The microscopic eggs of an endangered butterfly have been found in Scotland, suggesting the insect has returned to breed in the country for the first time in more than 130 years.
Lepidopterists discovered white-letter hairstreak eggs on wych elm trees at Lennel, Berwickshire, this month after an adult butterfly was spotted last summer 10 miles away – the first sighting in Scotland since 1884.
“Last year was an impossible find, but this year’s egg discovery is beyond anything we thought possible,” said Iain Cowe, butterfly recorder for the Borders, who found the adult butterfly last summer.
While most butterflies hibernate as caterpillars, the white-letter hairstreak spends nine months of the year as an egg, which is smaller than a grain of salt and stuck to slender branches of elm.
The eggs were detected by Jill Mills and Ken Haydock, volunteers for Butterfly Conservation who travelled from Bolton to scour trees in the Borders.
“We were searching the elm trees by the River Tweed at Lennel when Jill called me over,” said Haydock. “I could see by the look on her face that she had found something.
“We were both beaming with disbelief and delight when we realised what Jill had found and within seconds I was fumbling in my pack for the camera – my hands were shaking.”
Among the eggs found was an old, already-hatched shell, suggesting the elusive butterfly has bred in Scotland since at least 2016. Before the discovery at Lennel, the most northerly location for white-letter hairstreak eggs was in Northumberland.
The white-letter hairstreak has suffered a 72% decline over the last decade and is still suffering from the loss of elm trees in the 1970s caused by Dutch Elm disease.
A colony of the butterfly is threatened with extinction in Sheffield, where campaigners are fighting to save a rare surviving English elm. Sheffield council wants to drastically prune the tree as part of its controversial PFI contract to maintain the city’s streets. Butterfly Conservation is opposed to the pruning or destruction of the tree.