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Why This Harmless Caterpillar Disguises Itself as a Venomous Snake

A convincing disguise transforms the hawk moth caterpillar into a small snake to ward off potential predators.

When facing a potential threat, the hawk moth caterpillar takes the form of a pit viper.

If it was a snake, it would have bitten them. But luckily, it was only a caterpillar.

Filipe DeAndrade, a filmmaker and host of National Geographic Wild's Untamed, has seen it all. He lived out of a repurposed ambulance for months during filming for the first season of the wildlife series, and he's gotten within arm's reach of lions in South Africa, stalked turtle hatchlings in Florida, and had multiple close encounters with crocodiles during filming. But it took a caterpillar to knock the passionate filmmaker off his feet. (Related: get a behind-the-scenes look at the groundbreaking series)

After spending a day filming sharks, humpback whales, dolphins, manta rays, and "charismatic megafauna" in Costa Rica's Osa Peninsula for the show's upcoming second season, DeAndrade ventured out into the surrounding rainforest on a moonlight tour led by biologist Tracie "the Bug Lady" Stice. After an hour of watching Brazilian wandering spiders, coatis, and snakes, Stice and another guide dropped off the other guests. Then, they took DeAndrade and his filming partner McKenzie Barney to see a hawk moth.

A Stubby, Two-Headed Snake? Guess Again!

Specifically, they were on the hunt for a green morph of a hawk moth caterpillar that Stice had spotted previously. When startled, these crawlers can instantaneously transform into snake-like creatures, puffing out the front part of their bodies to rearrange their hidden yellow, white, and black spots. The look is complete with eye-like spots, faux reptilian scales, and a convincing, serpentine curve.

After a 10-minute walk from the nearby ecolodge where DeAndrade was staying, the group found the caterpillar attached to a leaf. As the crew members got closer to film it in 6K with their Hollywood-grade RED digital camera, the bug flared up and transformed into a "snake."

"The first time I saw it, I was in complete and utter disbelief," DeAndrade says. The sight of the bug sent him laughing and crying at the same time. When he got a little too close, the snake-like caterpillar felt his breath and jabbed at the air—the surprising, but harmless, strike sent DeAndrade reeling back.

The tour guides let the crew film the caterpillar for 15 minutes before escorting them away. In the clip, you can see the caterpillar munch a leaf, hang from foliage and—as DeAndrade is excited to say—excrete.

"That was awesome," he says.

Camouflaged Colors

DeAndrade and his team have filmed 30 animals in somewhat controlled environments in preparation for the new season of Untamed, which celebrates Costa Rica's diverse wildlife species. As one of the most biodiverse countries in the world, Costa Rica is home to more than 500,000 species, making up nearly four percent of species worldwide.

Untamed: To Escape Danger, The Helmeted Iguana Runs on Two Legs If playing dead doesn't work in the face of danger, helmeted iguanas run away from predators on their hind legs.

Hawk moth caterpillars, like the Hemeroplanes triptolemus in this clip, are critically rare. A hawk moth caterpillar can live for 10 to 30 days, and it only spends a few days of that molting, which is the small window in which it can appear snake-like, DeAndrade says. (Related: "'Two-Headed Snake' Shocks Homeowner")

"Not only is it rare to find the caterpillar, but you also have to hit it at the right time," he says. "I just so happened to be there at the right place at the right time."

H. triptolemus can only be found in Guatemala, Belize, and Costa Rica, where its natural pattern of greens and browns provides the perfect camouflage for blending in with rainforest flora. Mimicking the appearance of a snake by retracting its legs and expanding its anterior body segments helps the caterpillar ward off predators.

Impersonating intimidating or unappetizing animals is one of many camouflage techniques that both predator and prey species use to survive. Other species use concealing coloration to blend in with their background, like arctic foxes and polar bears in snowy landscapes. Some animals, like zebras, tigers, and leopards, employ disruptive coloration to make it hard for others to see the outline of their bodies. Others, still, disguise themselves to blend in with their surroundings in shape and texture rather than color.

The mimicry technique the hawk moth caterpillar uses can fool birds or other hungry caterpillars that might otherwise eat it. Evidently, this disguise can fool humans, too, and the bug's serpentine strike can feel lifelike and threatening.

"That is the majesty of nature," DeAndrade says. "You never know what the hell you're going to run into and how you're going to organically react to something and how that's going to shift how you think about the natural way of life. A [freaking] caterpillar blew my mind more than anything else."