Butterflies of Britain
Family - NYMPHALIDAE
Tribe - NYMPHALINI
Aglais urticae, Noar Hill, Hampshire ©
Small Tortoiseshells vary considerably in
some examples being a
unicolorous dull orange, while others are much redder with
contrasting yellow patches. In summers when weather conditions are
cool, a high percentage of the butterflies tend to have the black
markings enlarged, or merging together. In hot summers, and in
warmer parts of the butterfly's range these markings often become
reduced in size.
The race ichnusa,
found in mountainous areas of Corsica and Sardinia has a fiery
orange ground colour, and lacks the colon of black spots on the
forewing. Some authors regard it as a separate taxon. Captive reared
adults however closely resemble the normal form, so it seems likely
that ichnusa is merely a habitat /
climate generated form of urticae.
The Small Tortoiseshell occurs across the whole
of Europe and temperate Asia. A closely related and very similar
species Aglais kashmirensis is found in
mountainous regions of Kashmir, Tibet, Sikkim and Bhutan. In the
western Himalayas a third species occurs,
Aglais ladakensis, which looks like a very heavily marked
version of urticae. The only other
member of the genus Aglais milberti is
a north American species in which the basal half of the
forewings is black, and in which the 2 small black spots in the
median area are absent.
Aglais urticae, River Bure, Norfolk ©
has always been subject to dramatic fluctuations in abundance
from year to year and in some
seasons it can
be very scarce. Historically it has always had
the ability to bounce back, and was until recently regarded as one
of Britain's most familiar and common butterflies.
However after about 1990 the species declined sharply in southern
England, until the low point of 2007 when most recorders in
Hampshire, Surrey and Sussex failed to see even a single specimen.
There was some evidence of a minor come-back in 2008, when most
observers saw at least one or two specimens of the late summer
brood. Survival of hibernating adults in the cold and prolonged
winter of 2008-2009 was however exceptionally good, so the species
got off to a good start in spring 2009. Current signs are that the
Small Tortoiseshell has had a fairly good summer season, with most
observers seeing at least a dozen adults in June 2009. Despite wet
and generally cloudy mid-summer weather the resurgence in numbers
continued, with at least 2 or 3 adults recorded at almost every site
visited by recorders in southern Britain in late July and early
August 2009. These figures however still fall far short of the
numbers seen in the 1960's and 70's.
The cycles of
abundance are linked at least in part to
climatic variations, which affect the
population dynamics of the butterfly and it's parasitoids.
Luckily the population crashes are not
synchronous - at times when the species is scarce in one part of the
country it can be relatively abundant in another.
The Small Tortoiseshell
may have been present on Earth longer than any other butterfly
species - a mid-Miocene fossil of Aglais
karaganica estimated to be
15 million years
similar to the present day Aglais
urticae as to be virtually indistinguishable.
Aglais urticae, Noar Hill, Hampshire ©
Small Tortoiseshell is a highly
mobile species which can
occur in almost any habitat,
including woodlands, grasslands, heaths, gardens, country
lanes, and even in city centres.
It is a strong flyer, with high powers of
dispersal, reaching the most remote islands, and the peaks of
mountains. It has been recorded at altitudes as high as 1200m in
Scotland, and larval nests have been found at 335m. I have
watched adults flying near the peak of Ben Lawers
in Tayside, and high in the mountains at Langdale Pikes and various
other sites in the Lake District.
is perhaps commonest on dairy and cattle
farmland, where the application of fertilisers
and manure enriches the soil, encouraging the growth of
Urtica dioica and U. urens.
Aglais urticae, Alner's Gorse, Dorset ©
In northern Scotland there is usually
only a single generation, emerging in July, entering hibernation in
August, and reappearing in March or April. Elsewhere in
Britain there are normally 2 broods per year, one emerging in June,
and the other in August. Adults of the latter brood enter
hibernation in September or October, and reawaken the following
The resident population
is supplemented by the occasional arrival of migrants from the
continent. The numbers arriving however are normally very low, and
probably have no significant effect on population levels.
In spring, female Small Tortoiseshells
are often seen flying around young nettle patches, where they lay
their greenish eggs in large
untidy heaps of 80-100
on the underside of the upper
leaves. Often more than one female will lay eggs on the same leaf,
sometimes simultaneously. The females usually choose young plants
growing near the edge of the nettle bed, and always growing in warm,
sunny and sheltered conditions. Typical breeding sites include
field edges at the bottom of south-facing
hillsides, dykes, riverbanks, disused railway cuttings, and nettle
patches growing on the south side of hedgerows or dry stone walls.
Aglais urticae, egg batch on stinging nettle (
Urtica ), Hampshire ©
The summer brood is less fussy about
oviposition sites, and will lay on nettle patches in gardens, in
woodland glades and rides, and on exposed hilltops.
In June 2009, I watched a female
searching for oviposition sites at Martin Down in Hampshire. She
spent about half an hour flitting back and forth, settling for a few
seconds here and there on various terminal leaves, and took a great
deal of time before she eventually found one which suited her. To my
eyes it looked no different from any of the other leaves on which
she landed, so I assume that she just found that particular leaf
easier to grip. Once she had decided where to lay her eggs she clung
tenaciously to the leaf, which was constantly battered by strong
gusts of wind, until she had laid a batch of about 80 eggs.
The eggs hatch after
about 12 days. Immediately after hatching, the
larvae devour their empty egg shells, and
then spin a communal silk web around the terminal leaves of the
nettles. They shelter within the web at night, or in adverse weather
conditions, and feed avidly whenever the sun shines.
the larvae react in unison, wriggling and jerking as a defence
against parasitoid wasps or flies. Nevertheless
a high proportion of larvae turn out to be
parasitised, usually by the Tachinid fly
When young, they can easily be mistaken
for the caterpillars of the Peacock, but Small Tortoiseshell larvae
are paler, and even when quite small it is usually possible to
discern pale lines running along their backs.
Aglais urticae, 2nd instar larvae on stinging nettle, Dorset ©
As they grow, they
split up into progressively smaller groups,
spinning a new web after each moult. The
final instar sees a change in behaviour, with the larvae abandoning
their webs entirely and living solitarily. By this time they
are a dull blackish colour, spiky, with broad
yellow lines running along their backs and sides.
These lines are usually very prominent, but in
some batches of larvae they can be pale and obscure. The
fully grown larvae can often be seen
curled in a J-shaped posture, resting on nettle leaves, and if
disturbed will coil into a tight circle and drop to the ground.
The chrysalis is variable in colour, ranging from grey to olive
or buff, often with a pinkish
or golden metallic sheen. It can be found
suspended by the cremaster, on woody stems, fence posts, walls, or
beneath the stems or leaves of nettles.
The adults emerge at dawn, about 12 days after pupation.
research suggests that a tiny parasitic fly may have been
responsible for the recent decline of the Small Tortoiseshell.
The fly Sturmia bella
( Tachinidae ) occurs mainly
in warmer climates, and first arrived in Britain in 1998. It
lays it's eggs on nettle plants. When the Small Tortoiseshell
caterpillars eat the nettle leaves, the microscopic eggs are
ingested undamaged and pass into the caterpillar's gut. There
they hatch, and the resulting grubs bore their way through the
soft flesh, consuming non-vital body tissues. When the grubs
are almost full grown they eat the vital organs, and then
break out through the skin of the dying caterpillar to pupate.
The fly is
widespread throughout southern Europe, north Africa and Asia. In
Japan it parasitises the caterpillars of a Danaine,
Interesting research by Hirai & Ishii has revealed that
P. sita can
often survive attack by Sturmia
bella - in experiments over 70
percent of infested sita
larvae survived and went on to produce
perfect adult butterflies. Sadly the Small Tortoiseshell lacks
research appears to suggest that
Sturmia bella is at least partially
responsible for the decline of the Small Tortoiseshell,
experiments have shown that only about 18% of Small
Tortoiseshells are affected by parasitoids, and
is just one of several that attack the butterfly.
It is also notable
that other nettle-feeding Vanessids e.g. Peacock, Red Admiral &
Comma are apparently less affected, even though their larvae
also ingest the Sturmia
eggs. The Comma and Peacock in fact increased their numbers
substantially during the 2005-2009 period. All 3 species have
very similar body chemistry to that of the Small Tortoiseshell,
so it is unlikely that they possess a natural immunity.
is not host-specific, it parasitises a wide range of species in
Europe and Asia. One cannot help wondering therefore why the
Small Tortoiseshell seems to have been singled out, while Red
Admiral, Comma and Peacock continue to thrive.
It is feasible
that the decline of urticae
could be linked to pesticides. Small Tortoiseshells usually
oviposit on nettles growing in open sunlit places such as
farmyards and field edges - areas often exposed to high levels
of pesticide and other chemical sprays. The other Vanessids -
Commas, Peacocks and Red Admirals all tend to breed on nettles
in woodland glades, gardens and lanes where they are not exposed
to pesticides and would thus be relatively unaffected.
Climate change in
itself could be a major factor. The viability of each butterfly
species is limited by temperature and humidity. This defines
it's geographical and altitudinal distribution and is part of
the reason why some species are found only in the Arctic while
others only in particular elevations in cloudforest in the
tropics. It's quite possible that the Small Tortoiseshell simply
can't cope with the mild damp winters Britain has recently
experienced, but that these may be beneficial to the Comma, and
well tolerated by the Red Admiral and Peacock.
awaken in late March or early April, and remain on the wing until
are usually seen as singletons, nectaring
often in the vicinity of nettle patches.
On cool days in spring
they do not bask, but instead warm themselves up by shivering their
wings prior to flight. The rapid shivering generates warmth by
friction, and enables the butterfly to fly even in quite cool
conditions. On warm days they frequently bask on bare soil or low
foliage, but hot sunny conditions cause them to settle for long
periods on bare soil with their wings closed, at which time the sombre
"tortoiseshell" pattern on the underside affords them excellent
camouflage. When settled the abdomen is usually raised so that minimum
contact is made with the hot substrate.
Aglais urticae, female ovipositing on stinging nettle, Martin
Down, Hampshire ©
vantage points in
from which they
await passing females. When a female flies by she is intercepted and
the courtship ritual begins. The male chases her until she settles on
the ground. If she is receptive she opens her wings and the male
approaches her from behind, with his wings also open. He then
which he vigorously drums with with
his antennae. The pair then fly a short distance and repeat the
other males which attempt to interfere are briskly chased away by the
resident male, who then returns to his female to continue
continues for several hours, until just before dusk, when
the female accepts the
At this point
she leads him to a sheltered and shady spot, typically
a bush or
hedge. Both sexes then hold their wings erect,
and the male walks alongside the female, and curves his abdomen to
copulate. After about 20 minutes the pair straighten out to face
opposite directions. They remain
in this position until the following morning.
The summer brood
which emerge from mid June to early July,
will nectar at almost any available wild or cultivated flowers. Their
favourite however is undoubtedly creeping thistle. At Noar Hill in
July 2009 I watched a female nectaring for over 2 hours at a clump of
these flowers. When disturbed by a bee or hoverfly she would leave the
thistles and briefly investigate other nearby flowers including
marjoram, knapweeds, bramble, scabious and hemp agrimony, but after a
quick taste always returned to the thistles.
The second generation
is always more abundant than the first, and emerges
at the end of
In late summer
flowery areas in the countryside, where they congregate to nectar at
ragwort and other Compositae. They also commonly visit gardens,
where they are
strongly attracted to
Buddleia and michaelmas daisies. Their
mission at this time of year is to use every opportunity to gorge on
nectar, building up sufficient protein and fat reserves in their
bodies to enable them to survive hibernation.
In southern Britain
the butterflies fly until late September, when they enter houses,
sheds, churches and unheated farm buildings
to hibernate. In the north they enter hibernation earlier, typically
in late July or early August, after just a few days on the wing. They
often hibernate communally - on many occasions I have found groups of
3 or 4 nestling together in an attic or outbuilding, and I once found
17 hibernating adults clustered
together on the
ceiling in a hotel in Tayside,