The DIY Solution People Use To Kill Roly-Polies (& Does It Work?)
Roly-polies, also known as pill bugs (Armadillidium vulgare), are usually beneficial in the garden and can make the quality of your soil better; however, they are known to occasionally munch on produce, such as cucumbers, tomatoes, and lettuce. These bugs don't hurt humans, but some people try to repel or exterminate roly-polies with cayenne pepper. People often spread the powdered spice throughout their garden or sprinkle a cayenne pepper sauce or oil around the soil. Alternatively, some combine the cayenne pepper with water, rubbing alcohol, and soap and spray the solution in affected areas.
The main theories behind this pest control solution is that the spicy smell of the cayenne will deter these pests and that the capsaicin these peppers contain can kill insects. While there is proof that capsaicin can kill and repel certain insects, such as aphids, there is no scientific evidence that it's effective against pill bugs. Because of this, you might consider leaving the pill bugs alone if they aren't causing much harm or implementing a more reliable pest control solution that will ward off roly-poly bugs for good.
Why cayenne pepper isn't a good solution for roly-polies
Science has shown on several occasions that capsaicin is an effective control against insects, including lace bugs, spider mites, leafhoppers, thrips, aphids, whiteflies, and other insects. Additionally, a 2019 study in Insects found that capsaicinoids were capable of acting as a natural insecticide. These compounds in cayenne peppers are able to disrupt the nervous systems of the insects, as well as injure their cell membranes. Capsaicin has also been registered as an insecticide and miticide by the National Pesticide Information Center.
Despite this evidence that capsaicin, and therefore cayenne pepper, can repel and kill insects, there is no definitive proof that it works against pill bugs. One reason for this is that roly-polies aren't actually insects, but rather terrestrial crustaceans. Because of this, it is unclear if capsaicin would be able to kill pill bugs, as all the research applies to legitimate insects. It seems there have been no studies directly testing the effectiveness of capsaicin or cayenne pepper as a control method against pill bugs or other terrestrial crustaceans specifically, leaving no indication that this DIY pest control solution actually works. While there are instances where you can use cayenne pepper to deal with pests in your garden, this likely isn't one of them.
Alternative solutions to kill roly-polies
Since there is no guarantee that cayenne pepper or capsaicin would be able to kill the pill bugs in your yard, you'll likely need to find other ways to keep roly-polies from destroying your garden. One natural option, diatomaceous earth, is more reliable and considered relatively safe. Food-grade diatomaceous earth is made of diatoms, or fossilized aquatic organisms, and is a great choice for non-toxic pest control.
Diatomaceous earth is sharp and when the pill bugs move over the fine powder, it will cut them. From these wounds, the roly-polies' fat and moisture will leak out and the pests will die. This pesticide is effective on insects as well as other types of arthropods, like pill bugs. This natural pest control solution can be spread over the soil where you know the roly-polies are hiding. Though, when used properly, diatomaceous earth isn't harmful to humans, it can kill other insects that are beneficial to your garden.