Common Blue (Polyommatus icarus)
Species

Male. Taken at Aston Upthorpe Downs, Oxon., on August 16th 2014.
(1/160th sec at f11. Approx 3x lifesize)

Male underside. Taken at Whitecross Green Wood, Oxon., on May 22nd 2016.
(1/640th sec at f14. Approx 3x lifesize)

Female. Taken at Smardale Gill, Cumbria, on July 5th 2016.
(1/800th sec at f14. Approx 3x lifesize)

Female underside. Taken at Greenham Common, Berks, on August 4th 2013.
(1/400th sec at f11. Approx 3x lifesize)

Mating pair. Taken at Aston Upthorpe Down, Oxon., on August 14th 2011.
(1/200th sec at f13. Approx 3x lifesize)

© David Hastings

Description

Wing span: 29 - 36 mm
 
This butterfly is the commonest blue found in the British Isles. The male has violet-blue uppersides, whereas the female is usually primarily brown in colour, with a variable amount of blue on the forewings. Females usually have orange dots on the wing edges, which are absent in the male.
 
It can be found throughout the British Isles, although it is absent from land higher then 1500 ft in Wales and Scotland.
 
It is found in a wide variety of habitats, including unimproved grassland such as roadside verges and waste ground, downland, woodland clearings, heathland and even sand dunes.
 
This species has two broods in the southern counties of England, and one brood further north. There may be a third brood in favourable years. Time of emergence is highly variable. In good years, adults may be seen as early as the middle of May on the more southerly sites. These peak at the end of May, giving rise to a second generation that emerges in the second half of July, peaking in the middle of August. The larva is the over-wintering stage.
 
The main foodplant is Common Bird's-foot Trefoil. Black Medick, Common Restharrow, Greater Bird's-foot Trefoil, Lesser Trefoil and White Clover are also used. Adults feed primarily on Bird's-foot Trefoil, Bugle, Fleabane, Kidney Vetch, Knapweeds, Marjoram, Ragwort, Thistles, Thyme, Vetches and White Clover.
 
The Brown Argus and Common Blue can be differentiated from their undersides, since the Brown Argus lacks a spot on the underside of the forewing that is present in the Common Blue. The Brown Argus and female Common Blue can be difficult to tell apart from their uppersides. However, the Brown Argus is completely lacking in blue scales, although it may have a blue sheen. The highly-variable female Common Blue, on the other hand, always has some blue scaling, especially close to the body.
 
This species is listed as Least Concern in the latest Red List of British Butterflies (PDF).
 

Sightings

20-Aug-2017:Farmoor Reservoir, Oxon(5)
17-Aug-2017:Lardon Chase, Berks(12)
16-Aug-2017:Otmoor, Oxon(1m)
16-Aug-2017:Whitecross Green Wood, Oxon(1m,2f)
15-Aug-2017:Whitecross Green Wood, Oxon(10m,1f)
11-Aug-2017:Bucknell Wood, Northants(4)
10-Aug-2017:Farmoor Reservoir, Oxon(7m,1f)
06-Aug-2017:Dry Sandford Pit, Oxon(7)
03-Aug-2017:Otmoor, Oxon(2)
03-Aug-2017:Whitecross Green Wood, Oxon(2)
29-Jul-2017:Standlake Common, Oxon(1)
23-Jul-2017:Aston Rowant NNR, Oxon(50+)
18-Jul-2017:Allotment, Abingdon, Oxon(1)
18-Jul-2017:Greenham Common, Berks(18+)
16-Jul-2017:Allotment, Abingdon, Oxon(1)
08-Jul-2017:Aston Upthorpe Downs, Oxon(4m)
14-Jun-2017:Dry Sandford Pit, Oxon(1)
14-Jun-2017:Daneway Banks, Gloucs(15+)
11-Jun-2017:Velebits National Park, Croatia
08-Jun-2017:Paklenica National Park, Croatia
07-Jun-2017:Irinovac, Croatia
07-Jun-2017:Bjelopolje, Croatia
03-Jun-2017:Dry Sandford Pit, Oxon(4m,1f)
03-Jun-2017:Abingdon, Oxon(3m)
28-May-2017:Pewsey Down, Wilts(8m,2f)
14-May-2017:Rodborough Common, Glos(3m)
14-May-2017:Whelford Pools, Glos(1m)

18-Sep-2016:Otmoor, Oxon(3m)
29-Aug-2016:Aston Rowant NNR, Oxon(20m,7f)
21-Aug-2016:Hackpen Hill, Oxon(9m,4f)
14-Aug-2016:Whitecross Green Wood, Oxon(3m,1f)
07-Aug-2016:Cothill Fen, Oxon(1m)
06-Aug-2016:Greenham Common, Berks(35+m,1f)
30-Jul-2016:Aston Rowant NNR, Oxon(4m,1f)
19-Jul-2016:Allotment, Abingdon, Oxon(1)
11-Jul-2016:Whitecross Green Wood, Oxon(2m)
09-Jul-2016:Dry Sandford Pit, Oxon(1m)
05-Jul-2016:Smardale Gill NNR, Cumbria(8m,2f)
03-Jul-2016:Gait Barrows NNR, Lancashire(1m)
03-Jul-2016:Arnside Knott, Cumbria(1m)
02-Jul-2016:Allithwaite Quarry, Cumbria(2)
30-Jun-2016:Aston Rowant NNR, Oxon(2)
25-Jun-2016:Daneway Banks, Gloucs(2m)
19-Jun-2016:Whitecross Green Wood, Oxon(1f)
02-Jun-2016:Lymington-Keyhaven NR, Hants(1m)
29-May-2016:Pewsey Down, Wilts(2)
28-May-2016:Ardley Quarry, Oxon(9m,1f)
28-May-2016:Wicken Wood, Bucks(1m,1f)
22-May-2016:Lardon Chase, Berks(7m,2f)
22-May-2016:Goring Railway Bridge, Oxon(1m)

19-Sep-2015:Dry Sandford Pit, Oxon(2m)
13-Sep-2015:Farmoor Reservoir, Oxon(3m)
07-Sep-2015:Otmoor, Oxon(9m,1f)
06-Sep-2015:Farmoor Reservoir, Oxon(3m)
30-Aug-2015:Farmoor Reservoir, Oxon(1m)
29-Aug-2015:Lardon Chase, Berks(7m,1f)
22-Aug-2015:Aston Rowant NNR, Oxon(30+)
22-Aug-2015:Yeosden Bank, Bucks(19+)
21-Aug-2015:Marston Meadows, Oxon(1m)
16-Aug-2015:Hackpen Hill, Oxon(10m)
16-Aug-2015:Pewsey Down, Wilts(13m)
15-Aug-2015:Rushy Common, Oxon(13m,4f)
09-Aug-2015:Aston Upthorpe Downs, Oxon(30m,2f)
08-Aug-2015:Dry Sandford Pit, Oxon(24m,6f)
06-Aug-2015:Marston Meadows, Oxon(1m,1f)
02-Aug-2015:Bernwood Meadows, Bucks(13m)
02-Aug-2015:Otmoor, Oxon(20m,1f)
30-Jul-2015:Aston Rowant NNR, Oxon(5m)
26-Jul-2015:Bansko meadows, Bulgaria
23-Jul-2015:nr Novo Hodzhovo, Bulgaria
23-Jul-2015:Mesta River fishponds, Bulgaria
21-Jul-2015:Rupite Hot Springs, Bulgaria
21-Jul-2015:nr Petrovo, Bulgaria
20-Jul-2015:Kresna Gorge, Bulgaria
20-Jul-2015:nr Samokov, Bulgaria
18-Jul-2015:Crookham Common, Berks(2m)
11-Jul-2015:Aston Upthorpe Downs, Oxon(3)
04-Jul-2015:Calvert Jubilee, Oxon(1f)
03-Jul-2015:Bernwood Forest, Bucks(1m)
21-Jun-2015:Whitecross Green Wood, Oxon(3m,1f)
16-Jun-2015:Heddon Valley, Devon(3m)
15-Jun-2015:Collard Hill, Somerset(2m,1f)
07-Jun-2015:Lardon Chase, Berks(5m,1f)
07-Jun-2015:Goring Railway Bridge, Oxon(2m)
07-Jun-2015:Aston Upthorpe Downs, Oxon(27m,3f)
06-Jun-2015:Dry Sandford Pit, Oxon(1m)
04-Jun-2015:Marston Meadows, Oxon(3m,1f)
30-May-2015:Aston Rowant NNR, Oxon(20+m,3f)
28-May-2015:Marston Meadows, Oxon(1m)
23-May-2015:Dry Sandford Pit, Oxon(4m)
16-May-2015:Pitstone, Bucks(3m,1f)

31-Aug-2014:Farmoor Reservoir, Oxon(6)
28-Aug-2014:Otmoor, Oxon(11+m,1f)
24-Aug-2014:Dry Sandford Pit, Oxon(11m,1f)
24-Aug-2014:Cothill Fen, Oxon(1f)
23-Aug-2014:Aston Rowant NNR, Oxon(18+)
17-Aug-2014:Farmoor Reservoir, Oxon(1)
16-Aug-2014:Aston Upthorpe Downs, Oxon(30+)
09-Aug-2014:Pewsey Down, Wilts(30+)
03-Aug-2014:Otmoor, Oxon(24)
30-Jul-2014:Arnside Knott, Cumbria(1)
29-Jul-2014:Smardale Gill NNR, Cumbria(2)
26-Jul-2014:Aston Rowant NNR, Oxon(6)
12-Jul-2014:Watlington Hill, Oxon(1f)
30-Jun-2014:Tophill Low, E. Yorks(1)
30-Jun-2014:Kiplingcotes Chalk Pit, E. Yorks(8)
25-Jun-2014:Rupite Hot Springs, Bulgaria
25-Jun-2014:General Todorov, Bulgaria
24-Jun-2014:Papaz Tchair, Bulgaria
24-Jun-2014:nr Novo Hodzhovo, Bulgaria
22-Jun-2014:Plazishte, Bulgaria
21-Jun-2014:Byal gradets, Bulgaria
20-Jun-2014:nr Dolna Kula, Bulgaria
20-Jun-2014:Golobradovo, Bulgaria
20-Jun-2014:Arda River, Bulgaria
19-Jun-2014:nr Mirovo, Bulgaria
18-Jun-2014:nr Mirkovo, Bulgaria
16-Jun-2014:Daneway Banks, Gloucs(5)
14-Jun-2014:Dry Sandford Pit, Oxon(4m)
10-Jun-2014:Dry Sandford Pit, Oxon(2)
08-Jun-2014:Dry Sandford Pit, Oxon(3m,1f)
05-Jun-2014:Marston Meadows, Oxon(2)
01-Jun-2014:Lardon Chase, Berks(4m,4f)
01-Jun-2014:Dry Sandford Pit, Oxon(2m,1f)
31-May-2014:Salden railway cutting(9+)
25-May-2014:Bernwood Meadows, Bucks(9m,1f)
25-May-2014:Whitecross Green Wood, Oxon(4m,1f)
18-May-2014:Aston Upthorpe Downs, Oxon(9m)
18-May-2014:Lardon Chase, Berks(5m)
17-May-2014:Stockbridge Down, Hants(1)

31-Aug-2013:Aston Rowant NNR, Oxon(90+m,12+f)
26-Aug-2013:Otmoor, Oxon(24+)
24-Aug-2013:Radley Lakes, Oxon(3m,1f)
18-Aug-2013:Aston Upthorpe Downs, Oxon(60+m,5f)
18-Aug-2013:Lardon Chase, Berks(52m,11f)
11-Aug-2013:Dry Sandford Pit, Oxon(26+m,5f)
10-Aug-2013:Whitecross Green Wood, Oxon(3)
08-Aug-2013:Allotment, Abingdon, Oxon(1f)
04-Aug-2013:Bowdown Wood, Berks(7)
04-Aug-2013:Greenham Common, Berks(50+)
03-Aug-2013:Allotment, Abingdon, Oxon(1f)
01-Aug-2013:Allotment, Abingdon, Oxon(2m)
28-Jul-2013:Aston Rowant NNR, Oxon(3)
21-Jul-2013:Aston Upthorpe Downs, Oxon(1)
08-Jul-2013:Daneway Banks, Gloucs(2)
07-Jul-2013:Watlington Hill, Oxon(3)
07-Jul-2013:Aston Rowant NNR, Oxon(8+)
06-Jul-2013:Decoy Heath, Berks(1m)
30-Jun-2013:Whitecross Green Wood, Oxon(2m)
29-Jun-2013:Dry Sandford Pit, Oxon(2m)
27-Jun-2013:Narborough Railway Line, Norfolk(6m,3f)
15-Jun-2013:Dry Sandford Pit, Oxon(1m)
08-Jun-2013:Dry Sandford Pit, Oxon(6m,1f)
02-Jun-2013:Lardon Chase, Berks(34m,5f)
01-Jun-2013:Hackpen Hill, Oxon(1m)
26-May-2013:Stockbridge Down, Hants(1m)
01-May-2013:The Camargue, France(2)
29-Apr-2013:Vaison-la-Romaine, France(1)