When we grow tired of the lies and fakery of human life, we often turn to the natural world for all that is honest and true. “What strength belongs to every plant and animal in nature,” Ralph Waldo Emerson once exulted. “The tree or the brook has no duplicity, no pretentiousness, no show. It is, with all its might and main, what it is.”
A lovely sentiment to be sure, but the natural world is in fact overrun with fakes, liars, imitators, and con artists, of almost every color and description. There are beetles that pretend to be wasps, aardwolves that pretend to be hyenas, caterpillars that pretend to be bird poop (the better not to be eaten by birds), and a night-flying bird, the pootoo, that pretends to be a broken tree branch by day, so it can sleep in peace.
The natural world can seem at times like a grand charade, and with apologies to Mr. Emerson, there might just as well be a blinking neon sign at the entrance saying “Duplicity 'R' Us.” For a naturalist, this is a large part of the fun—and as two new studies demonstrate this week, an enduring subject of fascination. For the animals, it is a matter of life and death.
The first study, published in Behavioral Ecology and Sociobiology, looks at timid jumping spiders in the Philippines, which, contrary to what we might expect, like to make their nests near Asian weaver ants. These ants are fierce predators of, among other things, jumping spiders. So why hang out in their neighborhood? According to coauthors Ximena J. Nelson and Robert R. Jackson of the University of Canterbury in Christchurch, New Zealand, it’s because the jumping spiders have a much nastier hobgoblin to fret about.
The predatory spitting spider also likes to eat jumping spiders. It catches them, as its name suggests, by spitting sticky gum from its fangs and gluing its victim to the nearest surface. Then, with the leisurely deliberation of the television serial killer Dexter, it wraps its victim in silk and injects it with venom.
It turns out, though, that predatory spitting spiders hate the smell of Asian weaver ants. So the jumping spiders gain a measure of protection not just by making their homes near these ants but by taking on their smell and pretending to be them. Yes, they still have to deal with the annoying problem of living surrounded by killer ants—so the jumping spiders build their nests out of a dense, tough weave, to make them ant-proof. At the entrance holes, they rig hinged flaps of silk, like swinging doors, to slap shut again when a spider darts in or out, so no ants can enter.
The idea of deception and mimicry in nature got started in the 1860s, when Henry Walter Bates, a British naturalist in South America, noticed something peculiar. He was puzzled to observe that certain butterfly species show off with bright colors and yet manage not to get eaten by birds or other predators. Eventually, Bates figured out that they were mimicking the colors of another nearby butterfly species, which predators leave alone because they taste so bad.
The bright coloration of the model species is an honest signal, benefiting both the potential prey by keeping it unmolested and the would-be predator by sparing it from digestive woe. But the copycat strategy—harmless species borrowing the color or smell and thus the protected status of more dangerous or repulsive species—works too, and this form of dishonest signaling is widespread in the animal world. It’s now called Batesian mimicry.
The second study, published in the journal PLOS One, asks how these little miracles of deception could have evolved in the first place. If the starting strategy for a species is to hide itself from predators, how does it make the leap to life in full, flaming color? “How did these imitators get past that tricky middle ground, where they can be easily seen but they don't quite resemble colorful toxic prey? And why take the risk?" asks lead author Kenna D.S. Lehmann, a graduate student at Michigan State University.
She and her coauthors started from scratch, building a digital world in which each of their sim-species had to develop its own way of life, learning how to prey and how to avoid predators. Then they introduced a species that was poisonous and said so with an honest signal. Other studies in the real world have shown that a powerful poison can support the development of multiple copycat species. But they don’t all get it right from the start. The PLOS One study showed that a powerful poison in the model species can be enough of a deterrent to make predators take notice and steer clear of these imperfect mimics. “Even if they managed to look like a poisonous prey just 25 percent of the time, they still got protection,” says Lehmann. That means making small, incremental steps from camouflaged wallflower to colorful con artist could have been a workable evolutionary strategy.
It was like witnessing the birth of fraud.