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    Cyamus

    Tiny hitchhikers on the ocean's giants

    Despite their unappealing nickname, Cyamus species are fascinating, highly specialized creatures that live exclusively on large marine mammals, especially whales. They belong to the family Cyamidae and are amphipods, meaning they are crustaceans, like crabs and shrimp, but with a completely different lifestyle. Instead of swimming freely or crawling along the ocean floor, Cyamus species spend their entire lives clinging to the skin of their host whale, feeding on dead skin, sloughed tissue, and sometimes algae. Their bodies are flattened and equipped with strong, claw-like limbs that help them hold on tight, even when their host is swimming through icy waters or diving deep into the ocean.

    What sets the genus Cyamus apart is its extreme host specificity. Different Cyamus species are adapted to different types of whales. For instance, Cyamus boopis is found mostly on right whales, while other species prefer humpbacks or gray whales. These lice are so closely associated with their host species that they’ve become useful in whale research—their location, abundance, and species type can help scientists identify individual whales, track social behavior, and study whale migration. Unlike most marine parasites, Cyamus lice don’t swim, and they can’t survive off their host. They only get from one whale to another by direct contact, usually when whales mate, give birth, or rest closely together.

    Interestingly, Cyamus species are also unique among crustaceans because they don’t go through a free-swimming larval stage. Their young are born as tiny, fully-formed juveniles and immediately begin life on the whale’s body. You’ll often find them clustered around rough patches of skin, wounds, or natural features like callosities (especially in right whales), which provide both food and shelter. Some even prefer areas where barnacles grow, taking advantage of the crevices and flaking skin. In some cases, whales can carry thousands of Cyamus individuals, turning their bodies into a mobile microhabitat for these clingy crustaceans.