Butterflies of
Britain & Europe
Large Tortoiseshell
Nymphalis
polychloros
LINNAEUS, 1758
Family - NYMPHALIDAE
subfamily -
NYMPHALINAE
Tribe - NYMPHALINI
introduction
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habitats |
lifecycle |
adult behaviour
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Nymphalis polychloros,
( image
© Peter Bruce-Jones ) |
Introduction
The
Large Tortoiseshell is widely distributed in Europe, and common in the
Mediterranean region where it breeds in open woodland areas. It also occurs in
Morocco, Algeria and Tunisia; and across temperate Asia from Turkey to Kazakhstan and the
foothills of the Himalayas.
It
can confused with the similar Yellow-legged Tortoiseshell Nymphalis xanthomelas
which has much brighter and redder colouring, and enlarged blue lunules on the
hind-wings. The latter species is only found in eastern Europe and temperate
Asia, where it breeds in wooded river valleys. Old records of it's occurrence in Britain are dubious.
Nymphalis polychloros,
( image
© Lars Anderson )
Habitats
A century ago the Large
Tortoiseshell was a common butterfly in southern and eastern Britain. It had
always been subject to periodic fluctuations in abundance, but declined very
suddenly in the early part of the 20th century, and apart from a short period of
abundance in the 1940's never recovered.
By the 1970's it had become a great rarity.
The butterfly's decline was originally
attributed to increased parasitism but I believe this is unlikely. Parasitoid /
host abundance is normally cyclic, and linked to the differing climatic
requirements of host and parasitoid. After a period of parasitoid-induced
scarcity, butterflies generally recover and return to abundance until climatic
conditions again favour the parasitoid.
Whatever the cause of the decline, it was certainly exacerbated by
the arrival in Britain in 1976 of a particularly virulent strain of Dutch elm disease,
which rapidly proceeded to almost eradicate the main larval foodplants wych elm
Ulmus glabra,
and English elm
U. procera.
The disease arrived in Britain on logs imported from North America, and quickly
spread across the country, transported by
Scolytus elm bark beetles.
These live under the bark, and propagate an ascomycete
microfungus Ophiostoma novo-ulmi which is
responsible for the disease.
By about 1990
the Large Tortoiseshell was considered to be either extinct or on the verge of extinction
in the UK. It has been suggested by some that it still maintains its presence as a breeding
resident in southern England, but that populations have become reduced to the
point where the butterfly is now unobservable. It seems very unlikely though, as
the very conspicuous larval nests would surely still be found occasionally. None
have been reported in Britain for several decades.
Since about 1998, sporadic sightings of adults have been reliably reported from sites
along
the south coast of Hampshire and Dorset. Most of these records have referred to very worn post-hibernation insects
seen in early spring. It is unknown whether these represent the progeny of
migrants or of captive bred stock.
In
June and July 2007 several fresh specimens were recorded at
various locations on the Isle of Wight and scattered along several miles of the Hampshire coastline.
Records of worn specimens from other coastal
sites every spring from 2007 to 2010 appears to indicate that the butterfly
might now be breeding regularly but in very low numbers
in southern Hampshire or on the Isle of Wight. On the other and it is equally
likely that one or more amateur enthusiasts are releasing captive-bred European livestock
of this butterfly breeder's favourite in an attempt to re-establish the species in Britain.
In
Europe the Large Tortoiseshell is usually encountered as singletons, encountered widely
but never in numbers. It is a highly mobile species, and breeds in woodlands, parks, or
along hedgerows where
elms Ulmus glabra, U. procera, sallow Salix caprea, poplars Populus alba, P. nigra,
aspen Populus tremula or wild cherry Prunus avium grow.
Lifecycle
The adults emerge in late June or
early July, but are only active for about a fortnight, as they
enter hibernation very early - typically in late July, and are
not seen again until the following spring.
The eggs are laid in April, and
hatch after about 3 weeks. They are laid in large batches
in a neatly arranged ring around twigs, about 2-4 metres up, on
the sunny side of various trees, but particularly
on wych elm
Ulmus glabra.
The larvae are black, covered with sharp orange spikes and
peppered with tiny white dots, giving them a greyish appearance. They live
communally in conspicuous silk
webs spun on the twigs of the foodplants. If they are disturbed
by a bird the whole group jerks in unison. As they grow older
they split into smaller groups, and become solitary just prior to pupation.
When fully grown in early June,
the larvae descend from the treetops, and wander a short
distance to pupate. The pupa is brown, marked with gold spots,
slightly spiky in appearance, and resembles a withered dead
leaf. It is formed hanging by the cremaster from twigs or
branches on the lower part of various bushes and trees. In
Turkey I have found them commonly suspended from the walls and
eaves of buildings. In my experience at least 60 percent of
pupae are found to be parasitised.
Adult behaviour
Males are seen as solitary individuals, usually either in
flight, or when basking on bare ground in lightly wooded habitats.
In Britain they have been reported nectaring at sallow catkins in
spring, and bramble blossom and
various herbaceous garden plants in summer.
Females habitually bask on tree trunks, often in a head-downwards
posture. The males patrol along wood edges until they locate a
female, and then settle beside it. The female then flies off, with
the male in hot pursuit, until after an hour or more the pair
settle on a tree trunk and copulate. They remain paired all
afternoon, and possibly overnight.
In Europe they
are sometimes seen flying around the tops of sallows, elms and
poplars, but are normally encountered in flight, when dispersing in search of breeding sites.
In
western France
I have observed them flying in inhospitable terrain including
motorway car parks, petrol stations and town centres, indicating
that the species is highly mobile and probably migratory in
behaviour.
Near Dijon in central France I once found 3 Large Tortoiseshells
clustering together in the company of several bees and a dozen Woodland
Graylings, all feeding at a sap run on a hedgerow hawthorn.
While feeding the Large Tortoiseshells nervously fanned their wings,
but made no attempt to fly away even when I approached very
closely. However on most other occasions when I've encountered
this species, they have been extremely wary.
In Turkey I have
found recently emerged butterflies hanging from twigs along dry river beds.
They remained aestivating on the twigs for several days in late
May.
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