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Unlike most other "blues", the Brown Argus has no blue scales on its upperside, both sexes being primarily brown in colour as its common name suggests, although the butterfly does exhibit a blue sheen when at certain angles to the light. Both sexes have beautiful orange spots on the upperside of both forewings and hindwings. This widespread species can be found south of a line between Dorset in the west and South-east Yorkshire in the east, along with colonies in Derbyshire, North Devon, East Cornwall and West Cornwall. It is also found in north and south Wales, but is absent from central Wales. This species is also absent from Scotland, Ireland and the Isle of Man. This species occurs in small, compact colonies, and is not a great wanderer, only travelling a couple of hundred metres, at most, from where it emerged. Subspecies: Aricia agestis agestis The nominate subspecies was first defined in Denis & Schiffermüller (1775) as shown here (type locality: Vienna, Austria). The population in the British Isles is represented by this subspecies.
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. In north Wales and northern England, the first emergence starts in early June with any second brood appearing in early August. Subspecies: Aricia agestis agestis The chart(s) above have been correlated with the phenology plot below, taken from the UK Butterfly Monitoring Scheme. The blue line gives average counts over the full data set from 1976 to date, and the red line gives the average for the last year. 
Colonies are typically found on chalk or limestone downland where the foodplant is abundant. However, this species can also be found on heathland and in open woodland.
The primary larval foodplant is Common Rock-rose (Helianthemum nummularium). Common Stork's-bill (Erodium cicutarium) and Dove's-foot Crane's-bill (Geranium molle) are also used.
Adults feed primarily on Marjoram (Origanum vulgare), Ragwort (Senecio jacobaea), Thyme (Thymus polytrichus) and White Clover (Trifolium repens).
This is a warmth-loving species and, as such, is often found in sheltered areas or on south-facing slopes. When courting, the males congregate at the base of a slope where they either perch, waiting for a virgin female to fly by, or patrol the area looking for a female perched on a grass stem awaiting a mate. Mating takes place after a short flight low to the ground. When egg-laying, the female will make meandering flight close to the ground, searching out suitable foodplants on which to lay. Like its close relative, the Common Blue, this species will roost communally on grass stems at night. In fact, the two species are sometimes found roosting together. Subspecies: Aricia agestis agestis
Description to be completed. Unclassified Aberrations
Eggs are laid singly, typically on the underside of a leaf of the foodplant, close to the midrib. Eggs hatch after about a week.
The newly-emerged larva eats the underside of the leaf, but without breaking through the upper surface. The resulting patches are visible from above which can give away the presence of a larva underneath the leaf. More mature larvae feed more openly and are often given away by the presence of the ants that are in attendance. In the last instar, the larva develops Newcomer's glands that exude a secretion that is highly attractive to ants. The association with ants affords the larva some protection against parasites and predators. Larvae of the generation that overwinters generally do so while in their 3rd instar. The larva moults 4 times in total.
The pupa is formed on the ground at the base of the foodplant. However, pupae are often carried away by ants and buried in a cell in the earth.
Adonis BlueDescription to be completed. Chalkhill BlueDescription to be completed. Common BlueOf the two sexes, it is the female Common Blue that causes most confusion with the Brown Argus. The blue present in a female Common Blue is highly variable, with individuals ranging from almost completely blue through to completely brown. It is this latter colouring that causes the most confusion. Even so, the Brown Argus has no blue scales, but may give off a blue sheen from the wings and the hairs found on the thorax and abdomen. Another diagnostic is that the Brown Argus normally has a prominent dark spot in the centre of the forewings. 
Brown Argus (left) and female Common Blue (right) Differentiating Brown Argus and Common Blue from their undersides is even more problematic, and we need to resort to the pattern of spots. Here we have two distinguishing features. The first is that the Common Blue has a spot on the underside of the forewing that is absent in the Brown Argus. The second is that two of the spots on the leading edge of the hindwing are relatively-close in the Brown Argus, almost forming a "figure of eight", but are more spaced apart in the Common Blue. This diagnostic is particularly useful if the underside of the forewing isn't visible. 
Brown Argus (left) and Common Blue (right) Northern Brown ArgusAlthough very similar in appearance, the Brown Argus and Northern Brown Argus can be separated by location in the British Isles. However, this situation may change with global warming as the Brown Argus moves further north. 
Brown Argus and Northern Brown Argus distributions
Click here to see the distribution of this species overlaid with specific site information. Alternatively, select one of the sites listed below.
Both distribution and population trends show an increase and this butterfly is not, therefore, currently a species of conservation concern.
From The State of Butterflies in Britain and Ireland and the UK Biodiversity Action Plan (UK BAP) (2007 review).
The following links provide additional information on this butterfly.
The species description provided here has been derived from the author's own observations and the information contained in the following works:
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![Brown Argus - ovum - Broughton Down - 03-Sep-89 [Tim Norriss]](phpBB/gallery/images/upload/64254b7579bdada1eff4eec2631e348c.jpg "Brown Argus - ovum - Broughton Down - 03-Sep-89 [Tim Norriss]")
![Brown Argus - larva - Stockbridge Down - Jul-00 [Tim Norriss]](phpBB/gallery/images/upload/8231b1e42ef2314f95faafcdf2e56345.jpg "Brown Argus - larva - Stockbridge Down - Jul-00 [Tim Norriss]")
![Brown Argus - larva - Stockbridge Down - Jul-90 [Tim Norriss]](phpBB/gallery/images/upload/23d7ab6df488827c42c96c35d306aff1.jpg "Brown Argus - larva - Stockbridge Down - Jul-90 [Tim Norriss]")
![Brown Argus - pupa - Stockbridge Down - Jul-00 [REARED] [Tim Norriss]](phpBB/gallery/images/upload/146cdc697759762e02e51c5e0b03258f.jpg "Brown Argus - pupa - Stockbridge Down - Jul-00 [REARED] [Tim Norriss]")
