They eat the tenderest juiciest leaves they can find - unusually in my garden! They get moisture from the leaves. They hide deep in their shell when it is hot and light and come out at night to feed. Put half an empty grapefruit shell inside down and they will hide and you can pick them up in the morning. Go with a torch and pick them up. Don't throw them over your neighbour's wall - they make their way back. Some varieties can be cooked and eaten!
