I bet that's true about the betta, I recently bought some plants from someone and put the plants in two different tanks. In one tank I have baby snails all over the place, but only an occasional snail sighting in the betta tank. The betta doesn't bother my apple snails, but I suspect he's eating the new baby snails. However, bettas can often be aggressive towards other fish. I can't tell you what to expect if you do nothing though, since I am about to find that out myself in the non-betta tank. So far I'm not bothered by the snails, though.