Michigan has two species of Gray Treefrog – the Eastern (Hyla versicolor) and Cope’s (H. chrysoscelis) that are hard to distinguish, sometimes even sharing the same ponds. Check out the Hyla versicolor page at the UM Animal Diversity Web for a bit about that. Their color spans a range of gray, green or brown according to environment or activity. See a collection of photos showing their wide range of color at the UM Animal Diversity Web.
They can be found in woods, swamps and your own backyard. Their ability to climb vertically & horizontally is due to their specially adapted toe pads, and you’ll sometimes find them on your screen windows at night. You’ll hear their short musical trill on warm spring & summer nights.
Jamie writes that he walked 20′ into the woods off a heavily used path and ran into this little guy – small as his thumb and sitting on a milkweed. Check this out background bigtacular and see more in his Fauna slideshow.