The vanishing small blue: why butterfly is starving

Little bigger than a 10p piece, one of Britain's smallest butterflies is fighting for existence on the most northerly edge of its range.

Although common among the sheltered open spaces of Europe, from northern Spain to Scandinavia, and across Asia and Mongolia, the small blue, aka Cupido minimus, is just about clinging on to life in the north of Scotland.

As one of nature's most fussy eaters, the tiny creature eats only the yellow flowers of the kidney vetch plant which often grows among sheltered grasslands along the coastal areas of Britain, in man-made habitats such as quarries, gravel pits, road embankments and disused railway lines.

However, increasing pressure from human development, changing agricultural practices and coastal use has driven the tiny butterfly into just a few remaining selected strongholds in the south of England and northern Scotland.

"It is a species which needs open, warm, sunny habitats but, unfortunately, changes to many traditional habitats have meant that the kidney vetch has started to die out in areas and therefore so has the small blue," said Paul Kirkland, the director of Butterfly Conservation Scotland. "The trouble is that with habitats getting smaller with the encroachment of development or forestry the chances of the open patches needed by the small blue being created or preserved is getting smaller all the time."

The dusky butterfly lays eggs the size of pinheads on the yellow flower of the plant and, once hatched, the larvae burrow into the bloom and feed on the growing seeds. Eventually the larvae leave the plant and dig into moss and soil to form chrysalises before emerging the following spring as butterflies to repeat the breeding cycle.

However, changing land use has meant that many of the kidney vetch flowers are being strangled and overshadowed by other, more aggressive plants, leaving colonies of the small blue to die out.

Today, wildlife workers and volunteer conservationists will begin a rescue mission to help bring the tiny butterflies, with a wingspan of little more than an inch, back from the edge of extinction in Scotland.

A Highland Council countryside ranger, John Orr, and volunteers will begin to clear the sand dunes along the coast near Inverness of the plants which threaten to kill off the only food source of the small blue. They will start by clearing out hardier plants such as broom, which threaten vetches by blocking out sunlight which filters through among the sand dunes of the windswept beaches at Nairn.

"The small blue is one of our rarest butterflies and it needs the kidney vetch to survive as its caterpillar won't eat anything else," said Mr Orr. "The plant used to be common along the sand dunes at Nairn east beach but is becoming scarce as whin bushes are shading the existing plants.

"Action has to be taken or we will lose both the vetch plants and the small blue for good. Without the plant it just cannot survive.

"The small blue is a very delicate creature. Individuals can't travel very far, and if there isn't a kidney vetch within about one kilometre of where they emerge from the ground in the spring time then they just can't survive."

Mr Orr said the programme of clearing coastal areas for the small blue is likely to be a rolling project carried out over several years as volunteers try to cover more than nine kilometres of coastline.

"The next stage will be to try to propagate some kidney vetch seeds and plant them in the dunes to try to relocate colonies from other areas around the coast."