from the Common Dog-violets and germinating new plants in an off-site nursery that they can plant in new locations to increase the extent of potential breeding habitat.

Butterfly Conservation is training National Trust workers to maintain these precious habitats long into the future, but is looking for more volunteers to help.

National Trust ranger for West Exmoor Mathieu Burtschell said: "Collaborating with Butterfly Conservation has allowed us to do some exciting and much needed work in our woodlands that will benefit the high brown fritillary as well as many other species. Most of our wooded valleys on West Exmoor were exploited for oak timber and were cyclically clear felled. This industrial exploitation ended about a hundred years ago, and the oak trees were allowed to get away. The issue we now have is that most of the trees are the same species, same age, and featureless. ​​​​​​​

"The woodland work we are carrying out aims to diversify the structure of this oak monoculture. We have created a series of glade by felling, pollarding (felling above the reach of browsing animals), and ringbarking (leaving trees as standing deadwood). These interventions will allow light in the woodland which will increase the ground flora interest of the site, and add some complexity to the structure of the woodland."

Butterfly Conservation has identified 10 other National Trust sites where new colonies of High Brown Fritillary could establish, but it urgently needs to do further survey work and plan landscape restoration.

The work at Heddon Valley builds on the success it has already had conserving the High Brown at nearby Dartmoor: in 2022 the charity recorded a 20-year high in the population there after years of work which shows that major recovery of vulnerable species is achievable.