The common blue is a small blue butterfly with a wingspan up to 3.6 cm. It flies between April and October. The common blue is found in a variety of habitats including heathland, woodland rides, grassy meadows, parks and gardens.
Males are very consistent in appearance, the uppersides being violet-blue with plain white fringes. Females vary but are often brown and tinted with blue scales and orange crescents on the outer margins of the wings. The undersides of both sexes are marked with a pattern of white-ringed black spots and orange crescents. Males have a greyish ground color with bluish scales around the base of the wings. Females instead have greenish scales at the wing bases, and a pale brown ground color.
In Central Europe there are usually 2 generations per year. The first brood emerges in May and flies until mid-June. The second brood emerges in late July or early August and remains on the wing until mid-September or sometimes into early October.