Not aware of the risks
A major theme in the novel is the idea that humans and society is general is not aware if the risks that come with using dangerous chemicals in the lands from where food comes from. The government and the pesticide manufacturers pushed on numerous times for a more extensive use of pesticides in the fields and they ignored time and time the risk they imposed. Even after it was proven that there is a connection between pesticide use, cancer in humans and the death of various animal species, the pesticide manufacturers refused to admit their fault and give up using pesticides. In this case, the need for monetary gain won over the need to protect the environment and the health of the people living in the places treated with pesticides.
Everything is connected
Another theme is the idea that everything is connected. In the animal kingdom, there is a fragile hierarchy and animals are either predators of prey. With vegetation as well, some animals and insects depend on the presence of some plant species considered by humans as being weeds and when those plants are eliminated, the animals depending on them end up suffering. Because everything is connected, when an animal species or plant is eliminated, it affects a whole ecosystem as it eliminates an important part from a fragile system.
Destructive species
The humankind is portrayed quite in a negative way in the book. They are seen as destroyers, disrupting a perfectly good balance created by nature just because they see some part of it as being useless. Humans have influence the environment from the beginning, whipping out animal species and plant species from certain areas. Humans have done it from the beginning of humanity and Carson suggests that humans will never be able to stop themselves from destroying the planet.
