BMT Small Blue Project

The Small Blue: what is it and what does it need?

The Small Blue (Cupido minimus) is the UK’s smallest resident butterfly. Its survival is entirely dependent upon the presence of Kidney Vetch (Anthyllis vulneraria), a plant which can only flourish in early successional conditions (i.e. short-turf grassland with abundant bare ground). Whilst the larvae need the Kidney Vetch, the adult butterflies need places to perch and to roost. Ideal habitats include chalk & limestone grassland, especially with naturally occurring broken ground; man-made habitats such as quarries, gravel pits, road embankments, disused railways and other brownfield sites as well as coastal grassland and dunes.

UK decline and status in Hertfordshire

Across the UK, it’s estimated we’ve lost 80% of our chalk grassland habitat over the last 60 years. That's 80% of the sites where Kidney Vetch has the potential to flourish. And, according to Butterfly Conservation, we’ve lost nearly 40% of the UK’s Small Blue butterfly population since 1970. At the end of 2014, there were only 3 known colonies of Small Blues in the whole of Hertfordshire. It’s rare and is a high priority UK Biodiversity Action Plan species.

10/06/2015 Small Blue on Kidney Vetch at the A41 Bourne End exit
Hemel Hempstead 2015

On the 8th June 2015, David Kirk and I were on a day-flying moth hunt at Dellfield meadow at Westbrook Hay. We found the moths we were after but, more importantly, we also found a single Small Blue butterfly. We could hardly believe our eyes! It was the first to be recorded on Trust land. Further investigations revealed that the roadside verge of the A41, less than 200 metres away, had been planted with Kidney Vetch (KV) (thanks to a tip-off from Liz Goodyear, Herts Butterfly Conservation). Two days later, I counted up to 12 Small Blue butterflies on KV beside the A41 at the Boxmoor/ Bourne End exit. I was absolutely thrilled but now I needed to confirm breeding.

Over the next 9 weeks, I visited the A41 site at least once a week. By the middle of July, larvae were appearing on the KV flower heads and at the very end of July, a second, albeit modest generation emerged of at least 3 butterflies. It was the best possible news. And, the Box Moor Trust, who’d already been considering the feasibility of attracting Small Blues to the land, were keen to do everything in their power to help sustain this rare, local breeding population.

Small Blue: larvae through to adult at the A41 colony

The BMT Small Blue Project

The KV along the A41 isn't managed or protected. The Trust's aim is to attract the butterfly to food plants within managed habitat so that the colony is safeguarded. A handful of suitable sites nearby, on BMT land, were identified for an autumn planting of Kidney Vetch: 2 at Roughdown Common (chalk grassland) and a few at Bovingdon Brickworks (a brownfield site with areas of nutrient poor, bare sandy, clay soil). The Trust worked extremely hard to dovetail this project with county-level conservation objectives and researched thoroughly the various conditions needed to ensure that both Kidney Vetch and Small Blues would be given the best chance to thrive.

27/11/2015 Kidney Vetch plants (plugs & seed) protected from rabbits by wire mesh
Left: Lower Roughdown south-facing bank by A41. Right: Further Roughdown sheltered gully by railway line

04/12/2015 Kidney Vetch plants (plugs) protected from rabbits by wire mesh
South-facing bare-soil banks at Bovingdon Brickworks

04/12/2015 Left: a south-facing bare soil bank was sown with Kidney Vetch seeds. Right: more KV plugs protected by wire mesh
Bovingdon Brickworks

At the start of 2015, I couldn’t, in my wildest dreams have imagined that I’d come across a colony of local Small Blues. The fact that its significance was immediately appreciated by David Kirk, Chairman of the Box Moor Trust, was equally wonderful. I know that he and other key trustees, volunteers and staff have busted a gut to get this project off the ground before winter. I'm hoping the slugs munch elsewhere and we reap the well deserved rewards in the spring!

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