We've had all of those, too. At the stream downhill from our house we've seen watersnakes. My husband patrols the lawn before moving but we have had an unfortunate incident with a garter snake. Also, one day last summer he was chatting with a couple of neighbors when they heard a strange rattling noise coming from our (outside) air conditioner condensor unit. It turned out to be a snake that somehow got sucked into the fan on top of the unit. We thought it might have been a young rat snake but it was hard to tell due to the small pieces (eeewww).
I keep a little log of critters too. So far in the snake dept, in descending order of quantity, we have black rat, worm, garter, northern ringneck, green, and copperhead. The green, unfortunately, met his untimely demise from my lawn mower.
