Diatomaceous Earth Insecticide

- A natural insecticide made from ancient marine organisms -

Summary: Diatomaceous earth is a safe and effective alternative to conventional insecticides for a variety of pests. It can be used indoors and outdoors in dry situations against crawling pests.

Jack DeAngelis, PhD

OSU Ext. Entomologist (ret.)

What is diatomaceous earth?

Diatomaceous earth is composed of the fossilized shells of tiny marine organisms called diatoms. The shells are made mainly of silica sand. Ancient, land-locked, nearly pure deposits of diatomaceous earth are mined for use in manufacturing and agriculture.

Diatomaceous earth has a variety of uses in filtration, adsorbants, a component of dynamite (another name for diatomaceous earth is diatomite), and as a natural insecticide (right).

Diatomaceous earth is very effective against a number of crawling insect pests like cockroaches, ants, earwigs, silverfish, sowbugs/pillbugs, and bedbugs but, it must be kept dry to be effective (see below).

How does diatomaceous earth work?

Diatomaceous earth is a fine, light powder that is slightly abrasive but highly absorbant. It works as an insecticide because it absorbs and removes the protective waxy covering of insects that are exposed to it. This covering protects insects from water loss so they dehydrate when the protective layer is removed. The powder must be kept dry to be effective. Moisture causes the fine powder to clump and to loose its absorptive properties.

Because diatomaceous earth is a fine powder you should wear a dust mask when applying it, but except for this hazard diatomaceous earth exhibits very low mammalian toxicity compared to many other insecticides.

Another form of silica used in pest control is called amorphous silica which is made by heating ordinary sand to a very high temperature. Amorphous silica is often combined with the natural insecticide pyrethrum or it can be used alone. The tradenames of two commonly used silica dust insecticides are Tri-Die and Drione (see Natural Dust Insecticides).

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