Figsbury Ring, National Trust
Adonis blue butterflies and chalkland flora. Early June.
Figsbury Ring is a Neolithic and Iron Age archaeological site near Salisbury. It lies to the north of the A30 and reached along a narrow and bumpy chalk track. As the area is elevated it is prone to being windy, so select a calm and warm day for any visit if you aim to see the sites butterfly diversity.
This site is adjacent to the magnificent, but normally closed, Porton Down Ranges with their extensive chalky landscape, juniper, acres of anthill downs and very rare orchids – so Figsbury’s biodiversity is enhanced.
With an underlying chalk bedrock, the soils here are mostly thin and distinctly alkaline. That thinness is enhanced by the ancient digging of defences – banks and ditches. The flat sections are dominated by grasses and will hold sizeable populations of meadow brown, ringlet and marbled-white butterflies in high summer. In early June only a few meadow browns have emerged, yet the horseshoe vetches carpeting the thin-soiled rings provide an excellent food for the larval Adonis blue butterflies (Lysandra bellargus).
The Adonis Blue is a species of chalk downland, where it may be found in warm, sheltered spots. The male Adonis Blue has brilliantly-coloured blue wings that gives this butterfly its name. These adults can be found flying low over vegetation, seeking out the less-conspicuous females that are a rich chocolate brown in colour.
The white, textured disc-shaped eggs are laid singly under young, unshaded horseshoe vetch leaves in May-June and August-September. They can be found most easily in September where unshaded Horseshoe Vetch is growing on short turf.
The Adonis Blue overwinters as a caterpillar; it is green with short, yellow stripes, which camouflage it while it feeds on the vetch during the day. It is most commonly seen during April and late July as it searches for ants to ‘milk’ its sugary secretions.
In April-May and July-August each caterpillar forms into a chrysalis in small crevices or hollows and is then buried by ants in earth chambers connected to the ant nest. The ants constantly attend to it for around three weeks, protecting it from predators.
The diversity of herbs growing on Figsbury’s slopes provides food for many butterfly species. You should expect to encounter: Common Blue, Brown Argus, Small Blue as well as Small Heath butterflies. Grizzled and dingy skippers are found here too. The more widespread species such as the ‘whites’, brimstones and ‘Vanessids’ (Red Admiral etc) are also likely to be present.
Botanically, the three dominant orchid species will be seen in flower during early June. Fragrant and pyramidal orchids are usually in good numbers, and spotted orchids also present. Rockroses, salad burnet and milkwort coat the thin chalky soils and radiate their colour and shape. Together with the butterflies, bees and other insects the flora gives the site a wonderful biological aurora.
Porton Down Ranges have occasional open days. Nearby is Winterbourne Downs RSPB reserve.