The gaudy swirls of color on a butterfly's wing, the rococo curlicues on its riotously dressed caterpillars, may seem to be delightful examples of nature's artistry. But that is to miss nature's point.
Every feature of a butterfly or moth, throughout its life from egg to adult, has been shaped over millions of years of evolution for specific purposes. Salient among these is escape from predators like birds, monkeys, and the dreaded parasitic flies and wasps that lay their eggs inside the living caterpillar.
After nearly 30 years of studying these insects in the Guanacaste conservation area of Costa Rica, Daniel Janzen has become an adept translator of their body language.
In two recent books, "100 Caterpillars" and "100 Butterflies and Moths" (Harvard University Press, 2006 and 2007), he and Winifred Hallwachs, his colleague at the University of Pennsylvania, explain the meaning of the exotic colors and camouflage patterns. The full-page color photographs of each specimen were taken by Jeffrey C. Miller of Oregon State University.
The moth Calledema plusia never flies by day yet has learned how to imitate bright sunlight. A silvery gash on both sides of its brown wings, always folded over the body during daytime, mimics a shaft of light streaming through a dead leaf.
Many butterflies have gashes of iridescent color splashed across their wings. Why risk such a conspicuous display? The flashes of color accentuate the speed of flight. Their message to birds, Janzen suggests, is, "Don't even try to catch me."
Many butterfly and moth species try to pretend they are the least nutritious objects in the forest. This generally means imitating a piece of bird excrement if one is a caterpillar, and a dead leaf when one reaches adulthood.
Another variation is for a caterpillar to sport a disconcerting pattern like a giant eye that can be winked at an aggressor.
A moth on which evolution has lavished a remarkable degree of protective care is Oxytenis modestia. The first four stages of its caterpillar mimic a bird dropping, complete with mock seeds. The fifth caterpillar stage performs a brilliant impersonation of a green snake, complete with a bulging head and two menacing faux eyes.
As an adult, the Oxytenis moth resembles a leaf, but even here evolution's inventiveness is not an end. The moth breeds twice a year, and each form is different. The moths that hatch in the dry season are light beige, like dry, dead leaves, and those of the rainy season are dark, moldy looking.
Several butterflies practice a clever combination of camouflage and conspicuousness. Pieria helvetia has demure forewings and splashes of deep red on its hindwings. At rest, with its wings closed, it can hardly be seen. If disturbed by a predator, it darts into rapid flight, its red patches making it very visible. Then comes the disappearing act. It settles, folds its wings and is invisible again.
Why do birds and monkeys go to such lengths to consume these insects? The answer is simple. Moths taste "like raw shrimp," Janzen assures the reader.  
NYT News Service