Here’s a full natural history overview of the Common Blue (Polyommatus icarus), one of the most widespread and familiar butterflies in Europe:

Common Blue (Polyommatus icarus)

Taxonomy & Classification

• Kingdom: Animalia
• Phylum: Arthropoda
• Class: Insecta
• Order: Lepidoptera
• Family: Lycaenidae (blues, coppers, hairstreaks)
• Genus: Polyommatus
• Species: P. icarus

General Description

A small but vibrant butterfly, known for its striking blue males and more subdued females.

• Wingspan: 28–36 mm.
• Males:
  • Bright violet-blue upperwings with a thin black border and white fringe.
  • Underside pale grey with black spots and orange lunules near the wing margins.
• Females:
  • More variable: usually brown with orange spots, sometimes with blue dusting.
  • In warm southern populations, females can be as blue as males.
• Underside (both sexes):
  • Characteristic pattern of black spots, white rings, and orange crescents on hindwings.
• Caterpillar: Small, green, slug-like, with fine hairs.

Behavior & Lifestyle

• Flight Period:
  • 2–3 broods per year depending on region.
  • Active from April to October.
• Feeding (Adults):
  • Nectar from a wide range of flowers: clovers, bird’s-foot trefoil, buttercups, thistles.
• Feeding (Larvae):
  • Feed mainly on leguminous plants, especially bird’s-foot trefoil (Lotus corniculatus), clovers (Trifolium spp.), medicks, and vetches.
• Reproduction:
  • Eggs laid singly on host plant leaves.
  • Caterpillars often tended by ants (mutualistic relationship).
• Overwintering: As a caterpillar, in the third instar stage.

Habitat

• Highly adaptable, occurring in:
  • Grasslands, meadows, and heaths.
  • Road verges and railway embankments.
  • Gardens, pastures, and coastal dunes.
• Thrives in sunny, open habitats with plenty of flowers and legumes.

Geographic Range

• Europe: Widespread throughout, except the far north of Scandinavia.
• Asia: Extends eastward into temperate Asia.
• North Africa: Present in Morocco and Mediterranean regions.

Ecological Role

• Pollinator: Important for wildflowers and legumes.
• Prey: Consumed by birds, spiders, and predatory insects.
• Mutualism with Ants: Ants protect larvae in exchange for sugary secretions (a common lycaenid trait).

Special Adaptations

• Polyphagy: Larvae feed on a wide range of host plants, aiding adaptability.
• Ant Associations: Enhances caterpillar survival rates.
• High Reproductive Potential: Multiple broods each year allow rapid recolonization.

Conservation Status

• IUCN Red List: Least Concern (LC).
• Population Trends: Generally stable and common, though declines occur in areas with intensive agriculture.
• Threats:
  • Pesticide use and loss of flower-rich grasslands.
  • Habitat fragmentation.
• Benefited from roadside and urban wildflower schemes.

Interesting Facts

• Despite its name, the female is often brown rather than blue, making her easy to confuse with other brown lycaenids.
• It is the most widespread of all blue butterflies in Europe, often the first “blue” beginners learn to identify.
• The species epithet icarus refers to Icarus of Greek mythology, who flew too close to the sun—a nod to its sky-blue wings.
• Can hybridize with related blues in overlapping ranges, producing intermediate forms.

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