An elusive butterfly that has been officially extinct in Britain for more than half a century has been discovered while breeding at Knepp’s re-wild estate in West Sussex.
The large tortoise mysteriously disappeared more than 50 years ago, but this week male and female butterflies — much larger than the small tortoise and without its white pattern — were first spotted near Knepp.
Neil Hulme and Matthew Oatesthe lepidopterists who made the discovery also found signs of its caterpillars eating elm leaves in the re-wild farmland earlier this spring.
“This butterfly is still officially extinct, but the evidence suggests it is making a comeback,” Oates said. “This is a undergrowth and historically and culturally we have disliked the word ‘scrub’ and made every effort to eliminate it in rural areas. At Knepp there is an ideal scrub for this.”
Since 2019, small numbers of the butterfly breeding found in Portland on the Dorset coast, with adults identified alongside the egg boilers and tires produced by large turtle caterpillars. Another colony has been discovered in a valley in East Sussex.
Large tortoiseshell caterpillars feed on a variety of trees, including elm, aspen, vale, and fruit trees, and it’s not known exactly why the species became extinct in the 20th century. Theories include populations being attacked by parasites, Dutch elm disease, and the loss of orchards and scrub such as griffon, which were cleared from forests when conifers were planted. The butterfly feeds on pale yellow flowers in spring.
The butterfly was last widely seen in the late 1940s. Only occasional individual butterflies have been sighted since the 1950s, often close to shore, indicating that a few arrived from abroad without breeding.
According to Oates, the number of large tortoises is on the rise again on the continent – possibly due to climate change – and more and more numbers are crossing the Channel to arrive at the southern coast.
But the picture is confused because some maverick butterfly breeders have also secretly released the species.
Oates said there were too many sightings close to the south coast for them all to be the work of breeders, and the species is also difficult to breed in captivity. “I don’t believe butterfly breeders would all travel to the south coast just to let them go. They come in too,” he says.
The adult butterflies emerge in July and soon disappear to hibernate and mate only in the following spring.
“A lot of them have to come out to find a partner and they have to have a very sophisticated strategy for finding partners,” Oates said. “How do they mate when they live in this low density? We still have a lot to learn about this butterfly.”
It’s been a bountiful season for wildlife at Knepp, with a record number of nightingales – 40 singing males – taken to the estate this summer, in addition to a record nine stork nests, which have been reintroduced and already have other wild storks from the continent have attracted.
Isabella Tree, who began naturalizing 20 years ago with her husband Charlie Burrell Knepp, said: “We always think we need to step in and bring things back, but time and time again we see it’s just about habitat and providing of the space for nature and many species can come back on their own.”