Field Guide
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Adonis Blue
Polyommatus bellargus
Not yet photographed by the community
Dazzling intense blue; chalk downland specialist.
Species Profile
Red Data Book (nationally scarce); Nationally Scarce species in significant decline due to habitat loss and fragmentation.
- Lifespan
- 2–3 weeks as an adult butterfly; caterpillar stage lasts several weeks depending on generation
- Size & Weight
- Wingspan 32–36 mm
- Habitat
- Chalk and limestone grasslands with abundant horseshoe vetch, typically on warm south-facing slopes with sparse vegetation.
- UK Distribution
- Restricted to southern England, primarily Sussex, Kent, Surrey, and Hampshire; resident species with multiple generations per year, absent in winter as pupae.
- Diet
- Adults feed on nectar from bird's-foot trefoil, horseshoe vetch, and other wildflowers; caterpillars feed exclusively on horseshoe vetch (Hippocrepis comosa).
- Predators
- Spiders, robber flies, parasitic wasps, and insectivorous birds; caterpillars vulnerable to parasitoid wasps.
- Mating Season
- May to September with two or three broods per year
- Breeding
- Females lay single eggs on horseshoe vetch plants; caterpillar stage 3–4 weeks, pupation occurs either within weeks (producing summer brood) or overwinters as pupae; two to three generations annually.
- Behaviour
- Males are highly territorial, perching on low vegetation and pursuing rivals and females in rapid, erratic flight. They are strongly attracted to hilltops and warm, sunny conditions. Females are more cryptic and spend time laying eggs on host plants.
- •Males display brilliant iridescent blue wings, while females are predominantly brown with blue scaling at the wing base, making them sexually dimorphic.
- •The species name 'bellargus' derives from the Latin for 'beautiful silver,' referencing the males' striking appearance.
- •It is one of the most restricted butterflies in Britain, found almost exclusively on a few chalk grassland sites in southern England.
- •The caterpillar has a mutualistic relationship with ants, particularly Lasius species, which provide protection in exchange for honeydew-like secretions.
- •Population fluctuations are dramatic year-to-year, heavily influenced by spring and early summer weather conditions.
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