Chalk Hill Blue (Polyommatus coridon)
Species

Male. Taken at Hackpen Hill, Oxon., on July 13th 2023.
(1/640th sec at f11. © David Hastings)

Male underside. Taken at Hackpen Hill, Oxon., on August 9th 2023.
(1/640th sec at f13. © David Hastings)

Female. Taken at Aston Rowant NNR, Oxon., on August 17th 2023.
(1/800th sec at f13. © David Hastings)

Female underside. Taken at Aston Rowant NNR, Oxon., on July 26th 2021.
(1/400th sec at f11. © David Hastings)

Mating pair. Taken at Aston Rowant NNR, Oxon., on August 8th 2020.
(1/640th sec at f13. © David Hastings)

Description

Family: Polyommatinae

Wing span: 33 - 40 mm

The Chalk Hill Blue sexes are strongly dimorphic; the males are a pale sky blue, and the females are 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.

Near Threatened

Sightings

03-Sep-2023 : Hackpen Hill, Oxon (1)
17-Aug-2023 : Aston Rowant NNR, Oxon (75m,11f)
09-Aug-2023 : Hackpen Hill, Oxon (15)
13-Jul-2023 : Hackpen Hill, Oxon (11)
27-Aug-2022 : Hackpen Hill, Oxon (1f)
20-Aug-2022 : Pewsey Downs NNR, Wilts (1m,2f)
14-Aug-2022 : Hackpen Hill, Oxon (3)
05-Aug-2022 : Aston Rowant NNR, Oxon (85m,19f)
23-Jul-2022 : Hackpen Hill, Oxon (30+)
10-Jul-2022 : Hackpen Hill, Oxon (20+m,1f)
24-Aug-2021 : Pewsey Downs NNR, Wilts (5m,1f)
18-Aug-2021 : Lardon Chase, Berks (35m,13f)
04-Aug-2021 : Hackpen Hill, Oxon (20+)
26-Jul-2021 : Aston Rowant NNR, Oxon (300+)
19-Jul-2021 : Lardon Chase, Berks (75+)
23-Aug-2020 : Pewsey Downs NNR, Wilts (3m)
08-Aug-2020 : Aston Rowant NNR, Oxon (60+m,20+f)
28-Jul-2020 : Aston Upthorpe Downs, Oxon (3m)
20-Jul-2020 : Aston Rowant NNR, Oxon (43m.2f)
07-Jul-2020 : Lardon Chase, Berks (20m)
22-Aug-2019 : Aston Rowant NNR, Oxon (30+)
03-Aug-2019 : Lardon Chase, Berks (120+)
31-Jul-2019 : Aston Rowant NNR, Oxon (24m,2f)
21-Jul-2019 : Aston Rowant NNR, Oxon (5m)
15-Jul-2019 : Lardon Chase, Berks (80+)
07-Aug-2018 : Aston Rowant NNR, Oxon (60+)
02-Aug-2018 : Lardon Chase, Berks (48m,14f)
22-Jul-2018 : Vercors Natural Park, France
14-Jul-2018 : Aston Rowant NNR, Oxon (17m,4f)
04-Jul-2018 : Aston Rowant NNR, Oxon (9m,1f)
24-Aug-2017 : Pewsey Downs NNR, Wilts (2)
17-Aug-2017 : Lardon Chase, Berks (3)
23-Jul-2017 : Aston Rowant NNR, Oxon (70+)
08-Jul-2017 : Aston Upthorpe Downs, Oxon (1m,1f)
29-Aug-2016 : Aston Rowant NNR, Oxon (7m,8f)
30-Jul-2016 : Aston Rowant NNR, Oxon (90m,14f)
14-Jul-2016 : Lardon Chase, Berks (25m,5f)
29-Aug-2015 : Lardon Chase, Berks (18m,6f)
22-Aug-2015 : Yeosden Bank, Bucks (5m,3f)
22-Aug-2015 : Aston Rowant NNR, Oxon (30+m,20+f)
16-Aug-2015 : Pewsey Downs NNR, Wilts (17m)
09-Aug-2015 : Aston Upthorpe Downs, Oxon (13m,4f)
30-Jul-2015 : Aston Rowant NNR, Oxon (60m,8f)
26-Jul-2015 : Bansko meadows, Bulgaria
11-Jul-2015 : Aston Upthorpe Downs, Oxon (3m)
23-Aug-2014 : Aston Rowant NNR, Oxon (5m,3f)
16-Aug-2014 : Aston Upthorpe Downs, Oxon (12+)
09-Aug-2014 : Pewsey Downs NNR, Wilts (4m,2f)
26-Jul-2014 : Aston Rowant NNR, Oxon (30+)
06-Jul-2014 : Aston Rowant NNR, Oxon (8m)