March 15, 2001

2 min read

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Snake Study Supports Survival of the Mimics

By Kate Wong

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Image: DAVID PFENNIG

In 1862, a British naturalist named Henry Bates proposed that some harmless plants and animals evolve the appearance of deadly ones to protect themselves from predators. The Monarch butterfly, for example, is toxic to many birds, but the Viceroy butterfly¿a monarch imitator¿is harmless. Yet Bates never had proof for his idea. Now, nearly 140 years later, scientists have found strong support for Batesian mimicry. The new findings appear in today's issue of the journal Nature.

A key prediction of the mimicry theory is that when there is no dangerous "model" present, mimicry should fail to offer protection. To test that, David W. Pfennig of the University of North Carolina and his colleagues designed an experiment around deadly coral snakes and their harmless look-alikes, scarlet king snakes. The team built 1,200 life-size models of the two strikingly similar ringed snake species from plasticine and placed the copies both within the coral snake's natural range in the southeastern U.S. and north of it. If mimicry has shaped the appearance of the scarlet king snake (right), they reasoned, theory predicts that predators will more likely attack the king snakes in places where coral snakes are not found.

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The experimental data¿namely bite and scratch marks recorded on the plasticine by would-be predators¿bore this out. "Attacks were much more frequent on our ringed models in central North Carolina than they were in southern North Carolina and South Carolina, about 50 percent versus about 6 percent," Pfennig notes. "Various predators readily attacked our model scarlet king snakes, but only where no coral snakes lived." Comparable experiments in Arizona yielded the same findings.

"These are very exciting results," Pfennig says, "because they show how very strong natural selection is even in areas that are not so far away from each other."

Kate Wong is an award-winning science writer and senior editor for features at Scientific American, where she has focused on evolution, ecology, anthropology, archaeology, paleontology and animal behavior. She is fascinated by human origins, which she has covered for nearly 30 years. Recently she has become obsessed with birds. Her reporting has taken her to caves in France and Croatia that Neandertals once called home to the shores of Kenya’s Lake Turkana in search of the oldest stone tools in the world, as well as to Madagascar on an expedition to unearth ancient mammals and dinosaurs, the icy waters of Antarctica, where humpback whales feast on krill, and a “Big Day” race around the state of Connecticut to find as many bird species as possible in 24 hours. Wong is co-author, with Donald Johanson, of Lucy’s Legacy: The Quest for Human Origins. She holds a bachelor of science degree in biological anthropology and zoology from the University of Michigan. Follow her on Bluesky @katewong.bsky.social

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