Northern Rock Barnacles (Balanus balanoides) are crustaceans that attach themselves permanently to a hard substrate. They begin life as free swimming larvae and when it comes to settle, they “glue” their heads to hard surfaces, such as rocks, ships, pilings, and other hard-surfaced animals. Shell plates form to enclose the shrimp-like larvae that grow throughout their two to six year life. When water covers a barnacle, the trap door opens, and its feathery legs emerge to sweep the water for plankton and detritus. When the tide is out, plates close to protect them from hot sun, drying wind, rain and ice. Barnacles spend the rest of their lives in this position—head down and feet up. They are prey to dog whelks, flatworms, sea slugs and sea stars.