Although raising night crawlers is not difficult, you need to monitor their living condition to promote healthy growth and to encourage reproduction. Night crawlers require a specific soil environment with a good blend of organic material, moisture and soil texture.
Build a bed 16 to 24 inches deep, counting 100 to 500 worms per square foot of bed. The bed can be in-ground or above-ground depending on your primary goal in raising night crawlers. Make the bed from steel, plastic or wood, but avoid pressure-treated wood, as it contains chemicals toxic to the worms. If one of your goals is worm casting to use as fertilizer, use a mobile high-strength steel mesh bottom to collect the casting. Simply shake the mesh bottom, and the casting will fall. The worms are not affected, as they live near the surface.
Keep the soil loose. Night crawlers like loose soil where they can tunnel easily. Fill the bed with topsoil (without added fertilizer) if the soil in your area is clay. Clay soil is too compact, contains too little organic material, and will not absorb water readily. Although it is looser, sandy soil also does not contain the organic materials a night crawler likes.
Squeeze a handful of soil to see how much water comes out. Less than two drops of water means the soil is too dry; more water means the soil is too moist. Keep the soil appropriately moist.
Add 2 to 3 inches of fresh bedding every three months if you do not remove the casting from underneath the bed. Replace the entire bedding every year in a 16-inch bed.
Feed your night crawlers organic material. Organic means fruits, vegetables and noncolored paper. Avoid giving the worms leftover meat, because they will not readily eat it. Place the food on top of the bed, and cover it with an inch of soil to allow the microorganisms in the soil to begin decomposing the food. Give the night crawlers more food when they finish the previous serving.
Monitor the bed temperature and acidity. Ideally the bed should be between 65 and 75 degrees F. Extended periods of a lower or higher temperature will be fatal to the worms. Check the pH level of the bedding to maintain it between 6 and 7. Add limestone every two or three weeks to maintain a good pH.