Identifying features
Wingspan 21–28 mm. The male has a blue upperside with a fairly distinct transition to the black area along the wing margin; the female is dark blue with a broad, almost black area within the wing margin, and a suggestion of orange crescent shapes. The undersides of the wings are grey-brown with dark spots within very thin white rings; the underside of the hindwing has a clearly yellowish-orange band with some blue, rounded spots. Lacks the curved spur on the forewing, as Silver-studded blue does.
Similar species
Resembles Silver-studded blue and can be difficult to distinguish from it; Silver-studded blue has a small, curved ridge on the outer edge of the frontal bone, while this is missing in Idas blue.
Distribution
Throughout Norway, but unusually at the very edge of the coast and furthest north in Finnmark. Also found in Denmark, Sweden and Finland, and throughout Europe eastward to Japan.
Biology
The egg is round and flat with a finely dotted pattern. The larva is greenish with paler longitudinal stripes. Older larvae have tentacles and a honeydew gland on the seventh abdominal segment.