In Hembury Woods, we catch sight of two of Britain’s most elegant but elusive fritillary butterfly species. But which is which?

I am in Hembury Woods on the edge of Dartmoor, where two of Britain’s most elegant but elusive butterflies can be found at the end of May and beginning of June, when their flight periods overlap.

As soon as I emerge into the open at the top of a woodland track I catch sight of one: a petite, elegant butterfly, its black and orange upperwings glowing in the sun’s rays. It is one of Britain’s eight species of fritillary – a group of butterflies whose name derives from a Latin term referring to the chequered pattern on the underwings.

But which one? Its small size, the time of year and the habitat make me certain that I am looking at one of two butterflies so similar that the early lepidopterists considered them to be the same species: the small pearl-bordered and the pearl-bordered fritillaries.

To decide one way or another, it is those chequered underwings I need to see. For despite their names, size isn’t the best way to tell small PB from PB, as those in the know refer to them. I have come prepared with a large butterfly net and a couple of Perspex containers – and Donald, the twelve-year-old son of a friend whose reflexes are far quicker than mine.

A sweep of the net and the first butterfly is temporarily incarcerated. Having forgotten both my reading-glasses and my magnifying lens I squint carefully at the underwing. The row of white spots along the edge that gives both species their name is very obvious, but in the centre of the wing there are just two white spots; while the overall effect is more brown than multicoloured. I identify this individual as a pearl-bordered fritillary, now the scarcer of the two species, before granting its freedom.

Soon Donald catches another butterfly, and this time the underwings have a far bolder pattern: the white pearls are edged with black, not red; and there are far more white spots overall. This is a small pearl-bordered, the later of the two species to appear. Once again we take a close look before releasing it into the warm spring sunshine.

Both these exquisite creatures were once fairly common in the woods of lowland Britain, especially in the damper west, but have recently declined, along with so many of our woodland butterflies. Because we no longer coppice so much of our native woodland, we no longer provide the sunny, open clearings these butterflies both like.

Elsewhere in the UK, the small pearl-bordered can still be found in good numbers in parts of Scotland and Wales. The pearl-bordered can also be seen in Scotland, though its strongholds are in the Wyre Forest in Worcestershire, and in southern counties such as here in Devon.

Both species lay their eggs on violets, and can often be found in areas of dense bracken, which provides the violets with just the right amount of shade and warmth to grow. Such habitats are easily changed, either by overgrazing or by the removal of sheep and deer, and as a result both these stunning little butterflies are now critically endangered.

Their only hope is that now we understand their specific habitat requirements, efforts to manage their habitats will allow them to increase in numbers, and eventually spread out to recolonise their former haunts.

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Read the whole story on:http://www.guardian.co.uk/environment

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