An ancient beginning
Mined from ancient riverbeds and lakes, diatomaceous earth (DE) is the fossilized remains of prehistoric, freshwater phytoplankton or algae. Many years ago these single celled creatures, called diatoms, formed exoskeletons made up entirely of silica. Like the algae of today, diatoms were found in large colonies or “ribbons” in bodies of water. As these creatures died and piled on top of each other over eons, the exoskeleton compressed to form the sedimentary rock diatomite.
When mined, this crumbly rock forms a soft powder. Initially diatomaceous earth was used industrially as a component of dynamite. When its abrasive qualities were discovered, companies began adding it to toothpastes and polishes. Diatomaceous earth is now widely used, from grain storage (as an anti-caking agent) to an ingredient in boat epoxy. Gardeners and homeowners commonly use the fine powdered form for controlling unwanted insect pests.
Color and types
The different colors of diatomaceous earth reflect the regional differences of diatomite deposits from all over the world. Varying in color from light grey to brown to white, diatomaceous earth is graded by the purity of silica and the amounts of other minerals. For ‘food grade’ DE, there must be no more than 10mg/kg of lead or arsenic.
The diatomaceous earth found on the retail market is available in two forms, pool grade and food grade. Pool grade is calcined or treated with high heat, which turns the silica dioxide into crystalline silica. This process emphasizes the filtering qualities of DE but makes it very harmful to the respiratory systems.
Food grade diatomaceous earth is a freshwater form of diatomite. Although it can cause slight lung irritation over long exposure, it’s safe to use topically and is often taken as a health supplement. Homeowners and gardeners may be more familiar with food grade DE because it’s inexpensive and an important tool in many pest management strategies.
How diatomaceous earth works
Though diatomaceous earth is considered a pesticide under the Pest Control Act, its effectiveness is actually mechanical. If you looked at food grade, uncalcined diatomaceous earth on a microscopic level, it would look like a multitude of tiny hollow cylinders covered in barbs. These barbs make a very effective deterrent against a broad spectrum of insects.
As an insect or bug treads across the powder, the tiny barbed cylinders penetrate the waxy coating that covers the insect’s body. This creates wounds that let body fluid out. The porous nature of the powder also makes it an absorbent. This means diatomaceous earth works in two ways, both injuring the pest and drawing out fluid to dry and kill the insect. Death does not happen on contact, but over a short period of time. If left undisturbed, diatomaceous earth can be effective within 24 hours, though better results are usually apparent after five days.
| Type of Insect | Apparent Results |
|---|---|
| Bed bugs | 24 hours to 5 days |
| Darkling beetles | 7-21 days |
| Silverfish | 7-14 days |
| Black or red ants | 24 hours |
DE is effective on many more insect types than on the chart above. Most common household insect pests, including fleas and cockroaches, will be controlled or eliminated by persistent application of DE.
Several factors will influence the success of diatomaceous earth: the type of insect, size of infestation, temperature, and humidity. Because diatomaceous earth is so absorbent, excessive moisture or rain can limit its effectiveness. DE will be less effective if applied too thinly; better to lay out ‘lines’ of DE rather than dusting an area.
Additionally, all insects are susceptible to DE, even the good ones. In gardening, this means it’s essential to limit your application to wherever the pests exist and not where…
