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Butterflies of Britain & Europe
Mountain Ringlet
Erebia epiphron   KNOCHE, 1783
Family - NYMPHALIDAE
subfamily - SATYRINAE
Tribe - SATYRINI
Erebia epiphron Neil Hulme
Introduction
The Mountain Ringlet was almost certainly the first species to arrive in Britain as the last "mini Ice Age" ended 10,000 years ago, and at that time probably occurred across much of southern England. As the ice retreated the butterfly would have been forced to move to cooler regions in the north, and ultimately to seek refuge on the high mountains where it still breeds today.
Although it's distribution within Britain is now very limited, it is still widespread across Europe, but restricted to mountainous regions where it occurs at altitudes above 900m in the Vosges and Massif Central, and above 1200m in the Alps, Pyrenees, Picos de Europa, Tatra Mountains, Carpathians and other ranges.
There are no similar species in the British Isles, but in Europe there are no less than 46 members of the genus Erebia, and among these are several which could be confused with epiphron, and which share similar habitats. The use of a good field guide is therefore essential for identification.
Habitats
In Britain the Mountain Ringlet occurs in small isolated colonies, typically at altitudes between 450-800m although in parts of it's range it can be found as low as 100m, and it occurs as high as 1000m. In Scotland the butterfly is found in the Grampians from Ben Nevis in the west to Glen Clova in the east. The most well known and accessible colonies are at Ben Lawers, and in the mountains above Tyndrum. In England the species occurs in the Lake District  ( at Langdale Pikes, Stye Head Tarn, Red Screes, Helvellyn and elsewhere ), but it is absent from the Pennines and from Snowdonia.
At the peak of the flight season as many as 3000 adults may be on the wing at certain sites, but these high numbers tend to be concentrated within a very limited area, sometimes less than half a hectare in area. The butterflies breed in sheltered damp depressions where the larval foodplant mat grass thickly carpets the ground. These habitats are usually extremely localised, forming a small element within a montane landscape of scree slopes, tarns ( large shallow ponds ) and areas of flat or slightly undulating grassland.
Lifecycle
The flight period varies considerably according to elevation and seasonal weather conditions. In a warm summer populations at low altitudes in the Lake District can begin to emerge as early as mid June. At the other extreme, colonies at high altitudes in the Grampian mountains may be delayed until early July in a "late" season. The flight period at individual sites is very short - probably less than 3 weeks between the appearance of the first males, and the disappearance of the last females.
The butterflies lay their eggs singly at the base of blades of mat grass Nardus stricta.
After consuming its eggshell, the newly hatched caterpillar feeds solely on mat grass. In September when in its 2nd instar it enters hibernation, spending the winter deep at the base of the grasses, and may be buried under snow for several months. In the spring, after the snows melt, it awakens and resumes feeding, becoming fully grown by early May. Like most Satyrine larvae it feeds nocturnally. It feeds high up on the grass blades, leaving nibbled notches which give away it's presence. In poor spring seasons larval development may be very slow, and at some sites it is probable that some of the caterpillars are unable to complete their growth in a single season, and may spend 2 successive winters in hibernation.
The chrysalis is pale green, with brown striations on the wing cases. It is formed within a very flimsy cocoon - little more than a few strands of silk - at the base of grass tussocks.
The areas where the butterflies breed often have large populations of voles living nearby, causing one writer to speculate "it is believed that huge numbers ( of pupae ) are killed by the short-tailed voles that teem among the loose scree found alongside most Mountain Ringlet sites". This however is erroneous, as short-tailed voles are entirely vegetarian, unlike their relative the bank vole which eats insects as well as vegetation.
Adult behaviour

During cool or cloudy weather the butterflies hide deep amongst grass tussocks and are virtually impossible to find. Even walking through the middle of their breeding sites at such times usually fails to disturb the butterflies from their deep torpor. The appearance of sunshine however - even for a brief period, quickly arouses them, causing the entire colony to fly spontaneously.

Mountain Ringlets have a very weak fluttering flight just above the grasses. Males patrol back and forth while the sun shines, dipping down at intervals into the grasses to investigate any dark object that could potentially be a female. Females rest in grass clumps prior to mating, which takes place with little evidence of pre-nuptial ritual. After about an hour ( much longer if cloud cover returns ) the sexes separate, and the female rests for a day before beginning to lay her eggs.

I have not observed this species nectaring at flowers, either in Britain or continental Europe, even though plants including Alchemilla, Potentilla, Galium, Saxifraga, Vaccinium and Cerastium may be flowering in it's habitat. My own observations of adult feeding, both in Britain and the French / Swiss Alps, have been limited to finding males imbibing dissolved minerals from damp peaty soil or from rocky ground at the edge of tarns or streams. They are nevertheless known to nectar at Tormentil, and are also reputed to nectar at Thymus.

Erebia epiphron nectaring at Tormentil, Red Tarn, Great Langdale, Cumbria Nigel Kemp

 

 

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