Most bug sprays work by using a acetylcholinesterase inhibitor. Bug sprays with these chemicals prevent the body's neurotransmitters from processing the signals from the insect's brain and prevent the signals from moving properly through the body. Without the proper signals reaching the insect's limbs, it is unable to move.
How It Works
Acetylcholinesterase is the chemical in bug spray that breaks down acetylcholine. Acetylcholine is required to transmit directions from the insect's brain to all of the vital organs. Once the insect is sprayed, the chemicals begin entering the body, and slowly begin blocking the neurotransmitters. As the chemicals begin entering the body, the acetylcholine is interrupted, and the bug will begin losing control of its extremities. The signals degrade further, and as the bug moves its legs forward, they are unable to move back again. This process continues as the inhibitor moves further into the insect's body. As it penetrates more deeply, the signals from the insect's brain is inhibited from reaching the vital organs as well. The circulatory and respiratory systems are unable to respond to the commands coming from the bug's brain and begin to shut down. The insect will lose control of all of its motor functions and dies quickly.
The chemicals involved in using insect spray are extremely dangerous. Because the respiratory and circulatory systems on an insect are so vastly different than a human's, direct ingestion is generally required in order to be immediately harmful. Of course, prolonged exposure will certainly be a danger to anyone who comes in extended contact with pesticides, so extreme care should be taken when dispersing or storing pesticides.