Butterflies of Britain
Family - LYCAENIDAE
Aricia agestis, female nectaring at
germander speedwell, Dorset ©
Aricia agestis, male, Cerne Abbas,
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.
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.
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.
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.
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.
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.
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.
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.
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 ©
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.
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.
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.
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.
Aricia agestis, mating pair, Noar Hill,
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
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.
© Emily Halsey