The Brown Argus is small butterfly found on chalk and limestone grassland and on other open habitats such as coastal grassland and dunes. It is a resident in the UK. It is in the family lycaenidae that also includes the blues, coppers and hairstreaks. In fact it is often confused with the female Common Blue.
Distributed throughout southern England and as far north as Yorkshire. It is widely distributed in Europe as far north as Denmark across to the Middle East, Siberia and into North Africa. For further information about distribution please see the National Biodiversity Network.
The Brown Argus has a brown upper-side with orange markings and fringed with white. There is a black spot on the upper wing. Its under wings are greyish-brown with white ringed black spots and orange markings. It has a wing span of 29mm. Male and female are similar. It can be confused with the female Common blue, but these have a blue-ish tinge to the base of the upper wing.
When the Brown Argus flies it has a silvery appearance and can look ghostly as it flies low to the ground stopping frequently to perch or feed. Males will wait in sheltered hollows for females. They often roost communally in sheltered areas.
The Brown Argus has two flight periods. Adults emerge in May and August.
Caterpillars are a fleshy green with a pink strip down the side. You may be able to find them by looking for ants that attend them. Ants will bury the chrysalis making them hard to find!
They usually occur on open chalk or limestone grassland where its main food plants can be found, Common rock rose (Helianthemum chamaecistus). It prefers steep south facing banks where the vegetation is short and there are bare patches of soil. Where Common Rock rose is not present they will lay egss on Dove's-foot cranesbill (Geranium molle) and Common Stork's-bill (Erodium cicutarium). It may also use Cut-leaved Crane's-bill (G. dissectum), Meadow Crane's-bill (G. pratense), and Hedgerow Crane's-bill (G. pyrenaicum).
The butterfly spread rapidly in the mid-1990s but there have been losses in recent years.
The Brown Argus can be seen on Fleam Dyke and Devil's Dyke.
For further information about butterflies please see:Find out about what's been seen on our sightings page, or take a look at details of some of the projects and sites that we work on.