Tubifex worm ( tubifex tubifex ) is a native aquatic worm species ,these worms are detritus feeders and live in the substrate aereating it and eating waste ,sludge and left over fish food , these worms are an excellent natural food source for fish and amphibians aswell as a good addition to to a pond or aquarium ecosystem were they will live in the substrate or sponges of the filter and will help keep it clean and even reproduce providing a consistant food source ,the worms can also be stored for long periods if kept in a fridge or cold water.