Oat straw is great too. I give it fresh and dry to my crabs. One glass of oat straw tea has as much calcium as 8 glasses of milk. I get sea lettuce for my crabs http://en.wikipedia.org/wiki/Sea_lettuce localy. If you check with the local rangers and live near the ocean they can help you to safely gather seaweed and sea lettuce that is safe for both you and the crabs.. I gather and dry it for my hermit crab dollar store items in my etsy shop.