It's not common for black widow spiders to be so intrusive. They are typically solitary creatures that hide in sheltered spots. Are you sure you've identified them correctly?
Spiders nest in areas where both there are bugs, moisture and protection against the elements. You need to remove storage such as stored wood. Keep the area dry. And if your finding them around the light areas of the house, use bulbs that do not attract insects.
You may need to have an exterminator come in and professionally spray the grounds and perhaps fog the attic areas within the house. This will remove most of the insects so you can regain control of them. No one treatment will remove all of them at one time. The goal is to use what is called integrated pest management. This is where you control the environment in which they are living and make it hostile for them to survive. Then follow up if need be with chemicals. Controlling the environment is as simple as cutting the lawn, removing storage, keeping area dry by perhaps pitching soil away from home etc.
Spray the area with Tempo it is available at Orschelns and I am sure at other places also. It is the greatest thing I have found and it does not stink ! It is used in Nursing homes and restaurants so it is not as much of a threat to humans as most bug killers.
I used clear spray paint. Brake Parts Cleaner from an auto supply store works too. Since spiders will curl up so have to spray underneath to kill it. Two times a black widow has been aggressive. Both times I had disturbed them. Also black widows will nest about two feet apart. They like to eat ants and crickets so getting rid of those help too. Hope this helps. Good luck!
@Barbara Brown The Tempo that I suggested is not as fast as the Brake Parts Cleaner, but if you follow the directions and apply it over the entire area, it will wipe them out and can be used as a preventative with timely reapplication, again, FOLLOW THE INSTRUCTIONS ! it is more economical than the BPC and does a more thorough job of solving the problem. You can order it through Orscheln's.com website and you will be glad you did !