Hogs help to protect butterfly species
National Trust have recruited the help from some unusual volunteers to help save the UK’s most endangered species of butterfly at Heddon Valley in Devon
Curly haired Hungarian Mangalitsa hogs have been used on one of the National Trust’s Exmoor sites to create perfect habitat for the High Brown Fritillary.
Since 1978 this butterfly species 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 Heddon Valley near Barnstaple.
The have a 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 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 pigs, along with some longhorn cattle are acting like natural lawn mowers. As they graze on the aggressive growth to create space for the tiny, delicate Common Dog-violets which are the High Brown caterpillars' sole food plant.
Animals have been used for grazing on site of the National Trust for years, but it was noticed how the hogs snuffling around and digging up the ground were benefitting the soil and encouraged violets to germinate. So it seemed the perfect solution to help save the High Brown Fritillary.
Fencing is being put up around three fields to ensure the animals target specific areas.
Human volunteers are also working to clear other scrub plants like the thorny gorse that could take over the habitat.
They are also carefully 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 also training National Trust workers to maintain these precious habitats long into the future.
Most of the wooded valleys on West Exmoor were exploited for the oak timber. This ended about a hundred years ago and the oak trees were allowed to grow again. The issue now is that most of the trees are now the same species and age.
The woodland work aims to diversify the area. A series of glades have been created by felling, pollarding (felling above the reach of browsing animals), and ringbarking (leaving trees as standing deadwood). These interventions will allow light into the woodland which will increase the variety of the ground flora.
The work at Heddon Valley builds on the success at nearby Dartmoor. In 2022 a record 20 year high in the population after years of work which shows that recovery of vulnerable species is possible.
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.
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.