Large Blue, Collard Hill, Somerset

Large Blue butterfly

Britain’s rarest butterfly is thriving in Somerset thanks to an innovative grazing regime backed by farmers and conservationists.

Large blue butterflies disappeared from the UK in the 1970s and were reintroduced at Collard Hill, near Glastonbury, in 2000 by a partnership of 22 organisations – including National Trust, Butterfly Conservation, Oxford University and the Centre for Ecology and Hydrology.

Since 2000 the butterflies have boomed – with roughly 50,000 eggs laid annually in recent years. Around a thousand people visit the site every year in the hope of spotting the large blue.

Our rangers put the success of the large blue down to a conservation grazing scheme. The site is grazed by around 20 native-breed Dexter cattle, owned by Somerset grazier Pat Bishop.

Ian Clemmett, National Trust lead ranger, said: “The grazing provides the right conditions for wild thyme, which is the main food plant for the caterpillars and play an essential part in their lifecycle

“The tight grazing also makes sure the sun gets down to the ground, providing the right temperature for a single species of red ant to thrive.

“When out foraging the ants are duped into thinking the larva is one of their own and ‘return’ it to the nest whereupon the caterpillar turns from herbivore to carnivore, feeding on ant grubs throughout the winter until it is ready to pupate and leave the nest in early summer. The large blue caterpillars eat the ant grubs.

“The cows are on Collard Hill all year round, but we move them off the sensitive hillside from mid-May until late summer.”

Collard Hill is limestone grassland, one of fifty struggling ‘priority’ nature habitats hand-picked by government as needing help. The site is also home to a variety of butterflies and spectacular orchids.