Hi Kane,
Fire-bellied toads are native to south-east Asia. They spend most of their time at the water's edge blending in with the green algea and aquatic plants. Their cage should reflect their natural habitat. It should have a large water area that varies in depth and gradually slopes up to a land section where the toads can feed. Bumble bee toads are native to Argetina, Uruguay and one or two other South American countires where they live in a wide range of habitats but as far as I know, none of them are in the shallows of algea covered ponds. They are best kept in a terrestrial setup with a small pool of water.
The other concern that I had was related to the adult size of both animals. The bumble-bee toads that I've seen for sale have never been much larger than an inch in length. Some small toads (juveniles or males I'm assuming) that I saw at a reptile dealer were roughly about half an inch long. Fire-bellied toads (Bombina orientalis, not B. bombina) can grow to a length of a little over two inches. They have a huge appetite and will attempt to eat anything that moves. I've even watched larger fire-bellies try to eat small toads of the same species. There is no doubt in my mind that at some point one of your fire-bellied toads will attempt to eat the little bumble bee toad. If fire-bellied toads can eat full grown adult crickets then I'm sure they could eat a one inch long toad.
The other thing that just crossed my mind while writing this was that both species that you are keeping are poisonous. Not only would you loose a bumble bee toad if one of your fire-bellies ate it, but you could also loose a fire-belly. There is also the risk of either species being harmed by the other's poison in the cage itself.
In a large cage you might be able to overcome the differences in habitat and maybe if you provide enough hide spots for the bumble bee toad it will be able to stay away from the fire-bellied toads and maybe if you change the substrate and water in the cage often you won't run into problems with the frogs poisoning one another but to me it seems like there are too many risks involved to say it's a safe mix. Good luck,
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Devin
devin@amphibiancare.com
www.amphibiancare.com
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