Butterflies of
Britain & Europe
Wall Brown
Lasiommata megera
LINNAEUS, 1767
Family - NYMPHALIDAE
subfamily -
SATYRINAE
Tribe - SATYRINI
subtribe - PARARGINA
introduction
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habitats |
lifecycle |
adult behaviour
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Wall Brown
Lasiommata megera, male, Dorset,
England |
Introduction
This species is distributed across
most of Europe with the exception of northern Britain and northern Scandinavia.
It also occurs over much of north Africa, and in temperate regions of western
and central Asia.
Habitats
In England and Wales the
Wall Brown was formerly more widespread, and occurred in a wide range of
habitats. In the latter part of the 20th century it became evident that most of
the inland colonies were dying out, and the species was contracting it's range
westward, and towards coastal regions.
At the current time (
2008 ) the species is restricted largely to sites within about 10-15 miles of
the coastline, and is most frequently encountered at coastal habitats :
cliff-tops, undercliffs, south-facing grassy slopes, shingle banks, sea walls
and sand dunes.
There is some evidence
that the butterfly is beginning to regain lost ground, recolonising inland sites
e.g. in Dorset, Wiltshire, and in the north of England. The most northerly
colonies occur around the coast of southern Scotland.
The reasons for the collapse of inland colonies, and the recent slight recovery,
are probably related to climatic changes. The butterfly seems to thrive best
when cold and harsh winters are followed by warm dry summers, and to collapse
when winters are mild and wet. It clearly needs conditions to be warm and sunny
during the flight periods, and even if there is enough warmth for eggs to be
laid in reasonable numbers a few days of rain can easily cause them to be
washed away. Over 8 months of the lifecycle are spent in the caterpillar
stage, and if conditions are mild and wet between September and April, as they
have been in recent years, the larvae are more prone to viral attack; and
exposed for an extended period to predation and parasitism.
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Wall Brown
Lasiommata megera, male, Arnside Knott, Cumbria |
All habitats are characterised by
having extensive areas of exposed ground in the form of well trodden paths,
eroding banks, scree, rabbit scrapes etc.
Colonies tend to be small,
comprising no more than about 20 or 30 individuals on the peak day of the flight
season, even at the best sites.
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Wall Brown
Lasiommata megera, male, Dorset, England |
Lifecycle
The butterflies are double-brooded, the first generation
emerging in late April and early May, and the second generation
in late July or early August. In exceptionally long and warm
summers there may be a partial third brood emerging in October.
The pale greenish-white eggs are laid singly or in clusters of 3
or 4, on the roots of grasses where they overhang into sunny
recesses at the edge of eroded ground. Rabbit scrapes, path
edges, and crumbling undercliffs are typical situations. I have
also seen females laying on grass blades at the base of gorse
and bramble bushes on south-facing chalk grassland slopes. The
eggs hatch after about 12 days.
The caterpillars feed nocturnally on various grasses including
Agrostis tenuis,
Agrostis gigantea, Brachypodium
sylvaticum, Brachypodium pinnatum, Dactylis glomerata,
Deschampsia flexuosa and
Holcus lanatus. Summer brood larvae hatch in August
and enter hibernation while still quite small. In late February
they re-awaken, becoming full grown by late March or early
April. The mature larva is pale bluish-green, with whitish
stripes along the back and sides.
The pupa is virtually impossible to locate in the wild, and
varies in colour from pale green to deep olive and sometimes
almost blackish. It has reportedly been found hanging from grass
stems around the base of small bushes. The pupal stage lasts for
about 2 weeks.
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3rd brood Wall Brown, male, Ouse Estuary, East Sussex |
Adult behaviour
On
calm days the butterflies tend to inhabit cliff tops and other
high ground, but when it is cooler or windy they seek shelter and
warmth at the bottom of hills. They tend to spend long
periods settled on bare ground on paths, rabbit scrapes or
overhangs. In lightly overcast weather, or during cooler
conditions
cool early or late in the day, males bask with wings outspread,
exposing the maximum wing area to the sun. Another tactic they use
is to raise the wings to a 45° angle, which traps pockets of warm
air above the thorax and abdomen.
These thermoregulatory actions are essential, enabling them to
achieve the high body temperatures vital for rapid take-off and interception of potential mates.
They
intercept all passing butterflies of roughly similar size and
colour, including Peacocks, which they chase away from their
territories. Smaller butterflies, and those with much brighter
colouring such as Orange tips, Large Whites, Clouded Yellows and
Brimstones are ignored.
When a male
intercepts a female, a short but elaborate courtship ritual takes
place, in which the male chases the female until she settles on
the ground, and then flies around her, eventually settling in
front of her, face to face. The female then responds by quivering
her open wings, at which point the male half opens his own wings,
and "bows" several times to his prospective mate.
Wall Browns
Lasiommata megera,
courtship ritual ( male on left ), Alner's Gorse, Dorset.
In hot conditions Wall Browns
close their wings immediately on landing, with the fore-wings
raised so that the apical ocellus is visible. This probably acts
as a decoy, so that any bird which spots where the butterfly has
settled, attacks the false-eye marking, rather than the
butterfly's body. After a moment, when the butterfly is sure it
has not been followed, it lowers the forewing to hide the ocellus.
This behaviour is common to several other Satyrines including
Grayling, Small Heath and Meadow Brown.
Wall browns are at all
times extremely alert, and are notoriously difficult to approach.
Even in cool conditions they react instantly to the slightest
disturbance, rapidly flying up and disappearing over the top of
tall bushes. The high energy levels of males cause them to "burn
themselves out" very quickly, and thus they are one of the
shortest lived British species, with an adult lifespan of only 3
or 4 days. Females, being more sedentary, live longer, averaging
about 8-10 days.
The butterflies are notoriously difficult to photograph - I’m
well used to playing hide and seek with them
- clambering up slopes, peeking over tussocks of grass
at basking males, hoping I can press the shutter
release before they detect me. It
takes more than careful stalking to get the better of a Wall
Brown however.
One day in May 2008, I spent over 4 hours attempting to
photograph various individuals, but each time,
although the butterfly was static and composed nicely in the
centre of the viewfinder, by the time the shutter had fired it
had flown. I took over 20 photographs, but in 18 of them the
butterfly was absent from the final image, or caught in flight
at the edge of the frame.
Incredible as it seems, Wall Browns
are able to detect the sound of the
SLR mirror as it flips up, and shoot into
flight before the shutter
opens. The delay between mirror-up
and shutter release is just a few
milliseconds, but in that time the butterflies can not only
detect the sound and register it as a threat, but can
trigger an escape response and take flight,
becoming nothing more than a
blur at the edge of the image, or leaving the photographer
with a photograph of a patch of vacant soil.
Both sexes patrol back and
forth along a regular route, often along paths or areas of
broken ground, high on hillsides or cliff tops. They go
through a regular cycle of patrolling, resting and nectaring.
Favoured nectar sources include buttercups, dandelions
and common vetch in
spring, while in summer they favour scabious, hawkbit and hemp agrimony.
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