Chlorpyrifos (CPS) is an organophosphate pesticide used on crops, animals, and buildings, and in other settings, to kill a number of pests, including insects and worms. It acts on the nervous systems of insects by inhibiting the acetylcholinesterase enzyme. Chlorpyrifos is used to control many different kinds of pests, including termites, mosquitoes, and roundworms. Chlorpyrifos can be harmful if it is touched, inhaled, or eaten. Chlorpyrifos works by blocking an enzyme which controls messages that travel between nerve cells. When the enzyme is blocked, the nervous system can't send normal signals. This causes the nervous system to malfunction and this is how it eventually kills the pest.