Carpenter ants are the behemoths of the ant world. Growing to lengths of 1/2 inch, they are the largest ants in North America. They make nests inside house framing, and by hollowing the wood, they can damage your house. They also get into your cupboards and drawers -- and they bite. Spreading diatomaceous earth around their nests and trails is an effective way to control them without involving chemicals that can harm your family.
Biting, Destructive Pests
If there are carpenter ants on your property, they will probably eventually make nests inside your walls. Those are only satellite nests, though. The main nest is usually out in the yard, under a woodpile or bush. Ants bring benefits to your yard -- they aerate the soil, making it easier for plants to grow, and they feed on insect pests -- but in the case of carpenter ants, these benefits are outweighed by the damage they can do to your house. Moreover, although they don't sting, carpenter ants bite, and to make the bite worse, they inject formic acid into it, which makes it burn.
Of all the substances you can use to control ants, diatomaceous earth is one of the safest. It's composed of the fossilized remains of microscopic organisms called diatoms that have accumulated at the bottoms of rivers, streams and oceans. Composed mostly of silica, these fossils react with oxygen in the water and air to form silicon dioxide. Most of the material that makes it to market is the amorphous -- as opposed to crystalline -- form of this compound. Diatomaceous earth looks like white dust and is generally recognized as safe by the Food and Drug Administration.
Effects and Method of Use
Ants don't have to inhale or ingest diatomaceous earth for it to be effective. The silica absorbs oil from the skin of the insects, causing them to dry out and die from desiccation. Moreover, microscopic razor-sharp edges on the individual particles make abrasions in the exoskeleton and speed the desiccation process. You must spread the powder in a place over which the ants have to walk. Ideally, if you can find the main nest, you spread the powder all around it, even opening the nest with a shovel and pouring some in.
Diatomaceous earth must be dry to be effective, so don't spread it on damp earth or on days when rain is likely. If it rains after you've spread it, wait for the ground to dry and then spread it again. The powder doesn't pose any health threat to children or animals after it's on the ground, but they may inhale it if they are around while you're spreading it or if they enter the yard before the dust has settled. If so, it may irritate their nasal passages. Inhaling a large amount can lead to coughing and shortness of breath. If you're pregnant, wear safety glasses and a mask while spreading it.