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Butterflies of the
Amazon and Andes
Edessa Glasswing
Heterosais edessa
HEWITSON,
1855
Family -
NYMPHALIDAE
subfamily - DANAINAE
Tribe -
ITHOMIINI
subtribe -
GODYRIDINI
Heterosais edessa,
Rio Madre de Dios, Peru
Introduction
The Ithomiinae comprises of 376 known species, although it is
likely that at least another 30 will be discovered in the near
future. All are confined
to the neotropical region.
Ithomiines
are unpalatable to birds, and are consequently mimicked in
appearance by many other species. These include other unpalatable
species ( Müllerian mimics ), not only from the Ithomiinae but
also from several other butterfly families. There are also a large
number of edible species ( Batesian mimics ) which have evolved
similar patterns. Birds have the ability to memorise butterfly
patterns and so learn to avoid eating noxious species, but are
also fooled into ignoring similarly marked edible species.
Ithomiines are
characterised by having small eyes, slender abdomens and long
drooping antennae that lack distinct clubs. Males have a plume of
long androconial scales or "hair pencils" on the costa of their
hindwings. These are hidden from view when the butterflies are at
rest, but are displayed when the wings are held open during
courtship. Other Ithomiine characteristics include a very slow and
deep wing beat, and a preference for inhabiting the darkest
recesses of the forest understorey.
There are basically 2 types of Ithomiine. The first type are the
black and orange-banded "tigers", many of which are mimicked by
other species due to their unpalatability to birds. The second
type are the "glasswings", recognised by their transparent or
translucent wings, prominent veins, and orange wing margins. Many
genera contain examples of both of these types, and in some cases
an individual species may produce adults of both forms according
to location.
Most novices find the Ithomiinae very difficult to identify. Using
only the patterns to identify species is very unreliable because
there are so many similar species. Also many species produce a
variety of different colour forms according to locality and
season. The best approach therefore is to use the hindwing
venation and other anatomical features to identify the genus, and
to then look at the wing patterns to short-list the likely
species.
The genus
Heterosais
includes only 2 species, edessa
and giulia.
Both are Glasswings and can be recognised by the very simple
hindwing
venation and the slight concavity at the hindwing tornus. The two
species can be distinguished from each other by examining the
orange outer margins - in edessa
these are fairly even in width, but in giulia
their inner edges are distinctly scalloped, reminiscent of Greta.
Heterosais edessa
is distributed from Costa Rica to Bolivia.
Habitats
This
species occurs in swampy areas of primary rainforest at altitudes between about 200-900m.
Lifecycle
The
lifecycle is unknown.
Adult behaviour
Like other Ithomiines, the
butterflies spend long periods at rest on the foliage of small
shrubs in the darkness of their forest habitats. They are extremely nervous,
flying immediately if disturbed, only to resettle on another nearby leaf. The flight
is very fluttery, with characteristic deep wing beats.
Males sequester pyrrolizidine alkaloids from
Heliotropium, Tournefourtia,
Myosotis ( Boraginaceae ), Eupatorium,
Neomiranda
and Senecio ( Asteraceae ). These
chemicals confer toxic qualities to the butterflies which deter
bird attacks. The chemicals are also used in the production of
pheromones. Often the males of several
Ithomiine species will gather together at communal leks, where they release
these pheromones from hair-like androconial scales on the leading
edge of their upperside hindwings. These attract more males, which
in turn release
further pheromones. After a few days the lek may include 50 or
more adults comprised of as many as dozen
different species. Passing females are attracted to the
leks by the complex fragrances. Their presence stimulates the
males to open their wings and release further pheromones that
entice them into copulation. Females obtain sustenance from
nectar, and also visit bird droppings which provide them with a
source of nitrogen that assists with the development of their
eggs.
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