There is a silent killer of snails as well. Many tanks have them, and their keepers keep blaming hermits and are none the wiser. It is a common hitchiker known as a polyclad flatworm. They can scruntch up unnoticable under rocks by day, but at night they go on the prowl for their prey. They can grow as big or bigger than your hand, are generally a speckled color,transparent, and thinner than paper. They have a noticeable oral disc.It covers the snail with this, injects it's venom, which turns the snail into a digestable form.