Where have the garter snakes gone?

[Melantha]

I live in southeastern Minnesota. All through the spring and most of the summer, I enjoyed seeing the eastern garter snakes that live under my porch and driveway. I recognized several individuals who would sun themselves in a couple locations almost every morning. Then, in late July, they seem to have disappeared. Sightings are down from almost daily to maybe once a week. Whats up? where have they gone? I live in a suburban neighborhood that has great habitat, a huge field and pond out back.