Cranberry blue – plebejus optilete
is a butterfly of the family Lycaenidae. It is found in north eastern Europe, the Alps, North Asia, Japan, Korea and north western North America. The length of the forewings is about 14 mm. The butterfly flies from June to August depending on the location.

Both wings very broad and their outer margins strongly rounded. Male above very dull dark violet-blue, sometimes with a broader black margin, sometimes without black margin. In the female only the basal half of the upperside is dusted with glossy blue scales. Underside dirty dust-grey, the ocelli very large, often distorted; only the anal area of the hindwing beneath bears orange spots before the margin, from which they are separated by two large round dots with metallic centres. More in the North, in Central and North Europe as far as Scandinavia and the Baltic provinces, sporadic, on moors, also in the Alps in damp larch-woods, locally abundant.