NIEA discovers rare butterfly previously feared extinct in Northern Ireland

Date published: 19 June 2017

A surveyor from the Northern Ireland Environment Agency has discovered a rare butterfly previously thought to be extinct here.

Small Blue Butterfly

Bobbie Hamill came across the Small Blue Butterfly – Cupido minimus  while working in Co Fermanagh. Last recorded from its only known site in 2001, it was feared that the butterfly was extinct in Northern Ireland. 

The Small Blue is our rarest and most endangered butterfly and is listed as a Northern Ireland Priority Species for conservation action. Although the species can be found in other parts of the UK and Ireland, it is undergoing a significant decline.

NIEA’s Habitat Survey Team recorded a total of seven butterflies on the wing on May 31. They partially attribute the occurrence of the species in relatively high numbers to the unusually warm weather – Northern Ireland has enjoyed its warmest spring since records began. 

Bobbie 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 (ASSIs), just west of Derrygonnelly. An assessment of these special areas is undertaken by NIEA every six years to ensure that their scientific interest is being maintained. 

She said: “Not only is the Small Blue our smallest butterfly, but unlike other members of its family it is inconspicuous and can easily be overlooked. 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.

“We would especially like to commend the landowners and managers in the area for continuing to graze these special sites in a sustainable manner, 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.”

Catherine Bertrand, Head of Conservation for Butterfly Conservation in Northern Ireland, said: “I cannot articulate how delighted we are that the Small Blue has been reconfirmed. Our volunteers have revisited the 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 the Butterfly Conservation had followed up NIEA’s discovery 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. 

She added: “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."

The ecological requirements of the Small Blue are very specific as its existence relies on the presence of its sole food plant, Kidney Vetch. It requires taller plants where the males can take up station and attract females. Kidney Vetch is a beautiful low growing herb with bright yellow flowers in spring and early summer. It thrives in ecological niches where soils are very thin and the base-rich rocks are exposed preferring warm, sheltered south-facing slopes.

Similarly the Small Blue is generally found in these locations where the female lays a single egg on the flower bud of the Kidney Vetch. Once hatched the caterpillars (larvae) feed on the flower head and developing seeds. In autumn, they drop to the ground and overwinter in crevices.   Pupation occurs the following spring before the butterfly emerges in late May and June to repeat its life-cycle once more.   

Bobbie Hamill concluded: “West Fermanagh, with its outstanding limestone dominated landscape, would appear to have an abundance of potentially suitable areas for Small Blue. However, achieving the complex combination of the wide range of environmental factors required by the butterfly is more challenging. Extensive, low intensity grazing with traditional breeds of cattle is ideal for the management of these flower-rich, semi-natural grasslands.”

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