Chalk Hill Blue (Polyommatus coridon)
Male. Taken at Aston Rowant NNR, Oxon., on July 30th 2016.
(1/800th sec at f13. Approx 2.75x lifesize)
Male. Taken at Aston Rowant NNR, Oxon on July 30th 2015.
(1/640th sec at f14. Approx 2.75x lifesize)
Female. Taken at Aston Rowant NNR, Oxon., on July 30th 2016.
(1/500th sec at f13. Approx 2.75x lifesize)
Female underside. Taken at Aston Rowant, Oxon on July 30th 2015.
(1/400th sec at f16. Approx 2.75x life size)
Mating pair. Taken at Aston Upthorpe Downs, Oxon, on August 19th 2015.
(1/200th sec at f16. Approx 2.75x lifesize)
© David Hastings
DescriptionWing span: 33 - 40 mm
This butterfly is restricted to chalk and limestone grassland. The sexes are strongly dimorphic; the males being a pale sky blue, and the females being a chocolate brown. The black markings on the male's wings are highly variable.
The distribution of this species follows the distribution of Horseshoe Vetch which, in turn, follows the distribution of chalk and limestone grassland. This species is therefore restricted to England, south east of a line from the Wash to the Severn estuary.
There is one brood each year with the adults emerging in mid-July in typical years, with a peak being reached at the end of July and early August. The ovum is the over-wintering stage.
The larval foodplant is Horseshoe Vetch. Adults feed primarily on Bird's-foot Trefoil, Field Scabious, Selfheal, Thistles and Thyme.
The female Adonis Blue is easily mistaken for a female Chalkhill Blue. Distinguishing the two is not at all easy. One guideline is that the pale scales on the hindwings, between the red dots and the white fringe, are blue in a female Adonis Blue, and white in a female Chalkhill Blue. The female could also be confused with the Brown Argus and the female Common Blue.
This species is listed as Near Threatened in the latest Red List of British Butterflies (PDF).