What do "mud daubers" do? It's been so dry, I'd be surprised if it's from this year. Though I do water the garden every day and Lord knows the creek has dried up pretty good.
They actually sting and paralyze the spiders, pack them into a cell, lay an egg on them, cap the cell and start anoher . The spiders are there alive, but paralyzed ready to be eaten by the wasp larvae. Macabre, but sort of neat.