The common blue (Polyommatus icarus) is a small lycaenid butterfly widespread across Europe, North Africa, and temperate Asia to northern China. Males are bright iridescent blue above with a dark border and white fringe; females are brown with variable blue dusting and orange marginal spots. Larvae feed on legumes, with bird's-foot trefoil (Lotus corniculatus), white clover (Trifolium repens), and black medick (Medicago lupulina) among the documented host plants; adults nectar low among grassland flowers. Gardens with legume lawns or meadow patches containing white clover or bird's-foot trefoil provide both larval and adult resources for this butterfly.

Larval host plants · 1

Breeds throughout the Palearctic region from western Europe and North Africa east to northern China; in Britain it is the most widespread blue butterfly, found from southern England to Orkney and across Ireland. An introduced population first discovered near Montreal, Quebec, around 2005 is now well established and has spread into Ontario, suggesting the species may become more widespread in eastern Canada.