Simuliidae is the scientific name for buffalo gnats or black flies. There are more than 100 different species in North America alone. Gnats pose a health hazard for humans causing itching, swelling and pain where the gnats attack the skin. Therefore, killing them is priority in areas where they are prevalent. Livestock and chickens can actually die from bites, so keeping buffalo gnats away is a priority. Killing all the gnats will not happen instantly because first you need to put preventive measures in place to keep them from bothering you.
Identify the extent of the buffalo gnat problem. If there are great swarms of them, then you will need to take significant steps to remove the problem. However, if the problem is limited to indoors you can fix the problem relatively simply.
Assess areas where the buffalo gnats could be breeding or entering you house. Stagnant water is the prime breeding ground for larvae so look for a dirty pond, standing septic tank or pools of water on your property to source the problem. Open doors, holes in roof space or crevices could provide easy entry points for them.
Shut open doors or windows to keep the gnats from coming in while you prepare to kill them. Put up window screens or fine netting to prevent them from getting into your living space.
Spray pyrethrum aerosol inside crevices and in the areas of gnat activity. The spray is an insecticide so will kill the gnats using chemicals. Read the instructions to check if it can be used indoors, and remove children and pets from the area while it is treated. You can also prevent biting to skin by using a repellent that contains DEET. Although it won't kill the gnats, it will stop them biting you.
Remove the stagnant water areas you identified during step two. You may require specialist assistance for removing a large septic tank; however, you can deal with a pond by draining it and filling with fresh soil.
Fog out the gnats using a gnat fogger. It is a spray used to kill gnats which are currently present in your area, but is not successful in killing unborn gnats. Therefore, it is not a permanent solution and you will need to fog them out again, as their numbers build up.
Ask your local environmental agency if they can deal with the problem. Some local governments treat water sources with Bacillus thuringiensis Berliner to kill gnats. It won't harm to ask and it will save you a lot of frustration if they say yes.
Do not overwater plants, because this can cause fungus to grow and provide an ideal breeding ground for buffalo gnats.