Thanks for checking in, and sorry for not reporting back. He seems to be doing okay. Whatever it was I saw on his skin has gone away. It's possible he was dry. I keep a water bowl in his terrarium and change it every evening with fresh water, and I mist a couple of times a day. He sits in his water bowl most nights, but maybe he was still a bit parched on that particular day?

I'm no expert in interpreting frog behavior, but my impression is as a wild frog he is unhappy in his current environment. Daytime temperatures were down below freezing again today, but hopefully spring will arrive soon and we can let him go back into the wild. As soon as we hear his brethren sounding in the back yard as we do each spring, we'll know it's safe to turn him loose.

Thanks again for following up!