Butterflies of
the Amazon and Andes
Beautiful Glasswing
Ithomia terra
HEWITSON,
1853
Family -
NYMPHALIDAE
subfamily -
DANAINAE
Tribe - ITHOMIINI
introduction
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habitats |
lifecycle |
adult behaviour
Ithomia terra, Manu cloudforest,
1700m, Peru.
Introduction
Butterflies in the tribe Ithomiini are characterised by
having long thin abdomens, small eyes and drooping antennae. Also
typical of Ithomiines are the long legs, which are striped
longitudinally in black and white or cream, giving the thorax a
zebra-striped appearance when viewed from the side.
The butterflies can be divided rather unscientifically into two
types - the tiger patterned species and the transparent
"Glasswings".
The genus Ithomia
comprises 22 species, and includes both of these types.
Most
Ithomia species have slightly bluish translucent wing membranes.
They also have a small tuft of
orange scales just behind the head. This orange tuft is also found
in Napeogenes and
Aeria, but whereas
Ithomia have a bluish translucence,
Napeogenes are noticeably greenish,
and Aeria are a slightly opaque
greenish white.
Ithomia terra
is found from Costa Rica to Bolivia.
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All males in the tribe Ithomiini release
scent (
pheromones ). These serve a dual role - firstly to
lure and seduce potential mates, and secondly to act
as a chemical defence, a "nasty smell" to warn predators
that they are unpalateable and contain toxins. The toxins
are primarily derived from the caterpillar's foodplants Solanaceae, but are supplemented by pyrrolizidine alkaloids
sequestered by the adults from fluids imbibed from the flowerheads
and stems of Eupatorium,
Heliotropium,
Senecio and various other plants.
In
Ithomia males these pheromones
are stored within a reservoir which forms a distinctive black blister just below the costa
on the underside hindwings. This reservoir corresponds with a patch of
long hair-like androconial scales on the upper surface.
These "hair pencils" disseminate the pheromones and are erected during courtship,
or when the
males are displaying at a lek.
Ithomiine leks sometimes
comprise of just a few males of a single species, but often
occur as aggregations of up to 20 or 30 males of various
Ithomiinae species. A long established lek may include a
dozen or more species. Leks are often located in the vicinity
of small streams in deeply shaded parts of the forest.
Passing females are attracted by the complex
fragrances, and their presence stimulates the males to open their
wings and release further pheromones that entice the females into
copulation. |
Habitats
Butterflies in the genus Ithomia
are migratory, and occur in rainforest and cloudforest at elevations between sea
level and about 2000m. They spend much of the time deep in the
forest, but emerge in early morning or in overcast weather to
visit flowers along roadsides and riverbanks.
Lifecycle
I have no data regarding the early stages, but if these are likely to be similar
to other members of the genus, as described below :
The eggs of Ithomia
are typically white, and laid singly on
the underside of leaves of
Witheringia,
Solanum, Acnistus
and other Solanaceae.
These
foodplants are highly toxic to
birds and other small vertebrates. At one time it was
thought that the chemicals within them
were accumulated by the larvae,
and passed on to the adult butterflies,
rendering them distasteful to birds.
Research by Edgar
et al in
the 1970's and 80's however revealed that the alkaloids found in adult
Ithomiines and Danaines is sequestered from flower nectar and plant exudates,
rather than being derived from the larval foodplants.
The larvae are
greenish and devoid of filaments, but have a row of lateral
tubercles. The head is pale green, marbled with blackish.
The pupae are a very shiny chrome-silver, and are suspended by the cremaster
from leaves and stems, and from a distance can be mistaken for large droplets of
water.
Adult behaviour
In cloudforests the
adults are attacked by Ceratopogonid midges, which feed on the
blood in the butterfly's wing veins and eyes.
Like other Ithomiines, the
butterflies spend long periods at rest on the foliage of small
shrubs in the darkness of their rainforest and cloudforest
habitats. They are extremely nervous, and if disturbed fly
immediately, but quickly resettle nearby. The flight
is slow and bobbing, with characteristic deep wing beats.
When feeding
in the open they behave very differently - being very placid and
reluctant to leave their flowers. They feed at dead flowers on the
forest floor, as well as at living ones, and also imbibe fluids
from the stems of dying plants.
Both sexes, but in particular the males, are also carrion feeders,
and can often be seen imbibing bodily fluids from the decomposing
corpses of flies, spiders and other invertebrates. However, unlike
certain other Nymphalidae ( e.g. Apatura,
Charaxes,
Doxocopa ) they are not attracted to the carrion or dung of
vertebrates.
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