These are not worms but the aquatic larvae of nonbiting mosquitoes.Although it is sometimes thought that they live in mud, they are actually found in the water of areas that are well endowed with organic matter. They are sold live, frozen and freeze-dried in the aquarium trade. Live bloodworm can be kept for a few days in a refrigerator, wrapped in moist newspaper. Freeze Dried Bloodworm supposed to be much safer, because of the risk of pathogens being passed onto aquarium fish through live bloodworm. I like to feed frozen bloodworm to my fish and have never had any problems with it. They are a excellent source of nutrition, because they are rich in protein. And the fish seem to love them.