STUDY by ecologists has confirmed the existence of a rare butterfly on three chemical sites on Teesside.
Grayling, which have died out in many parts of the North-East, like dry, dusty areas with poor soil and poor vegetation, a combination that often occurs on brownfield areas.
The team from the Teesside-based Industry Nature Conservation Association (Inca) conducted searches of several areas during the summer.
They confirmed the insect's presence at the Wilton International chemical complex, where Inca has its offices, Huntsman Tioxide's Greatham Site, near Hartlepool, and Lucite International's Cassell
Works, in Billingham.
Jonathan Gibson, one of the Inca ecologists, said: "The grayling butterfly is a rare sight in the North-East. They require areas of bare ground on which to bask and on Teesside, the species is
found on railway sidings and brownfield sites associated with heavy industry."
Grayling, which are also found on sand dunes, and limestone grasslands, were common near Hartlepool during the 19th Century. However, there had been no recent reports, apart from unconfirmed ones
from Teesmouth in the Sixties and from the former Furnaces Shipyard, at Haverton Hill, on Teesside, in the mid-Eighties.
Over the past five years, though, the reports have been growing and in 2001 the butterfly was recorded at Maze Park, next to Thornaby Marshalling Yards, also on Teesside.
Since then, its range has expanded and the butterfly has colonised several other industrial sites, including Corus, in Redcar.
Before the recent sightings, the nearest known 20th Century colonies were in the Yorkshire Wolds and Northumberland.
Ken Smith, another Inca ecologist, said: "Despite this expansion on Teesside, the grayling is declining elsewhere in the UK, and is one of the top ten most threatened species."
He said the number of its sites had dropped by 45 per cent and the number of butterflies was believed to have reduced by 51 per cent.
The main threat to the species is the loss of habitat through redevelopment or inappropriate management.
Mr Smith said: "It is important that appropriate measures are taken to conserve this species wherever it is found."