Beasts That Bluff

Whether to ward off predators or to exploit their victims, creatures can gain advantage by posing as different creatures. Illustration by Lou Benesch

When Elizabeth Kolbert reviews a book we know that at least the review is a must-read:

Why the Animal Kingdom Is Full of Con Artists

Some crows “cry wolf” to snatch food from their neighbors; some caterpillars trick ants into treating them like queens. What can we learn from beasts that bluff?

On April 20, 1848, Alfred Russel Wallace and Henry Walter Bates set off for the Amazon on a boat named Mischief. The two young men—Bates was twenty-three, Wallace twenty-five—had met a few years earlier, probably at a library in Leicester, in England’s East Midlands. Both were passionate naturalists, and both were strapped for cash. (Neither had been able to afford university.) To finance their adventures, they planned to ship specimens back to London, where they could be sold to wealthy collectors.

For reasons that no one has ever been able to explain—but that many have speculated about—Wallace and Bates separated soon after they reached Brazil. In the decade that followed, Wallace amassed an immense trove of new species; lost most of them in a ship fire; set off again, for Southeast Asia; and, with Charles Darwin, discovered natural selection.

Bates, meanwhile, remained in Brazil. He sailed up the Tapajós, an Amazon tributary, and then up the Cupari, a tributary of the Tapajós. Travel in the region was often agonizingly slow; to get from the town of Óbidos to Manaus, a journey of less than four hundred miles, took him nine weeks. (At some point during the trip, he was robbed of most of the money he was carrying.) Bates would find a congenial town and spend months, even years, there, making daily forays into the surrounding rain forest. He tromped around in a checked shirt and denim pants, an outfit considered outré by the British merchants he encountered in Brazil, who wore their top hats rain or shine.

As a collector, Bates was primarily interested in insects, of which there seemed to be a nearly limitless variety. Just in the area around Tefé, a town a few hundred miles upriver of Manaus, he discovered three thousand species of beetle. Bates would rise with the sun, spend five or six hours in the field, and then work until dark preparing and labelling what he had caught. He kept meticulous records—notebooks filled with descriptions of the animals’ body type, preferred habitat, and behavior, often accompanied by delicate watercolor drawings.

Assessing his specimens, Bates came to notice something curious. Some of the butterflies he had netted, which had appeared more or less identical while flitting through the forest, turned out, when pinned and examined closely, to belong to entirely different families. This was the case not just with one pair of lookalikes but with several. Careful study of the doppelgängers revealed an intriguing pattern. Members of one species in the pair usually gave off a strange odor; Bates surmised that these butterflies were probably unpalatable.

By the time Bates returned to England, in the summer of 1859, both Wallace and Darwin had published their earliest papers on evolution. Bates was an instant convert. The new theory allowed him to explain what he had seen. The impostor species, he decided, had, under the pressure of natural selection, evolved to look like the noxious ones. In this way, the nontoxic butterflies gained protection from predators.

Bates laid out his ideas in a paper that he delivered to the Linnean Society, in London. Though the officers of the society weren’t especially interested in the phenomenon he described, Darwin immediately recognized its significance. “I cordially congratulate you on your first great work,” he wrote to Bates in 1862. The imitation of a harmful species by a harmless one has since become known as Batesian mimicry.