Erebiola butleri

Butler's ringlet (Erebiola butleri) is an elusive New Zealand endemic butterfly, discovered in 1879 by John D Enys at the alpine pass at the head of the Rakaia River. It is the only member of the genus Erebiola.

Erebiola is derived from “erebus”, the ancient Greek world of darkness between Earth and Hades, while the species name, butleri, was after Mr A.G. Butler of the British Museum who played a major role in early descriptions of New Zealand butterflies.

Its Māori name is pepe pouri, which means dark moth, and shares the name with the Black Mountain ringlet and the forest ringlet butterfly.^[2]

Description

Butler’s ringlet have a wingspan of 35-43mm, with a 40mm average for males and a 37mm average for females.

Both males and females are smoky brown, though males tend towards the richer browns while the females tend towards the paler browns. The underside of the hindwing has wedge-shaped silvery-white marks.

Both the underside and the topside of the wings have eye spots at the distal-most ends, surrounded by reddish-brown shading. There is variation between individuals in the number of eye spots, the extent of the reddish-brown colouring around the eye spots, and the silvery-white markings on the undersides of the hindwings.

The egg is ivory with vertical ribbing. The larvae is similar coloured from head to tail, being yellow-brown with dark and light lateral striping. A fully grown larvae is roughly 20mm long. The pupa is grey and cream with fine black spotting along the abdomen, changing to a brown on the rest of the body. The style of pupation is unknown.

Life stages

The egg is laid singularly on a nearby shrub and hatches after 14 days. The larvae grows from 3mm to 20mm over an unknown length of time, before pupating. Pupation lasts about 21 days. It is unknown how long adult butleri live for.

Distribution

Butler’s ringlet is confined to the subalpine zone in the South Island. It has been identified at only a few sites along the main divide of the Southern Alps.

It favours subalpine terraces at altitudes 900-1300m in areas of snow-tussock with Hebe and Dracophyllum shrubs. Its preferred locations are often damp, almost boggy, or next to mountain lakes . It is very difficult to find even in areas where it has previously been seen, and so little is known about its actual range.

Museum specimen records identified it as active from 27 December to 11 March. It is known to be able to remain aloft for long periods of time and to cover great distances.^[3]

Misclassification and similarities with other species

Butler’s ringlet appears very similar to some species of the Erebia genus, and was included in that genus until 1967, when Erebia butleri was reclassified as Erebiola butleri due to structural differences found between butleri and other members of the Erebia genus.^[4]

Butler's ringlet is visually similar to the black mountain ringlet, Percnodaimon pluto. The two species may be differentiated by where the individual in question is sighted. Butler’s ringlet prefers to fly over vegetation, settling among snow-tussock, subalpine shrubs and herbaceous flowers, whereas the black mountain ringlet tends to congregate over rock and scree.

References

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