A hawk moth caterpillar is pictured in a snake mimic defense display.
John Cancalosi/National Geographic Creative
Walking in her yard in Santa Fe, Argentina, one recent morning, Luján Eroles found what appeared to be a two-headed snake. At about four inches long, the creature greatly resembled a viper with a head at each end and one eerily blinking eye.
She took to Facebook asking for help identifying the creature and received thousands of responses.
When flipped over, the creature clearly displayed small legs underneath, and experts think it is really a type of hawk moth caterpillar. Some commenters and media outlets claimed the creature is an elephant hawk moth caterpillar, but the elephant hawk moth is only found in Europe, and the specimen in question was spotted in Argentina, meaning its particular species remains a mystery.
Though this specimen is likely not an elephant hawk moth, most hawk moth caterpillars are known to disguise themselves as snake-like creatures to appear dangerous and protect themselves from predators.
"Caterpillars are nature's hot dogs, with many other animals regarding them as a tasty snack," says Katy Prudic, an entomologist at the University of Arizona.
As caterpillars develop and get closer to becoming moths or butterflies, the metamorphosis process completely changes their body structure, and a large part of that involves putting on body fat, making them even tastier.
To avoid getting eaten during this stage of their lives, many caterpillar species put on multiple kinds of disguises. For instance, the giant swallowtail caterpillar mimics bird poop-right up to the smell.
The giant swallowtail (Papilio cresphontes) caterpillar disguises itself as bird poop, down to the smell. The orange protrusions are scent organs that give off a stench that wards off predators.
Frank & Joyce Burek/National Geographic Creative
The hawk moth's disguise capitalizes on most predators' natural proclivity to avoid anything snake-like.
Prudic describes the scenario from the bird's perspective:"You think you've got this tasty hot dog you're going to eat, but it turns around and puffs up its head to make it look more like a snake," she says. "What happens is, the predator will often drop the prey or run away."
So how does the hawk moth master the convincing blinking eye? It's all part of perfecting the disguise.
Known as an anal horn, the feature "becomes a posterior eyespot structure capable of rapid palpitation," according to a paper in the Journal of Natural History.
The spicebush swallowtail caterpillar displays mimic eye-spots to confuse predators.
Photograph by Darlene A. Murawski, National Geographic Creative
While snakes don't blink, it's possible this behavior helps the caterpillar mimic a "more generalized" eye, according to the paper.
The eyespot, combined with the defensive puffed head, made the hawk moth caterpillar in Eroles's courtyard look truly otherworldly.
"I had never seen anything like it," she told the Daily Mail. "It was just like a snake, and its eyes were so strange."
She was also worried it was poisonous, which was, after all, exactly the creature's goal.