No, they aren't harmful to your fish. The live foods are prepared from healthy ingredients like fish meat, shrimp paste, wheat flour, corn oatmeal, veggies, etc. They are different in shape and look since they are given the shape of worms so that the fish can eat like they would in their natural habitats. So, there are no bacteria or parasites in live foods, and you can feed them to your fish without worrying about the health of the entire aquarium.