In her book, Silent Spring, Rachel Carson wrote about a chain of events that ended in tragedy for robins. It all started when people wanted to protect American elm trees from a deadly disease. They sprayed the elm trees with an insecticide that contained a powerful chemical called DDT. The chemical pesticides ended up killing backyard robins, but long after the elm trees were sprayed. How did this happen?
 
Follow the Food Chain
In the 1950's, pesticides containing DDT were sprayed on tall elm trees. The chemicals stuck to the leaves and the bark. Rain did not wash the coating away. In autumn, the leaves fell to the ground. Earthworms fed from the litter of leaves, and the DDT entered their bodies. The following spring, robins returned and ate the earthworms. Sadly, the poison was so concentrated in the earthworms that as few as eleven earthworms could kill a robin. A robin can eat a worm every minute, so the effect of the pesticides was severe.  The death of the robins--the silent spring--made people realize that DDT had long-term, unintended consequences. 

Unintended Consequences
Researchers discovered that DDT persists in the environment long after it is sprayed. They also saw the effect of biomagnification—the poison became more concentrated at each level of the food chain. At this concentrated level, the DDT inside the earthworms was even more toxic to robins than the direct spraying of the DDT. After learning about the unexpected effects of pesticides, Rachel Carson believed it was important to share the information with the world.

The Courage to Speak: Pass It On
Rachel Carson did not stay silent when she saw how chemicals were affecting the environment.  She had the courage to speak out. She said her book was an attempt to explain what silenced the voices of spring in countless towns across America. Rachel Carson inspired change. Nearly fifty years after its publication, her book is still widely read. Her words still speak today. Silent Spring"reminds us to think before we act, to make informed decisions, and to try to anticipate the consequences of our actions.