Science Questions

Why are so many dead bugs lying on their back?

Sat, 28th Apr 2012

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Mike Finley asked:

Seems very hard for a bug to flip itself over. Why would it waste it's last breath turning over? Or do healthy bugs that somehow get flipped over just die? Seems like a terrible design flaw in otherwise amazing creatures. Evolution should have fixed that!




Diana -   This is a bit of a mysterious one, because there's no actual research that has gone into looking at this statistically to prove if itís true.  What I think is happening is that when a bug dies, it gets a sort of rigor mortis, and either all of its legs on one side will fold up or it will suddenly get a spring in one side of its legs, and it will sort of flip it over onto its back.  And it also could be a question of whether or not itís more stable lying on its back because that's the heaviest part, and it might be the more natural side for it to lie once its legs are all folded up and no longer supporting its body weight.  And I have a very sad story to tell actually.  I used to have a pet budgie and one day, I came home from school and I found him lying on his back at the bottom of his cage.  But obviously, when he was dead, that was the way he was going to lie down because his legs could no longer support him and it would be unstable if he would be on his front so he ends up on his back.

Dave -   It could also be that quite a lot of bugs spend their time crawling up walls and things.  And so, when they die, they might fall off the wall and so, it could be that falling upside down is the stable way for it to fall through the air because the legs are going to act as tails, so it should fall through the air upside down and end up upside down on the ground.


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I think this is the most probable answer. Don_1, Wed, 2nd May 2012

I've seen dying flies spinning on their backs. 
That would indicate that at least for some of them, they flip over before death and rigor mortis.  Nor have they necessarily fallen off a window onto their backs. 

So, I think I'll go with a fundamental stability issue.

It would be easy enough to test.  Take a bucket of dead flies and dump them...
See how many land right side up, and how many land upside down. CliffordK, Wed, 2nd May 2012

It's a case of lowest potential energy. Geezer, Thu, 3rd May 2012

The last thing they are likely to do is try to pump air through their spiracles, which requires muscular contractions which would likely flip it over since the rest of them had already given up the ghost. grizelda, Thu, 3rd May 2012

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