AS discoveries go in the natural world, a find by two Bolton wildlife lovers is being hailed as a find of a lifetime.

Friends, Ken Haydock and retired school teacher Jill Mills, aged 69, discovered that a rare butterfly has bred in Scotland for the first time in more than a century after coming across a handful of White-letter Hairstreak eggs in East Scotland.

The find comes after the declining butterfly was discovered in the country after a 130 year absence in August of last year.

The amateur naturalists made the find on some Wych Elm trees near Coldstream, Berwickshire, East Scotland, where the butterfly was spotted — the first sighting in Scotland since 1884.

The two ,who live in  Horwich ,volunteer for wildlife charity Butterfly Conservation — the president of which is David Attenborough . They have been monitoring the gradual spread northwards through the UK of the White-letter Hairstreak, which experts think is most likely the result of a warming climate.

Ken, aged 70, a retired joiner, said: "Our personal challenge was the distribution of the White-letter Hairstreak on the west side of the Pennines, with our finds taking us from Greater Manchester, through Lancashire and then up as far as north Cumbria. We also ventured over the border into South West Scotland, but as yet, this little butterfly is eluding us there, though we will keep on trying!

"This year we were asked to head to East Scotland to see if we could find any evidence the butterfly was breeding. It was a lovely sunny morning and we were searching the elm trees by the River Tweed at Lennel when Jill called me over.

"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."

The White-letter Hairstreak, which has a distinctive ‘W’ marking on the underside of its wing, is widespread across England and Wales, but the butterfly has suffered a 72 per cent decline over the last decade.

The butterfly’s caterpillars feed on elm and the White-letter Hairstreak declined dramatically in the 1970s as a result of Dutch Elm disease.

They have both volunteered for the charity for a number of years and are already planning their next adventure back to Scotland to see if they can find more eggs!

Butterfly Recorder for the Scottish Borders, Iain Cowe, said: "Last year was an impossible find, but this year’s egg discovery is beyond anything we thought possible. It is hugely significant as it not only confirms the White-letter Hairstreak is breeding in Scotland, but one of the eggs Ken and Jill found was an old, hatched shell — so the butterfly could have been breeding here since at least 2016."

Before the discovery in Berwickshire, the most northern location for White-letter Hairstreak eggs was about an hour south, at Rothbury in Northumberland.

Director of Butterfly Conservation Scotland, Paul Kirkland, said: "We will need to have a few more years of confirmed sightings before we can officially class this butterfly as a resident species in Scotland. If this happens, it would take the total number of butterflies found in Scotland to 34, which really would be something to celebrate."