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.
Zeller (1847) described the summer generation of A. agestis as f. aestiva, having a deep brown-grey underside.
This species was first defined in Denis & Schiffermüller (1775) as shown here (type locality: Vienna, Austria).
Both distribution and population trends show an increase and this butterfly is not, therefore, currently a species of conservation concern.
The table above shows the distribution and population trends of species regularly found in the British Isles. The distribution trend represents a comparison between data for the periods 1995-1999 and 2005-2009. The information provided is taken from the Butterfly Conservation report The State of the UK's Butterflies 2011. The UK BAP status is taken from the UK Biodiversity Action Plan (UK BAP) (2007 review).
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.
Click here to see the distribution of this species or here to see the distribution of this species together with specific site information overlaid. Alternatively, select one of the sites listed below.
|Aldbury Nowers, Alner's Gorse, Ardley Quarry, Arlington Reservoir, Arreton Down, Ashampstead Common, Aspal Close, Aston Rowant NNR, Aston Upthorpe Downs, Avon Heath Country Park, Badbury Rings, Ballard Down, Bannerdown, Banstead Downs, Barnack Hills and Holes NNR, Barton Hills, Beachy Head, Bedfont Lakes Country Park LNR, Bingham Linear Park, Bison Hill, Black Rock, Bolt Head, Brackett's Coppice, Branscombe, Braunton Burrows, Brean Down, Brigstock, Broughton Down, Burham Down, Butts Brow, Carymoor Environmental Centre, Castle Hill NNR, Cerne Hill Giant, Chambers Farm Wood, Clubmen's Down, Collard Hill, College Lake, Corfe Castle, Crook Peak, Darlands Banks LNR, Deep Dale, Denbies Hillside, Devil's Ditch, Devil's Dyke, Ditchling Beacon, Draycott Sleights, Duchie's Piece, Duncliffe Woods, Dunwich Heath, Durlston Country Park, Durlston NNR, Eaglehead Copse, Eakring Meadows Nature Reserve, Ellerburn Bank, Eyarth Rocks, Fackenden Downs, Finemere Wood, Fontmell Down, Forest of Dean, Foulden Common, Frog Firle Farm, Goblin Combe, Grangelands, Great Orme, Greenham Common, Greenhill Down, Hadleigh Country Park, Ham Common, Hartslock, Hethfelton Wood, Hexton Chalk Pit, Hinkley Point Nature Reserve, Hod Hill, Hog Cliff Bottom, Holkham Meals, Hounslow Heath LNR, Howardian Local Nature Reserve, Jerry's Hole, Kemsing Downs, Kingcombe Stones, Landguard, Lankham Bottom, Larden Chase, Lathkill Dale, Levin Down, Llanymynech Rocks, Lorton Meadows, Lydden Down, Lydlinch Common, Magdalen Hill Down, Malling Down, Mansmead wood, Martin Down, Mill Hill, Millenium Arboretum, Monk's Wood, Moors Valley Country Park, Mount Caburn, Mumbles Hill, Norton Green, Nupend Wood, Old Castle Down, Old Down, Basingstoke, Old Winchester Hill, Over Cutting, Oxwich, Pamphill Moor, Pegsdon Hills, Penhale Sands, Pewsey Down, Pexton Bank, Piddles Wood, Pitstone Hill, Potteric Carr, Powerstock Common, Prestbury Hill, Pulborough Brooks (RSPB), Ringstead Bay, Risby Warren, Rookery, Ryton Woods Meadows, Sand Point, Seven Barrows, Shapwick Heath, Sharpenhoe Clappers, Somerford Common, Sovell Down, Springhead, Spurn Peninsula, St Catherine's Hill, Start Point, Steyning Rifle Range, Stockbridge Down, Stoke Camp, Stubhampton Bottom, Tadnoll, Telegraph Hill, The Trundle, Therfield Heath, Thixendale, Thorndon Country Park, Thurlbear Quarrylands, Tickenham Ridge, Tophill Low, Totternhoe Knolls and Quarry, Townsend Quarry, Trench Wood, Twywell Hills and Dales, Tyttenhanger Gravel Pits, Ubley Warren, Ufton Fields, Walton Common, West Yatton Down, Whipsnade, White Sheet Hill, Whiteford Burrows, Wicken Fen, Windmill Hill and Cleeve Prior, Yew Hill|
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.
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.
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.
Adults feed primarily on Marjoram (Origanum vulgare), Ragwort (Senecio jacobaea), Thyme (Thymus polytrichus) and White Clover (Trifolium repens).
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 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.
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.
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Of 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)
Although 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
The following links provide additional information on this butterfly.
The species description provided here references the following publications: