Butterflies of
Britain & Europe
Brown Argus
Aricia agestis
DENIS & SCHIFFERMÜLLER, 1775
Family - LYCAENIDAE
subfamily -
POLYOMMATINAE
Brown Argus
Aricia agestis, female nectaring at
germander speedwell, Dorset ©
Adrian Hoskins
Brown Argus
Aricia agestis, male, Cerne Abbas,
Dorset ©
Adrian Hoskins
Introduction
The Brown Argus
is a widespread and fairly common species found throughout most of Europe,
with the exceptions of Scandinavia, Ireland and northern Britain.
It also occurs in north Africa, the Middle East, and across temperate Asia as far east as Siberia and Amur.
Across most of
it's range there are 2 overlapping generations, emerging in May and
August, but in the Mediterranean region there are usually 3
broods, in April, July and October.
In northern
England, Scotland, Scandinavia, and the high alpine regions of
Europe it is replaced by the Northern Brown Argus ( = Mountain
Argus ) Aricia artaxerxes,
which differs from the Brown Argus in being single brooded. There
is much variation between the various races of
artaxerxes, the Scottish form for
example having a white discal spot on the upperside forewing, and
greatly reduced black spots on the underside. The subspecies
allous, found in
the Alps and Pyrenees, is virtually identical to
agestis on the underside, but has
reduced orange lunules on the upperside.
Habitats
In England the Brown
Argus
breeds mainly on calcareous ( limestone / chalk ) grassland, where the
caterpillar's foodplant
common rockrose grows amongst fine grasses. Many sites are on south facing
slopes, often heavily grazed by rabbits, and characterised by an abundance of ant-hills on which the
foodplants grow.
Around the coast of Britain there are colonies on cliff tops, and on the
calcareous dunes of Wales, Cornwall, Norfolk, Suffolk, Essex and Kent.
Away
from calcareous habitats the butterfly is much scarcer, but is sometimes found
in odd habitats, e.g. a friend photographed a fresh female seen along a track
through a Surrey woodland on clay in late July 2008.
Lifecycle
Males of the first brood begin to emerge in
early May, and females about a week later. They have a potential lifespan of
about 2 weeks, but on average most live for less than a week. The emergence is
protracted, and the 2 broods often overlap at sites where populations are large.
The
disc-shaped dull whitish eggs are laid singly on the
underside of leaves of common rockrose Helianthemum chamaecistus, usually close to the stem.
At certain sites, other
foodplants are used, including common storksbill Erodium cicutarium and dove's foot
cranesbill Geranium molle.
The eggs hatch after about 7 days.
When
young the caterpillars nibble at the underside of the leaves, leaving the upper
cuticle intact, which creates distinctive shiny patches visible on the upper
surface.
The
fully grown larva is plump and green, with a purple stripe below the
spiracles, and another on the back. It feeds
by day, resting on the upperside of the leaves, and is attended by ants
including Lasius niger, L. alienus, L. flavus
and Myrmica sabuleti, which "milk" it for a
sugary secretion.
The chrysalis is
formed in July on the ground, and is also attended by ants, which bury it just
below the surface. It is dull olive in colour, marked with a pinkish lateral
line.
The
second generation of adults emerges from mid July and continues well into August.
Caterpillars resulting from
this brood go into hibernation when quite small, in the 2nd or 3rd instar. The
diapause continues until February or
March of the following year when they awake and resume feeding. They develop quickly, and pupate at the end of March.
Aricia agestis, Hod Hill, Dorset ©
Adrian Hoskins
Adult behaviour
Brown
Argus males tend to congregate in sheltered areas along dykes or at the bottom of south facing
hills. They do not have fixed territories, but perch in various
positions on grasses and flowers, and fly up instantly to
investigate every passing insect. They are not the cleverest of
butterflies, and seem unable to differentiate visually between
flies, Skippers, Blues and Fritillaries.
They also seem unable,
from more than a few centimetres away,
to recognise butterflies with which they have already had
sorties, and will e.g. intercept the same individual Common Blue
or Marsh Fritillary numerous times if it crosses their path
again. However, during these inter-species aerial encounters they make
very close contact,
and almost certainly "exchange names" via pheromone detection.
At this point they recognise that the intruder is not of their
own species, and break off the encounter.
Females
that have already mated are chased by males until they settle.
They then close their wings and remain motionless in an attempt
to escape detection. This ploy rarely works however and the
males usually locate them and attempt to copulate, but quickly give up and fly
off if the female is unwilling.
When
virgin females are intercepted, the female weaves in flight just
above the grasses, closely followed by the male. This is very
brief however, and copulation takes place within a few seconds
of the sexes meeting. Once copulated the
butterflies are extremely reluctant to move from the grass
blades on which they settle.
Brown Argus
Aricia agestis, mating pair, Noar
Hill, Hampshire ©
Adrian Hoskins
After mating the females roam
randomly, searching for spots where the larval foodplants grow
in warm and sheltered positions. At many sites, e.g. Martin Down
in Hampshire, and Levin Down in West Sussex, the females seek
rockrose plants that are growing on ant-hills, and it is
possible that they are genetically programmed to
recognise the chemical odours produced by the ants.
Adults of both sexes nectar at a
wide variety of low growing flowers, the first brood favouring
daisy, buttercup, bird's foot trefoil, horseshoe vetch, common
vetch, milkwort, dandelion and rockrose. Summer brood adults tend to congregate to nectar at clumps of
marjoram at the base of hills.
In late afternoon the butterflies
roost communally on grass-heads, usually with the males and
females forming separate groups. The roosting sites are often on
the top of banks, where the adults are exposed to the last rays
of the setting sun.
Brown Argus
Aricia agestis
© Emily Halsey
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