Stupid Question ™
Aug. 19, 1999
By John Ruch
Q: Why do roaches always die on their backs?
—Dumb and Dumber
A: There are a lot of people with opinions on cockroach death positions, but as far as I can tell, none of them have specifically studied the matter.
So be warned that the following answer is really just an educated guess that will hopefully one day be tested by some grad student, perhaps in his or her undoubtedly cockroach-ridden campus apartment.
The most important observation, from entomologists and pet store owners, is that cockroaches do not always die on their backs. Sometimes they die very much upright.
So I think our question actually is: why are roaches usually found dead on their backs? It’s a subtle but important difference.
Many insects tend to topple onto their backs when incapacitated, especially those with a flat back and legs positioned directly under the body. Flies are the classic example.
Roaches have a similar design, but a lower center of gravity. They probably need a stronger force than gravity to topple them over. Dehydration may be the destabilizing factor.
Insects are extremely susceptible to dehydration. Shortly after death, their legs dry and curl up. This makes toppling over almost inevitable. Ohio State University entomology associate Kyle Jordan said this is a common problem when mounting insects for display: “They’re very difficult to get to stand up. They’re unstable.”
Roaches in the home are usually found on smooth surfaces in the bathroom or kitchen. While a healthy roach is pretty good at righting itself, the smooth surfaces no doubt aid a sick or dead roach in toppling over.
If you know roaches are in your home, you’re probably also trying to poison them. Many off-the-shelf insecticides are neurotoxins that cause spasms and uncoordination. Between those two symptoms, roaches commonly fall onto their backs and are unable to right themselves, dying that way.
So to sum up: roach corpses in the home often have had all night to dry out and are on a smooth surface, making it very likely they’ll topple over. And if you’ve killed the roach with a dessicating or neurotoxin insecticide, it’s all the more likely to be on its back.