By Lucy Goodchild van Hilten

A towering elm tree stands 30 meters (approximately 98 feet) tall, somewhere near the border between England and Scotland, defying the fate that so many of its cousins met when Dutch elm disease ravaged the species in the 1970s. One of relatively few elm trees left, it is a haven for wildlife. Look closely and you can see the erratic fluttering of a small brown butterfly, with a W-shaped white streak across its wing.

This butterfly is making history: It's crossed the border into Scotland, where it has settled happily in a native wych elm tree and been sighted in the country for the first time in 133 years. The white-letter hairstreak—Satyrium w-album—has been squeezed slowly out of its habitat over the last 40 years, but now it seems to be getting a helping hand from an unexpected source: climate change.