Butterflies of
Britain & Europe
Speckled Wood
Pararge aegeria tircis
BUTLER, 1867
Family - NYMPHALIDAE
subfamily -
SATYRINAE
Tribe - SATYRINI
subtribe - PARARGINA
introduction
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habitats |
lifecycle |
adult behaviour
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Speckled Wood
Pararge aegeria, female |
Introduction
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 very similar
Pararge species - xiphiopides
which is endemic to the Canary Islands, and
xiphia
which is endemic to Madeira ( where
aegeria
also occurs ).
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Speckled Wood,
male, Pararge aegeria,
Powerstock Common, Dorset |
Habitats
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, but is quite
tolerant of shade and can also be found in conifer plantations, where it breeds
along grassy rides.
In recent years it has
demonstrated 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.
Lifecycle
The
Speckled Wood is unique among British species in that it can hibernate as either a
caterpillar or chrysalis. Thomas states that "as a rule, caterpillars which
experience 12 or more hours of light a day go on to form adults in 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. At any given site however the adults tend to emerge in
synchrony, suggesting that the hibernation stage is dependent on habitat and
local climate.
There is disagreement
among entomologists about how many broods occur in various parts of Britain. It
certainly produces 3 broods in southern Britain, and Thomson states that there
are also 3 broods in Scotland, "where the 3rd brood is partial".
Normally the first adults
appear in late March but the emergence is very protracted, extending 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 - and late emerging adults may still be flying as late as mid
November. Individuals have a lifespan of between about 7-20 days.
The spherical egg is
straw coloured, and finely ribbed. It is laid singly on the underside of grass
blades, always where the grasses are growing in dappled light, usually at the base
of bushes. It hatches after about a week.
Unlike most other Satyrine larvae, which are generally nocturnal, the
caterpillar of the Speckled Wood feeds by daylight. It is pale green, marked
with thin longitudinal 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,
wood millet Milium effusum,
Yorkshire-fog
Holcus lanatus,
creeping soft grass Holcus mollis,
and wood meadow grass Poa nemoralis.
The
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.
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Speckled Wood
Pararge aegeria, male, Purbeck
Hills, Dorset, England |
Adult behaviour
The 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.
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Speckled Wood
Pararge aegeria, female, Crab
Wood, Hampshire, England |
On 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 encounters.
When 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.
Either way, after a few moments 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.
Some 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 patrol".
Males
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 probably enables the
male to "taste" her 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.
Copulation takes
place in the late morning and lasts for about an hour.
The adult butterflies feed mainly on honey dew ( aphid secretions
) on the upper surface of oak, ash or hazel leaves. The
spring and summer adults rarely visit flowers, although I have at
times seen them nectaring at wood spurge. In late summer 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 - individuals often spend several minutes at a time
walking about on ash twigs, avidly feeding on the sticky secretion
which coats the buds. They also visit the flowers of certain trees
and bushes including pear, hawthorn, lime and buckthorn.
Overnight and in dull, cold or wet weather, the butterflies go to
roost in bushes - e.g. at Ballard Down in Dorset I have watched
them go to roost in prickly gorse bushes, at Stansted Forest in
West Sussex I have seen them roost in bramble bushes, and at Noar
Hill in Hampshire I have watched them enter blackthorn and dogwood
bushes in late afternoon.
Speckled Wood
Pararge aegeria aegeria, male, Andalucia, Spain
( image © Peter Bruce-Jones )
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