Percnodaimon

Genus of butterflies

Percnodaimon merula, the black mountain ringlet, is a satyrid butterfly in the family Nymphalidae. It is currently the only recognised species in the monotypic genus Percnodaimon, endemic to New Zealand, although there may be other undescribed species in the genus. The black mountain ringlet is notable for living exclusively in rocky areas of New Zealand's Southern Alps, usually above 1200 m. Its eggs are laid on rocks, its larvae feed on mountain Poa species, and it pupates under a stone. It has distinctive dark velvety wings and a zig zag flight pattern over the scree slopes on which it lives.

The wingspan of the Percnodaimon imago can be between 35 and 55 mm, and its broad velvety wings are usually black or brown across the dorsal surface, sometimes with a purple reflection. Forewings have characteristic black and white circles inside a patch of brown at their distal ends. There is little sexual dimorphism: males and females are similar in appearance, with females a little larger. The row of large pale spots often found on the underside of the hindwings is more noticeable in females.</blockquote>

Wing colour plays an important physiological role: the dark wings with a large surface area absorb sunlight and store heat, essentially acting like solar panels, an adaptation to the cool climate of the Southern Alps. The butterfly sits with its wings open and turned towards the sun, flying while the sun is shining and hiding amongst rocks when clouds intervene. At night they shelter deep in rocky crevices. Black mountain ringlet larvae are night feeders to avoid predators, which can easily spot them feeding on the tips of tussock blades. They spend little time feeding, but instead conceal themselves in nearby hiding spots.

At the start of pupation the black mountain ringlet turns grey with brown speckles to match the surrounding stones. Unlike most butterflies pupae are suspended horizontally rather than vertically, and are attached to the undersurface of a rock with a large cremaster, a hook shaped protuberance on the abdomen. Pupae have been found up to 3 feet away from the nearest food plant. The adult butterflies emerge 2 to 3 weeks later.

Adult black mountain ringlets are found in summer, from December to February, and the Patricks note that early versus late emergence is one of the characteristics distinguishing the undescribed species. This species is considered to live about a year in its adult stage, but as the larvae can take two or three summers to grow to full size there is a possibility that it can live up to four. This slow growth may reflect the extreme climate and conditions of New Zealand's Southern Alps.