[ intro ].

You might notice something odd about those flies you just swatted, or the cockroaches you nuked with insecticide. It seems like they almost always wind up on their backs.

And that’s not your imagination. Dead bugs really do end up belly up quite often thanks to a combination of physics and biology. If you think about the shape of your typical insect, like a cockroach or fly, it’s rounded with fairly thin legs relative to its body.

That means most of its body weight is concentrated near the top of its body, so it has a high center of mass. That’s the point of an object where external forces like gravity appear to act. And the higher it is, the less tilt is required before it’s no longer over the object’s base—at which point the object, or insect in this case, topples.

In fact, many bugs would just tip over if it weren’t for the constant work of their teeny leg muscles—they’re pretty much always doing a push up to stay upright. Sure, a bug will occasionally stumble onto its back or purposely roll over as a defense mechanism. But whenever it finds itself in a supine position, it can right itself with a little coordinated leg or wing action.

There’s even one family of insects called click beetles that launch themselves into a somersault to land right way up. But that all kind of falls apart when an insect is injured or sick because it loses the ability to perform complex muscular movements. I mean, just picture trying to do a cartwheel when you’ve got the flu or a broken arm.

And any weakness in those leg muscles and they’ll naturally curl inwards, a bit like how your fingers curl when you rest your hand. Curled legs can’t support that top-heavy body. The chemicals used to kill bugs also usually mess with their nervous system directly.

Insecticides generally contain neurotoxins, like organophosphates or pyrethroids, which cause convulsions or paralysis in insects by over-stimulating or inhibiting their neuronal signals. Either way, the loss of muscular coordination combined with a high center of mass means the animal probably ends up on its back before it dies. In fact, if you see a bug on its back, it’s likely not long for this world.

In a 2002 study on Mediterranean fruit flies, researchers found that as flies aged, they were more likely to go belly up temporarily—and when that happened, their chances of dying jumped by close to 40 percent. Bugs pretty much never choose to be supine unless they’re playing dead, so their inability to get up quickly is probably an indicator that something is wrong. Thanks to our patron Carol for asking, and to all our other patrons that voted for this question in our Patreon poll.

If you want to suggest questions like this one, vote on which questions we should answer, or just get some really cool rewards like exclusive blooper reels, you can head over to Patreon.com/SciShow to learn more about becoming one of our patrons. [ outro ].