DDT, a synthetic insecticide that belongs to the family of organic halogen compounds and is highly toxic toward a wide variety of insects as a contact poison that apparently exerts its effects by disorganizing the nervous system.

As a result of repeated sprayings, DDT accumulated in soils in surprisingly large amounts (10–112 kilograms per hectare [10–100 pounds per acre]). Its effects on wildlife greatly increased as it became associated with food chains. The stability of DDT led to its bioaccumulation in the bodily tissues of insects that constitute the diet of other animals higher up the food chain, with toxic effects on the latter. Songbirds and birds of prey, such as eagles, hawks, and falcons, were usually most severely affected, and serious declines in their populations have been traced to the effects of DDT. Use of DDT began to be restricted in the 1960s.