Gardeners commonly use it to control ants and other crawling insects in the garden. It comes in the form of a dust or wettable powder that is spread around areas that ants are known to crawl. It has sharp edges, cutting into the exoskeleton of the bug, causing it to dry out and die. It remains effective as long as it is kept dry and undisturbed. This means that you must re-apply DE after a storm.
DE is not poisonous; it is a completely organic method of pest control. It is considered to be non-toxic and not harmful to wildlife, including fish and birds. Since DE is a fine dust, it is irritating to human nasal passages when it is breathed in, but applying DE in a sensible manner, on a day with low winds will help prevent this.