Scientific name: Aricia agestis
The Brown Argus has dark brown wings fringed in white, with a row of orange spots along the outer edges of the wings. The wings have a blue sheen at certain angles.
The underwings are a pale grey-brown, with orange spots and white-ringed black spots. Both sexes look similar, although the orange spots are more faded on the forewings of the males.
This small butterfly is characteristic of southern chalk and limestone grassland, but occurs in a variety of other open habitats as far north as north Wales and Yorkshire. It is a close relative of the Northern Brown Argus, which is restricted to Scotland and northern England.
The adult has a silvery appearance as it flies low to the ground, stopping frequently to perch or feed on flowers. It can be confused with Common Blue females, which also have brown upperwings, but usually with some blue at the base. It is also very similar to Northern Brown Argus, which usually has no orange spots on forewing.
The egg is a pale white disc-shape, laid singly underneath the leaves of its foodplant and hatching after around one week.
The caterpillar has five stages (instars) in its life, moulting four times. It changes in appearance at each stage, starting off a pale yellow colour, changing to greenish-yellow white and, finally, a pale green with dense white hairs and a pinkish stripe down each side, which camouflages it while it feeds openly during the day. The Brown Argus has a close relationship with ants which starts in this final instar, when the caterpillar grows Newcomer's glands. These glands produce a secretion so attractive to ants that they protect the caterpillar to maintain their supply of it.
The chrysalis is pale brown and forms at the base of its foodplant, on the ground. It is often taken away and buried underground by the ants.
The butterfly spread rapidly in the mid-1990s, but lost ground in the last three years of the twentieth century.
Size and Family
- Family: Blues
- Size: Small
- Wing Span Range (male to female): 29mm
- Butterfly Conservation priority: Low
- European status: Not threatened
Common Rock-rose (Helianthemum nummularium) is used almost exclusively on calcareous grasslands. In other habitats it uses annual foodplants, mainly Dove's-foot Crane's-bill (Geranium molle) and Common Stork'-bill (Erodium cicutarium). There are also recent reports of egg-laying on Cut-leaved Crane's-bill (G. dissectum), Meadow Crane's-bill (G. pratense), and Hedgerow Crane's-bill (G. pyrenaicum).
The main habitats are chalk and limestone grassland. However, the butterfly can occur in a range of habitats with disturbed soils including coastal grassland and dunes, woodland clearings, heathland, disused railway lines and road verges.
- Countries: England, Wales
- Widespread in southern and central England as far north as Yorkshire. Less common and mainly coastal in Wales and south-west England.
- Distribution Trend Since 1970’s = +16%.