AT A GLANCE
- Common Name: Chalkhill Blue
- Scientific Name: Lysandra coridon
- Category: Invertebrates
- Subcategory: Insects
- Range: Temperate Europe, from southern England and northern Spain east across Central Europe to the Balkans, Greece, and northwestern Turkey
- Habitat Type: Warm, sunny, south-facing calcareous chalk and limestone grasslands, downlands, and flowery limestone slopes with short, sparse turf
- IUCN Red List Status: Least Concern
- Lifespan: Adult lives 7 to 14 days; one single annual generation in midsummer
- Diet: Herbivorous (adults nectar on wild marjoram, knapweed, scabious, and wild thyme; caterpillars feed strictly on horseshoe vetch, Hippocrepis comosa)
- Average Size/Weight: Wingspan 32 to 38 mm; weight less than 0.3 g
- Key Defining Feature: Exquisite chalk grassland butterfly; males are a distinctive, shimmering pale silvery-sky-blue with dark margins and checkered wing fringes, while females are warm chocolate-brown
Overview
The Chalkhill Blue (Lysandra coridon) is a quintessential and magnificent butterfly of Europe’s sun-drenched calcareous chalk downlands. Flying in shimmering clouds over steep, flower-rich limestone slopes in midsummer, this delicate lycaenid is an iconic flagship of unimproved limestone grasslands. While females are warmly dressed in chocolate-brown with orange submarginal spots, the males possess a unique, ethereal coloration: not the deep blue of common blues, but a luminous, pale, icy silvery-sky-blue that gleams brilliantly under the July sun.
Biology and Physical Characteristics
Lysandra coridon exhibits marked sexual dimorphism. The upperside of the male is a soft, pale, shimmering milky-blue or frosted silver-blue, bordered by a broad dusky dark brown outer margin and a diagnostic, crisp fringe of alternating black-and-white checkered hairs. The female is rich velvety chocolate-brown, bordered along the hindwings with neat orange lunules (crescents). Both sexes share an intricate underside: warm pale greyish-buff on the forewings and cinnamon-brown on the hindwings, adorned with an elaborate constellation of black spots circled in white and a submarginal row of fiery orange spots.
Behavior and Ecology
Chalkhill Blues fly during warm, sunny weather from July through September, often congregating in staggering densities of thousands of individuals on prime chalk slopes. Males patrol back and forth across the turf, actively seeking newly emerged females resting in the grass. The caterpillar is an obligate specialist, feeding exclusively on the leaves of Horseshoe Vetch (Hippocrepis comosa) growing on thin, lime-rich soils. The larva lives in an intimate mutualistic symbiosis with yellow meadow ants (Lasius flavus): the caterpillar possesses specialized glands that secrete sweet, amino-acid-rich nectar that the ants eagerly drink; in exchange, the ants guard the caterpillar night and day from parasitic wasps and predatory spiders, even burying it in soil shelters to pupate.
Conservation and Human Impact
The Chalkhill Blue is classified as Least Concern on the IUCN Red List globally due to its wide distribution across southern and central Europe. However, in the United Kingdom and northern Europe, it is a protected species of conservation concern that suffered severe 20th-century declines following the abandonment of traditional sheep and rabbit grazing, which allowed scrub to overgrow horseshoe vetch. Targeted conservation grazing on nature reserves has spurred major recoveries.
Interesting Factoid
The caterpillar of the Chalkhill Blue hires its own personal army of bodyguard ants; it secretes sweet sugary drops from its back to pay the ants, who fight to the death to protect the caterpillar from wasps.