The ecology and conservation of the brown argus butterfly Aricia agestis in Britain

The ecology of the declining butterfly Aricia agestis was studied in southern England by measuring oviposition preferences, and from population estimates and habitat analyses of colonies on seven sites. The adults live in small, predominantly closed populations, although movement is not as restricted as in most other lycaenid butterflies studied. Butterfly collectors pose little threat to this species; population size is instead restricted by the precise ecological requirements of the egg site, and hence the larval stage. A. agestis chooses ‘lush’, sheltered growths of the larval foodplant, Helianthemum chamaecistus . The organic nitrogen content and mesophyll thickness of plants selected for oviposition on study sites were significantly higher than in randomly selected plants. Structural features of the foodplant and its surroundings were less important than for other lycaenids; although the presence of bare ground influenced oviposition, turf height — at least at the study sites—did not. A survey of seven sites showed no correlation between the densities of A. agestis and H. chamaecistus , but there was a strong correlation between butterfly density and the number of the lush foodplants that were growing in the form chosen for oviposition. Priorities for the management of sites are suggested.