I try to use everything that's of value. Including eggshells. My favorite use for them is to feed them right back to the hens. Eggshells are almost pure calcium and calcium in a chicken's diet ensures that future eggs will have nice hard shells. I collect the empty shells and keep them in the refrigerator. Once I have a big pile I place them into the microwave, on high, for 3 minutes. This sterilizes them.