That's crazy man, I've never of an infestation that bad! Hope you figure that out. I never have seen one here at the farm but we do have our share of black widows in the sheds and barns. Always heard if you can black widows you won't see brown recluses and vice versa

There may be poisons that kills them, I don't know. May take a professional tent and bombing setup.

From what I've seen and read on other infestations, if you get rid of the food source they will go away.

One example was a home with literally millions of them. They tried everything and finally a company came in and determined they were feeding on lady bugs that were getting into the home. They treated and sealed the home against the lady bugs and bombed the property afterwards and that solved the problem.

I, however, would lean towards a big dang fire.