Carson had been hearing about DDT since a Swiss chemist discovered it could be used to kill insects in 1939. To many people, DDT seemed like a miracle substance. Farmers were excited about saving their crops from pests. Doctors and others were excited about saving people's lives by killing disease-carrying insects. But to Carson, DDT appeared to be dangerous to all living creatures.

The more Carson found out about DDT and other pesticides, the more she realized that she needed to help stop future spraying. Carson decided to write a book about pesticides. She said, "…there would be no future peace for me if I kept silent." She called her book Silent Spring.