A rare butterfly’s numbers have soared at a nature reserve within the space of a year.

Royston Crow: Therfield Heath saw a huge increase in the Large White, Small White and Small Tortoiseshell butterflies last yearTherfield Heath saw a huge increase in the Large White, Small White and Small Tortoiseshell butterflies last year (Image: Archant)

Members of the Butterfly Conservation group recorded 6,642 sighting of the rare Chalkhill Blue butterfly at Therfield Heath in 2013, a rise of more than 50%.

Latest records for other more common butterflies also saw large increases including the Large White, Small White and Small Tortoiseshell.

In 2012 numbers counted at the site were six, five and four for each of the three species, which rose to 80, 15 and 81 respectively in 2013.

Andrew Wood, chairman of Butterfly Conservation for the Hertfordshire and Middlesex branch, said there that Chalkhill Blue butterflies build up tight colonies and are abundant in a small area, unlike other species who spread out more sparsely.

He added: “Hertfordshire’s butterflies fared well in 2013, despite the long cold spring, a particular winner was the rare Chalkhill Blue, whose local stronghold is Therfield Heath.

“Numbers were up by more than 50% on 2012 and almost 900% compared to 2005-2009. There were so many, that almost uniquely, they were found at over a dozen sites far away from their normal chalkland habitats and caterpillar food plants.

“Familiar garden butterflies such as the Small Tortoiseshell and Peacock were much more abundant than in the last few years when fears had been raised for their long term future.”

For more informationabout the conservation group visit www.butterfly-conservation.org