This Moth's Weird Inflatable Butt Is Going Viral, But It Has a Real Purpose

A Creatonotos gangis expanding its coremata, or "hair-pencils." Juan Manuel Sanchez on Flickr

A video from Indonesia is making the rounds on social media, and it shows a bizarre sight—a moth with long, pulsing tentacles coming out of his backside.

Speculations ran wild—is the moth infected by a parasite that is emerging? Are we looking at some sort of huge, weird penis? Maybe the video is simply CGI. As it turns out, none of those are correct. This moth is inflating his scent gland.

Creatonotos gangis is a species of moth that lives in Southeast Asia and parts of Australia. Most of the time it looks like a normal moth with white and black wings and a red or yellow body. It's in the Eribidae family of moths, which includes some of the largest moth species.

But when preparing to mate, four tubular, translucent scent glands, or coremata, inflate like balloon animals from his behind.

Some male moths and butterflies have these coremata, or "hair-pencils." They use them to expel pheromones to attract mates, and the hairs waft the smell toward the females. WIRED wrote a detailed analysis of these odd organs. You can also learn more about the weird body parts of moths and butterflies in this Powerpoint slideshow (PDF), complete with macro photos.

Comments on the video of C. gangis, which six days after posting has more than 200,000 shares, express fear and confusion at this strange creature's inflating organs which are each about the length of the rest of his body. The behavior is confusing and makes it look a bit like a sinister alien. But the animal is harmless, as long as you don't eat too many of them.

When C. gangis is just a caterpillar, before it has transformed into its mothy self, it eats plants with alkaloid chemicals. These plants evolved toxicity to discourage insects from eating them, but the caterpillars bit back evolutionarily—in fact, it's necessary for them to eat the toxic plants in order to grow these glands as moths. The more toxins they eat, the bigger their hair-pencils ultimately will be. These toxins also have the added benefit of making them taste terrible.

Similar images have gained internet popularity before. For example, this tiger moth, or Chionarctia nivea, is having his glands inflated by hand.

If you see an animal like this, don't kill him or be scared. He's just looking for a good time. Instead, upload the video to the internet.