Butterflies of
Britain & Europe
Swallowtail
Papilio machaon
LINNAEUS, 1758
Family -
PAPILIONIDAE
subfamily -
PAPILIONINAE
Tribe - PAPILIONINI
Papilio
machaon gorganus, St Germain l'Herm, Auvergne, France ©
Adrian Hoskins
Introduction
Back in the 18th century when Linnaeus created the
System Naturae, the word Papilio was used as the genus name for every known
species of butterfly in the world. Since then much has been learnt
about the relationships between different species. Consequently
most have been reassigned to new genera, and only about 215 of the
17600 currently known species are retained in
Papilio.
Papilio machaon
is widespread and common throughout much of the northern hemisphere. It occurs
over the whole of continental Europe, eastward across temperate Asia to Japan;
in Africa north of the Sahara; and throughout much of North America. In Britain
it is locally common on the Norfolk Broads, an area of fenland and lakes in
eastern England.
Individuals originating from France
occasionally migrate across the English Channel and have been periodically
recorded in Hampshire, Dorset, Sussex and the Isle of Wight, but such sightings
are very rare - perhaps one or two sightings per year. Genuine migrants can
usually be recognised by their faded and worn appearance. Fresh looking
insects seen anywhere apart from
Norfolk can be attributed to escaped or deliberately released
livestock - both the British subspecies brittanicus
and the continental gorganus are commonly reared by hobbyists.
( it is illegal to capture or breed stock of British origin, but nevertheless a
widespread practice ).
There are no similar species occurring in Britain. On the Mediterranean islands
of Corsica and Sardinia machaon shares it's habitat with
Papilio hospiton,
which is similarly marked but has much shorter tails on the hindwings. In
Algeria the distribution of
machaon overlaps
that of the Saharan Swallowtail
Papilio saharae,
which is identical in appearance except for the antennae, which have 30 segments
in saharae,
and 33-36 segments in machaon.
Papilio
machaon gorganus, female, Mont Dore, France ©
Adrian Hoskins
Habitats
Throughout most of it's
range the Swallowtail shows itself to be highly adaptable, utilising a wide variety
of habitats including sub-arctic tundra in Canada, prairies, woodlands and arid
canyons in the south of the USA; hay meadows, roadside verges, river banks and sub-alpine
pastures in Europe; high montane habitats in the Atlas mountains of north
Africa, and semi-cultivated habitats in the Mediterranean area.
It's adaptability extends
also to it's choice of foodplants - in North America the caterpillars
usually feed on Compositae (
Artimesia, Petasites
), while in Europe Rutaceae (
Ruta, Haplophyllum
) and Umbelliferae (
Foeniculum, Peucidanum
etc ) are used instead.
In
Britain however the butterfly is restricted to a single foodplant - milk
parsley, and breeds only at a very small number of wet fenland habitats in
north-east Norfolk. Individual specimens have been tagged and found to fly over
quite a large area, often reaching adjacent fens, but the butterflies do not
stray beyond the general area of the broads.
Several centuries ago the species almost certainly occurred as a resident
species over a much wider area of southern and eastern England, but later
contracted it's range to the Great Fen - a vast area of wetlands covering
Cambridgeshire, Lincolnshire and Norfolk. Following the drainage of this area,
and it's conversion to agriculture, the butterfly was forced to contract it's
range even further - to the Norfolk Broads. In such isolation the genetic
diversity would have diminished, causing the so-called "sub-species" machaon brittanicus
to become far less adaptable, and to acquire minor differences in appearance
from the ancestral stock.
In
the last 100 years the average wingspan of Swallowtails, and the average width
of the thorax, have reduced in size, an indicator of further genetic
impoverishment, which is likely to result in further contraction and eventual
extinction. Expansion of the gene pool can only be accomplished by the
introduction of genetically richer livestock from Europe, a policy which
hopefully will eventually be adopted by conservation groups.
Although the butterfly only breeds in the wet fenlands and
broads of Norfolk, migrants from France
are periodically observed at coastal sites in Dorset, Hampshire, the Isle of
Wight, Sussex and Kent. On 1st Sept 2003 for example I watched an immigrant
Swallowtail flying across a main road at Milford-on-Sea in Hampshire. In most
years less than half a dozen are recorded, usually in August or September.
Individuals very occasionally penetrate further inland, and are reputed to
sometimes breed on chalk grasslands, reportedly feeding as larvae on wild carrot Daucus carota,
although I know of no recent records.
It is planned that by the end of the
21st
century the Great Fens which formerly occupied much of eastern England will be
partially restored, leading to a sizeable increase in suitable habitat. Whether such a project is
feasible in the face of population expansion however remains to be seen.
Papilio machaon gorganus, Loire valley, France ©
Adrian Hoskins
Lifecycle
The butterfly is bivoltine on the
continent, emerging in May and August, but in Britain the second
brood is either partial or non-existent.
In the Norfolk
fens where the butterflies emerge in late May, they lay their large brown globular eggs singly on the fine
leaves of milk parsley
Peucidanum palustre. The eggs are nearly always laid
on the upper foliage of tall plants which project above the
surrounding reedbeds. They hatch after about a week.
The young caterpillar is black,
marked with a band of white. It looks remarkably like a small
bird-dropping as it rests openly on the leaves. According to
Thomas the camouflage is not effective against spiders, which
may predate up to 65% of 1st instar larvae. When fully grown
in July, the caterpillar is a most magnificent creature - bright green,
marked with narrow black bands and orange spots. Behind it's
head is an eversible fleshy pink forked structure called an
osmaterium, which is raised if the larva is irritated. This
structure emits pungent chemicals, capable of deterring ants,
wasps, and flies, but does not deter birds - reed buntings,
sedge warblers and bearded tits between them devouring at least
50% of mature larvae.
The chrysalis occurs in 2 colour
forms, being either plain green, or light brown with a dark
lateral stripe. It is attached vertically by a thin silken
girdle and by the cremaster, usually low down on the stem of a reed,
where it hibernates until the following May.
Papilio
machaon gorganus, Loire valley, France ©
Adrian Hoskins
Adult behaviour
The
butterfly has a characteristic powerful gliding flight, and is
capable of covering large distances. In France and Spain for
example I have often observed males indulging in "hill-topping",
i.e. flying to congregate at the top of hills, where they compete
for the attention of passing females. In Britain the
butterfly breeds only on the flat terrain of Norfolk, and probably
only covers short distances, although it can be seen crossing open
expanses of water on the Broads.
On warm sunny days, male Swallowtails
patrol back and forth along a regular route in search of females.
Often both sexes home in on a particular clump of bushes where
courtship and copulation take place. The pair often remain joined
for 2 or 3 hours before the female departs to oviposit.
In
the morning, and again in late afternoon both sexes can be seen
flying freely about their habitat, pausing regularly to nectar at
the pink flowers of angelica, knapweeds, marsh thistles, red
campion, ragged robin and valerian. When nectaring they keep their
wings constantly fluttering to prevent the weight of their bodies
from dragging down on the fragile flowers. This fluttering
behaviour is typical of all Papilioninae, wherever they occur in
the world. In Norfolk the butterflies also often nectar at the
spectacular bright yellow flowers of yellow iris.
In
cool but sunny weather,
or during periods of hazy sunshine, Swallowtails can sometimes be seen
basking amongst dry grasses. During overcast weather they roost
hanging from reed stems, and probably also amongst the foliage of
sallow and alder bushes, and other fenland vegetation.
In the French
Alps and the Pyrenees the butterflies commonly indulge in
mud-puddling - siphoning mineral-rich moisture from damp mud and
cattle dung, but I have not observed this behaviour in Britain.
Swallowtail
Papilio machaon, River Bure,
Norfolk ©
Adrian Hoskins
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