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The Grand Animal Costume Party

Posted by Richard Conniff on October 26, 2013

Macrocilix maia: Mimicking  bird poop and two flies?

Macrocilix maia: Mimicking bird poop and two flies?

My latest, for The New York TImes:

IT’S every traveler’s little dream.

Early this year, Rohit George was staying at a hostel in the city of Shillong in northeastern India, when he encountered what appeared to be a large, hairy spider in the bathroom. Later, he spotted another one that seemed to perch on its orange legs atop someone’s laundry. O.K., every traveler’s little nightmare.

For Mr. George, though, it really was a dream, because the spider turned out to be a moth. Even better, it might just be a new species in the genus Siamusotima, which specializes in scaring the wits out of potential predators by imitating spiders. Those eight orange legs were actually just a pattern on its wings, an evolutionary byproduct of living forever among moth-eating predators.

Mr. George, who likes to photograph insects, posted his pictures on iNaturalist, a site where anyone can put up photos for experts to identify. (You can try it with whatever strange hairy things turn up in your bathroom.) Then he sat back as the kudos came rolling in.

The strategy of pretending to be something other than what you really are is of course common, and not just for humans. In my backyard in Connecticut, for instance, the caterpillar of the swallowtail butterfly Papilio troilus does a brilliant imitation of bird poop, to avoid being eaten by birds. Later in its development, it turns green and produces eyespots so it can pretend to be a snake.

This sort of trickery is called Batesian mimicry, and no, it’s not named after Norman Bates in “Psycho.” (Pretending to be something milder and more innocent than you really are? That’s Mertensian mimicry.) Mimicry in the natural world was first described in the 1860s by Henry Walter Bates, the great Amazonian naturalist. He saw what’s now known as Batesian mimicry in certain colorful butterflies, and the examples he provided became crucial supporting evidence for Charles Darwin’s theory of evolution by natural selection.

Bates knew that one group of butterflies should be easy targets for predators, because they fly by day, dawdling along la-lala-lala in plain sight. But he was also puzzled to notice that these butterflies dressed themselves up in flashy colors, as if to advertise their vulnerability. He eventually realized that those flashy colors matched the colors of another species in the neighborhood. And this model species turned out to taste so thoroughly repulsive that predators quickly learned to leave them alone. The mimics, on the other hand, tasted just fine. But their disguise tricked birds, lizards, dragonflies, robber flies and other predators into leaving them unmolested.

Masters of Batesian mimicry abound in the natural world. For instance, the mimic octopus (Thaumoctopus mimicus) can’t deliver a venomous bite or sting. But it changes its shape to mimic dangerous sea snakes and lionfish, which can. Aardwolves are harmless and solitary insect eaters on the African plains, but they wear the same stripes as their fierce pack-hunting neighbors, the hyenas, which might discourage predators. Cuckoos also put on stripes, more aggressively. They live by tricking other birds into rearing their young, and that means slipping an egg into its foster home undetected. So they mimic sparrow hawks to scare off the future foster parents. And meek little moths, beetles and hoverflies do an almost perfect imitation of common wasps.

Modes of disguise also tend to be repeated from place to place. If a disguise works in one place, it is highly probable that species elsewhere will have tried it, too. (Scientists call this convergent evolution.) Mr. George says there’s another bird poop mimic, a moth, near his home in Bangalore, India. (He recognized it only because he was puzzled one day to notice two exactly identical bird poops side by side on a leaf.) In Malaysia, a spectacular adult moth, Macrocilix maia, one-ups the poop mimics by mimicking bird poop on its body, and two flies feeding on the poop on its wings.

And in Costa Rica, metalmark moths in the genus Brenthia flare out their wings at a slight angle above the body to imitate jumping spiders. Looking at photographs, I don’t quite see the resemblance. But it works well enough, according to a 2006 study in the journal PLoS One, that predatory jumping spiders almost always leave them alone — and sometimes run away screaming into the night.

All this is just Batesian mimicry. We’re not even going to talk about Müllerian, Wasmannian or Bakerian mimicry. Or the kind of mimicry that happens only by sound or smell. Oh, and then there’s intersexual mimicry — that is, cross-dressing. (Good morning, Mr. Cuttlefish, love the skirt.)

The bottom line is that when folks head out to trick or treat this Halloween, even that Miley Cyrus costume will not rate as the strangest and scariest disguise in the neighborhood. A Ted Cruz costume, on the other hand, just might be a contender.


One Response to “The Grand Animal Costume Party”

  1. Some interesting discussion of mimicry and possible wishful thinking:

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