Is it planorbis the troublemaker ?
They are really nasty to get rid of.
I have something more to suggest to use along with Scott's advice.
Get a bottle and cut the "throat" and flip the plastic inside, lure some fish food inside and place it in the water before you turn off the lights.
Here is 1 terrible paint to understand what im trying to explain.
Thats a little trap i use for shrimps (easy to get inside, but hard to find the way out), but i noticed that many of my melanoides get inside aswell
Oh and btw dont forget to drill a small hole on the bottom of the bottle so the air can escape, else it will be floating around.
P.S. And if you do this, move your buddies to other tank for the night cuz you dont want a curious toad to get trapped inside and drown.