Brown Argus (Aricia agestis)

Species description
© - Nick Greatorex-Davies

The Brown Argus is a species of open grassland and disturbed habitats. Until the late 1980s this was a declining butterfly that had become largely restricted to calcareous grassland and coastal dunes where its caterpillars fed mainly on Rockrose (Helianthemum nummularium) and Storksbill (Erodium cicutarium,) respectively. Now it occurs much more widely breeding on annual cranesbills (Geranium spp.) on such places as roadverges, setaside and old industrial sites (For further details on this species see

LCI summary

Log Collated

This chart shows the index of abundance (LCI = Log Collated Index) over time. It shows fluctuations in populations from year to year, and is scaled so that the average index over the whole series is equal to 2 (horizontal line). Further details on the analysis of UKBMS data can be found [here]

This chart shows the average number of butterflies seen on transects between April and October across all sites (fitted values from a Generalised Additive Model). The blue line gives average counts over the full BMS series (1976 to date) and the red line gives the average for the last year.

This map shows symbols for the mean abundance at transect sites, with the colour of the symbol reflecting the level of abundance. Means are over all years. Grey background squares are the occupied cells as shown by the Butterflies for the New Millenium over the previous ten year period.