Most of the primitive fish known as lampreys spend their childhoods as filter-feeders, taking nutrition from the organic scraps floating in the water. As adults, many lamprey species turn parasitic. A lamprey latches onto a fish with its sucking mouthparts, then gouges into its flesh with teeth and a tongue like a drill bit. It drinks the blood of its host and sometimes grinds up muscle tissue as well. A lamprey attack can kill its host.
The species pictured above, the sea lamprey, may be familiar to many readers for its well-publicized invasion of the Great Lakes, where it has depleted indigenous species like lake trout. Recently, though, the sea lamprey has made its return to the Balkan Sea. The lampreys announced their return by attacking a couple of swimmers. Lampreys are a fairly minor danger to a creature with hands to remove them--but the removing isn't much fun.