Have you ever been swimming in the ocean and felt a sharp prick but seen nothing? Maybe you forgot about it until the next day when painful, red, itchy bumps emerged in the outline of your bathing suit. Some people refer to the attacker as sea lice, but it is no relation to blood-sucking head lice or fish lice. In Spanish there is a better name for it: pica pica. It means itchy itchy.
The little animal behind that painful itch is larvae of Linuche unguiculata, the thimble jellyfish. In spring and early summer adult thimble jellyfish, which are the size and shape of thimbles, congregate in giant orgies. Soon after the females release hordes of young larvae, each the size of a speck, into the ocean. Under a microscope they look like an oval with fuzzy, leg-like cilia surrounding it. Zoom in further and you can see their nematocysts or stinging cells. The thimble jellyfish is endowed with powerful nematocysts because a little, jelly-like animal that doesn’t sting is just that–a little, jelly-like animal. Thimble jellyfish would be defenseless in an ocean of predators and powerless over prey without their nematocysts.
Nematocysts have a spring loaded, toxin-filled thread with a sharp barb at the end. You might feel the pinch of nematocysts when you collide with larvae in the ocean. If, however, you don’t simply collide with larvae, but they instead get squeezed between your bathing suit and your skin, the pinch is more severe. Lots of nematocysts from well-stocked arsenals trigger at once, and poison-filled barbs pierce your flesh. Adults have more nematocysts, there are hundreds or thousands on their tentacles. Unlike larvae, they probably won’t swim down your bathing suit.
How can you swim with the larvae and avoid days of itchiness afterwards? Florida’s Department of Health warns: “the surface area of a bathing suit may increase the area over which stings can occur.” So when choosing a suit, remember small is good and two pieces are better. If you really want to be safe, swim without one, though this isn’t legal at most beaches. The Department of Health also recommends that swimmers in larvae-filled waters take their suits off before showering to prevent more firing of nematocysts as larvae are shocked with fresh water. Unfortunately, showering naked at the beach is also illegal.
A purple flag at the beach is a warning that dangerous sea life, like itchy itchy, is present. Reluctant to get naked but don’t want to waste a good day at the beach? Then grab a bag from the BlueTube at your beach and pick up trash instead. While we can’t keep itchy itchy out of the ocean, we can keep plastic out of it.