Glanville Fritillary Melitaea cinxia
Feed on Narrow-leaved Plantain. Easiest to keep on potted foodplant, enclosed in a sleeve. The larvae are gregarious, living in a tight bunch at the base of the plant, and spreading out more as they grow larger. The ginger head capsule and jet black body distinguish these larvae from other species.
In Britain this species lives mainly on the Isle of Wight coast, but they have been established elsewhere in Britain. Maybe they could be encouraged in more localities.
These larvae will produce butterflies this spring.