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If you’ve ever made the mistake of squishing a stink bug, you know exactly how they earned that name. If you haven’t, might I suggest keeping it that way?

Stink bugs give off an awful smell when they’re attacked or squashed. It’s a defense mechanism… and a pretty powerful one. There are several species of stink bugs, which together make up the family Pentatomidae.

But the most common type is the brown marmorated stink bug, an otherwise banal, penny-sized insect that’s native to Asia, but has invaded all over the world. Some call them “shield bugs” because of their distinct trapezoidal shape. The hardened shell of their broad bodies acts as a defensive armor, protecting them from predators and the elements.

But their most recognizable defense is that unmistakable odor — something like a cross between cilantro and skunk. The smell comes from a waxy liquid that contains aldehydes, compounds that have a central carbon atom double-bonded to an oxygen and single-bonded to a hydrogen. They also tend to be very smelly.

A common one is formaldehyde, which is used for preserving tissues. If you’ve ever hung out in the back rooms of a museum or biology lab, you might be familiar with that particular stench. But aldehyde aromas can also be found in your kitchen, since they give some foods their smells — including, you guessed it, cilantro.

The aldehydes found in stink bugs are contained in specialized scent glands on the bottom side of the animals’ thorax, or middle body part. And they’re highly concentrated, so even a little bit causes a big stink very quickly. Some research suggests these aldehydes also have anti-fungal and antibacterial properties, so they may be helping stink bugs fight diseases at the same time.

But as anyone who’s been sprayed by a skunk can tell you, making a stink is a pretty good defense mechanism. So it’s not surprising that these bugs don’t seem to have many natural predators. That’s what allowed them to go global—and become a huge pest.

They’re known to eat more than a hundred types of plants, including valuable crops like apples, corn, and soybeans. In 2010, it was estimated that the mid-Atlantic states in the US lost about $37 million from damages to apples alone. So finding ways to control their population is important for agriculture.

But they’re not just bugging farmers. When colder weather rolls in, stink bugs look for a comfy place to over-winter—like your home. When one finds a cozy spot, it releases pheromones that encourage others to join it.

Other than offending your nose, stink bugs are pretty harmless to humans. But if you don’t want them to snuggle into your house for the winter, it’s best to keep your windows and doors sealed tight. If some get in anyway, whatever you do, just don’t squish them unless your nose is prepared!

Thanks for asking, and thanks as always to our patrons on Patreon. If you want to suggest questions like this for us to tackle, as well as gain access to a suite of awesome rewards, you can head over to Patreon.com/SciShow. [♪♩OUTRO].