The Ulster Museum and Butterfly Conservation have announced the discovery of a new species of butterfly, a variety of the wood white. The find has cleared up a long-standing mystery: why the wood white is in serious decline in Britain but spreading rapidly on this island.
An irony of the discovery is that the "newcomer" isn't new to Ireland at all. It has lived here for many years but remained hidden because of a case of mistaken identity.
The confusion was cleared up by Maurice Hughes, Northern Ireland development officer for Butterfly Conservation, the largest insect-conservation charity in Europe, which seeks to protect butterflies, moths and their habitats.
A variety of wood white has rapidly been expanding its range in Ireland over the past 40 years, particularly in the Republic. It had always been assumed that the variety was the common wood white, Leptidea sinapis.
A recent analysis by Hughes showed, however, that the variety doing so well here was another species, Leptidea reali. "They can tell the difference, but we physically can't just by looking at them," says Hughes.
"Brian Nelson in the Ulster Museum had asked me to look at a couple of wood-white species which he had. This was really the first time we had looked at local species," he says. "Until then, all of the wood whites here we had assumed were sinapis."
The only way to tell them apart is to dissect them. The genital capsule is longer in both male and female reali than in sinapis. "Another difference is the habitat preference," says Hughes. Sinapis likes the cover of woodland but reali prefers wide-open spaces, such as road verges and sheltered grassland.
The specialists recognised that the wood white was in trouble in Britain but was spreading here, which encouraged them to take a second look at the insect. "You wouldn't normally go out and dissect a butterfly to see if it was different than you expected."
When Hughes started to examine wood whites, he found that the butterflies sourced in Ireland were not the assumed sinapis but were reali. He then followed the trail backwards in time, dissecting museum specimens that had been held for decades. The oldest was collected 97 years ago.
"Most of the ones I have dissected have been museum specimens. The old ones are just as easy to dissect as new ones."
His work immediately revealed the long-standing misidentification of the wood whites that thrive in Ireland. "This is an exciting and important discovery, which helps to explain the puzzle," says Hughes.
"In Ireland we have found that the 'normal' wood white is apparently confined to the scrubby woodland around the Burren, in Co Clare, making it the rarest Irish butterfly. The 'new' species occurs throughout Ireland, but is absent from Britain."
The work also highlights the need for renewed efforts to protect the shrinking habitats suitable for sinapis if this species is to survive on these islands, says Hughes.
His research will also continue, trying to find simpler methods to identify the wood white in the field. One approach involves illuminating the butterflies using ultraviolet light.
"They see each other in ultraviolet," he explains, so there may be striking visual differences in this wavelength.