Butterflies of
Britain & Europe
Mountain Ringlet
Erebia epiphron
KNOCHE, 1783
Family - NYMPHALIDAE
subfamily -
SATYRINAE
Tribe - SATYRINI
introduction
|
habitats |
lifecycle |
adult behaviour
|
 |
|
Erebia
epiphron, Ben Lawers, Tayside, Scotland |
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.
|
The range of the Mountain Ringlet in Britain is contracting
in response to global warming. Populations in Cumbria and
southern Scotland are expected to be lost within a few years
as these sites become too warm for them. The more northern
populations are expected to survive longer by moving to
higher elevations where temperatures are cooler, but are
likely to shrink and ultimately be lost as the butterflies
literally run out of space to breed. |
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 it's 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
highly respected author 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 is erroneous however, 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 to investigate any dark object amongst the grasses.
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 mainland Europe, even though plants including
Alchemilla,
Potentilla,
Galium, Saxifraga,
Vaccinium and
Cerastium may be flowering in
it's habitat. They are nevertheless reputed to nectar at
Thymus.
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.
|
