Experts have even concluded that “housefly control has escaped insecticidal techniques and once more must be based on general sanitation.” Moreover, they develop resistance: “The list of resistant species now includes practically all of the insect groups of medical importance.” Carson notes the worldwide insecticide resistance of houseflies, body lice, mosquitoes, and others. Once their enemies are gone, they explode. Yet, in our society, “most of the chemicals now used kill all insects, our friends and enemies alike.” Second, species do not simply multiply. Each time we breach these defenses, a horde of insects pours through.” First, in nature, insect populations are controlled by the internecine war they carry on among themselves. In Chapter 15, titled “Nature Fights Back,” she argues that not only do insects develop resistance to insecticides, but also “our chemical attack is weakening the defenses inherent in the environment itself, defenses designed to keep the various species in check.

The ultimate result: “a brown bullhead had the astounding concentration of 2500 parts per million.” Worse, “the poison had not really left the lake it had merely gone into the fabric of the life the lake supports.” They had concentrated the chemical and passed it along to the plankton eaten by the fish. That tiny, minutely measured 1/50th part per million application of DDD to the water had been picked up by the smallest organisms.

They were examined and found to be loaded with DDD “in the extraordinary concentration of 1600 parts per millions.” Then the fish themselves were analyzed, and the picture became clear. In the following winter, the western grebes began to die. It was very judiciously applied, 1/50 part per million. DDD was chosen because it was harmless to the fish. Nothing was able to control these gnats until DDD ( dichlorodiphenyldichloroethane), a relative of DDT, was applied. She tells the story of Clear Lake, north of San Francisco, a popular lake for amateur fishermen, but an ideal habitat for a harmless but very annoying mosquito-like gnat. One of the chief villains in her story is, of course, DDT, the synthetic pesticide dichlorodiphenyltrichloroethane. Carson’s systematic analysis includes a technical discussion of the toxicity of the chemicals that have been used to control insects.

The sea rachel carson