These are not worms, but the larval form of Chironomus, a species of the fly. They are bright red in color and are sometimes found in pools with decaying leaves. Even though they have a somewhat hard shell, they form an excellent food for mature fishes. They are easily recognized by their color and and their method of populsion - snapping their body in and out of an "S" shape. Do not trust them in a tank that contains small fry; they are capable of catching and killing them. Blood Worms are excelent food for Corydoras catfish.