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Chalkhill Blue

Polyommatus coridon

Not yet photographed by the community

Pale silvery-blue; restricted to chalk and limestone downland.

Species Profile

Nationally Scarce; listed as a species of conservation concern in the UK due to habitat loss and fragmentation.

Lifespan: 2–4 weeks as an adult butterfly; caterpillars overwinter and take several months to develop
Size & Weight: Wingspan 32–35 mm
Habitat: Warm, dry chalk and limestone grasslands, typically on south-facing slopes with sparse vegetation and plenty of bird's-foot trefoil.
UK Distribution: Southern England only, with strongholds on the North and South Downs, Chilterns, and scattered sites in southern counties; a resident species that does not migrate.
Diet: Adult butterflies feed on nectar from wildflowers such as bird's-foot trefoil, marjoram, and vetches.
Predators: Spiders, robber flies, insectivorous birds, and small mammals; caterpillars are preyed upon by parasitoid wasps and tachinid flies.
Mating Season: June to August
Breeding: Females lay eggs singly on bird's-foot trefoil plants; caterpillars hatch and feed before overwintering; single brood per year with larvae pupating in spring.
Behaviour: Males are highly territorial and patrol grassland slopes, perching on low vegetation to watch for females; they are more active in warm, sunny weather. Females are more cryptic and spend more time in vegetation. The species exhibits strong site fidelity.

Did You Know?

•Only the males are bright sky-blue; females are predominantly brown with orange spots, making them appear to be different species entirely.
•The caterpillar has a symbiotic relationship with ants, which tend and protect it in exchange for honeydew-like secretions.
•Chalkhill Blues are completely dependent on bird's-foot trefoil (Ornithopus perpusillus) as their larval food plant.
•Adults often roost low to the ground at night, making them vulnerable to damp weather and frost.
•The species has declined significantly over the past century due to the loss of chalk grassland habitat through agricultural intensification and urban development.

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