An explosion of rare butterflies is being anticipated on a Scottish island in what is being billed as a unique spectacle of nature.

Staff on RSPB's Islay reserves are hoping for thousands of rare butterflies to emerge in the next few weeks.

An unprecedented number of marsh fritillary caterpillars, one of the UK's rarest species of butterfly, were spotted at The Oa and Loch Gruinart reserves.

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Both sites have been carefully managed to create a home for the caterpillars and resulting butterflies.

They eat the leaves of only one particular type of wildflower called "devil's bit scabious" and in Scotland, their population is almost entirely limited to the Inner Hebrides and coastal Argyll.

The population boom on Islay this year is part of a natural seven-year cycle that involves the butterflies, their food plant and a parasitic wasp. This year numbers favour the butterflies but next year an abundance of parasite wasps could lead to a population crash.

RSPB Scotland's Jack Fleming, said: "Marsh fritillaries are stunning little insects, and Islay's one of the most important sites for them in the country, so if you want to see them, you really need to come here.

"They've declined severely in the last century. With luck, visitors will be able to see upwards of 50 at once on patches of wild thyme and other wild plants. The hope is that these will then disperse and spread the population over a wider area, which is great news for the species."