The largest reintroduction of a butterfly once extinct in Britain has been a success after they bred in their first year.

The large blue butterfly was introduced to Rodborough Common in Gloucestershire in 2019 after five years of preparing the landscape for the species.

Globally endangered, large blue butterflies’ life cycle involves the larvae tricking a particular species of red ant into carrying them into their nest.

They then feed on ant grubs before emerging the next year as dusky blue butterflies with distinctive black spots on their wings as well as a black border.

The species was declared extinct in Britain in 1979 before being reintroduced from European populations nearly 40 years ago and is the largest and rarest of all nine British blue butterflies.

Several sites across southern England have had the butterflies established there but the scheme at Minchinhampton and Rodborough Commons is the largest ever reintroduction in the UK.

Successful reintroductions have had to create the right conditions for the Myrmica sabuleti ant species and encourage the growth of wild thyme and marjoram, which the butterfly feeds and lays its eggs on.

On the 867 acre National Trust common, near Stroud, 1,100 larvae taken from other West Country locations were released last August.

An estimated 750 butterflies have successfully emerged at the site over the summer, while the team monitoring the scheme have recorded large blues mating and eggs laid on thyme and marjoram.

It is the first time for 150 years the large blue butterfly has been recorded at Minchinhampton and Rodborough Commons.

The site had to be prepared for them by creating small temporary grazing areas with electric fences to allow cows, including Hereford, long-horn cattle and Luing to graze slopes to provide the right conditions for the ants, while scrub control was also carried out.

David Simcox, research ecologist and co-author of the commons management plan, said: “The butterfly needs high densities of the heat-loving red ant Myrmica sabuleti, which has a crucial role to play in the lifecycle of the butterfly.

“The grazing cows create the ideal conditions for them by keeping the grass down so sunlight can reach the soil which gently warms it, creating perfect conditions for the ants, which are cold blooded and therefore need warmth in order to actively scout for food throughout the spring, summer and autumn.”

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