Clashing colonies of sea anemones fight as organized armies with distinct castes of warriors, scouts, reproductives and other types, according to a new study. The sea anemone Anthopleura elegantissima lives in large colonies of genetically identical clones on boulders around the tide line. Where two colonies meet they form a distinct boundary zone. Anemones that contact an animal from another colony will fight, hitting each other with special tentacles that leave patches of stinging cells stuck to their opponent.