Field Guide
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Brown Argus
Aricia agestis
Not yet photographed by the community
Small brown butterfly with orange spots; looks like a female blue.
Species Profile
Amber List; declining in northern parts of its range due to habitat loss and fragmentation, though stable in core southern populations.
- Lifespan
- 2–4 weeks as an adult butterfly; larvae develop over several weeks depending on temperature and food availability
- Size & Weight
- wingspan 28–34 mm
- Habitat
- Sunny, sheltered grassland and scrubland, particularly on chalk and limestone downland with abundant bird's-foot trefoil and other low-growing legumes.
- UK Distribution
- Resident in southern and central England, with populations concentrated in the Midlands, southern counties, and scattered locations northward; absent from much of Scotland, Wales, and northern England. Produces multiple generations per year with peak flight periods in spring and late summer.
- Diet
- Larvae feed exclusively on bird's-foot trefoil (Lotus corniculatus) and related legume species; adults feed on nectar from small flowers and occasionally on rotting fruit.
- Predators
- Small birds, particularly warblers and wrens; spiders; parasitoid wasps and flies attack larvae and pupae.
- Mating Season
- April to September (multiple broods)
- Breeding
- Females lay eggs singly on or near food plants; larvae develop through four instars; two to three broods per year in the UK, with some populations producing a fourth partial brood in warm years.
- Behaviour
- Males perch on grass stems or bare ground in sunny spots, flying up to intercept passing females; they are highly territorial and quick, darting fliers. Females are more cryptic and spend much time near food plants. Both sexes bask with wings open.
- •The Brown Argus is one of the few UK blue butterflies with no blue coloration on the male's wings, instead displaying warm brown uppersides with distinctive orange spots.
- •It is the only Aricia species found in the UK and is closely related to southern European populations.
- •Larvae can enter diapause (suspended development) to overwinter as pupae, allowing them to synchronise emergence with spring food plant growth.
- •Males perform 'hilltopping' behaviour, gathering on elevated areas to locate mates.
- •The species has shown a northward range expansion in recent decades, possibly linked to climate warming, though it remains absent from most of Scotland.
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