A butterfly once thought to be dying out in the UK has colonised Scotland, thanks to the stinging nettle.
The comma butterfly was in severe decline in the 20th century and had become restricted to south-east England and a few counties in the Welsh borders.
But in a dramatic comeback, the UK population has increased by 138 per cent over the past 40 years, expanding more than 250 miles to cross the Border into Scotland and spread as far north as Inverness.
One of the few butterflies bucking the trend by expanding its range, scientists believe its “extraordinary” success is due to a combination of climate change and the comma’s increased use of nettle as a caterpillar food plant.
Richard Fox, head of recording for the charity Butterfly Conservation (BC), said: “The comma is clearly responding to climate change, which is driving its spread northwards.
“We have seen this in a number of other species that have spread up from England in to Scotland, but the comma is by far the most dramatic example.
“It now has spread not only through the whole of northern England but up through the Scottish Borders and Lothians, through Fife and Angus. It is now on the outskirts of Aberdeen and has been spotted in recent years near Inverness.
“The comma was once very firmly associated with hop – and was sometimes nicknamed the hop dog.
“Although hop is still around as a wild plant, the mass agricultural growing of hop for brewing is much diminished nowadays. It is also much more thinly spread in Scotland. But commas have become less dependent on hop and started to specialise on other things, particularly on the stinging nettle.
“Climate is driving the change but the comma has only been able to achieve this amazing spread north because it has become more specialised on stinging nettles, which are very widespread.”
Conservationists want nature-lovers to chart the progress of the remarkable comma during this year’s annual Big Butterfly Count.
The world’s largest butterfly survey, which runs until Sunday, encourages people to spot and record 18 species of common butterflies and two day-flying moths across the United Kingdom.
The results will help track the spread of the comma and could shed more light on the long-term population fluctuations of the butterfly.