Brown Argus (Plebeius agestis)

Family: Lycaenidae Checklist: 61.015

 
Description
Wing span: 25-31 mm. The Brown Argus is an attractive butterfly, particularly when fresh, with bright orange marks contrasting with the dark chocolate-brown wings and the white wing borders. The sexes are similar; the female is larger. The female can have blue thoracic hairs, but never has blue scales (a means of differentiating it from the female Common Blue). It is primarily found south-east of a line between the Severn and the Humber, although it has been spreading further north in recent years. It occurs in small, compact colonies, and is not a great wanderer; adults only travel up to a few hundred feet from where they emerged. Colonies are typically found on chalk or limestone downland where the larval food plant is abundant, but they can also be found on heathland and in open woodland.
 
Images (click to enlarge)
Brown Argus ♂ © David Hastings
Brown Argus ♂ underside © David Hastings
Brown Argus ♀ © David Hastings
Brown Argus ♀ underside © David Hastings
Male Male underside Female Female underside
 
Life Cycle
This species generally has two broods a year in central and southern England, and there is sometimes a third. 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. Both broods are protracted, so it is possible for second-generation adults to be on the wing before the last first-generation adults have died. The larva is the over-wintering stage.
 
Larval Foodplants
The main foodplant on calcareous soils is Common Rock-rose (Helianthemum nummularium). Common Storks-bill (Erodium cicutarium) and Doves-foot Cranes-bill (Geranium molle) are used on other sites.
 
Nectar Sources
Adults feed primarily on Marjoram, Ragwort, Thyme and White Clover.
 
UK Conservation Status
Least Concern
 
Earliest UTB first sighting (since 2004) : 4th April
Mean UTB first sighting (since 2004) : 5th May
 
 
Distribution and Sites
 

Key
1 sighting 2-9 max seen 10+ max seen
This species is a habitat specialist. It can be found at these sites:
Berkshire
Lardon Chase
Buckinghamshire
Bernwood Meadows
Yoesden Bank
Oxfordshire
Aston Rowant NNR
Dry Sandford Pit
Otmoor
Sydlings Copse
Watlington Hill
Whitecross Green Wood

 
Related Species
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