Earthworms have a high nutritional value and are ideal for most fish that are large enough to accept them. Don’t use worms dug from ground that has recently been treated with fertilizers, pesticides, herbicides, fungicides or any other chemical.You should never feed the earthworms directly to your fish. You should first place the earthworms into a clean, damp container to allow them to clear out their digestive track. They should be left in the container for at least six hours and then thoroughly cleaned with water to remove any dirt. They can then be chopped up or fed whole. Earthworms should be kept alive until ready for feeding. It is also possible to buy earthworm flakes, frozen and freeze-dried earthworms.