Butterflies of
West Africa
Western Pearly
Eresiomera
bicolor
GROSE-SMITH & KIRBY, 1890
Family - LYCAENIDAE
subfamily -
LIPTENINAE
Tribe - LIPTENINI
Eresiomera bicolor,
Likpe Hills, Ghana / Togo border
Introduction
The
subfamily Lipteninae is wholly African in distribution, and comprises of no less
than 600 species, varying from the tiny
Eresiomera bicolor to the dazzling bright metallic blue
Epitola posthumus - a species which with a wingspan
of 65mm is massive by Lycaenidae standards.
The Lipteninae are fascinating
because of their association with "ant trees", i.e. trees which support colonies
of Crematogaster ants. As with most other
Lycaenidae species, the caterpillars of Liptenids have ants in almost constant
attendance. The ants "milk" a sugary substance from a gland on the caterpillar's
back, and in return for this reward the caterpillar benefits because the
presence of the aggressive ants deters other insects such as wasps and flies
that would otherwise attack them.
Eresiomera comprises of 13 West African butterflies which are included by
some writers within the genus Pseuderesia, but
which differ from it regarding wing shape, underside pattern, genitalia and
behaviour. Pseuderesia ( excluding
Eresiomera ) comprises of an additional 13 species.
The popular name "Pearly" given
to the Eresiomera species, refers to the
pearly-grey appearance of the underside hindwings.
Eresiomera bicolor is one of the commonest of the Lipteninae, and is
found from Cote d'Ivoire to western Nigeria.
Habitats
This is a rainforest species, found at altitudes between about 100-500m.
Lifecycle
The caterpillars browse on the trunks of
their "ant-trees". These trees can be any one of a number of species from
different plant families. There is conjecture about what exactly it is that the
larvae feed upon - e.g. some writers consider them to feed on lichens, while
others insist it is blue-green algae. It may even be the case that they feed on
microscopic fungi, and it is possible that ants play a part in cultivating these
fungi.
The pupa is attached by the cremaster to a tendril or thin twig on the tree.
Eresiomera bicolor,
Likpe Hills, Ghana / Togo border
Adult behaviour
Nether sex ever seem to stray more than a few metres away from an
"ant-tree", around which they constantly flutter. During periods
of cloud cover they settle at the tips of leaves, often quite high
up, holding their wings erect, and tilting slightly forward. When
the sun breaks through the clouds they slowly open their wings and
bask until their body temperature is high enough to allow them to
resume flight.
Both sexes commonly feed at
extrafloral nectaries on the stems of Marantaceae. When nectaring,
they periodically
fan their wings in such a manner that the apexes of the forewings
meet beneath the abdomen. This is done in a very deliberate way
which may indicate that it is some sort of signal, and at least
one writer has suggested that the butterflies may be signalling to
the ants. It seems more likely however that the behaviour serves a
simpler purpose, e.g. it may be necessary to invert the wings in
this way to facilitate the release of pheromones to attract mates.
Eresiomera bicolor,
Likpe Hills, Ghana / Togo border
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