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This question has always mystified me since young. For beetles, I can reason that they flip over because they have a higher centre of gravity causing them to be in unstable equilibrium when they tuck in their legs when they are about to die. For cockroaches with a lower profile, I would expect them to stay upright. But why do they flip over? Is it more comfortable for them to die this way or is there a scientific explanation for this?

image for reference

Edit:

As noted in some of the comments below, this is a general observation based on cockroaches being killed by insecticide. I haven't got the chance to observe (or notice) cockroaches that die in other ways and therefore do not want to limit the scope of my question to just insecticide poisoning.

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  • $\begingroup$ Do they flip over? I’ve always considered that to be just a comic representation. Maybe it’s just easier to spot dead cockroaches which have flipped over, since the others aren’t easily distinguishable from live ones? … $\endgroup$
    – Konrad Rudolph
    Commented Aug 22, 2012 at 9:07
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    $\begingroup$ That's a picture of some cockroaches on their backs. There's no way for the viewer to know whether they died that way, or (as it seems) were arranged that way. $\endgroup$
    – Rik Smith-Unna
    Commented Aug 22, 2012 at 11:17
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    $\begingroup$ I agree, I was just pointing out the the picture doesn't demonstrate anything. The reason, if I remember rightly, is that most cockroach control agents are neurotoxins which cause the legs to spasm, so they get flipped onto their backs. $\endgroup$
    – Rik Smith-Unna
    Commented Aug 22, 2012 at 13:24
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    $\begingroup$ Yesterday I found ~200 dead chinese stink bugs on my hallway carpet(I assume they crowded the light and someone sprayed them with insecticide) and spent some time cleaning that up, having an opportunity to observe A LOT of dead bugs. A lot of them were indeed on their backs, which puzzled me. It might be of interest to clarify your question with the cause of death. Is it natural death of "old age" or due to poison bait /insecticides? $\endgroup$
    – Alex Stone
    Commented Aug 27, 2012 at 23:09
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    $\begingroup$ Flying insects land on their back when they fall since it's heavier. Stands to reason whether that applies to cockroaches. $\endgroup$
    – Armatus
    Commented Sep 25, 2012 at 15:46

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It is a result from the insecticide you are using. From this excerpt from the 10th Edition of the Mallis Handbook on Pest Control:

Neurotoxic insecticides cause tremors and muscle spasms, flipping the cockroach on its back. A healthy cockroach can easily right itself, but without muscle coordination, the cockroach dies on its back. Cockroaches exposed to slow-acting insecticides that target respiration (energy production) also can die “face-down,” as they run out of energy without experiencing muscle spasms.

Here's also a website from UMass describing it in more detail:

Most of these insecticides are organophosphate nerve poisons. The nerve poison often inhibits cholinesterase, an enzyme that breaks down acetyl choline (ACh), a neurotransmitter. With extra ACh in the nervous system, the cockroach has muscular spasms which often result in the cockroach flipping on its back. Without muscular coordination the cockroach cannot right itself and eventually dies in its upside down-position.

And an entomology professor even answered this for Maxim:

Most insecticides are poisons that target a bug’s nervous system. When you spray a roach, those neurotoxins cause tremors and muscle spasms, which flip it onto its back, and without muscle coordination, that’s the position it dies in

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    $\begingroup$ Thanks. This answer is really useful. I guess the rapid leg kicking caused by muscular spasms is powerful enough to lift the cockroach on one side and flip it over. $\endgroup$
    – Question Overflow
    Commented Sep 25, 2013 at 4:43

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