Country Diary: Gloucestershire

My last meeting with Matthew Oates, the National Trust's butterfly specialist, was in June last year when he took me to a south-facing combe on the edge of Rodborough Common to see the duke of burgundy, his own special-interest butterfly and an early-season flyer, in the warm sunshine of a valley with its own microclimate and butterfly-friendly habitat. Last week he kindly took me to Swellshill Bank, above Brimscombe, on another warm sunny morning. He set the scene as we travelled: the year started well for butterfly populations, but the heavy rains of early summer destroyed much of what had promised to be a record season; but the species we were going to see, the adonis blue, is, on its own, a remarkable success story of dynamic recolonization of a territory.

From 1963 until the turn of the century, adonis blues were not found on Cotswold sites. Then they reappeared, first on the fringes of Stinchcombe Hill, but now widely over downland stretches in the south of the county. Matthew said the reappearance was largely due to climate change but added that the determination of the butterfly should never be underestimated. The closest population in the years when the species was missing was at Calne in Wiltshire, 20 miles away. Last week adonis blues, which have a shimmering blue double wing, edged in white with black interstices, appeared on the sunlit slope - although not as many as my host had hoped for. They fluttered around us, as did meadow brown, brown argus, chalkhill blue and gatekeeper butterflies. The grazing regime on downland sites is critical. They need short grass with a content of horseshoe vetch, and the trust's herd of belted galloway cattle are moved around to maintain such habitats. A rabbit population also helps in maintaining the short turf.