Like HowStuffWorks on Facebook!

How Bug Spray Works

Insecticides: The Big Guns

Have you ever wondered why there are so many different types of bug sprays for the pests in and around our homes -- one for wasps and hornets, one for ants and roaches, and still another for fleas and ticks? As it turns out, they contain very similar insecticides, although their specific ingredients and formulations differ depending on how and where the sprays will be used.

Most household bug sprays contain one or more insecticides in the pyrethroid family. Pyrethroids are synthetic chemicals designed to mimic the natural oils found in chrysanthemum flowers [source: National Pesticide Information Center]. They affect an insect's central and peripheral nervous systems on contact, causing tremors, paralysis and a quick death [sources: EPA, NPIC]. Pyrethroids are effective against all sorts of insects, including beneficial bugs like bees and butterflies. They're also highly toxic to fish.

Pyrethroids such as permethrin, prallethrin and cypermethrin are the active ingredients in many wasp and hornet sprays. If you've ever had to deal with a nest in your yard, you know that it's best to spray in the evening, when these insects are less active. This is partly so they won't dive-bomb your head as you attempt to wipe out their home and family, but it's also for efficiency, since the spray is likely to instantly terminate any wasps that are in the nest.

Pyrethroids are also found in sprays targeting ants, roaches, silverfish and other crawling critters. Since it's not always easy to find the source of an ant or roach invasion, these sprays need to work over an extended time to effectively kill insects outside their nests. For this reason, ant and roach sprays usually contain piperonyl butoxide, an additive that prevents the insecticide ingredients from degrading before they can work [source: NP IC]. These sprays are applied along walls, doorways and insect trails, and the bugs are killed when they ingest or crawl over the residue.

Household flea and tick sprays use pyrethroids to kill adult fleas and ticks, piperonyl butoxide to extend the life of the insecticide ingredients, and a growth inhibitor like pyriproxifen to prevent new eggs and larvae from developing [sources: Doctors Foster and Smith, NP IC].