Scientific name: Polyommatus bellargus
This beautiful species of butterfly is one of the most characteristic of unimproved southern chalk downland, where it can be seen flying low over shortly grazed turf (typically steep, south-facing slopes).
The males have brilliant sky-blue wings, while the females are chocolate brown and far less conspicuous. Both sexes have distinctive black lines that enter or cross the white fringes of the wings.
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 is green with short, yellow stripes, which camouflage it while it feeds on Horseshoe 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 the 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.
This species has undergone a major decline through its entire range but, despite its restricted distribution, on good sites it can be seen in many hundreds, as it has recently re-expanded in some regions.
Colonies vary in size considerably from year to year, depending on the weather. Many thousands can be seen emerging towards the end of a hot summer, constrasting with under a hundred from a spring emergence.
Size and Family
- Family: Blues
- Size: Small/Medium
- Wing Span Range (male to female): 38mm
- UK BAP: Not listed (formerly Priority)
- Butterfly Conservation priority: Medium
- European status: Not threatened
- Protected under Schedule 5 of the 1981 Wildlife and Countryside Act (for sale only)
The sole foodplant is Horseshoe Vetch (Hippocrepis comosa).
The butterfly prefers the hottest areas of dry chalk or limestone grassland with abundant foodplants in short turf, although slightly taller vegetation may be used in sheltered quarries. Most colonies occur on warm, south-facing slopes, where favoured breeding areas are sheltered hollows (especially old chalk pits and quarries).
- Countries: England
- Restricted to southern England, but not in the far south-west
- Distribution Trend Since 1970’s = -19%