Does Soap and Water Kill Roaches?
Soap has long been touted as a quick, easy way to kill pest insects without using harmful pesticides. What could be better than using basic dish soap to clean your home and kill unwelcome insect visitors? Insecticidal soaps are common in garden centers and greenhouses, where they are used to treat aphids, fruit flies, and other pest insects. But what is the effectiveness of soap when it comes to dealing with cockroaches?
How Do Soap and Water Get Rid of Cockroaches?
Soap and water is an unorthodox combination for dealing with cockroaches. But it does kill cockroaches if used correctly. The issue is that soap and water is not a way to wipe your home of a cockroach infestation completely. The effectiveness of soap and water solutions when dealing with cockroaches depends on you hunting down each cockroach. This is not an easy thing to do, as the cockroaches will slip into the smallest cracks and crevices in your home, rendering your soap and water solution useless when it cannot reach them.
That being said, let's explore how soap and water kills a cockroach. This combo exploits the anatomy of the cockroach's respiratory system. Insects do not have lungs like humans. Instead, they breathe through tiny openings in the sides of their bodies called spiracles. The air is transmitted to different parts of the body by spiracles in different locations along the insect's exoskeleton. This means that they cannot hold their breath and are continuously breathing.
Water will not kill cockroaches because of its surface tension. Water molecules tend to stick together. Certain insects can even "walk on water" because the feet at the end of their legs are so small and fine that they do not break the layer of water molecules on top of the water. This is also why cockroaches can still survive water being poured on them. Their spiracles are so small that water will not enter but instead run off of their backs.
By adding soap to water, you get rid of this surface tension. The mixture can enter much smaller spaces, such as the spiracles of an insect. Spraying a cockroach with soap and water drowns its spiracles. And because a cockroach cannot hold its breath, it suffocates almost instantly. Insecticidal soaps for gardeners often work in this manner, although some may also dry out and dehydrate the insect to death.
Types of Soap that Kill Roaches
Soap that kills cockroaches is reliant on drowning them where they stand. Theoretically, you can use any soap that disrupts water's surface tension to do this. Dishwashing liquid (Dawn) has been shown to be very effective. A 2002 study proved the efficiency of common dishwashing liquid when applied directly to German cockroaches (one of the most common species). Adults and nymphs were completely dead within 72 hours of the liquid coating them.
The main advantage of the soapy water approach to killing cockroaches is how it cleans while affecting the insect. Because cockroaches like the German cockroach track bacteria and other gross stuff around, you want to wash any area that they have been through. Using a soap and water mixture for treatment, you are already disinfecting where the pests have crawled!
Does Laundry Detergent Kill Roaches?
Laundry detergent has also been used in roach extermination. Just like regular soap and water, the laundry detergent works by suffocating the cockroaches through their spiracles. Laundry detergent can be just as effective as soap and water when it comes to killing roaches.
Making a Water and Soap Spray to Kill Roaches
So how do you make a soap mixture to kill roaches? When mixing dishwashing liquid (Dawn) or laundry detergent with water to kill roaches, the general rule is only to add enough to break up the water's surface tension in the mixture. Fill your spray bottle almost entirely with water, then add a squirt of your soap and shake the bottle well. Make sure the soap is dissolved into the water before using it as a roach spray.
As an alternative to making a soap and water spray, you can also try making an essential oil spray to get rid of roaches naturally. A 2016 study found that rosemary, peppermint and oregano essential oils are incredibly toxic to roaches. When working with essential oils, always remember to dilute them and avoid direct skin contact.
Is soap and water the best way to kill roaches? It seems safe, cheap, and disinfects the area while killing the pests! Well, while it may work on individual cockroaches, a soap mixture will not cure your home of a roach infestation. It will only kill cockroaches that you hit directly with the solution. Cockroaches will still be hiding in their chosen locations. There is no way to get them all with soap and water. Hidden egg cases will constantly add more roaches for you to kill.
If you have an infestation, call a pest control professional, or use other methods of killing roaches such as boric acid, gel bait, and diatomaceous earth.