Why do cockroaches burst from soapy water?

Question

(careful, disturbing!)

I was experimenting with some stray cockroaches that ended up falling in my bath tub overnight (there is currently an infestation undergoing in my apartment building) and I found out that they are very easily killed by simply soaking them in soapy water.

I read that soap blocks some pores in insects' bodies which leads to suffocation, which appears to be the cause of death for my test cockroaches. But what I don't get is why about a half of them died with their innards bursting from their tail end. The water wasn't too hot to make them boil. Is it that they suffocate so hard that attempting to breathe they blow out their insides? Or is it the soap's reaction with the cockroach's bodily materials? Or is something else causing this?

I remember watching a documentary on injecting various insects with hydrogen peroxide which caused much more dramatic explosions, but it's not like I was injecting cockroaches, I just sprinkled them with soap water.

Answer 1

As far as I am aware, cockroaches don't burst from being sprayed with soapy water (water + some liquid dish detergent). We previously had many cockroaches in our apartment (some came back after a year of nothing!), and we regularly sprayed the cockroaches with soapy water plus some vineger (more as a disinfectant/cleaner) and they never burst. We've killed at least 30 using this method.

Having said that, what you likely witnessed was the egg sacs dislodging from the back of the female cockroach. As you didn't mention what species of cockroach you were dealing with, I am assuming you had German cockroaches as they seem to be the most common type in non-tropical/hot areas.

According to a number of biology sites, German cockroaches are particularly difficult to control and eradicate is because they carry their egg sacs with them until they are ready to hatch. At which point they drop the sac.

If you are able to catch a few that seem especially big, you will notice that they have a sac at their back.

If you don't have German cockroaches, I have not idea why they would burst...

Answer 2

What you saw was simply female cockroaches expelling their many eggs as they approached death.

We have German cockroaches here in Australia. I am always astonished at how quickly they spread and equally how easy to is to kill them. While there are many poisons on the Australian market for spraying them, which generally work, often quite slowly, any water which is marginally hotter than what is comfortable to keep your hand in will kill a cockroach in a matter of 10 seconds. If cockroaches are silly enough to be around the kitchen sink, shower or any basin they are very quickly dead meat. Pouring boiling water on them would kill them in seconds.

Many insects will quickly die if exposed to hot water.

I don't like sprays because they indiscriminately kill all insects, good and bad. We have encouraged huntsman spiders in all of the houses we have lived, as they are excellent roaches and fly killers.

But short of flooding everywhere with hot water which isn't a useful plan in most instances, sticky roach baits, which are placed in strategic positions to attract and kill roaches, are the best way to kill (only) roaches over time. They ensure that the roaches get stuck in the bait, and lay their eggs in the bait, thus keeping roach reproduction down.

Answer 3

Cockroach abdomen burst out when it sinks in soapy water. A white color thing burst out from the body which are not eggs.They lay only one big egg which will be in brown color. Cockroach lack hemoglobin(red pigmentation) in their blood. White color busting out is actually blood. So even male cockroach burst out when it is in soapy water. May be due to some soap reactions with blood it burst i guess.