Why the Animal Kingdom Is Full of Con Artists

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.

Lixing Sun relates an abbreviated version of Bates’s story in his new book, “The Liars of Nature and the Nature of Liars” (Princeton). Sun, a professor of animal behavior and biology at Central Washington University, is, like Bates, fascinated by fraud. It can be found, he says, at all levels of “the biological hierarchy, from the most complex organisms to the least sophisticated.” And this is all for the best. Cheating is a driving force in the history of life—“a powerful catalyst for the creation of diversity, complexity, and even beauty.”

Sun devotes the first half of his book to a sort of biological “FBI: Most Wanted.” One of the slyest, or at least most studied, of nature’s scam artists is the Alcon blue, a lovely, silvery butterfly native to Europe and Central Asia. Female Alcon blues lay their eggs on gentians. The caterpillars that emerge feed on the plants until they have completed three molts. Then, as what is known as fourth instars, they drop to the ground and wait for a passing ant.

To identify their kin, ants rely on chemicals called cuticular hydrocarbons. Alcon-blue caterpillars secrete chemicals that are similar enough that ants are tricked into carrying them home. Once inside the nest, the butterfly larvae are nurtured by their formic friends, who feed them as if they were their own. Research by British and Italian scientists shows that the caterpillars employ an additional ruse. They vibrate to produce a sound that ants normally associate with their queen. Alcon-blue butterflies can be such convincing cons that ants will neglect their own larvae to care for them.

Many species employ similar tactics, a practice known as brood parasitism or, depending on the details, kleptoparasitism. In the insect world, these include cuckoo bees, cuckoo bumblebees, and cuckoo wasps. Among birds, several species of cuckoo, several species of cowbird, some finches, and even some ducks slip their eggs into other birds’ nests. Not infrequently, the interlopers go so far as to kill off their adoptive siblings. The chicks of the greater honeyguide, a brood parasite native to Africa, have special barbs at the end of their beaks just so they can murder their nest mates.

As parenting strategies go, brood parasitism is ugly. Clearly, it is also effective: it has evolved independently many times, in several different orders. Sun, for his part, refuses to cast aspersions. “Evolution is not a Socratic philosopher,” he writes.

Another grift common in nature is aggressive mimicry, which is pretty much Batesian mimicry in reverse. Instead of masquerading as a dangerous creature, an aggressive mimic poses as one that’s benign. The Australian death adder spends most of its days hidden in leaf litter, often with only the tip of its tail exposed. It wiggles the tip in a movement that looks just like the writhing of a worm. When an unsuspecting lizard takes the bait, the death adder strikes. (As its name suggests, the death adder is one of the world’s most venomous reptiles.)

“It’s funny how people suddenly come out of the woodwork when they know you’re taken.”

Cartoon by Suerynn Lee

The bluestriped fangblenny is a color-shifting fish that lives in the Indian and Pacific Oceans. Fangblennies hang out around so-called cleaner fish; the latter make their living eating parasites and other types of gunk that build up on the scales of larger fish. The relationship between cleaners and their “clients” is mutually beneficial: the smaller fish get a meal; the larger get rid of a nuisance. Young fangblennies assume the coloration of a cleaner fish; then, once a client draws near, the fangblennies remove not gunk but a chunk of the fish’s flesh. As Martin Stevens, an ecologist at the University of Exeter and the author of “Cheats and Deceits” (2016), points out, “Fangblennies are not only costly to the fish they attack, but also to the real cleaner fish.” Client fish naturally grow wary once they’ve been bitten. Sun compares fangblennies, not unadmiringly, it seems, to “gangsters running a racket.”

Sun is given to punchy pronouncements. There are, he claims, two “laws” of cheating in the animal kingdom, by which he appears to mean two basic methods of deception. In one, an animal exploits another animal’s cognitive weaknesses. Batesian mimicry falls into this category: the strategy works because potential predators either can’t see well enough or lack the wherewithal to distinguish a poisonous butterfly from its double. Brood parasites, too, take advantage of their victims’ cognitive limitations. Birds, it turns out, have poor egg-recognition skills—in some cases, almost comically poor. In one of a series of famous experiments, the Dutch animal-behavior expert Niko Tinbergen showed that a greylag goose, when faced with a choice between rescuing its own egg and rescuing a volleyball, would pick the ball. “To exploit the cognitive loopholes of another species, you only need a good enough disguise to fool your target,” Sun observes. “Often a very crude mimic will suffice.”

The other way that animals cheat, in Sun’s schema, is by issuing false information, or, more plainly, by lying. Many animals (and even plants) communicate with one another; this is often a critical survival skill. But the possibility of communication inevitably opens up the possibility of miscommunication. Crows, for example, issue alarm calls to alert other crows to potential danger. Conniving corvids, according to Sun, “cry wolf” to scare their neighbors from food. Formosan squirrels also issue alarm calls: during mating season, sneaky males squeak out alarms to distract competitors.

Sex, Sun observes, is fertile ground for deception. Male fireflies from the genus Photinus flash to attract mates. If females are interested, they flash back. Females from the genus Photuris mimic Photinus females’ flashes; then, when males get close enough, they eat them. (Photuris females have become known as the firefly “femmes fatales.”) Some male garter snakes emit faux female pheromones; by confusing their rivals, they increase their chances of scoring.

Blister beetles belonging to the species Meloe franciscanus, in the American West, practice an elaborate, sex-dependent form of kleptoparasitism. Newly hatched Meloe franciscanus larvae hang out together in clumps and collectively emit chemicals that attract male bees. When a male tries to mate with the clump, the larvae attach themselves to his back with special hooks on their feet. If the male is later lucky enough to find an actual mate, the larvae relocate to her back, hitch a ride to her nest, consume the pollen she has gathered, and, for good measure, eat her young.

Frauds like those perpetrated by femme-fatale fireflies and kleptoparasitic beetles obviously take a heavy toll on their victims. This is precisely why, Sun contends, deception is such a powerful evolutionary force. The cheated are under heavy selective pressure to outwit the cheaters, who then come under heavy pressure to refine their techniques. The choice is innovate or die.

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