Deep in the Peruvian Amazon, an odd-looking caterpillar is doing its best to look like just another rain forest twig. But its four long tentacles are coiled, ready to respond to the first sign of danger.

Suddenly, a group of people approaches. Sensing vibrations from the group's voices, the caterpillar unleashes its defenses. Boing! The four tentacles sprung outward like a jungly jack-in-the-box before recoiling.

"It was super bizarre," says Aaron Pomerantz, an entomologist with the ecotourism company Rainforest Expeditions, who found the caterpillar about 100 feet (30 meters) up a tree near the Tambopata Research Center in southeastern Peru.

"All of a sudden there was this little thing that went 'bloop' when I called out to a couple of people in my group," who were climbing to a canopy tower, says Pomerantz. (Read his blog post on the caterpillar encounter.)

Pomerantz was so amused by the creature's response that he recorded what could be the first video showing the spectacular tentacular display.

"I've never seen anything like the behavior exhibited by the caterpillar," says Jason Weintraub, collection manager at Drexel University's Academy of Natural Sciences, when shown the video.

Keeping an "Ear" Out

Pomerantz and other entomologists suspect the caterpillar could be a species in the genus Nematocampa, which belongs to the family of Geometrid moths. Geometridae are found throughout the Americas, and their caterpillars are known to sport peculiar projections.

But determining exactly what the creature is requires rearing it to adulthood or sequencing its DNA, says Andy Warren, senior collections manager at the Florida Museum of Natural History.

"Immature stages of South American moths remain pretty unknown," Warren says. "But this one is extremely similar to the larvae from the North American species [Nematocampa resistaria]."

As for the weird tentacle action? Scientists' best guess is the erupting tentacles are used for defense—though how it deters predators or parasites, and which ones it's combating, are unknown.

"It is fascinating defensive behavior," adds Weintraub, who specializes in the Geometridae. "But I can't begin to speculate as to what potential predator or parasitoid might be deterred by this apparent defensive response." (Also see "Watch: Bird Mimics Caterpillar [and Other Animal Imposters].")

One possibility is that the tentacles' white tips direct attention away from the main body of the caterpillar, says Andrei Sourakov, collections coordinator at the Florida Museum of Natural History. He has observed something similar in adult hairstreak butterflies.

He and others suspect the caterpillar detects approaching dangers using a set of vibration-sensitive hairs at the tips of its tentacles.

"The video of this Peruvian caterpillar confirms the supposition that these caterpillars can 'hear'—probably thanks to sensory organs located on these tentacles," says Sourakov, who's looked at these types of projections in caterpillars.

Jungle Oddities

The truth is, not much is known about the caterpillar or its behavior—let alone how many other caterpillars might be similarly spring-loaded.

"South America is so vast and there's just a gazillion moths down there that I wouldn't be surprised if there's other neat things like this going on," Warren says. (See "The Caterpillar Defense.")

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Pomerantz, who scours the jungle for curious critters like this one, has come across plenty.

So far, the forests around the research center have yielded a variety of oddities, including spiders that build spider-shaped decoys in their webs, still-mysterious silken structures, and colorful caterpillars that look like an improved version of Donald Trump's toupee.