- Latin synonym: Plebejus nicias
- Family: Gossamer-winged Butterflies – Lycaenidae
- Subfamily: Blues – Polyommatinae
- Wing span: Very small, 23–28 mm (0.9–1.09 in.).
- Wing upper side: Females brown, basal part slightly bluish. Males sky-blue, wing margins broadly dark.
- Wing underside: Pale grey–light brown, with white-edged black blotches. Light-coloured stripe on hind wing reaches from basal part to margin. Hind wing margins with faint red blotches.
- Habitat: Abundantly-flowered meadows, under power-lines, roadsides and overgrown fields.
- Flying time: July.
- Overwintering form: Semi-grown caterpillar.
- Larval foodplant: Wood cranesbill (Geranium sylvaticum).
- Endangerment: Vulnerable.
The Blues (Polyommatinae) are one of three subfamilies of the Gossamer-winged butterflies (Lycaenidae) family in Finland. The two others are the Hairstreaks (Theclinae) and Coppers (Lycaeninae). The Gossamer-winged butterflies family is large with over 6,000 species and is the second-largest family worldwide (the Brushfooted butterflies family is largest).
The silvery argus is a very rare blue in Finland. The best area to see it is the eastern part of central Finland. The upper side of the male’s wing is turquoise blue with a broadly dark wing margin, both of which make good identification markers. Both genders can also be recognized by the underside of the hind wings which have an unclear red pattern, small black blotches and a long, light-coloured stripe. Males fly around looking for females, who lay their eggs individually on drying wood cranesbill leaves.