Q: I was surprised the other day to find a small gray frog in my watering can. I helped the frog get out, then filled the can with water and watered my flowers. The next day, the tiny frog had taken up residence again in the empty can. What kind of frog is it, and why is it still around as the weather is turning colder?
A: It is likely to be one of two species: Cope’s gray treefrog (Hyla chrysoscelis) or Eastern gray treefrog (Hyla versicolor).These two species so closely resemble each other that they can only be reliably distinguished in the field by the breeding calls of the males. The Eastern gray treefrog has a musical, birdlike trill. The call of the Cope's gray treefrog is similar, but is a faster metallic, buzzy/burry trill.
The Eastern gray treefrog has twice as many chromosomes as the Cope's gray treefrog. They also differ somewhat in their distribution in Minnesota. Currently there no records for the Cope's gray treefrog in northeastern Minnesota, and no records for the Eastern gray treefrog in southwestern Minnesota. Eastern gray treefrogs reportedly prefer more wooded habitats than Cope's gray treefrogs.
Both species actually overwinter on land under shelters of bark, leaves, rocks or logs. Their bodies can withstand partial freezing; converted glucose from the liver protects their vital organs from freezing.
People should check their potted plants before bringing them indoors—Copes' and gray treefrogs like to take shelter in the leaves and watering trays where they can stay moist (like in a watering can). If possible, people should let soil dry thoroughly before bringing plants in. That way there will be less of a chance for the frogs to hitch a ride inside.
Click here for more information on reptiles and amphibians of Minnesota.
Click here for distribution maps of reptiles and amphibians in Minnesota.
Information provided by the Minnesota Department of Natural Resources.