- Family: Gossamer-winged Butterflies – Lycaenidae
- Subfamily: Blues – Polyommatinae
- Wing span: Very small, 18–26 mm (0.7–1.01 in.). The smallest Finnish butterfly.
- Wing upper side: Dark brown, slightly blue sheen.
- Wing underside: Greyish brown, with white-edged black blotches.
- Habitat: Open, sandy and gravelly ground.
- Flying time: Late May–late June.
- Overwintering form: Caterpillar.
- Larval foodplant: Kidney vetch (Anthyllis vulneraria) and yellow oxytropis (Oxytropis campestris) in southern Finland and alpine milkvetch (Astragalus alpinus) in the north.
- Endangerment: Critically endangered.
The little blue, the silver-studded blue and the northern blue are not only Finland’s smallest blues but its smallest butterflies altogether. The little blue is found only rarely in Finland and can be told apart from other blues, apart from the female mazarine blue which is clearly bigger, by the brown upper side of its wings and the black-blotched underside that lacks red patterns. It can be told apart from the female mazarine blue not just by size but also the straighter line of blotches on its forewing.
Although the little blue can only be found in a few places, it is abundant there. Females stick to the same location and lay their eggs individually on the inflorescence of the host plant. The larvae develop a gland which secretes a sweet, nourishing liquid that ants like to lick, so ants occasionally visit the larvae and protect them.