A rare butterfly thought to be extinct in Northern Ireland has been discovered in Co Fermanagh.

The Small Blue butterfly was discovered by Bobbie Hamill, a surveyor from the Northern Ireland Environment Agency.

While the Small Blue (cupido minimus) is found in other parts of Ireland and Britain, it is undergoing a significant decline. It is the North’s rarest and most endangered butterfly and is listed as a Northern Ireland “priority species for conservation action”.

The agency’s habitat survey team recorded a total of seven Small Blues on the wing on May 31st. It has partially attributed the occurrence of the species in relatively high numbers to the unusually warm weather.

Ms Hamill spotted the butterfly while assessing the condition of the flower-rich plant communities in one of Northern Ireland’s most important grassland areas of special scientific interest, just west of Derrygonnelly.

“Not only is the Small Blue our smallest butterfly, but unlike other members of its family it is inconspicuous and can easily be overlooked,” she said. “Rather than blue, the upper wing is actually dull brown in colour, fringed by white hairs with a dusting of blue scales at their base and the underside is silver blue with dark speckles. In addition, at little more than 20mm, it is not surprising that these beautiful little butterflies are difficult to spot.”

Ms Hamill commended the landowners and managers in the area for continuing to graze these special sites in a sustainable manner, thus “creating the ideal conditions for plants to flourish and the Small Blue and other important invertebrates to breed”.

“It is still possible that other colonies of this tiny butterfly are surviving in suitable quiet corners of Fermanagh and beyond, so be on the lookout,” she advised.

Catherine Bertrand, head of conservation for Butterfly Conservation in Northern Ireland, said its volunteers had revisited the Fermanagh site sporadically over the past 16 years since the butterfly was last seen, with no success.

“We genuinely believed it was extinct from Northern Ireland,” she said.

She said Butterfly Conservation had followed up on the find with a further visit to the site, specifically to survey the extent of Kidney Vetch, the caterpillar’s sole food plant, and to hunt for Small Blue eggs laid on the flower heads.

“The outlook for the Small Blue is currently very positive, with plenty of the food plant across the site, lots of eggs for the coming season and most importantly, a landowner who is working to ensure this remains one of the most important wildlife sites in the country,” said Ms Bertrand.