Mountain Ringlet (Erebia epiphron)

In this guide

1. Description and identification
2. Life cycle: egg, caterpillar, chrysalis and adult
3. Where the mountain ringlet lives
4. Host plants and diet
5. Behavior: sunshine, flight and daily routine
6. Similar butterflies and how to tell them apart
7. Quick facts
8. Did you know?
9. Pictures
10. Frequently asked questions

Description and identification

The mountain ringlet is a small member of the brush-footed butterfly family and belongs to the Satyrinae, the browns, whose caterpillars all feed on grasses and whose adults stand on four legs because the front pair is reduced to brushes. Within that group it sits in Erebia, a genus of about forty European species known collectively as the alpines, almost all of them dark butterflies confined to mountains. Erebia epiphron is one of the smallest of them and the only member of the genus in Britain outside Scotland's Scotch argus.

Adult butterfly

• Wingspan: 1.1–1.5 in (28–38 mm), with a forewing 16–19 mm long. Accounts that give 16–22 mm as the wingspan are quoting the forewing length instead.
• Upperside: sooty brown-black, velvety and almost matt on a fresh insect, fading to dull brown with wear. Both wings carry a band of orange-red running parallel to the outer margin, broken by the dark veins into a chain of separate oval spots. Most spots contain a small black dot, which is what gives the butterfly its name.
• Underside: the forewing repeats the orange band and its black dots. The hindwing is different and diagnostic: plain greyish brown, sometimes faintly reddish, with the band reduced to a shadow and usually no dots at all.
• Sexes: very similar. Females average slightly larger and paler, with broader and better-defined orange bands; freshly emerged males look darker and more velvety. The difference is subtle and unreliable in the field.
• Variation: the size and number of the orange spots vary enormously between mountain ranges. Scottish butterflies commonly lack the black pupils altogether, while Alpine populations may have large, boldly pupilled spots.

Two subspecies are recognised in Britain, mnemon in the Lake District and scotica in the Scottish Highlands, and many more have been named across the mountains of continental Europe.

How to identify a mountain ringlet in the field

Habitat and date do most of the work. On high grassland between mid-June and early August, a small dark butterfly bobbing weakly a few inches above the sward in bright sunshine is almost certainly this species. Confirm it by the chain of orange spots on a sooty ground and by the plain grey-brown hindwing underside when it settles. The main pitfall is the Scotch argus, which is larger, flies later in the summer at lower altitude, and has clear white pupils in its black eyespots. Above all, watch the weather: a mountain ringlet colony disappears into the grass within seconds of the sun going in, and reappears just as quickly.

Life cycle: egg, caterpillar, chrysalis and adult

There is a single generation each year, squeezed into the short mountain summer. The whole cycle is slow by butterfly standards, because the larva spends the autumn, winter and much of the spring in the base of a grass tussock.

Eggs

The female crawls into the sward and lays her eggs singly on or beside the blades of the food grass, and some simply drop loose among the tussocks. Each egg is barrel-shaped with fine vertical ribs, pale cream to yellow at first, changing to fawn mottled with darker marks as it develops. A female may lay up to about seventy over her short life, and they hatch after roughly two to three weeks.

Caterpillar

The caterpillar is green with darker green and yellowish-white lines running the length of the body and a small brownish head. It feeds at night on the tips of grass blades and spends the day hidden low in the tussock, where its striped green body is almost invisible against the leaf bases. Feeding continues into October, after which the part-grown larva hibernates at the base of the tussock, often under snow, and resumes in spring. At the highest and coldest sites the larval stage can stretch over two winters instead of one.

Chrysalis

Pupation takes place in late spring, low down among the grass in a loose silk cocoon spun between the leaf bases. The chrysalis is about 10 mm long, with a pale green thorax and wing cases and a greyish-white abdomen marked by a blackish-brown streak. It is well hidden and practically never found by chance. This stage lasts about three weeks.

Adult butterfly

Adults emerge from mid-June, with the peak in late June and July on British hills and later at high altitude in the Alps, where flight can continue into August. Individual butterflies live only a few days, perhaps up to a week or two in poor weather when little flying is possible, so the three-month span often quoted for this species is the flight season of the colony, not the lifespan of one butterfly.

Where the mountain ringlet lives

The mountain ringlet is a European mountain specialist with a broken, island-like distribution. It occurs through the Alps of France, Switzerland, Italy, Austria, Germany and Slovenia, in the Pyrenees, the Massif Central and the Jura, in the Tatra and the Carpathians, in parts of the Balkans, and in the Sudetes. It is absent from Scandinavia and from Ireland. Isolated British colonies survive on the Lake District fells and in the Scottish Highlands around Rannoch, Glen Coe and Ben Nevis, and among the butterflies of the United Kingdom it is the only true montane species.

Altitude matters more than latitude. In Britain colonies sit between roughly 200 and 1,000 m; in the Alps the butterfly is usually found between about 900 and 2,500 m and occasionally close to 3,000 m. The habitat is damp, unimproved mountain grassland where mat-grass grows in tussocks, typically on gentle slopes, in sheltered hollows and around flushes and seepages that stay wet through the summer. Shelter from wind and long hours of direct sun are both essential, so north-facing crags and heavily shaded ground are avoided. Colonies are small, discrete and extremely sedentary, which means that once a site is lost it is very rarely recolonised.

Host plants and diet

Caterpillar host plants. The principal host plant is mat-grass, Nardus stricta, a wiry, pale, tussock-forming grass that dominates acid mountain grassland and that grazing animals largely refuse. Sheep's fescue (Festuca ovina) is also used, and in the Alps other fine-leaved mountain grasses including species of Poa, Festuca and Sesleria have been recorded. The full list is still incompletely known, partly because the larvae feed at night and are so difficult to find. What is certain is that the butterfly needs a tussocky, lightly grazed sward: close-cropped turf offers neither food nor winter shelter.

Adult diet. Adults nectar at the small flowers of the same grassland, above all tormentil (Potentilla erecta), whose yellow petals they visit persistently, and also thyme, heath bedstraw, bird's-foot trefoil and thistles. They take moisture from damp peat and bare ground, and in dull weather they may not feed at all for a day or more. Because adult life is so short, most of the energy that makes the next generation was gathered by the caterpillar, not by the butterfly.

Behavior: sunshine, flight and daily routine

A butterfly ruled by cloud. The mountain ringlet flies only in direct sunshine. When a cloud crosses the sun the whole colony drops into the grass within a few seconds and sits out the shade, and it takes off again as soon as the light returns. On a broken day a hillside can therefore switch between dozens of butterflies and none, several times an hour, and a visit in overcast weather will usually find nothing at all.

Flight. The flight is weak, low and bobbing, a few inches to a foot above the sward, with the butterfly following the contours of the tussocks rather than crossing open ground. Individuals rarely travel more than a short distance, and colonies stay put on the same slope for decades.

Warming up. The sooty colouring is a heating device. Dark scales absorb sunlight quickly, and a mountain ringlet basking with its wings half open, angled towards the sun and pressed low out of the wind, can raise its body temperature well above the surrounding air. At 900 m that is the difference between flying and not flying.

Courtship. Males spend the sunny hours patrolling slowly over the tussocks, investigating anything dark, while females sit low in the grass and fly less. Pairs settle deep in the sward to mate, and mated females begin egg-laying almost at once; our guide to how butterflies mate and reproduce sets out the usual sequence.

Similar butterflies and how to tell them apart

Quick facts

Did you know?

• It is the only true mountain butterfly in Britain. Every other British species can be found somewhere in the lowlands; this one is restricted to the fells of Cumbria and the Highlands, and it is easier to see in the Alps than in England.
• It is often said to have been among the first butterflies to recolonise Britain after the last ice age, surviving on high ground as the climate warmed and the lowland fauna arrived behind it. The idea fits its present-day distribution, though direct evidence is hard to come by.
• Its black wings are a solar panel. Dark scales absorb radiation fast, and a basking adult can run its flight muscles at a temperature far above that of the air around it, which is what makes flight possible at 900 m in a British June.
• At the coldest sites the caterpillar takes two years. A larva that cannot reach full size before the snow returns simply hibernates a second time, so one colony may contain larvae of two different ages at once.
• The colonies barely move. Adults seldom travel more than a few hundred metres, so a hillside that loses its butterflies through overgrazing or afforestation may stay empty even when the grass recovers.
• Warming is squeezing it upwards. Colonies at the lowest altitudes have been the first to disappear, and a butterfly that is already near the top of its hill has nowhere left to climb.

In summary

The mountain ringlet is a small sooty butterfly with a chain of black-pupilled orange spots, living on damp, tussocky mat-grass grassland in the mountains of central and southern Europe and on isolated British fells. It lays cream barrel-shaped eggs among the grass, its striped green caterpillar feeds at night and hibernates in a tussock for one winter or two, and it flies in a single brood from mid-June. Watch for a weak, low-bobbing flight in bright sun, and remember that the whole colony vanishes the moment a cloud arrives.

Mountain Ringlet butterfly pictures

Frequently asked questions about the mountain ringlet butterfly

What does a mountain ringlet caterpillar look like?

It is green with darker green and yellowish-white lines running the length of the body and a small brownish head, which makes it very hard to see against the leaf bases of a grass tussock. It feeds at night on the tips of grass blades, hides low in the tussock by day, and hibernates there from about October until spring.

How long does the mountain ringlet pupa stage last?

About three weeks. The chrysalis is roughly 10 mm long, with a pale green thorax and wing cases and a greyish-white abdomen carrying a blackish-brown streak. It is formed in late spring inside a loose silk cocoon spun low among the leaf bases of a grass tussock, where it is sheltered from both predators and mountain weather.

How do you identify an adult mountain ringlet?

Look for a small, sooty brown-black butterfly with a chain of orange-red oval spots running parallel to the outer edge of both wings, most of them containing a tiny black dot. The underside of the hindwing is plain greyish brown with the band barely visible. The wingspan is about 1.1 to 1.5 inches and the flight is weak and low.

Where does the mountain ringlet butterfly live?

In the mountains of central and southern Europe, including the Alps, Pyrenees, Massif Central, Jura, Tatra, Carpathians and Balkans, with isolated colonies on the Lake District fells and in the Scottish Highlands. It needs damp, tussocky, lightly grazed grassland with mat-grass, in sheltered sunny positions, mostly between about 200 and 2,500 metres depending on region.

Is there a difference between male and female mountain ringlets?

Only a slight one. Females average a little larger and paler, with broader and better-defined orange bands, while a freshly emerged male looks darker and more velvety. The difference is too small to rely on in the field, and wear changes the appearance of both sexes within days of emergence.

How long does it take for mountain ringlet eggs to hatch?

Roughly two to three weeks, commonly quoted as about sixteen days in warm conditions. The eggs are barrel-shaped with fine ribs, pale cream or yellow when laid and turning fawn with darker mottling as the larva develops inside. They are laid singly on or beside grass blades, and some are simply dropped among the tussocks.

Why does the mountain ringlet only fly in sunshine?

It is a cold-climate butterfly that relies on solar heating. Its dark scales absorb sunlight quickly and raise the flight muscles above air temperature, so without direct sun it cannot generate enough power to fly. When a cloud crosses, the entire colony drops into the grass within seconds and waits, then takes off again as soon as the light returns.

How can you tell a mountain ringlet from a Scotch argus?

The Scotch argus is clearly larger, with a richer and broader orange band and black eyespots that carry obvious white pupils, while the mountain ringlet's spots have at most a tiny black dot. Season and altitude help too: the mountain ringlet flies from mid-June to early August on high ground, the Scotch argus from late July into September, usually lower down.

What do mountain ringlet butterflies eat?

Caterpillars eat mountain grasses, chiefly mat-grass, with sheep's fescue and other fine-leaved grasses also used. Adults take nectar from small grassland flowers, above all tormentil, and also thyme, heath bedstraw and bird's-foot trefoil, and they drink from damp peat and bare ground. In dull weather they may go a day or more without feeding.

Is the mountain ringlet rare or threatened?

It is widespread in the mountains of continental Europe but very local in Britain, where it is treated as a priority species. Its colonies are small and extremely sedentary, so losses from overgrazing, afforestation or drainage are rarely made good. Climate warming is the main long-term threat, because the lowest colonies are being lost and the butterfly can only retreat uphill.