Tarantula Or Caterpillar? The Incredible Camouflage Of The Monkey Slug Caterpillar

Mimicry is one of nature’s craftiest tricks. Whether it’s to avoid being eaten by posing as something venomous or making sure everyone gives you a wide berth by replicating a nasty predator, it's a technique employed by animals from all walks of life to stay alive by pretending to be someone else.

One such animal is the larval form of the hag moth, also known as the monkey slug caterpillar. The larva itself is not dangerous, feeding mostly on trees and shrubs, and despite widespread misconceptions, its hairs don’t sting (unlike this walking-toupee for a caterpillar). Take a glance at this caterpillar however, and you may feel threatened, as this clever organism has evolved to look like a giant hairy tarantula.

Pedants might note that the monkey slug is only sporting six hairy “arms”, which curl along the edge of its body. This gives the appearance of spider legs and – as we’re well aware – spiders actually have eight legs. You might be wondering why, then, an animal that looks just like a tarantula isn’t named after one. The "monkey" in their name refers to their dense brown fur. The “slug” is in reference to what you see when you flip the caterpillar belly side up. Here, you’ll find tiny legs that act like suction cups and do indeed look like a slug.

The strangely shaped and weird-looking animal unfortunately missed out on the ugly duckling effect, as after pupation it emerges as a hag moth. These winged insects aren’t much of an improvement aesthetically speaking, with slender bodies and dark brown fur that resemble a fluffy turd.

David Weiller, a wildlife photographer and videographer from France, was lucky enough to capture the amazing footage showing a monkey slug caterpillar doing its best tarantula impression in the video above. We caught up with him to find out more about these bizarre caterpillars.

Where and how did you spot this amazing caterpillar?

I spotted it one morning on the underside of a palm leaf in the Amazon rainforest at the Tamandua Ecological Reserve about 1 hour north of Puyo, Ecuador. I immediately recognized it as I spotted another one (greying color) 4 years before in another area of Ecuador. What amazed me was its beautiful bright color and that all the 'arms' were intact, meaning that it must have shed its skin the night before.

What can you tell us about monkey slug caterpillars?
It is fascinating to know that with its bright colors and odd shape, it is probably mimicking either a tarantula spider or the shed skin of a wild hairy spider or dead leaf debris. Like all limacodids, the underside looks like a slug with suction cups in place of the prolegs. Thanks to these 'suckers' the caterpillar can glide using a slug-like locomotion. The caterpillar is actually covered with dense brown setae which looks like hair or fur (thus the common name monkey slug). The extra "arm" protrusions can fall off without harming the caterpillar which is useful as an extra protection in case a predator tries to catch it. Despite looking very hairy, I read that it is not poisonous and doesn't sting, but it's still better not to poke it.