Northern Brown Argus

Taxonomic information

Common Name: Northern Brown Argus

Latin Name: Aricia artaxerxes

Family: Lycaenidae

Description

Northern brown argus butterflies
Photograph by Ian Powell

The northern brown argus is the subject of a local Species Action Plan in the Yorkshire Dales area and in the national Species and Habitats Review 2007, it was added to the UK list of priority species for biodiversity action. This species is one of only a few butterfly species that have primarily a northern distribution in the UK, occurring in Scotland, Cumbria, Lancashire and Durham. The populations in the Yorkshire Dales National Park are at the southern edge of its British distribution and it may be encountered in limestone areas of the Dales from early June until mid August.

The prime sites for northern brown argus are sheltered areas of unimproved limestone grassland where light stock grazing allows the larval food plant the common rock rose (Helianthemum nummularium), to thrive. Research has shown that a sward height of between six and ten centimeters provides females with the optimum egg laying habitat.

Historically there were relatively few records of northern brown argus in the Dales but an increase in the amount of fieldwork by a number of lepidopterists in the 1990s led to a discovery of a number of new colonies. A comprehensive survey of all known colonies in the Dales and visits to a number of potential sites in 2002, resulted in the recording of 33 occupied sites. This apparent population increase is more likely to be due to increased observer effort than any real population expansion. The key strongholds for this species remain in the Ribblesdale/Ingleborough and Wharfedale/Littondale areas of the National Park with a smaller number of sites in other areas.

Monitoring work has shown that there have been declines in northern brown argus populations in other areas of northern England and Scotland. The establishment of several monitoring transects in the Dales will help contribute to a better understanding of how this characteristic species is faring in northern England.