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Butterflies of the Andes
 
Owl butterfly
Caligo idomeneus LINNAEUS, 1758
Family - NYMPHALIDAE
subfamily - MORPHINAE
Tribe - BRASSOLINI
subtribe - BRASSOLINA
 
 introduction | habitats | lifecycle | adult behaviour
 
Caligo idomeneus, Rio Frio, Venezuela
 
Introduction
 
The Tribe Brassolini comprises 93 species, all of which are confined to the neotropical region. All are crepuscular or nocturnal in behaviour, although a few species also fly by day in the darkest areas within their habitats.
 
The Owl butterflies belong to the genus Caligo, of which there are 21 known species, some of which are found as far north as Mexico, or as far south as Paraguay and northern Argentina.
 
The species illustrated, Caligo idomeneus, occurs throughout most of the Amazon and eastern Andes, from Venezuela to Ecuador, and south to the Mato Grosso in southern Brazil.
 
Various theories have been proposed to explain the presence of the huge eyespots that adorn the underside hindwings of all species. The butterflies rest for very long periods on tree trunks, and can be quite difficult to spot, but if accidentally disturbed by a bird, the butterfly take flight, and if seen from below with wings fully open, could feasibly be mistaken for an owl. When at rest however, only one side of the wings can be seen at a time, and the appearance then is not owl-like. Another theory is that the eyespot and surrounding dark areas are mimetic of a species of tree frog which sometimes rests on tree trunks where Owl butterflies are seen. It is however difficult to imagine what possible advantage a butterfly might have in resembling a frog !
 
A far more rational likelihood is that the eyespot functions as a decoy. The butterflies have a slow flapping flight, so a bird could easily follow one to it's resting place. Once settled however the mottled patterning provides the butterfly with superb camouflage against the bark of a tree trunk, with only the eyespot remaining prominent. Birds don't direct their beaks aimlessly - they normally aim for the head or body of a butterfly, but when the butterfly is well camouflaged they would aim instead at the most obvious and prominent feature, which in this case is the eyespot. I have seen many Owl butterflies which have had large chunks pecked out of the hindwings, and this would tend to support the decoy theory.
 
Habitats
 
The natural habitat is dense, dark primary forest, where the larval foodplant Heliconia grows. The butterflies also occur in more open secondary forest where the butterfly is often seen at dawn or dusk. In these habitats the butterflies lay their eggs on banana leaves. Several Caligo species have become pests of commercial banana plantations since the fruit was introduced from Africa.
 
Lifecycle
 
The eggs of Owl butterflies are parasitised by tiny Trichogrammatid wasps that ride from place to place on the hindwings of the butterflies. They only leave the female's wings when she lays eggs, and then return, to be transported to the next egg laying site. The eggs laid by any individual female may be laid either singly, or in groups of twenty or more.
 
The larvae normally feed on Heliconia leaves ( Heliconiaceae ), but some species have become pests of banana ( Musaceae ). They are highly gregarious, and tiny first instar larvae can be found amongst clusters of much larger larvae. When fully grown they are a dull brown colour, marked with darker longitudinal stripes, and have prominent forked tails, and a crown of horns arising from their heads. The larvae are nocturnal, and rest during daylight hours on dead leaves of the foodplants, where they are superbly camouflaged.
 
The large squat pupae are formed hanging by the cremaster from woody stems, and are pale brown with streaks of darker colour, and closely resemble bits of dead foliage.
 
Adult behaviour

 

The adults frequently come into buildings, attracted by tungsten lighting, but are more frequently encountered flying around glades or along forest trails at dusk, or when disturbed from rest during the early mornings. They usually rest on slim tree trunks, at a height of about 1 - 2 metres above ground.

 

I once observed a Caligo nectaring at flowers in mid-elevation rainforest in Ecuador, but they more usually feed at fallen fruit on the forest floor, and can be baited with rotting bananas or plantain.

 

The butterflies are known to live for up to 3 months in captivity but it is not known how long they live in the wild.

 

 
 
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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