What Are Sea Lice? Beachgoers Are 'Losing Their Minds' After Seabather's Eruption

Sunbathers crowd the beach in Ocean City, Maryland, on July 22, 2017. DANIEL SLIM/AFP/Getty Images

Maryland swimmers are frenetically scratching after an outbreak of sea lice struck the state's eastern Ocean City Beach.

"We have been getting a lot of calls about sea lice today. The Eastern Seaboard is experiencing this nature phenomenon," The Ocean City Beach Patrol wrote on Facebook on Thursday. "They can get into bathing suits while swimming and cause discomfort. Our best advice is to rinse with fresh water."

Potomac resident Laura Gwyn told The Baltimore Sun that a lifeguard warned her about the sea lice but said she should not worry too much. Gwyn's two teenagers entered the water, and while "they were fine for probably 10, 15 minutes," they soon "started losing their minds" as they became increasingly itchy.

Sunbathers crowd the beach in Ocean City, Maryland, on July 22, 2017. Sea lice struck Ocean City Beach, sending swimmers into an itching frenzy. DANIEL SLIM/AFP/Getty Images

While certainly irritating, sea lice are not actually lice; they are the larvae of jellyfish and sea anemones.

"The larvae may be small, but they're not defenseless. Like mature jellyfish and anemones, the larvae are covered in cells that contain toxin-filled harpoons, called nematocysts, that are ready to launch into the skin of a threat," according to National Geographic. "When the larvae find themselves in a stressful situation, like getting caught in an armpit or under a swimsuit, their harpoon-shooting cells are activated."

A rash typically appears on affected swimmers within 24 hours of being stung, CNN reported.

Although predominantly just an irritant, the larvae can cause fever, nausea and chills in extreme cases.

Sea lice have appeared in the northeast before, but seabather's eruption, as it's known, occurs much more commonly in waters near Mexico and the Caribbean.

Florida has documented sea lice outbreaks since at least 1903, when a Miami resident wrote that "we were all poisoned... with some kind of rash which set up an intense itching. It was not so bad for us as we could stay home and doctor ourselves with lotions but the poor men having to work in the fields or hot packing houses were the ones who really suffered."

The stinging larvae invaded Florida two months ago, flooding the shores of Pensacola Beach. The Florida Department of Health estimates that since 1992, at least 10,000 cases have occurred in the state.

"It's just one of those things you have to deal with when you go into the Gulf of Mexico," Pensacola Beach Water Safety Chief Dave Greenwood said. "You are a land animal, and the Gulf is not our native environment."