If you avoid pesticides, predators such as mud dauber wasps will appear as your system becomes more balanced, and go to work controlling the Black Widows for you. I would look into planting some trees and shrubs that will provide food and shelter to attract birds. As Renate suggested, adding a small pond would also be helpful. I would try to change the areas where you find the Black Widows so that they don't want to be there, and whenever possible, encourage other spiders that compete with Black Widows for food. As mentioned above, the other backyard life you identified is either harmless or beneficial.