Butterflies of Britain
Pararge aegeria tircis
Family - NYMPHALIDAE
subfamily - SATYRINAE
Tribe - SATYRINI
subtribe - PARARGINA
Pararge aegeria, female ©
This common woodland butterfly was originally known in Britain as
the Enfield Eye or Wood Argus. The name Speckled Wood first appeared
in 1766, in Moses Harris's famous book The Aurelian.
The butterfly is widely distributed in Europe but is absent from the
sub-arctic areas of Norway and Sweden. Beyond Europe it occurs in
the Atlas mountains of north Africa and extends into Asia as far
east as the central Ural mountains.
The British / northern European subspecies
tircis is marked with pale creamy
spots, but in southern Europe the normal form of the butterfly has
the wings patterned with large orange blotches, and can be mistaken
for the Wall Brown Lasiommata megera.
There are 2 other similar
Pararge species - xiphiopides
which is endemic to the Canary Islands, and
xiphia which is endemic to Madeira ( where
aegeria also occurs ).
Speckled Wood, male,
Pararge aegeria, Powerstock Common,
It is often stated that butterflies make excellent "indicator"
species, as their distribution ranges and population dynamics adjust
rapidly in response to changes in the environment. This is
particularly true of the Speckled Wood. The butterfly was widespread
and fairly common in Britain until the late 19th century when it
suffered a sudden and unexplained collapse in numbers. Then from the
1930's onwards it gradually expanded it's range : this species
favours darker and damper woodlands than most other butterfly
species, so it's populations expanded in response to the large scale
conversion of coppiced woodlands to plantation management.
Today the Speckled Wood is regarded as a common woodland butterfly
which breeds in damp areas where dappled sunlight filters through
the trees. It can commonly be seen basking on low foliage or on
forest paths in deciduous woodland. It is quite tolerant of shade
and can also be found in conifer plantations, where it breeds along
In recent years it has shown a favourable response to climatic
change, having expanded into more open habitats, and can regularly
be seen in gardens, along hedgerows, and scrubby areas of open
grassland. It has also extended it's range northwards, now reaching
Ullapool in n.w. Scotland.
Speckled Wood, male,
Pararge aegeria, Leicester ©
Speckled Wood is unique among British species in that it can
hibernate as either a caterpillar or chrysalis. Thomas states that
"...caterpillars which experience 12 or more hours of light a day go
on to form adults the same year, whereas those that receive less
light either form hibernating pupae, or overwinter as
caterpillars". The consequence of this dual overwintering strategy
is that the spring emergence of adults is very protracted.
There is some disagreement about how many broods occur in various
parts of Britain. It certainly produces 3 broods most years in
southern England. In Scotland the 3rd brood is partial.
Normally the adults begin to appear in late March or early April but
the emergence extends well into June, overlapping with the second
brood which flies between late June and August. The third brood
begins in August at some sites, but not until September at others,
where late emerging adults may still be flying in early November.
Individuals have a lifespan of between about 7-20 days.
The egg is spherical, straw coloured, and finely ribbed. Sometimes
the eggs are dropped randomly among grasses while the butterfly is
in flight, but equally often the females settle and glue the eggs
singly to the underside of grass blades. Oviposition always occurs
where the grasses are growing in dappled light, usually around the
base of bushes or sapling trees.
hatches after about a week.
other Satyrine larvae are crepuscular but the larva of the Speckled
Wood feeds by daylight. It is pale green, marked with thin
longitudinal pale yellow and whitish stripes, and is perfectly
camouflaged at rest on grass blades. It feeds on soft grasses,
principally cocksfoot Dactylis glomerata,
couch Agropyron repens,
creeping soft grass
millet Milium effusum and wood meadow
grass Poa nemoralis.
chrysalis is formed hanging by the cremaster from woody stems. It is
variable in colour, some being pale green, while others can be quite
dark, particularly those of the over-wintering brood.
Pararge aegeria, male, Evington
meadow, Leicestershire ©
Speckled Wood flies in shadier habitats than most other British
butterflies, and is commonly active on dull overcast days when other
species refuse to fly.
Pararge aegeria, Evington meadow,
sunny mornings the males take up residence in areas of woodland where
dappled sunlight filters through the trees. Each male selects a
"perch" in the form of a sunlit leaf, from which it can survey and
intercept passing females. During the course of the morning, the
changing position of the sun causes the various perching places to be
periodically shaded, at which time each male has to move to establish
a new perch. Inevitably this results in a high number of male-male
males meet, they engage in a sortie, spiralling up to the tree tops.
This appears to be a test of strength, but probably also involves
chemical messages. After each sortie a "winner" emerges to return to
his chosen perch. Experiments have shown that the winning male is
usually the one which first established his perch. The intruding male
is ousted and has to establish a new perch elsewhere in the vicinity.
In experiments when 2 males have been introduced simultaneously into
an area, and both believe they have ownership of a perch, the ensuing
sortie can continue unabated for several minutes. Ultimately one of
the combatants seems to get lost or gets distracted, leaving the other
to reclaim its perch.
males adopt a different mate-location strategy, choosing to patrol in
search of females. In his fascinating book Butterflies of Britain and
Ireland, Jeremy Thomas states that "certain individuals - especially
those possessing 4 spots on the upperside of each hindwing, are more
inclined to perch, whereas males with 3 spots have a tendency to
always intercept other Speckled Woods of either sex but usually ignore
other species. When a receptive female is intercepted, she settles on
foliage, and spreads her wings. The male then settles below her, and
gently walks onto her hindwings. Butterflies have olfactory sensors on
their feet, so this ritualised behaviour enables the male to taste her
chemical scent and determine whether she is recently emerged - vital
information because younger females have a longer life ahead of them
and are therefore capable of laying more eggs.
adult butterflies feed primarily on aphid secretions on the upper
surface of oak, ash or hazel leaves. The spring generation
rarely visit flowers, although I have at times seen them nectaring at
wood spurge. Summer brood males sometimes nectar at fleabane or
knapweed flowers, but are more often seen feeding at the juices oozing
from fermenting blackberries. Females prefer to feed on the sticky
secretion which coats ash buds. I have often seen individuals spend
several minutes at a time walking about on ash twigs, avidly feeding
on the sticky secretion which coats the buds. I have also observed
them nectaring at the blossom of trees and bushes including pear,
hawthorn, lime and buckthorn.
Overnight and in dull, cold or wet weather the butterflies roost in
bushes - e.g. at Ballard Down in Dorset they commonly roost in prickly
gorse bushes, at Stansted Forest in West Sussex they roost in bramble
bushes, and at Noar Hill in Hampshire I have seen them enter
blackthorn and dogwood bushes in late afternoon.