One lonely MTS hitched a ride on a plant from the LFS and now I have hundreds in the substrate and tons of babies on the glass. Too bad I can't feed them to my puffer fish. He ate all my pond snails faster than they could breed so they're pretty scarce right now. I don't suppose the MTS are doing any harm. They don't harm plants but seriously the entire substrate is moving. It is a heavily planted tank but their favorite food is those Hakari algae wafers. Many of them congregate in that area and compete with the cories for them. Water parameters have been good in spite of all the snails.