Polyommatus coridon
This is a fairly common, single-brooded, blue butterfly of flower-rich, chalk downland. Its larval foodplant is Horseshoe Vetch, which is common in good-quality chalk turf, and is strongly-associated with south-facing, downland slopes. There are many such slopes on the eastern downs between Eastbourne and Arundel and that is where the larger colonies of this species may be found. By contrast there are relatively few areas of good-quality chalk turf remaining between Arundel and the Hampshire border (and most of these are north-facing), and consequently there are far fewer colonies.
Male Chalk Hill Blues have pale blue uppersides, a wide brown margin to the wings, and a white border which is chequered (broad dark marks that cross the whole of the border). They are relatively easy to identify. Female Chalk Hill Blues are chocolate-brown and also have a distinctive chequered border and the only confusion species is female Adonis Blue. If these two species are flying together in late summer, then a high-quality photograph and a good ID book is required to distinguish between them.
Between 2006-2024 an “average first sighting” was July 2nd (range, June 24th to July 16th). For the same period, the “average last sighting” was September 15th (range, August 28th to October 3rd). Records for late September and even early October appear to be more and more common.
Described as “fairly common” in the introductory paragraph, this species may sometimes be spectacularly abundant, as in 2012. The weather was interesting in 2012, with an unseasonally warm, sunny March, followed by a very wet April and May. The Horseshoe Vetch grew lush, and this may have been the reason for the explosion that occurred in early August, when an estimated 828,000 Chalk Hill Blues were recorded at The Gallops, in Friston Forest, on 03/08/2012. An astonishing sight.
Locations to see Chalk Hill Blues, include: Birling Gap at TV562957, Chantry Hill at TQ085123, Friston Forest Gallops at TV553997, Medley Bottom (Amberley) at TQ044116 and Windover Hill at TQ537034 (Ewe Dean) and TQ543030 (Deep Dean).
Male Chalk Hill Blue at rest – photo by Dave Brown
Female with open wings – photo by Dave Brown
Female with closed wings – photo by Dave Brown
A “tatty” female – photo by Dave Brown
Male Chalk Hill Blue - Graham Hubbard
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Male nectaring on Birdsfoot Trefoil – photo by Martin Kalaher
Male with open wings - photo by Nigel Symington
Mating pair - photo by Bob Eade
Feeding on thistle - photo by John Williams
Male Chalk Hill Blue - John Williams
Aberrant female Chalk Hill Blue - Martin Kalaher
Male Chalk Hill Blue - John Williams
Butterfly Conservation Chalk Hill Blue
