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(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.

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I sprinkled them first, some bursted and then it got weird, so I decided to flush them all :p – user1306322 Apr 27 '14 at 6:18

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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...

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