the blackworm ( lumbriculus variegatus ) is a native aquatic worm species ,its also called the california black worm but this species has a large range from north america ,canada and europe including the uk ,these worms are detritus feeders and live in the substrate aereating it and eating waste and left over fish food , these worms are by far one of the best live food sources available for fish ,amphibians and aquatic insects ,they are highly nutritious and can be added to the substrate or sponges of the filter were they will help keep it clean and even reproduce providing a consistant food source ,these worms reproduce through regeneration meaning when the worm splits or seperates each half will regrow creating 2 new worms ,the worms can also be stored for long periods if kept in a fridge or cold water.