Scientific name: Polyommatus coridon
The Chalk Hill Blue is a small, widespread butterfly that occasionally visits gardens. It is confined to chalk and limestone grassland in southern England and has declined in some areas during recent decades.
At some sites, many hundreds may be seen in August, flying just above the vegetation in search of females. Large numbers of males may also congregate on animal dung and other sources of moisture and minerals. Females are much less conspicuous, being duller in colour, more secretive in their habits, and spending less time than the males in flight.
The males have milky blue upperwings, with a thin black-brown border and a thin white fringe. They are paler and, apart from the Large Blue, larger than other blue butterflies seen in Britain and Ireland.
The females have darkish brown upperwings, with orange spots around the edges of the wings and a dusting of blue near the body. They are similar to the Brown Argus, which lack the blue dusting near body, and to the female Adonis Blue, which have dark veins extending into white fringe on wing edges.
The Chalk Hill Blue hibernates as an egg. The off-white eggs can be found on the stems of the larval foodplant - Horseshoe Vetch - from August to October, after which they fall to the ground, where they spend the remainder of this phase of their lifecycle, until hatching in spring.
The caterpillar is light green with yellow lines along its body. It feeds at night on Horseshoe Vetch leaves and hides at the base of the plant during the day. It produces secretions that are attractive to ants, and continues to do so as a chysalis. It moults four times, finishing its growth by mid-June.
The pale green chrysalis forms under its foodplant, then is taken by ants and buried underground to protect it from predators. It remains here for around four weeks, until the butterfly emerges in July.
Size and Family
- Family: Blues
- Size: Small/Medium
- Wing Span Range (male to female): 38mm
- Butterfly Conservation Priority: Medium
- European status: Not threatened
- Protected in Great Britain for sale only
The sole foodplant is Horseshoe Vetch (Hippocrepis comosa).
The foodplant and the butterfly are restricted to chalk and limestone grassland.
- Countries: England
- Restricted to southern England, but not in far south-west
- Distribution Trend Since 1970’s = -36%.