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Text and photographs protected by Copyright © Adrian Hoskins 2007, and must not be published in part or in whole elsewhere without prior written permission from the author.
Butterflies of the Amazon rainforest
 
Antisao Glasswing
Pteronymia sao HÜBNER, 1813
Family - NYMPHALIDAE
subfamily - ITHOMIINAE
Tribe - DIRCENNINI
 
 introduction | habitats | lifecycle | adult behaviour
 
Pteronymia sao, Madre de Dios, Peru
 
Introduction
 
The Ithomiine Glasswings are amongst the most difficult butterflies to identify, as all seem to have fairly similar patterns, with wings transparent except for dark veins, a white subapical band, and orange margins. To make matters worse, there are also members of the Pieridae ( Dismorphiines ) which mimic the butterflies very well, and breed in the same habitats.
 
The Dismorphiines can be eliminated as candidates by simply counting the butterfly's legs - they have 3 pairs of legs, whereas Ithomiines have only 2 pairs.
 
The next step is to establish the genus, reasonably easy for an expert lepidopterist, as the venation ( the layout of the wing veins ) is different with each genus. Fortunately the venation of Glasswings is easy to see, due to the transparency of the wings.
 
Having established the genus, it is then a matter of examining the layout of the white spots and orange borders to establish the species.
 
The genus Pteronymia contains 46 known species, many of which are very similar to the illustrated insect, although some such as donella, picta and lonera are more heavily marked and have orange hindwings.
 
The illustrated butterfly was kindly identified for me by Andrew Neild as Pteronymia sao, and confirmed by Ithomiine expert Keith Willmott. The butterfly is also known by the junior synonym antisao.
 
It occurs in the Upper Amazonian region from Brazil to southern Peru and Bolivia.
 
Habitats
 
Pteronymia sao breeds at altitudes between about 200 - 1600m in wet primary rainforest and transitional cloudforest habitats.
 
Lifecycle
 
The precise details are unknown, but the following applies in general to butterflies in the genus Pteronymia :
 
The eggs are white, and laid singly on the underside of leaves of Solanaceae. Females of most species return several times to the same plant, laying up to a dozen eggs in total.
 
The larvae of Pteronymia species vary in appearance, some being dark along the back, with a pale central stripe, while others are banded in black and white, and characterised by the presence of a pair of soft fleshy horns projecting forward from the first thoracic segment.
 
The pupae of this genus are typically squat in shape, with compressed abdominal segments, and a bulbous thoracic section. They are generally silver or gold in colour, shiny, and resemble large raindrops hanging from stems or the undersides of leaves.
 
Adult behaviour

 

The butterflies are usually encountered singly, flying in deeply shaded areas of the forest understorey. Like other Glasswings, they tend to spend long periods stationary, perched on foliage in light gaps. When disturbed they fly rapidly, but with slow wing-beats, and resettle a short distance away, usually higher up, but tend to return to their home ground within a few minutes.

 

Males visit the stems of Eupatorium and Heliotropium plants, from which they acquire pyrrolizidine alkaloids which they convert within their bodies into pheromones. They gather, together with males and females of various other Ithomiine species, at "leks", where the males of each species release their pheromones, which are disseminated via "hair pencils" of androconial scales on the wings.

 

This behaviour attracts more males and females of each species, until upwards of a 20 butterflies are present. It is believed that females may be able to assess the alkaloid content of a male, and may elect to mate with the male with the highest concentration. The alkaloids are probably then transferred to the female during copulation, implying that males with high concentrations are essential for the production of fertile and viable eggs by the female. Other studies have demonstrated that the alkaloids also function as toxins to deter avian predators.

 

Females do not acquire the alkaloids from plants, but do visit Eupatorium and various other flowers for nectar and pollen, and also visit the droppings of antbirds and antwrens, from which they obtain nitrogen compounds.

 

Pteronymia, like most Ithomiines, demonstrate strong seasonality, being most abundant at the beginning of the rainy season. In the transition period between seasons they show a tendency to migrate, both laterally and altitudinally - a behaviour that is probably linked to the movement of the ant swarms, and thereby to the location of the antbirds and antwrens that follow them.

 

Text and photographs protected by Copyright © Adrian Hoskins 2007-2008, and must not be reproduced or published in part or in whole elsewhere in any form without written permission from Adrian Hoskins. Breach of copyright will be pursued by litigation.

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