There are also Salt water varients of Scuds. I had (and still have) them in my reef tanks, and they serve a number of purposes - Algae control, tasty snacks for my other fish and larger inverts, as well as mini-hoover's that stir up and sift through my sands, eating pretty much everything, and keeping the substrates well turned. I personally love the little things, and have never noiced any "downside" to having them in your tanks.