Rachel Carson wants the reader to imagine a town in which an evil swept over. The animals became sick, the plants became sick, and people began to fall ill and die.  

This town does not exist, but all of these instances have occurred because of what man has done to the environment.

"Man can hardly recognize the devils of his own creations." -Albert Schweitzer

Carson wants to make the reader aware of the environmental issues, specifically pesticides, but in an educational way rather than pointing the finger. This quotes starts off her essay by making the reader know that she is not blaming anyone for the harmful actions that have been done against the environment. 

Why do the smartest human beings think it is okay to use chemicals to reduce the amount of an unwanted species when the chemicals harm their own kind?

"It is believed generally that reduction of crops acreages under provisions of the Soil Bank will stimulate interest in the use of chemicals to obtain maximum production on the land retained in crops." - Agriculture Department

She adds this source to show that even the people who should know the most about the topic of pesticides (The Agriculture Department) send out conflicting statements about how to reduce the use of pesticides.

Insects used to roam free all over the earth, but when man came along, he upset the natural checks and balances that were already in place. A check that was already in place was that there was a limit in the amount of suitable habitat for every species.

"Colossal separate nature reserves." - The Ecology of Invasions

By using Charles Elton's The Ecology of Invasions as a source Carson's claim, that a natural check and balance system was already in place, is supported.

The invasions of these species will continue to happen forever if there is not a big fix.

"... promote an even balance and damp down the explosive power of outbreaks and new invasions." - The Ecology of Invasions

By using this quote from The Ecology of Invasions, Carson's provides the audience with a possible solution to one of the main problems she is discussing. 

".. idealizes life with only its head out of water, inches above the limits of toleration of the corruption of its own environment.." - Paul Shepard

She uses this quote to explain that we know that our leaders know better than to use these harmful chemicals, so why do we put up with it?