Butterflies of
Britain & Europe
Small Blue
Cupido minimus
FUESSLY,
1775
Family - LYCAENIDAE
subfamily -
POLYOMMATINAE
introduction
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habitats |
lifecycle |
adult behaviour
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Small Blue
Cupido minimus, male, Martin Down,
Hampshire, England |
Introduction
Speckled in
metallic powder blue on a sooty ground colour, the male of this delightful
butterfly is the smallest in the UK, and one of the smallest in Europe. The
female is slightly larger and lacks the blue speckling. On the underside both
sexes are silvery with tiny black spots, and when seen in flight the butterflies
have a very silvery appearance, like tiny spinning coins.
It is a widespread and common species
in Europe, where it occurs from the Cantabrian mountains of northern
Spain, eastward across Europe, and thence across temperate Asia to Mongolia and
Amur.
In mainland Europe there are 3 other members of the genus
Cupido,
with which the Small Blue can very easily be confused. Males of C. osiris,
which occur in the same habitats as
minimus,
have deep blue uppersides, but the females are dark grey, peppered with
greyish-blue scales like the male of
minimus.
The other 2 species, lorquinii
and carswelli,
occur only in southern Spain, where
minimus
is absent.
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Small Blue
Cupido minimus, female, Martin Down,
Hampshire, England |
Habitats
The butterfly is
widely distributed across southern England, but extremely localised, and
confined to small corners of its habitats where the foodplant grows in profusion.
Typical sites include sheltered, ungrazed or lightly grazed
habitats in old chalk or limestone quarries, calcareous sand dunes, south facing grassland
slopes, cliffs and limestone pavements. Colonies also exist on steep and
well-drained road and rail embankments. In Europe the butterflies also
breed in limestone gorges, sub-alpine hay meadows, and in grassland / woodland
mosaics.
All sites are characterised by the presence of kidney vetch Anthyllis vulneraria,
growing amongst sparse fine grasses, typically at the edge of paths or on eroding
banks. There also need to be tall grasses
or bushes growing nearby, where the adult butterflies can find shelter overnight
or during periods of
inclement weather.
The vast majority of colonies comprise of only a
couple of dozen
insects, although there are a small number of sites where populations run
into a few hundreds.
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Small Blue
Cupido minimus, female, Martin Down,
Hampshire, England |
Lifecycle
The main emergence of Small Blues is in late May and June,
sometimes running into early July and overlapping with the 2nd
brood, which flies from mid July until late August. This 2nd
brood however is only partial, producing only about 5% of the
numbers occuring in the spring brood.
The butterflies lay their pale greyish-blue eggs singly on the flowers
of kidney vetch, at the base of the calyx. They then rub their
abdomens all over the flower head, marking them with scent to
deter other females from laying on the same flower. A single
flower head can only support one larva, and if two or more find
themselves on the same flower head they become cannibalistic.
Unfortunately the scent wears off after a day or two however, so
sometimes several eggs can be found together, probably laid singly by different females,
but only one of the resulting larvae will survive.
The eggs hatch in about 10
days, and the tiny larva immediately burrows into the flower
where it feeds on the anthers and seeds. When it is older
and too big to feed inside the flower the caterpillar
rests on the calyx tube, facing downwards, and makes a hole at
the base, through which it feeds on the tissue of the developing
seed.
In common with most
Lycaenid species, caterpillars of the Small Blue possess
ant-attracting organs. Their relationship with ants is probably
beneficial ( ants would deter other insects from attacking the
larvae ), but there is no symbiotic interdependence. This is
demonstrated by observing that while most European populations
of minimus larvae are attended by
ants e.g.
Lasius niger
and Myrmica
rubra, there are no records of this in the UK.
The fully grown larva leaves the foodplant and settles
into a crevice in the ground, where it spends the winter. Most
larvae pupate the following May, and produce butterflies in
June, but some larvae remain in diapause for up to 15 months,
emerging in August of the following year. It is in fact quite
possible that the apparent "2nd brood" adults may be nothing
more than a delayed emergence of a single brood.
The slightly hirsute chrysalis, which is greyish-buff and spotted with black, is formed at ground level,
hidden in a crevice, or amongst leaf litter. Like the
larva, the pupa can secrete a sugary substance that is
attractive to ants, and it is probable that it in both the UK
and Europe the pupae are attended by ants and probably buried
and protected by them until the adult butterflies emerge.
The pupae of many Blues, Hairstreaks and Coppers possess
microscopic ridges on the abdomen which can be rubbed as the
pupa wriggles, to produce a stridulating squeak. This may help
the ants to locate the pupa, but it is more likely that the
sound is used to appease the ants and deter them from eating it.
The pupal stage
lasts about 2 weeks.
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Small Blue
Cupido minimus, male, Portsdown Hill, Hampshire,
England |
Adult behaviour
The
butterflies are usually found in small groups of a dozen or so,
although at some sites I have found up to 200 at roost on grasses
in sheltered depressions.
The
males spend most of their time basking with wings half-open, on
grass blades or on the foliage of bramble and other low plants,
where they await passing butterflies. They will intercept Brown
Argus or other Small Blues, but ignore larger species.
Periodically several
butterflies will erupt into flight, and during male-male
encounters a very brief sortie takes place, after which each male
returns to another perching place.
When virgin females are intercepted copulation takes place almost
instantaneously, but when gravid females are intercepted they
immediately settle deep amongst grasses, where they hide until the
male flies away.
Copulated pairs
can often be found sitting amongst lush foliage in depressions or
ditches close to the breeding sites. After separating the males
remain at their territories to await further females, but the
mated females move away, dispersing onto more open areas to seek
egg-laying sites.
Both sexes nectar
mainly on leguminous plants including kidney vetch, bird's foot trefoil,
horseshoe vetch and black medick, but will also imbibe dissolved minerals
from animal dung - I once found a group of over 50 Small Blues
feeding at a very dry cowpat in the French Alps, and have often
found singletons or small groups on animal faeces in the UK. In
Vanoise national park in the French Alps I have also found large
aggregations imbibing dissolved minerals from mud at the sides of
streams.
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Small Blue
Cupido minimus, male, Hod Hill, Dorset,
England |
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