Ever heard that killing a roach will attract more roaches? Normally, it’s the opposite. Both ruptured and unruptured dead cockroaches emit a scent (oleic acid) that repels other cockroaches. Researchers have observed similar behavior is observed in many types of insects.
It seems the scent of their dead brethren serves as a warning for some insects to steer clear. They sense some looming danger that might spell their early demise too. However, it is unclear how long this scent lasts, given the many anecdotal and documented cases of living cockroaches consuming dead cockroaches. The below video is one such documented case.
In this article, we’ll explain where the theory that dead roaches attract more roaches originated, what to make of it, and how this affects the best way to go about handling a cockroach you might see in your home. You can skip to a specific section via our table of contents below. If you have additional questions, please ask them in the comment section below this article.
Why would a dead cockroach attract more roaches?
One theory that some folks put forth is that when cockroaches die, they release pheromones that affect the behavior of other roaches. Evolutionary biologist, David Rollo, hypothesized that the smell that dead cockroach releases would attract other cockroaches. He thought the same might happen with other insects too. But his labs’ findings were the opposite—many types of insects are repelled by the scent of their own dead. Rollo found that cockroaches tend to stay away from dead cockroaches. Likewise, pill bugs tend to avoid dead pill bugs. Rollo’s lab observed the same behavior with many insect species.
So, does crushing a cockroach attract more roaches?
Crushing cockroaches releases oleic acid, which, according to Rollo’s research, tends to repel other roaches. What we don’t know is how long oleic acid smells strong enough to other roaches to scare them away. It is also not known whether a hungry living cockroach would ignore the oleic acid a recently dead cockroach emits.
Some folks hypothesize that if nearby roaches are hungry enough, the oleic acid, instead of repelling living roaches, might actually attract craved, living roaches.
The jury is still out on this but suppose you kill a roach and promptly dispose of it. Even if it released a scent that attracted nearby hungry cockroaches, they would come to investigate and not find the dead cockroach. They would then have to move on to look for food elsewhere.
Do cockroaches release pheromones when killed?
Cockroaches release pheromones when they die. Specifically, roaches release oleic acid. Rollos’ research suggests other cockroaches interpret oleic acid as a danger sign.
Most humans find that oleic acid smells pungent and moldy. Anyone who has stepped on or smacked a cockroach will attest to this. Research suggests that this scent allows cockroaches to understand that another cockroach died nearby.
If you step on a cockroach, does it release its eggs?
Some cockroaches release their egg pods (oothecae) when frightened. For example, female German roaches normally carry their ootheca until hatched but can release their eggs when threatened.
This means if you attempt to step on a female German cockroach and miss, the roach might release its egg pouch. If you missed and don’t notice a released egg pouch (they’re small), you potentially just made your roach problem worse.
If you successfully squish the female roach, you’ll likely simultaneously squish her egg pouch though, so you probably don’t need to worry about spreading roach eggs when squishing a cockroach.
So, should I kill a cockroach if I see it inside?
If you see a cockroach inside your home, you should exterminate it. If you think you can step on it, go ahead. But if you miss, be aware that female German cockroaches can release their eggs, so ensure you don’t see an egg pod on the ground after your failed squashing attempt.
Also, if you do step on a cockroach in your home, remove it in a timely manner. Other insects like ants or crickets will eat dead cockroaches. Even other living cockroaches will eat dead roaches if the living cockroaches are hungry enough.
Is there a way to kill roaches without attracting more?
One way to remove a cockroach that you see without crushing it is to spray it with soapy water. Dish soap works best for this.
Soapy water interferes with cockroaches’ respiration system and they’ll somewhat suffocate. You’ll see that they stop moving and appear dead a while after being sprayed. However, soapy water doesn’t seem to completely kill cockroaches.
Rather, soapy water just temporarily disables cockroaches. It’ll make a cockroach nearly comatose. So, you’ll still need to scoop up the disabled roaches and remove them from your house. Though removing comatose roaches might be annoying, this method doesn’t release roach guts or the nasty smell that accompanies them.
Some folks hypothesize this method has less potential to attract other hungry roaches. Their reasoning is based on the following: 1) soapy water doesn’t involve squishing the cockroach and 2) the cockroach isn’t actually perishing.
Cockroaches sprayed with soapy water might not release as much oleic acid as roaches that die via ruptured exoskeletons. But if this were true, other cockroaches wouldn’t be as repelled by the “scent of death” from soap-covered roachesas they might be from squashed roaches.
Conclusion about dead roaches attracting more roaches
Generally, killing a cockroach should not attract more roaches because dying cockroaches release oleic acid which typically deters other roaches. However, if nearby roaches are hungry enough, they might interpret what is normally a warning signal as an easy meal.
But you shouldn’t overthink this.
If you see a cockroach on your floor or wall, either try to smash it or spray it with soapy water. Once the roach is dead or incapacitated from soapy water, remove it from your house.
As long as you promptly remove the dead roach from your home, you don’t need to worry about it attracting additional roaches.
If you’re worried about a roach bait or trap exterminating a good number of roaches and then attracting more roaches, it sounds like you might have a significant cockroach infestation. If this is the case, we suggest you contact a pest control professional to discuss some solutions or learn more about how to handle large cockroach infestations.
