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First, a major qualifier here; by naturally, I mean not forced to die on its "stomach" (like by being stepped on). Secondly, I live in the U.S., so maybe this applies to only American roaches.

Literally every time I remember having seen a dead roach I did not kill or that wasn't squashed, it was lying on its back. I have looked on the internet, and I only found one decent answer to this question saying that they do not have this tendency. Considering the sheer magnitude of times I have noticed the contrary—inside, outside, in many different geographic locations—I do not believe that answer. I have asked other people, and they have noticed the same thing.

  • This answer does not contain any notable claim, see Welcome to New Users . It might have been better to quote articles claiming this not to be the case. – David Mulder Jun 14 '14 at 22:35
  • Thank you. When I looked on the internet, I saw other people had asked the same question. Some of the questions on here seem to be about bringing conclusions to long-believed rumors or myths. I thought "roaches dying on their backs" would fit here. To be honest, your answer seems to indicate it is notable, considering it has been discussed by experts even. – Just Some Old Man Jun 14 '14 at 22:43
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    As observed by @HappySpoon, this is covered by Biology.SE – Oddthinking Jun 15 '14 at 2:14
  • Thank you for the link. Though, I have seen far too many roaches whose cause of death was not insecticide end up on their backs. – Just Some Old Man Jun 15 '14 at 6:49
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    Next time you happen on a dead roach, try dropping/flipping/throwing it from a height n times. Count the number of times it lands on its back. This could help confirm the 'aerodynamics' hypothesis. – Benjol Jun 16 '14 at 11:15
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It's hard to find reputable sources on this issue, but let me present the two different takes on it that I found. According to this article:

Cockroaches, apparently, have bulky bodies (composing of 3 heavy body segments) which are only supported by 6 long thin legs, As they die, they lose muscle-control causing the leg muscles to contract. As a result, the legs are forced to be pulled beneath the body causing them to lose their balance, and topple over. This also explains why cockroaches on the wall fall off when they were crawling on the wall and got sprayed with insecticides.

Is flipping over always the case?

No. There is still a possibility for a cockroach to die without toppling over. However, it is inherent upon these insects to involuntary experience muscle contraction and end up lying on their back upon dying.

On the other hand, this article addressing specifically this question takes a slightly different take on the issue (point 3 is similar to the previous article):

I've been discussing the subject with the crack bug scientists at some of the nation's leading institutions of higher learning, and we've formulated the following Roach Mortality Scenarios, which represent a major step forward in our understanding of roach postmortem positioning:

(1) Roach has heart attack while crawling on the wall. OK, so maybe roaches don't have heart attacks. Just suppose the roach croaks somehow and tumbles earthward. The aerodynamics of the roach corpse (smooth on the back, or wing side; irregular on the front, or leg side) are such that the critter will tend to land on its back. Or so goes the theory. Admittedly the study of bug airfoil characteristics is not as advanced as it might be.

(2) Roach desiccates, i.e., dries out, after the manner of Gloria Vanderbilt. This is what happens when you use Cecil's Guaranteed Roach Assassination Technique, described elsewhere in this archive. The roach saunters carelessly through the lethal borax crystals, causing him to lose precious bodily fluids and eventually die. Since this process is gradual, it may happen that the roach simply conks out and dies on its belly.

(3) Roach dies after ingesting potent neurotoxins, e.g., Diet Coke, some traditional bug poison like pyrethrum, or the food served at USC cafeterias. Neurotoxins cause the roach to twitch itself to death, in the course of which it will frequently kick over on its back, there to flail helplessly until the end comes. No doubt this accounts for the supine position of the deceased cockroaches you observed.

I found no serious articles claiming this to be simply not the cases.

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    Well, it's a nicely written answer and the claims look reasonable, but the sources are hardly authoritative. And besides, its not clear to me that USC cafeteria food really has any advantage over other institutional food as a roach poison. – dmckee --- ex-moderator kitten Jun 15 '14 at 1:27
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    @dmckee: I wholeheartedly agree and if you can find actual research on roach postmortem positioning I would love to hear about it. These were two of the more serious articles I found addressing this issue. And regarding the USC food, check the Q&A format in the actual article and you will understand. – David Mulder Jun 15 '14 at 1:38
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    @AndrewGrimm, I think if you read all the way to the end of that sentence you'll get a second clue :) – Benjol Jun 16 '14 at 11:14
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I think the answer is really in the physics of the cockroach, or other insect bodies.

When the insect dies, rigor mortis sets in. Since the flexor muscles are almost always larger than the extensor muscles, the contraction causes the legs to bend inwards into the crossed position. The bug pulled into a cylindrical shape by rigor is now unstable, and is pulled by gravity to roll over to lie on its back as that's the most stable position, and it is the point where the center of gravity is lowest to the ground.

So, the answer is that roaches don't naturally die on their backs, but end up there after death. Death by insecticide may be a different issue.

http://www.ibtimes.com/why-do-insects-cross-their-legs-when-they-die-434286

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