Even before we took on the Holtspur Bottom reserve just outside Beaconsfield in Bucks, we knew that the Small Blue butterfly was in the Holtspur Valley. It had been seen, sporadically, in tiny numbers in the last decade of the 20th century. Each year brought fewer sightings until, in 2002 and 2004, none was recorded. There was a real probability of the species disappearing from this built up area between High Wycombe and Beaconsfield for ever.

So in addition to trying to secure a home for the Striped Lychnis moth (which had a notably strong but highly vulnerable population in the valley and is now virtually extinct save for our own safeguarded population on our reserve), the Dark Green Fritillary and various other butterflies and moths, we were keen to create conditions for the successful return of the Small Blue.

Small Blue
Photo © Nick Bowles

Horseshoe Vetch
Photo © Nick Bowles

Initial efforts at recreating the chalk flora (ploughed up by the tenant before us), were blighted by rampant ragwort; but eventually, after 4 years we saw the hard work paying off. Among the low growing chalk flora was a small amount of Kidney Vetch. This is the only known food plant of the Small Blue. Whilst the amount that returned from seed might just attract a passing Small Blue it would be unlikely to provide enough food for more than a few caterpillars. It was essential to boost these small amounts growing on site if we were to create sufficient habitat for a viable colony of the butterfly.

The opportunity to do so came with the creation of a long shallow scrape into the bedrock chalk, backed on the 'up-hill' side by a low bank of the bare chalk spoil from the scrape itself. This feature (installed in 2003/4) was created in the knowledge that many of our rarer species need bare ground around their food plants, or the warmth required to promote egg laying and effective development of the larvae will not be achieved. Into this bare soil a few choice food plants of various species were planted by our hard working conservation volunteers.

Shallow scrape into bedrock chalk.
Photo © Nick Bowles

Grazing sheep at Holtspur
Photo © Nick Bowles

Kidney Vetch plants are relatively good at surviving in bare soil especially if it is nutrient poor. They do well at first, but soon lose the competition for the space they occupy as nutrient levels increase and more dominant plants, like tough grasses, arrive. Some Kidney Vetch was deliberately planted as tiny 'plugs' (small bare rooted seedlings), but happily other plants have self-set on to the bare soil in and around the scrape and both the plants we provided and those germinated on site, are now home to a small but ever increasing colony of Small Blue. The sheep that graze the site each winter help to deter the coarser grasses from dominating and also do a certain amount to create tiny bare areas with their hooves that can be perfect for Kidney Vetch germination.

Years of work by a small team of volunteers has changed the rather rough grassland of the Upper Field into a far more varied and colourful turf. The warden shaped a scrape into the turf to create a bare patch and from it created a steep bank of south facing, chalky spoil. Our volunteers have planted (and tended) foodplants for various species in several areas but especially here on this warmer surface of the spoil bank.

Work in future will see the amounts of Kidney Vetch maintained, partially through the creation and 'plug' planting of further scrapes, as the first one (as the photo of vetch planting shows) is inevitably succumbing to denser vegetation which will eventually cover the bare areas and outcompete the foodplants.

Part of the volunteer team planting vetch to
maintain a strong population of
essential foodplants.
Photo © Nick Bowles

The beauty of the Small Blue flicking from flower top to flower top looks set to be the reminder that conservation work can turn the tide and increase species' numbers (if we are prepared to persist in our efforts).

Small Blue pair mating at Holtspur Bottom
reward volunteer efforts.
Photo © David Redhead