Rigor Vitae: Life Unyielding

Tuesday, June 27, 2006

OWLET BUTTERFLIES

In tropical forests all across the world, large and showy butterflies are a dime a dozen. In the jungles of the New World, the most conspicuous butterflies are the morphos (Morpho spp.). Some species are brown or white, and some are rather small, but the scrawny body of the typical morpho is supported on outsized wings of shimmering blue that can span seven inches, and can send it flopping buoyantly across the understory like a piece of fine blue tinfoil. Less showy, but no less splendid, are the 12 genera of owlet butterflies in the subfamily Brassolinae, which are found from Mexico to Argentina, and on Trinidad and Tobago.

Except for the little brown members of the genus Narope, the owlet butterflies are characterized by tasteful vermiculated patterns on the underwings, with one or more ocelli on each hind wing. When the wings are spread, the ocelli strongly resemble two large eyes, hence the common name of the subfamily. The ecological significance of this marking is hard to understand. One author put forth the notion that it mimics certain unpalatable treefrogs, and if you squint just right you can almost see a vague frog or the Virgin Mary. Others have suggested the false eyes may frighten potential predators or cause them to lunge for the hind wing instead of the more vital body. The fact that the ocelli are most conspicuous when the insect is at rest seems to belie either hypothesis.

Male brassoline butterflies have complex scale tufts on their hind wings and the sides of their abdomens, called androconial tufts. These organs store pheremones, which are released during courtship, and are produced by cells at the base of the tuft. The androconial pheremones give many species a characteristic odor; the males often smell strongly of vanilla. Brassoline eggs come in a variety of shapes, and are deposited on the leaf of a host plant singly in some species, and in clusters in others. A variety of monocotyledonous host plants are exploited, from bananas (family Musaceae) and heliconias (Heliconiaceae) to grasses (Poaceae), bromeliads (Bromeliaceae), and palms (Aracaceae and Cyclanthaceae). Some brassoline caterpillars are important agricultural pests, particularly certain Caligo species that feed on the leaves of bananas (Musa spp.) and the gregarious Brassolis larvae that spin communal silk tents on Coconut Palms (Cocos nucifera). In some areas, Opsiphanes caterpillars can cause problems on either crop. The mature caterpillars of owlet butterflies are cigar-shaped, with a pair of caudal appendages. Many species have a row of soft spines running down the back. In all genera except Brassolis, the caterpillar's head is ornamented with two or more pair of horns. A gland on the prothorax can be everted to secrete noxious chemicals if the caterpillar is attacked. The genera Brassolis and Dynastor form amazing chrysales that look very much like the heads of vipers.

Adult owlet butterflies are often crepuscular, sometimes bordering on nocturnal. They feed on rotting fruit, whose skins are pierced by sturdy probosces. In many species, the proboscis is usually infested with various mites, whose ecology is still poorly understood. A number of species of tachinid flies and chalcid and trichogrammatid wasps are important parasites of brassoline caterpillars and eggs. Among the best studied of these relationships is the one between Caligo butterflies and Xenufens wasps of the family Trichogrammatidae. The adult Xenufens wasp is tiny: less than half a millimeter long. The gravid adult female attaches herself to the hindwing of a butterfly. If her host is a male, she will transfer to the female when he mates. Once the female Caligo lays her eggs, the wasp disembarks, and parasitizes them. Managers of banana plantations within the range of these Xenufens wasps have learned that spraying pesticides affects the wasps more profoundly than it does the caterpillars, and crop damage is far less severe where no pesticides are used.
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upper: A QUESTION OF TIMING--DOUBLE-CRESTED BASILISK & BLUE CALIGO (1993) acrylic 30" x 20"
middle: BAMBOO OWLET BUTTERLY (2005) acrylic 8" x 4"
lower: OPSIPHANES TAMARINDII (1995) acrylic 11" x 7"

3 Comments:

Anonymous Carl Buell (OGeorge) said...

Wonderful information Carel: the older I get it seems the more there is I know little about. The butterflies are exquisitely painted, but as an old commercial artist who painted too many frosty mugs in my early career, I especially appreciate your water droplets! ;-)

2:22 PM  
Blogger cpbvk said...

Thanks, Carl. Our fascinations are similar. You painted too many frosty mugs, I spent too many hours staring at them.

3:24 PM  
Anonymous Cindy said...

wonderful art, as always.. I would love to visit S. American forests to view not only the avifauna, but the many species of lepidoptera.. what a visual treat. Owlet butterflies would definitely be on my 'must see' list :)

11:46 AM  

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