It seems as if every time the scientists from Peru's Tambopata Research Institute set off into the Amazon they discover something new. This time, it's a caterpillar that entomologist Aaron Pomerantz describes as the "craziest" caterpillar that he's ever seen. When you yell at it, its tentacles fire off in all directions, retracting as quickly as they explode.

He explains that after noticing the odd behaviour, he and his colleagues "proceeded to take turns yelling at it and filming its contorting reactions for over an hour." If you ever wanted to know what field research looks like, think of a group of biologists yelling at a caterpillar for an hour in the heat of the day.

After poking through the scientific literature, Pomerantz determined that the critters belong to the Nematocampa genus of moths, also referred to as "horned spanworms," or appropriately, "filament bearers." They range from North America south to the Neotropics. The caterpillars extend their tentacles by forcing hemolymph – the insect version of blood – into them, causing them to become erect. 

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But what nobody seems to know is where the peculiar behaviour comes from, though there are lots of ideas. It could be a form of camouflage; the movement of the tentacles might make the caterpillar look as if it's just a plant blowing in the wind.

It could also be an attempt to avoid being gobbled up by a predator. If there's a hungry bird looking for a tasty snack, the caterpillar might push out its filaments as a distraction, luring the bird towards the tentacle and away from the main part of its body – think of the way a lizard drops its tail to escape predation.

Or, it could be that the hairs on the end of the tentacles work as makeshift ears, allowing the caterpillars to detect vibrations in the air that herald the arrival of predatory insects or birds nearby.

For now, this is yet another jungle mystery, just waiting for a researcher to take a closer look.