Biological pest control involves the use of another living organism to kill a pest. No chemicals are needed, there is no environmental contamination with pesticides and the pests don’t become resistant to the control method. Many different chemicals are used to kill pests. These pesticides often work well, but since they're designed to kill living things they may cause serious problems in humans or pets. Pesticides contaminate the environment. They sometimes harm other organisms in addition to their target pest.