Butterflies of
Britain & Europe
Heath Fritillary
Mellicta athalia
ROTTEMBURG, 1775
Family - NYMPHALIDAE
subfamily -
NYMPHALINAE
Tribe - MELITAEINI
subtribe -
EUPHYDRYINA
introduction
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habitats |
lifecycle |
adult behaviour
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Heath Fritillary
Mellicta athalia, male on sweet
chestnut, Kent, England |
Introduction
In mainland Europe the
Heath Fritillary is a common and widespread species, absent only from the southern Iberian peninsula and the
Mediterranean islands. It's range also extends eastward across temperate Asia to
Japan. In Britain however it is a scarce and localised species confined to a few of the
southern counties. By the late 1970's the butterfly had in fact become extremely
scarce and was in danger of extinction. Fortunately research into its
ecology by Martin Warren enabled new habitat management strategies to be
implemented, and the species has since made a remarkable comeback.
The adult
cannot be confused with any other British species, except perhaps the Glanville
Fritillary, which only occurs on the Isle of Wight, an area from which the Heath Fritillary is absent.
In
Europe and temperate Asia there are several other species with which
the Heath Fritillary can be confused. These include at least 6 other members of
the genus Mellicta,
and several members of the allied
Melitaea.
The differences between some species are very minor and it takes a very
experienced eye to tell them apart, and the use of a well illustrated field
guide is essential.
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Heath
Fritillary
Mellicta athalia, female, Kent,
England |
Habitats
In Europe the butterfly
can be found in a wide range of habitats including woodland, hay meadows,
sub-alpine pastures, scrubby grassland and roadside verges.
In Britain it is at the
edge of it's range, and is restricted to a very limited range of habitats. It
was formerly widespread in southern counties of England, and was once abundant
in Killarney, Ireland, but loss of habitat, and possibly other factors including
climate and parasitism, led to it's decline. Now, in the first decade of the
21st century, it is restricted to just a handful of sites in Kent, Devon and
Cornwall, and a few sites in Essex where it was re-introduced as part of a
conservation program.
In
Kent and Essex the species is confined to a complex of small to medium
sized woodlands which are managed as sweet chestnut coppice, with a fairly open
canopy of oaks. Here the butterflies breed in small temporary clearings, where
the larval foodplant cow wheat grows
profusely. Populations tend to peak about 2-3 years after coppicing. After this
the habitat becomes shaded out and the butterflies disappear. Both sexes are
capable of dispersing over short distances, so if newly coppiced areas are
available nearby, they are quickly colonised. It is essential however that the
habitats are coppiced regularly so that suitable areas are always available for
colonisation, and that there are sufficient sunny tracks or rides in the wood
which the butterflies can use as dispersal corridors.
An
unpublished survey of north Kent in 2007 by Hoskins & Meredith
found that Heath Fritillaries were present in almost all of the woodlands north and west
of Canterbury. A total of 13 separate colonies were located, each comprising
between 10 - 60 adults per day during peak flight season.
The
sites on Exmoor in Devon are entirely different in nature - sheltered hillsides
and lightly wooded valley bottoms where the foodplant grows amidst bracken or
heather.
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Heath
Fritillary
Mellicta athalia, male, Kent, England |
Lifecycle
The Heath Fritillary is single
brooded in Britain and northern Europe, but double brooded in
Spain, Portugal, southern France and Italy.
In Britain the adults emerge in late May /
early June ( Devon ), or in mid-late June ( Kent / Essex ).
The eggs are yellow at first, but later
turn greyish, and hatch after about 10 days. They are laid in
large untidy batches on the underside of bramble, foxglove or
other large leaves low on the ground. Sometimes they lay under
dead fallen leaves of sweet chestnut or oak, in the vicinity of
the larval foodplants, but rarely on the foodplants themselves.
The young caterpillars spin thin
silk webs over the leaves of the foodplants, and bask on these
in groups of about a dozen or so. They enter hibernation in
September when still quite small, spending the winter clustered
together on dead leaves on the ground.
In March they awaken to
resume feeding on cow wheat
Melampyrum pratense leaves, although this
is sometimes
supplemented by germander speedwell
Veronica chamaedrys
or foxglove
Digitalis purpurea.
In Cornwall the foodplant is usually plantain
Plantago lanceolata.
The
older larvae, which live solitarily, are quite distinctive, with
black bodies and rows of short white and yellow spikes along the
back and sides. They become full grown in early May, when they
feed and bask openly on the upper surface of leaves of the
foodplants.
The chrysalis, which is formed
amongst dead leaves and twigs on the ground, is white, decorated
with numerous small black and yellow spots. The pupal stage is
short, usually only about 8-12 days.
Adult behaviour
Adults are usually found flying
in groups of between 10 - 100, in isolated sunny pockets within their
habitats. Sometimes when breeding sites
are well managed and climatic conditions are suitable, much
larger populations can arise, comprising of several hundred
individuals.
Males patrol lazily about the habitats
searching for freshly emerged females. Copulation takes place
in late morning. I have found mated pairs on several occasions,
often sitting in exposed positions on bramble flowers or on the
terminal leaves of low growing plants. The
pheromones emanated by the females appear to be highly potent,
often attracting several additional males, which cluster around the copulated pair,
trying to force themselves on the female. Gravid females are also
continually pestered by males, which are rarely deterred by the
female's "raised abdomen" rejection signal.
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Heath Fritillary
Mellicta athalia, male at roost on
red clover, Kent, England |
The butterflies
nectar at various flowers including bugle, heather, lesser
stitchwort and buttercups, but
show a strong preference for hawkbit and bramble blossom. Females
often feed for several minutes at a particular blossom, but
males tend to flit more frequently from flower to flower. On
several occasions I have found adults in the grip of crab spiders Misumena vatia, which lie in
wait on bramble flowers, ready to ambush any butterfly that
settles to feed.
Even in warm
sunny conditions the butterflies are decidedly lethargic, and rarely attempt
to fly more than 2 or 3 metres at a time. They spend long periods
resting with wings closed on the foliage of sweet chestnut,
bramble or oak saplings. In hazy or lightly overcast conditions
both sexes will bask on low foliage. It
is very common to find 2 or 3 Heath Fritillaries basking side by side
on bramble or sweet chestnut leaves.
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Heath Fritillary
Mellicta athalia, males basking on
bramble leaves, Essex, England |
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Heath Fritillary
Mellicta athalia, freshly emerged female, Kent, England |
Small groups of
adults can be found at dusk on dry days, roosting on sedges, rushes, or on
the terminal foliage of low-growing herbs. I have also found them
roosting on grass-heads, red clover, bracken fronds, or amongst
the foliage of coppiced sweet chestnut.
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