When I bought my house, the home inspector I hired was a woman. I followed her around as she checked stuff out so I could see what she saw. We go under the crawlspace, she shines her light towards that scene, and [nonplussed] says "You have a lot of snakes out here." I said "The only reason I'm not screaming like a school girl and heading for the exit is I'm under here with a woman, so I'll pretend I'm OK." Those sheds are pretty old and have not increased since I moved in. That being said, there are years where I see black snakes all the time. You can move just about any piece of insulation in the crawlspace and one will be laying there. This year they have often been sunning on my deck and the concrete slab as you walk out the side door. Snakes are a sign of a healthy ecology, and they keep the rodent population in check. In only hope it's not mice that's keeping them here at the house. I get the occasional field mouse in the house, but that's only every few years. They may be after all the skink lizards out here.