Keep egg shells in open container in fridge. When the container is full, crush shells into small bits and sprinkle them around base of your plants. Sharp eggshells will deter slugs, snails other bugs & adds touch of calcium to soil.
Save eggshells & coffee grounds & sprinkle them around hydrangeas & roses. The calcium is good for the roses & the coffee grounds make the soil more acidic for the hydrangeas. Organic Gardening - How to Deter Slugs and Snails With Eggshells