Smaller than but nutritionally similar to the white worms, grindal worms can easily be cultured at home. Start with a small, waterproof container such as a plastic bait or shoe box, an ice cream container, or one of the Styrofoam boxes used to ship fish. Fill it two-thirds of the way with commercial potting soil (if you prefer to use dirt or compost from your yard, sterilize it in the microwave before using it) and mist it with water until it is damp but not drenched. Add a worm culture (available from a biological supply company or other hobbyists) and lightly sprinkle the soil with flaked baby cereal or cooked white rice. Cover the box loosely, since the worms need to breathe, and put it in a warm (68°-75°F), damp place, checking it daily. Re-mist the soil if it becomes too dry, and replace the baby cereal as it disappears, removing any that has become moldy. Within a week or two, you’ll notice clumps of worms beginning to appear on the surface of the soil and on the sides of the container. Use tweezers to harvest them, or place a chunk of potato into the culture box; by the next day, it will be covered with worms, which can be harvested by dunking the chunk into a cup of water, then straining the water through a net. Rinse before feeding. Some aquarists add grindal worms directly to the tank; if it is aerated, they will circulate for a while in the water column. But others prefer to dispense them in a worm feeder, since grindal worms are capable of burrowing into the gravel substrate where fish can’t get them. When they die, they pollute the water.