This Insect Spits Poop-Smelling Chemicals into Predators' Mouths

Donald Hobern/Flickr. CC BY-NA-2.0

Insects make a tasty meal for many animals, even humans (they’re not half bad with a sprinkling of garlic). So how do they prevent themselves from swishing around in a hungry predator’s saliva before meeting their untimely demise? Bugs employ a variety of defense mechanisms, such as slashing attackers with a pair of sharp nippers (technically called mandibles), or violently shooting out a fiery hot mix of nasty chemicals from around the anus, like the triumphant bombardier beetle.

But it turns out there’s a novel mechanism on the scene, so far only known from one species. According to a new study, the shore earwig is not only a voracious predator, but a master of stench also. When chomped on by an attacker, it spits out a “fetid odor” that stinks of rotting flesh and feces. While the researchers can’t be certain, this could be the first documented case of an insect defending itself by mimicking the rank stench of poop or decaying corpses.

The discovery was made by a team of scientists, headed by John Byers from the U.S. Arid-Land Agricultural Research Center, after they noticed a rancid whiff coming from a female shore earwig (Labidura riparia) following experimental capture. After collecting and analyzing the compounds in the odor, the scientists discovered that it mainly consisted of two sulfur-containing chemicals: dimethyl disulfide and dimethyl trisulfide.

These compounds, which smell like carrion (dead flesh) and dung, are known to be released by a species of fungus (the aptly named stinkhorn) and by flowers that deliberately mimic the smell of flesh to attract insect pollinators. Since various animals are deterred by these smells, likely to avoid bacterial infections like salmonella, the researchers hypothesized that the creepy crawlies may be using these chemicals to deceive predators into believing they are unsuitable for eating.

To explore this idea further, the team collected a bunch of earwigs and put them into enclosures with anole lizards, which are assumed to be predators of these insects since they feed exclusively on bugs and inhabit the same area of the U.S. As soon as the lizards went for a cheeky nibble, the insects spurted out the offensive mix of chemicals from their mouths, causing the predator to immediately spit it out and fling it away with a swift head whip, Byers told National Geographic. They even tried to wipe off the gross taste.

What was also interesting was that it only took one offensive mouthful for the lizards to learn that these insects were not for eats. Even though the lizards were presented with more of the earwigs, they wouldn’t go for another bite during several weeks of study, despite happily gobbling down other prey. But the stinky discharge didn’t work every time, as a different predator, the harvester ant, didn’t seem bothered by it, forcing the earwigs to instead resort to their forceps. These findings have been published in The Science of Nature.

So did the creepy crawlies evolve this foul defensive strategy as a means to trick predators into believing they are dangerous to eat? Possibly not, earwig expert Tina Gasch told National Geographic, since many earwigs are known to release a variety of chemicals that are both irritating and toxic. The fact that their spit smells like decaying flesh could therefore be a coincidence, rather than mimicry. 

[Header image: Donald Hobern/Flickr]

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