The larva feeds on grasses (Poaceae, rarely also Cyperaceae). I found caterpillars especially on Festuca ovina agg., Bromus erectus (grasslands of the eastern Swabian Alb) and once on Phalaris arundinacea (Iller valley in Southern Germany).
Erebia medusa inhabits nutrient-poor grasslands, extensive meadows, fens, marshes, forest meadows and clear-cuttings. The butterfly prefers slightly higher and denser growing grasslands, but does not require necessarily a woody component. On the other hand, I also observed larvae together with those of Apamea furva in isolated Festuca tufts on rocks.
The adult flies in one generation between May and June. At higher elevations, it is still flying in July (e.g. Olympus, Northern Greece, 2500m above sea level, in late July 2010) The caterpillar overwinters as L4 and is mature in April or early May. I found overwintering caterpillars repeatedly in the base of tufts of Festuca ovina agg. (eastern Swabian Alb) between November and March.
Endangerment: regionally endangered or decreasing
Overall, Erebia medusa is still well represented in Central Europe, especially in Southern Germany, but more rarely in the north. It is in decline outside of the larger nutrient-poor grassland regions because of eutrophication, intensification, overbuilding and afforestation.
The distribution ranges from central and Eastern Europe to China. In the Alps Erebia medusa is found in the north only in the valleys, while it is represented in the south up to more than 2000m above sea level. The reason is probably the dense occurrence of the sister species Erebia oeme in the northern Alps.
To the southeast Erebia medusa reaches Central Greece (e.g. on Mount Olympus up to 2600m above sea level and in the Pindos range).