My worm bin hasn't been growing very fast but i only started out with 200 worms in a 30-50 gallon tub. My frogs really like european nightcrawlers which are in my bin, especially my african clawed frogs. The substrate for my worms is peat, I wouldnt use newspapers because then the worms will eat the paper and that will then go into your frog. Make sure to keep the soil moist if you do get a worm bin, then the worms will eat off the surface and it will be easier for you to pick one off for feeding. You can also raise springtails in your worm bin mine is infested with them lol.