Hi
Sounds like a good idea to me.The only danger might be too much water and cause drowning.
I've kept worms in my greenhose soil for years,mainly as a treat for the birds but they do a great job of keeping the soil fresh.
Gary

You are thinking of red wiggler worms. I haven't grown these worms in a terrarium but I have a worm bin. A good resource to learn about them is "Worms Eat My Garbage" by Mary Applehof. They have different requirements than earthworms for successful maintenance. They need a lot of aeration, and room to move to keep them from dying. They are best at eating rotting food and not humus. Also their eggs are really small and depending on the size of your mesh, could probably slip through. And, they multiply like mad! Get a big frog if you try this--

I didn't even think about them reproducing! And I didn't realize they did it with eggs either. They probably would fall through the screening. . . but then wouldn't they just die in the water? Of course that would foul the water. . . hmmmmmmmmmmmmmm. . . well what about normal earthworms and not the red wigglers? space isn't really a problem, as I have an 85 gallon long vivarium, and if the moisture balance is right, then soggy soil shouldn't be a problem either. any further thoughts?

I think it might be better to have worms "on the side" to feed your frog. Once you get things established, you wouldn't want to have to take the terrarium apart because the worms weren't working out. It is really easy to grow red wigglers-the only problem is that they reproduce like mad! I don't know enough to recommend the earthworm--it just seems unnatural to have them in a terrarium (but then, I do have my red wigglers in a Rubbermaid container so. . . )

IME regular earthworms seem to require cool soil so in part you may need to determine just how warm your soil gets. Be interested to hear what you find out and how everyting goes for you.
Good luck. : )

Well, I did some research on the internet, and it looks like my idea is a no-go. Earthworms require cool soil and LOTS of it for their extensive tunnel systems, and the red wigglers multiply too fast. I *might* still try just 2 or 3 red wigglers after I have a frog in the hopes that he'll eat them as fast as them can multiply, but I'm a little cautious to try this in case I have to rip everything up and start over in order to exterminate them if they take over. I think I'd do a small trial of this first though.

One problem I could see happening is that the worms, not liking the humid environment you may have for the toads (that they do like) would frequently inhabit the surface...in other words, fewer worms & fatter frogs.

red wigglers WILL get through your screen if it just an average window mesh size. They also secrete a foul slime when they are disturbed so many animals don't like eating them.