Compare with: brown argus

Common blue Polyommatus icarus

Best time to see: Jun to mid Sep

Key facts

Our commonest and most widely distributed blue butterfly

Habitat: anywhere where the caterpillar foodplant, birdsfoot trefoil, occurs – heaths, downland and short grassland

Common throughout the British Isles except in highland areas


Male is bright blue above, female dark-brown with orange crescents; both have pale brown u/s spotted black and orange

Flit just above ground by day and roost communally at night in sheltered clumps of tall grass; wingspan 35 mm


Eggs are small white discs laid on foodplants in June and again in August

Caterpillars are plain green and slightly furry, hibernating among dead leaves when quite small

The chrysalis forms on the ground and is buried by ants; adults emerge in May/June and again in August

  • Main photo
  • female

Photo © David Corke

Photo © Iris Newbery