Wisconsin's Tree Frog Species

Two Unique Types Call Our State Home

by Annie Shao, age 16

Shy, swift, and elusive, tree frogs leap from tree to tree with amazing agility, making them difficult for humans to observe. Wisconsin is home to two different species of tree frogs: the eastern gray (hyla versicolor) and the Cope’s gray (hyla chrysoscelis).
The eastern gray and Cope’s gray tree frog are almost identical, with a few subtle differences. The eastern gray is about two and a quarter inches larger than the Cope’s gray and also has bumpier skin. The two species also prefer different habitats; the eastern gray lives in wetter places like marshes, while the Cope’s gray can be found in drier hardwoods near water. Finally, the frogs’ songs differ.  The eastern gray is known for its three-second trill, while a faster, more nasal song belongs to the Cope’s gray tree frog.
The life cycle of a tree frog begins when a female lays one to two thousand eggs. She lays her eggs in groups of 10 to 40 on plants, where they hatch in three to seven days. In about two months the tadpoles become mature frogs.
After the frogs spend their summers eating insects and trying not to become food themselves, they search for a safe place to hibernate during the winter. Usually they settle down on the ground in leaves, under logs or loose bark, and in animal burrows. When winter arrives, snow covers them, giving the frogs insulation from wind and the cold air.
Their bodies also prepare for winter. Glycerol, an alcohol in their tissues and fluids, increases. Since glycerol has a lower freezing point than the water in their bodies, it acts as an antifreezing agent for tree frogs. The rest of their bodies will freeze until the spring when they revive again.
Many people wonder how tree frogs are able to stick to smooth surfaces. Some may guess that their feet have suction cups on them or that they can cling to small irregularities on surfaces.
Both of these guesses are incorrect. Tree frogs’ toe pads have flat, hexagonal-shaped cells surrounded by miniscule openings. These openings let each cell move around and stick to the surface at a relatively flat angle. The cells then release a mucus-like liquid that flows between and over the cells, creating surface tension. This surface tension helps the frogs bind strongly to any surface, but not so securely that they are unable to break the bond.
Although we may not always see them, the eastern gray and Cope’s gray tree frogs live alongside us year-round. As eggs hatch into tadpoles and then grow into frogs, humans marvel at their climbing agility. Of course, we also enjoy their chorus in the spring after a long, silent winter.

[Source: Wisconsin Natural Resources]

I have two decorative bird houses attached to our fence. I have had a little green frog in one and a little gray & brown one in the other. Their little noses peek out of the opening in the bird houses. We have enjoyed watching them all summer. I am wondering if they are tree frogs? – BettyNew Holstein, wi (2011-08-12 22:28)
Very nice article Annie. I myself have been an avid frog, turtle, and snake enthusiast since I was a young kid. Used to always poke around and search for tree frogs, painted turtles, garter snakes, salamanders, etc. I am kind of wondering though, do we only have 2 species of tree frogs here in WI? I live here in River Falls with the Kinnic Kinnic River right out our back door, and have been taking a lot of pictures lately of our frogs and toads we have. The frogs I have pictures of are different than what you describe though. Of course I have caught pictures of the more common Green tree frogs, but, I also have several of some that have camouflage light grey / dark grey patterns, and also the other night I got a picture of one with a green / grey camo pattern. I typically see them only at night, between 12 - 4am. Is it possible we do have other species? Just curious as I have been facinated with tree frogs since I was young, and it's cool to be seeing them more often now, usually sitting near lights & lamps catching bugs. Beautiful animals. Would be glad to share my pics if anyone is interested. – Tony S.River Falls, WI (2011-08-29 09:47)
We found a tree frog living in our hanging plant and he was bright yellow on his and very pretty. He or she is welcome to stay as long as he or she pleases – BrianDeerfield, Wi (2014-07-18 18:14)
Excellent article! Found what I think is an Eastern Grey climbing my office window this The one I found this morning was definitely more green than grey, but with narrow gray bands near eyes and under chin and a bit of variegated markings that are mostly green over most of the body. Seemed quite happy when I set him/her loose on a cup plant in my prairie. Thanks for your help ID'ing this little guy! – TerryAmersonWaukesha (2014-08-04 13:55)
These little guys love to cling to my house. – JackiCenturia (2015-07-27 16:02)
Hi...I found a one eyed toad with yellow on its butt..as well suction cup feet...is that common for wi? – ChrisBangor wi (2016-04-29 19:13)
We have two tree frogs that came in form our deck, hidden in a couple of plants, in the fall. When is it time to re-introduce them to the outside? Our over nite temp is predicted at 30 degrees. – Wally MulvaneyWaukesha, WI (2020-04-21 09:45)
I live on a lake & have 2 tree frogs on my garage. I was just wondering how long they live. – Jill HuebschenPost Lake, WI. (2020-08-28 13:23)