Cranberry blue is a small day butterfly that flies from mid-June to mid-July. The upper surface of the males’ wings is a shimmering violet blue and black at the edges. In females, the upper surface of the wings is brown, and the base parts are bluish. The gray-white underside of the wing has white, black spots.

Cranberry blue lives in swamps, especially with shrub-morass, and it can also be found in open heaths and wooded meadows. Its range extends from Central Europe to Eastern Siberia and it is also found in Northern America.

Cranberry blues are very territorial. They can easily be mixed with the northern blue (Plebejus idas) and the silver-studded blue (Plebejus argus). The larva usually lives among and eats the bog billberry or cranberry from which it gets its name.

Cranberry blue is a very common basic species that lives especially in morass. Bogs are important habitats for many butterfly species. Natural-state bogs are protected for preserving their hydrological conditions and microclimate.