There's great news for two rare butterfly species in Devon, where numbers have surged by more than 200 per cent over the past two decades.

A 20-year survey of pearl-bordered and small pearl-bordered fritillary butterflies at Devon Wildlife Trust's (DWT) Marsland nature reserve has revealed that numbers have increased dramatically compared to an overall national decline.

DWT attributes the increasing numbers to careful management of the north Devon reserve.

The trust's nature reserves officer, Gary Pilkington, has been managing the site for over 20 years to improve the wooded valley's glades and pastures for the benefit of these rare butterflies.

The 212-hectare site supports five species of fritillaries and last year received funding from the North Devon AONB Sustainable Development Fund to further boost numbers.

Mr Pilkington said: "We have worked hard over the last two decades to improve the habitat for these beautiful and rare insects and it is great to see such positive improvements compared to the over 50 per cent decline nationally for both the species.

"Over the years we have learnt exactly what they need to thrive here including appropriate bracken control, scrub management and providing the open ground loved by the pearl-bordered fritillaries.

"This is the ideal time of the year to see small pearl-bordered fritillaries in flight so our next job this month will be to monitor their numbers."

The management work, carried out by DWT staff, local contractors and volunteers, has helped to remove gorse, willow, alder and other scrub in the habitats best suited to the butterflies.

The work has seen large increases in the numbers of common dog-violets which is the food plant of the fritillaries' caterpillars as well as bugle which is the main nectar source for the adults.

And with each of the species preferring slightly different habitat, Mr Pilkington says it has been a balancing act over the years.

"The small pearl-bordered fritillary thrives in the damper sections of the woodland, whilst the pearl-bordered fritillary enjoys the sunny west-facing slopes," he said.

"Even though we are doing well, the work still has to continue each year, it's a constant battle. One of the other fritillaries, the high brown is only just hanging on here so we certainly can't rest on our laurels!"