I'm not sure the anemones are nearly as much danger to your reef as the crab himself. The anemone hermit is fast-moving and aggressive, and will go after all kinds of inhabitants, including fish,crabs, snails, starfish, and others. I'll never forget the call I got as the one we briefly owned was ripping apart our 4" spider-decorator crab and eating him in front of my kids. He was not your average hermit crab, and had to go "away" after proving himself too rough for our tank on several occasions.