Coenonympha hero (Linnaeus, 1761)

Host plants:
The larva feeds on grasses with usually rather low production (as with many Satyrinae both Cyperaceae and Poaceae). More important are especially Carex brizoides (multiple observations on the eastern Swabian Alb), but also Deschampsia caespitosa (Swabian Alb), Festuca sp. (observations on Festuca ovina agg. in nutrient-poor forest fringes in N-Bavaria), Agrostis (eastern Swabian Alb) and probably also Calamagrostis sp. (only in still loose, unfelted flocks, single caterpillars observations on the Swabian Alb) and a few other species.

Habitat:
Coenonympha hero inhabits floodplain forest clearings, woodland fringes, clearcuttings in moist forests, coppice woodland and shrubbery-rich fen meadows. Coenonympha hero partly occurs in rather lean, nutrient-poor sites, but on the other hand also in somewhat higher growing stocks as long as the entanglement/felting is not too strong. The best is probably a mix of both forms as well as of moisture gradients.
I observed larvae on Festuca ovina agg. during the day in such a mix in a small embankment on a clearing in a coppice forest (24 March 2005). All caterpillars were found in moderately lean spots. Because of the early activity the caterpillar has to rely on partial green overwintering grasses such as Festuca, Deschampsia and some Carex species or on species that start growing very early in the spring (e.g. Carex brizoides).

On the eastern Swabian Alb (S-Germany) Carex brizoides and Deschampsia caespitosa play an important - but not the only - role (young caterpillar records in autumn on Carex brizoides, observations in spring, many butterflies in almost pure stands of this species). Heavily felted, dense and high growing areas of about Calamagrostis epigejos are avoided. Coenonympha hero usually has high densities on sunny, small-scale patches with stagnant moisture, high air humidity, windbreak und structurization (groves). But it often shows only low densities on large, very open clearcuttings. As many other species Coenonympha hero needs a network of habitat patches for long-term survival.

Life cycle:
The adults fly in one generation from mid-May to early July. In years with cool spring they sometimes appear not until June (e.g. 2013). Coenonympha hero is our second earliest species of the genus after Coenonympha pamphilus. Fairly high abundances can be observed at appropriate locations. On the eastern Swabian Alb I was able to count partly over 80 adults on older clearcuts. The butterflies visit flowers only rarely and if they do, then especially at the end of the flight time (Valeriana, Cirsium palustre, Veronica, Rubus idaeus, other Rubus, Trifolium, Aegopodium etc.). However, the adults should feed on aphid honey (sugar secretions) and dew on leaves, too. Sometimes they suck humidity on the ground and a single observation (June 2013, eastern Swabian Alb) succeeded on sheep excrements on the edge of a habitat.

The blue-green eggs are individually attached to vegetation parts (mostly grasses) near the ground. Therefore the female lands in the vegetation (e.g. a loose Deschampsia tussock) and then crawls further down to the ground where it searches for a suitable place to attach the egg. The caterpillar overwinters half-grown (usually in penultimate instar) and immediately begins to feed after the snow has melted. The last moult takes most often place in April and pupation in late April or in May in the grass layer.

Endangerment: threatened with extinction

Endangerment factors:
Coenonympha hero is threatened with extinction because of the darkening processes in the populated forests (single tree selection in densely afforestated forests without clearings), the destruction of wood-rich wetlands, general eutrophication and the decline of traditional forest management practices. In wetlands Coenonympha hero is edangered by reed and bush encroachment, but also by intense mowing. The butterfly obviously needs quite meager and unmown places within the habitat for larval development such as small embankments, low-growing gappy spots or borderlines and not too felted areas. Only weakly entangled areas should be important on fens, too.

In populated forests it is extremely important that sufficient young clearcuts are available (best of medium sizes). A pure single tree selection without sunny clearings would displace Coenonympha hero and many others and is thus the worst of all management forms in the forest from a nature conservationist's point of view!

Remarks:
The distribution ranges from eastern France very locally across Central Europe and Southern Scandinavia until well into temperate Asia and there to Japan.