Common blue butterfly – olyommatus icarus
is a butterfly in the family Lycaenidae and subfamily Polyommatinae. The butterfly can be found in Europe, North Africa, [iran] and the Canary Islands, but it is especially common throughout the British Isles. Recently, however, there has been an estimated 96% population loss due to habitat loss. Butterflies in the Polyommatinae are collectively called blues, from the coloring of the wings. Common blue males usually have wings that are blue above with a black-brown border and a white fringe. The females are usually brown above with a blue dusting and orange spots. Polyommatus icarus has a wingspan of 28–36 millimetres (1.1–1.4 in). The dorsal side of the wings is an iridescent lilac blue with a thin black border. Females’ wings are brown with a row of red spots along the edges of the wings and usually some blue at the base. The extent of blue and brown is extremely variable depending on location. The top of the wings in the female may be mostly blue, especially in Ireland and Scotland, but it always has red spots.

The ventral side has a grayish base color in the males and a more brownish hue in the females. Both sexes have a row of red spots along the edge of the hindwing and extending onto the forewing, though they are generally fainter there, particularly in the males, where they are sometimes missing altogether. There are about a dozen black-centered white spots on the hindwing and nine on the forewing. These usually include one in the middle of the forewing cell, absent in Chapman’s and Escher’s blues. The fringes on the outer edge of the wings are uniform white, not crossed with black lines as in the chalkhill and Adonis blues (that is, the common blue lacks checkering).

The caterpillar is small, pale green with yellow stripes and, as usual with lycid larvae, rather slug-like.