Brown Argus (Plebeius agestis)
Male. Taken at Starosel, Bulgaria, on June 19th 2014.
(1/125th sec at f11. Approx 4x lifesize)
Male underside. Taken at Aston Rowant NNR, Oxon., on May 30th 2015.
(1/400th sec at f11. Approx 4x lifesize)
Female. Taken at Greenham Common, Berks, on July 23rd 2011.
(1/250th sec at f11. Approx 4x lifesize)
Female underside. Taken at Abingdon, Oxon., on July 27th 2013.
(1/160th sec at f13. Approx 4x lifesize)
Mating pair. Taken at Sydlings Copse, Oxon, on July 24th 2011.
(1/400th sec at f14. Approx 3x lifesize)
© David Hastings
DescriptionWing span: 25 - 31 mm
This is an attractive butterfly, particularly when fresh, with bright orange marks contrasting with the dark chocolate-brown wings and the white wing borders. It is very similar to the Northern Brown Argus.
It is primarily found south-east of a line between the Severn and the Humber, although it has been spreading further north in recent years. It is also found on the northern and southern Welsh coasts.
This species occurs in small, compact colonies, and is not a great wanderer; adults only travel up to a few hundred feet from where they emerged. Colonies are typically found on chalk or limestone downland where the foodplant is abundant, but they can also be found on heathland and in open woodland.
This species generally has 2 broods a year in central and southern England, with only a partial second brood in north Wales and the north of England. In good years, a partial 3rd generation may appear in the south. The adults emerge first in central and southern England in early May, peaking at the end of May and beginning of June, and giving rise to a second brood that emerges at the end of July. Both broods are protracted, so it is possible for second-generation adults to be on the wing before the last first-generation adults have died. The caterpillar is the over-wintering stage.
The main foodplant on calcareous soils is Common Rock-rose. Common Stork's-bill and Dove's-foot Crane's-bill are used on other sites. Adults feed primarily on Marjoram, Ragwort, Thyme 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, but 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. The male and female Brown Argus are similar in appearance.
This species is listed as Least Concern in the latest Red List of British Butterflies (PDF).