- Family: Gossamer-winged Butterflies – Lycaenidae
- Subfamily: Blues – Polyommatinae
- Wing span: Very small, 19–26 mm (0.74–1.01 in.).
- Wing upper side: Males shiny blue, narrowly black-edged. Hind wing margin often fragments into separate blotches. Females brown, blue at base of hind wings and forewing. Females’ forewings with broad, brownish violet margin. Both genders with black, half-moon-shaped blotch in middle of forewing and fainter blotch on hind wing.
- Wing underside: Pale greyish white with black blotches. Edge of hind wing also with red blotches.
- Habitat: Sparsely-wooded sandy and gravelly land.
- Flying time: June.
- Overwintering form: Caterpillar.
- Larval foodplant: Breckland thyme (Thymus serpyllum).
- Endangerment: Critically endangered, protected in all of Finland.
The baton blue’s only confirmed habitat in Finland and the Nordic countries is around Säkylä in Satakunta, where the army has a shooting range. Missing the target could be costly, because the fine for killing a baton blue is currently 1,682 Euros (the highest butterfly fine existing today, only the large copper carries the same penalty).
The baton blue can be confused with the chequered blue, which also has half-moon-shaped blotches on its forewings and hind wings. The chequered blue has larger margin blotches on the upper side of its wings, however, and strong black blotches on the underside.
Females lay their eggs individually on the leaves of the host plant, in this case Breckland thyme. The larvae have a gland that secretes a sweet, nourishing liquid that ants love to lick, so there are often ants around the larvae. They do not disturb the larvae but rather protect them.
The most expensive butterflies
The baton blue is protected and the price of its destruction is currently 1,682 €. Only the large copper carries the same price tag.