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Heathland Creation Attracts Rare Butterflies

One of the UK?s scarcest butterflies has been discovered thriving at an RSPB reserve.

A colony of silver-studded blue butterflies has been found on former farmland at Minsmere, which has been transformed into the Sandlings-type heath traditional for the Suffolk coast. Created to attract rare breeding birds like the woodlark and stone-curlew, the RSPB believed the heath would also allow other species to move in from nearby pockets of surviving heath. The arrival of the silver-studded blue butterflies has proved them right and has highlighted how work to preserve habitats can help a whole range of different wildlife. It has also contributed to the UK’s Biodiversity Action Plan, which aims to halt the loss of the country’s species and habitats by 2010.Minsmere is world famous for its bird life but the reserve has also become increasingly important for its population of insects. As well as the butterflies, volunteers have discovered several unusual beetles and the reserve can now boast 1,000 different species of moths and butterflies. Nationally, silver-studded blue butterflies are restricted to areas of heath and grassland in southern and eastern England and around the Welsh coast. They need a mix of short, sparse vegetation, often maintained by grazing, burning and/or mechanical cutting, as well as mature stands of vegetation on which to sun themselves. Such a mix is rare, but on the Suffolk coast there are relatively large colonies on several heaths, including Minsmere and Westleton heaths – both managed by the RSPB.At Minsmere the RSPB bought several arable fields during the late 1980s and, since the late 1990s, these have slowly been converted to a mixture of heathland and acid-type grassland, typical of the heaths found on the Suffolk Sandlings. Even so, the 200 hectares at Minsmere represents just a small fraction of the old Sandlings heathland, which once stretched along the Suffolk coast from Lowestoft to Ipswich.

Silver-studded blues have an interesting lifecycle, as the caterpillars are picked up by black ants and kept inside their colonies. Here the caterpillars are `milked’ for sugary secretions, which they exude from special glands. The ants, in turn, protect the caterpillars in their nests, where they pupate and ultimately emerge from the ant nests as mature butterflies.

Mel Kemp, Minsmere’s heathland warden, said: This is a great reward for years of hard work to re-create heathland. The heather looks fantastic in the late summer, and it’s great to see these lovely insects spreading into new sites after decades of habitat loss. This is an important contribution, not only for the survival of the silver-studded blue butterfly, but also towards the national target for re-creating heathland habitats.During survey work on the newly re-created heathland and grassland, RSPB researchers also identified several uncommon ground beetles that are dependent on open areas with short vegetation and bare ground. The most significant of these is a beetle called Polystichus connexus, which is known as the ‘Cockney’. This species had not been recorded anywhere in Suffolk since 1828. A total of eleven ground beetle species were found at Minsmere that are classified as nationally scarce, having occurred in less that 100, 10 km squares in the UK since 1970.

The arable reversion fields at Minsmere cover 203 hectares (515 acres), of which 122 hectares are being reverted to acid-type grassland and 25 hectares to heathland. A further 56 hectares are still to go through the reversion process. The UK Biodiversity Action Plan includes targets for the re-creation of both heathland and acid grassland.

The Suffolk Sandlings heaths formerly stretched from Lowestoft to the Orwell Estuary. Pockets of heathland remain, with one of the largest being around RSPB Minsmere, Westleton Heath and Dunwich Heath National Trust.

Surveys of the silver-studded blues, Plebejus argus, at Minsmere were carried out by RSPB staff with the assistance of volunteers from Butterfly Conservation. The silver-studded blue is listed as a UK Biodiversity Priority species by the UK government. Conservation organisations, including the RSPB and Butterfly Conservation, are working to maintain existing populations and manage heathland to allow natural re-colonisation. It is distinguished by silvery-blue scales within the black spots on the rear of the underwing. This is what gives them their name, but the spots can be difficult to see in the field. The full list of uncommon beetles discovered on the arable reversion fields at Minsmere is: Polystichus connexus (8), Harpalus smaragdinus (9), Amara equestris (20), Amara consularis (22), Calathus ambiguus (34), Harpalus attenuatus (37), Amara fulva (47), Syntonus truncatellus (50), Harpalus anxius (58), Laemostenus terricola (77) and Harpalus rufipalpis (79). None of these species have English names. The figures in parentheses are the number of 10 km squares in the UK from which the species has been recorded since 1970.

Lowland heathland and chalk grassland have suffered loss and degradation since the 1800s. More than 70% of lowland heathland has been lost from Britain since the 1800s, and the areas that are left are often small, isolated and becoming degraded without traditional management. Chalk grassland has been similarly affected with 80% lost to farming since the 1940s.

4th July 2014