Bifenthrin (Biphenthrin, (2-Methyl-3-phenylphenyl)methyl-(1S,3S)-3-[(Z)-2-chloro-3,3,3-trifluoroprop-1-enyl]-2,2-dimethylcyclopropane-1-carboxylate, CAS#82657-04-3) is a pyrethroid insecticide used primarily against the red imported fire ant by influencing its nerve system. It has a high toxicity to aquatic organisms. Although it is listed as a restricted use chemical in the United States, it is allowed to be sold for daily use, provided that the product sold has a low concentration of bifenthrin. Currently there is no known treatment.

On a large scale bifenthrin is often used against red imported fire ants. It is also effective against aphids, worms, ants, gnats, moths, beetles, grasshoppers, mites, midges, spiders, ticks, yellow jackets, maggots, thrips, caterpillars, flies and fleas. It is mostly used in orchards, nurseries and homes. In the agricultural sector, it is used in great amounts on certain crops, like corn. About 70% of all hops and raspberries cultured in the United States are treated with bifenthrin. Bifenthrin is very toxic to many insects, fish and other aquatic animals. It is only slightly toxic to mammals and not at all toxic to plants. Even though it does not have a large toxicological risk towards mammals or birds, bifenthrin is able to accumulate in food, and therefore might be dangerous to mammals or birds in some scenarios.