Bugs are our forever neighbors. For every person on Earth, there are about 1.4 billion insects, from the tiniest of mites to enormous stick bugs.
Many of these invertebrates are beneficial to people, particularly those that support healthy soil and plants. Honeybees, for instance, pollinate $15 billion worth of crops in the US each year, which includes 130 types of fruits, nuts, and vegetables, according to the US Department of Agriculture (USDA).
However, many species like to visit our kitchens and gardens, such as ants, cockroaches, and mealybugs. Keeping them away is a challenge, especially when trying to find a more natural approach to pest management.
So C&EN asked some experts about chemicals proven to kill or deter household invaders without harming the environment-or ourselves.
Boric acid
Boric acid is an inorganic substance that naturally occurs in seawater and in trace amounts in some natural foods, including apples and peanuts, says Ameya Gondhalekar, Sapp Associate Professor of Urban Entomology at the University of Florida. The type used to control insects is made from mined raw materials or minerals; for example, borax is a powdery or granular substance that contains the elements boron, sodium, and oxygen as well as water.
Placing small amounts of boric acid in out-of-the-way places, such as under the fridge, is effective at killing cockroaches, Gondhalekar says. German cockroaches are a widespread species that can carry infectious bacteria, such as Salmonella and Escherichia coli.
Cockroaches are fastidious groomers, and if the insects encounter boric acid, they will eventually lick it off themselves. The chemical damages their midgut, causing them to ultimately starve.
Boric acid can be harmful if inhaled or ingested in large amounts, especially for children and pets, which is why the chemical should be used sparingly and in little-trafficked areas of the home.
Citrus oil
Citrus oil contains limonene and linalool, aromatic compounds that have evolved to protect plants from harmful insects, including aphids and mites.
Classified as terpenes, these compounds damage insects' nervous systems, disrupt their digestion, delay pupation, and more (Heliyon 2024, DOI: 10.1016/j.heliyon.2024.e39120).
Citrus oil is a potent and toxic tool against ants, says University of Central Florida biology professor Joshua King. Research shows it reduces ants' ability to forage as well as reducing a colony's likelihood of survival.
King also created a nonpesticide method for controlling invasive fire ants in the southern US, particularly the red imported fire ant, Solenopsis invicta, whose sting can cause painful and sometimes severe reactions in people and can harm wildlife. They can also damage farm equipment and eat crops.
Called the Antheater, King's machine injects targeted amounts of boiling water into fire ant mounds, destroying the mounds and the ants without harming the landscape.
"We use it in agricultural settings and [in] wildlife protection, where pesticides are not an option, and it's very effective," King says.
Peppermint oil
Peppermint oil-whose essential ingredient is menthol-can keep mosquitoes at bay by overwhelming their sense of smell and nervous system, says Dmitry Eremin, a staff scientist at the California Institute of Technology.
A 2022 study in the journal Insects found that peppermint oil disrupts the endocrine and water-regulation systems of many mosquitoes, including species in the genus Anopheles, which can carry malaria. Premade peppermint oil sprays are available online and in stores, and DIYers can find recipes to make their own.
Clove and cinnamon oils also offer natural mosquito protection. A study in the journal Nature showed that applying the oils to human skin worked better than 18 other essential oils tested in keeping the blood-sucking insects away for up to an hour.