When you come upon a dead insect, such as flies or cockroaches, they’re always upside-down; laying on their back, little legs folded up. Why is this?
It seems to me, when an insect dies, it would probably be in an upright position, therefore, why do you always find them upside-down? I have two hypotheses to explain this:
after death, the insect body, being very light already, gets tipped over by a gust of air. The problem with this is that you often find dead insects on their backs in places where there’s not a lot of moving air.
Just as they die, insects do some sort of “death jump” and end up on their backs. The problem here is that I’ve never spoken to anyone who’s witnessed anything like this.
You may have noticed that the same is true with spiders. The reason, with regard to our arachnid friends, is that the motion of their legs relies on two elements: fluid pressure and muscle. Spiders have muscles to contract their legs, but use ‘hydraulic’ pressure to extend them. Thus, when they dry out, their musculature tends to contract their legs. I confess a degree of ignorance when dealing with insect leg movement, but I wouldn’t be surprized to find that they had similar properties in some cases (not that they rely on fluid pressure, but that when they dry their muscles tend to contract their legs).
As for them ending up on their backs, I would think that as the legs contracted, narrowing the base supporting the body, that they just tip over.
Many insecticide sprays rely on a cholinesterase inhibitor to do the dirty work. Since the insect’s central nervous system is incapable of shutting down properly, it pretty much has a grand mal seizure that never ends, and which ultimately kills it. Many of the insects I’ve watched write around quite a bit before actually dying, and they usually curl up and end up on their backs.
I couldn’t say if baits have the same effect, but it’s possible that any slow-acting agent, whether a nervous system agent or a stomach poison, would cause “death throes” in an insect, resulting in the body being flipped over.
Thanks, everyone, especially for the link to Cecil’s column. I guess I just didn’t know the right combination of words to find it.
**DAVEW0071 wrote:
Since the insect’s central nervous system is incapable of shutting down properly, it pretty much has a grand mal seizure that never ends, and which ultimately kills it.**
There’s a proper way to shut down an insect’s nervous system? Now we know where MS gets its ideas
I think most insects are more stable body down, once their legs are curled to make the whole assembly a hollow cage with a body at one point.
Try rolling one, like dice. I bet it tends to stop body lowest. I’d try it, being an avid experimentalist, but it seems I’m fresh out of them…
