We often find gray tree frogs in our greenhouses. We're not really sure how they get inside. Maybe they come in on plants we overwinter in the greenhouses (like this banana, below), or maybe they slip through cracks. No one knows. In any event, this is the third one I've found this year, which is way more than normal!
This little guy was sitting on a metal bench in a greenhouse used by a crop and soil sciences class. I moved him into our children's garden greenhouse. We don't use pesticides in that house, and there are some larger plants (like the banana it's climbing on) to hide in. Hopefully he'll survive long enough to move back outside this spring.
Here's another one I found a few weeks ago. This tiny guy was hanging out on a philodendron in our houseplant production area. I assume they must be eating fungus gnats, because that's the main insect we have in the greenhouses right now.