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Man-of-war washing up on St. Augustine Beach

Photos by Jenn O'Brien
Photos by Jenn O'Brien

ST. AUGUSTINE BEACH, Fla. – Some people heading to St. Augustine Beach have seen some Portuguese men-of-war on the sand. Members of the St. Augustine Lifesaving Association said they have a couple of the hydrozoans but nothing too much out of the ordinary.

They said they get pushed onto shore by winds and tides every so often.

The Portuguese man-of-war is a predatory species. It uses its feeding tentacles to sting and paralyze small fish, pelagic crustaceans and other invertebrates. The feeding tentacles may be up to 160 feet long in some individuals! These tentacles deliver a powerful sting and are also used for defense against predation. 

Each individual Portuguese man-of-war is either a male or a female, and they reproduce sexually via a method known as broadcast spawning. Large groups of individuals come together, where females release their eggs and males release their sperm into the water column, all at the same time. This method increases the likelihood that eggs will be fertilized.

The Portuguese man-of-war is not valuable, commercially, and is common throughout the tropics. In some places, it is increasing in numbers, likely a result of changing open ocean food webs. This species’ sting can be very painful if encountered by people. When there are large numbers of individuals in an area, it is best to avoid swimming.

They are covered in venom-filled nematocysts used to paralyze and kill fish and other small creatures. For humans, a man-of-war sting is excruciatingly painful but rarely deadly.