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Butterflies of
the Amazonian rainforests
Agnosia Glasswing
Ithomia agnosia HEWITSON,
1855
Family -
NYMPHALIDAE
subfamily -
DANAINAE
Tribe - ITHOMIINI
introduction
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habitats |
lifecycle |
adult behaviour
Ithomia agnosia,
Rio Madre de Dios, 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, 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.
The Ithomia
Glasswings include
patilla, terra, arduinna
and agnosia,
all of which have slightly bluish translucent wing membranes, and
veins which are outlined in orange on the underside, and with
black on the upperside.
Males of Ithomia
have a distinctive blister on the costa of the underside hindwings
that corresponds with a patch of androconia ( pheromone producing
scales ) on the upper surface.
Ithomia agnosia
is found from Colombia to Peru.
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 highly 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, only to resettle on another nearby leaf. The flight
is very fluttery, with characteristic deep wing beats.
When feeding
in the open they behave very differently - being very placid and
reluctant to leave their flowers.
Males sequester pyrrolizidine
alkaloids from plants including
Heliotropium, Eupatorium
and Senecio, which they
chemically convert into pheromones.
Males, often of several
Ithomiine species, gather at communal "leks", where they release
these pheromones from hair-like androconial scales on the
upperside hindwings. These attract more males, which release
further pheromones. After a few days the lek may include a dozen
or more different species. Passing females are attracted to the
leks by the complex fragrances, and their presence stimulates the
males to open their wings and release further pheromones that
entice the females into copulation.
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