a gnat is a small biting fly, a small two-winged biting fly e.g. a black fly or a midge a fruit fly is a small insect that eats decaying fruit. To kill existing fungus gnats indoors, use Pyrethrin space sprays and pheromone traps or small, low profile Cento Fly Trap. To actually control and/or eliminate fungus gnat infestations in structures, the breeding sites of these flying pests must be addressed. Understanding the biology of fungus gnats is also of utmost importance if you wish to control the situation. Outdoor Control The first step in controlling outdoor Fungus Gnats is to locate the moist soil where fly eggs are being laid. Rake the mulch and underlying soil, exposing the top layer of soil to sunlight and air flow. This will dry the soil, killing the fungus which feeds immature flies. After preparing the soil, use a good surface treatment such as Deltamethrin Spray, Talstar liquid concentrate, Demon WP, Demon EC or Cypermethrin EC 4 ounce. Talstar is best, but Demon EC (or other products containing Cypermethrin) will suffice for smaller jobs. Mix a medium to weak solution of your pesticide and spray all suspected breeding sites, as well as the immediate surrounding areas. The treated areas will be perfectly safe for pets and children to re-enter when label instructions are followed and treated areas are allowed to dry. Repeat the application in 7 to 10 days, for heavier infestations. The key to controlling fruit fly infestations is to locate and eliminate their breeding sources. Although there are several sprays and traps used to kill flies in a home, restaurant or other structure, the infestation cannot be eliminated without eliminating their source. A space spray (Pyrethrin spray) can be used as a quick kill, reducing populations of flying insects. Pyrethrin spray is also a crack and crevice tool that is used by pest control operators to spray the tiny areas where fruit flies and other insect pests breed. To monitor the area, use a Gold Stick trap. These traps use a fly sex lure to attract flies to their doom. Every fruit fly caught is one less breeding adult! i got this off the internet