Butterflies soar at Studland

The increase in silver-studded blue and grayling butterflies has far exceeded the countrywide trend. The silver-studded blue is known for the vivid, shimmering blue colour of the males, whereas the grayling is a master of disguise, its brown and grey colouring perfectly blending in with bare earth, stones and dry vegetation.

Volunteers have monitored butterflies from April to September at Studland annually for almost 50 years. Figures showed:

• There were 18 times as many silver-studded blues in 2023 than in 1976 (21 butterflies were counted in 1976 and 376 in 2023). Nationally, the rise has been just 67 percent.
• Grayling numbers have increased by almost three times (50 in 1976 to 134 in 2023), but they have declined nationally by 70 percent.

Dr Martin Warren, one of the UK’s leading butterfly experts, has been counting butterflies there as a volunteer for the past four years. He said:

“These figures really are something to celebrate, at a time when many butterflies aren’t faring well at all. It’s especially good to see that the graylings are increasing, when they are in serious decline elsewhere in the country. We are hoping the 2024 count will tell an equally positive story.”

Once the butterflies are on the wing (July to September), Martin and a team of volunteers monitor the same transect every week. The monitoring sites are on heathland either side of Ferry Road in Studland, part of the Purbeck Heaths National Nature Reserve (NNR).

David Brown, National Trust ecologist said:

“This is fantastic news, one of the many success stories for wildlife across the Purbeck Heaths NNR. We aren’t exactly sure why these two species are doing so well, but both need areas of bare ground where they can bask. That’s often provided by the hoof prints of grazing animals, or by pigs rooting out vegetation. At Studland, the butterflies are thriving beside a track used by walkers and cyclists – and it’s the track that provides them with the bare ground habitat.

“We are incredibly grateful to the volunteers who diligently carry out this important work across the NNR – without their consistent records, we wouldn’t have a clear picture of the state of nature in Purbeck.”

Female silver-studded blues are less showy than the males, being brown with metallic blue spots. Their caterpillars have a fascinating relationship with ants. The ants protect the caterpillars from predators and parasites, and in return they get to feed on a sugary substance that the caterpillars produce.

The grayling is mainly dark brown above, with washed-out orange markings. The underside of the forewing is orange with two large eyespots. Many butterflies have eyespots, thought to either intimidate predators or distract them away from the main body parts.