Borax and Boric Acid for Insect Control

by David Moore
Manager of Technical Services and Board Certified Entomologist
with contributions by Eric Smith, PhD, BCE

When looking for options to control pests in the home, many people turn to borax or boric acid. These substances are known to be harmful to certain types of insects, so it may seem easier to just attempt to control the pests on your own than to call a professional. However, there is a lot of misinformation about what borax and boric acid are and what they can do, information which may also prove dangerous to the health of those in your home.

Borax vs. Boric Acid

Borax and boric acid are distinct formulations of the same compound-boron. Borax, or Sodium Tetraborate (Na₂B₄O₇*10H₂O), is made up of sodium, oxygen, and boron. Boric acid is created from the mixture of borax with other naturally occurring minerals such as boracite and colemanite. Both borax and boric acid are known as borates.

In layman’s terms, borax is a mineral that is taken straight from the ground (a form of the element Boron) and is used in cleaning products. Boric acid is essentially its extracted, processed, and refined form, found in a variety of chemical products.

Borax and boric acid are only toxic when ingested. Products containing them will be labeled for external use only, but can be dangerous for children and pets.

How Boric Acid Works

Boric acid is most often used in pesticides, and can be found in tablet form, liquid form, powder form and in various types of traps. It kills insects by absorbing into them, poisoning their stomachs, affecting their metabolism and abrading their exoskeletons. It’s far more likely to kill pests than borax is, due to its finer grain, which is harder for pests to detect and easier for them to ingest. When pests come into contact with it, whether through a trap or through walking across it a thin layer of it, it sticks to them, and they ingest it while cleaning themselves.

Most baits containing this compound usually only a 5 percent formulation of boric acid, since high amounts of it can repel insects. However, fine powders or dusts that one would spread out in a thin layer contain 98-99 percent boric acid.

What Boric Acid Will and Won’t Kill

Homeowners buy boric acid to kill many types of insect pests. However, there are only a certain few it will actually affect, namely insects that groom themselves and will therefore ingest it, like ants and cockroaches. Pests it will not kill include: