I kept getting them in my tanks with live black worms. Even after I tried to separate them. So I stopped ordering them. But I was left with leeches afterwards. They loved it when I’d feed the tank white worms. I’d watch them eat them. But trying to catch them wasn’t easy. I bought some cheap glass trap on Amazon. That has helped. Also, my pea puffers seemed to take care of them on their own. lol, so I didn’t need to worry about that tank, but I wouldn’t consider them to be as good as the glass trap. It took them awhile/don’t always get along with other fish. I have gotten them from other things, such as plants, but it wasn’t nearly as many as the black worm fiasco. Probably baby leaches that I couldn’t see?