Nature's Tricks Help Moths Say 'Don't Eat Me' In Many Ways
By NICHOLAS WADE
Published: May 29, 2007
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.
People arrived far too recently on the evolutionary scene for moths and butterflies to have anything to say to them. But 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, Dr. Janzen suggests, is, ''Don't even try to catch me.''
Other bold color patterns, however elegant they may seem to people, are just toxic warning labels, real but often feigned, to would-be consumers.
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, to resemble dry dead leaves, and those of the rainy season are dark and 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, quickly folds its wings and is invisible again.
Why do birds and monkeys go to such lengths to consume these insects, stimulating such a rich array of evolutionary strategies to evade capture? The answer is simple. Moths taste ''like raw shrimp, if one should care to try,'' Dr. Janzen assures the reader.
Photos: DISGUISES -- The mechanisms for warding off predators include a pattern on Z. ellops mimicking a dead leaf, below, and, clockwise from top center, dark coloring that allows the H. amphinome to blend in to tree bark; a resemblance, during caterpillar stages, to a bird dropping in O. modestia; silver stripes on the C. plusia that look like sunlight streaming through a dead leaf; and the release of a bitter yellow fluid by the H. icasia, if bothered. (Photographs by Jeffrey C. Miller/From ''100 Butterflies and Moths'')