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The San Diego Union-Tribune

Caterpillars remain mainly a mystery

Biologist studied, found many species


August 24, 2006

David L. Wagner was beating the bushes in a state park in Connecticut when a colleague walked over and presented for inspection a plump, milky-green creature.

The New York Times
A generator-powered light lured caterpillars to biologist David Wagner (center), during a sweep for new species in Connecticut. Wagner has discovered and described dozens of caterpillars new to science.
The caterpillar was not particularly rare, but Wagner set down his stick to greet an old friend. “Abbot's sphinx!” he called out. “One of our only talking insects.”

He trained his ever-present field magnifier on the bug's back, which sprouted a horn-shaped protuberance. After the next molt, Wagner said, “the horn turns into an eyelike button. If you touch the eye the caterpillar reels around and squeaks like a mouse. Scares the bejesus out of you, is what it does.”

Wagner went back to whacking at grass stalks with renewed vigor. “You don't need to go to the Amazon. You go out your back door with a hand lens and you'll find some pretty amazing things.”

In just the past year, Wagner has discovered and described a half-dozen species that had either never been observed in their caterpillar state or were new to science altogether. His book, “Caterpillars of Eastern North America” (Princeton University Press), is generally regarded as the most comprehensive field guide ever to caterpillars.

Tough to keep

“Caterpillars are the last unknown group of big things on the terrestrial world,” said Daniel H. Janzen, an ecologist at the University of Pennsylvania who has studied the caterpillars of Costa Rica for 25 years.

“In some place like Venezuela, you walk out into the forest, pick up a fruit, skull, butterfly or bird and it's got a name, and there is someone who can tell you what it is,” he said. “That's not true for caterpillars, the world around.”

There are several reasons. Few reference-quality collections of specimens exist, because dead caterpillars do not keep well. Scientists have tried pickling them in alcohol, or hollowing them out and blowing them up, but both techniques distort them badly.

And until recent advances in DNA science, the only way to identify a caterpillar positively was to rear it to adulthood, which requires careful husbandry. Most caterpillars shed their skins five or six times as they grow, and each stage can have radically different markings from the previous one.

“In order to do this well, you sort of had to know the entire universe,” said Wagner, who said that 5 percent to 10 percent of the caterpillars in his book had never before been studied through their entire life cycles.

Wagner said caterpillars deserved appreciation for their indirect benefits to the world. They are a dietary mainstay of beloved songbirds, and it is to defend themselves against caterpillars that plants have developed many of mankind's favorite chemical compounds, including nicotine, caffeine and tannins.

“When somebody tips back a glass of wine, they should be thanking caterpillars,” Wagner said. “You should be raising a toast.”

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