Hmm. I have a piece of slate that I use to prop the pen door open. Each morning, the chickens and ducks all rush out into the lawn and the little turkey poult comes over to eat any slugs or pill bugs that used the slate for a bed the night before. I'd love to put something out to attract more, but I don't really have space for it. For now, I have mealworms growing out, but want to use them sparingly, since they actually hurt your feed conversion rates. I also toss them any of those grubby things that I find in the garden soil.