Portuguese Man o' War washing up on Cornish beaches.

A warning has been issued to bathers after a large number of Portuguese Man 'o War, Physalia physalis, were found washed up on Sennen and Portheras Cove beaches near Penzance in west Cornwall on Sunday 6 October 2019. People are being urged to be wary of both the animals themselves, and any detached tentacles, as the venom of the species is particularly potent, and can occasionally kill Humans, though children and pets are thought to be more at risk than adults. 

 A Portuguese Man 'o War, Physalia physalis.  Islands in the Sea 2002/NOAA/Wikimedia Commons.

Portuguese Man o' War are colonial Siphonophores only distantly related to true Jellyfish, Scyphozoa, though commonly referred to as such. Their bodies are made up of thousands of individual zooids, each with their own sting, tentacles and digestive system. New zooids are formed by budding from other members of the colony, but remain attached to these to form a single colony. Each year a generation of specialist sexual zooids (gonozoids) is produced which produce eggs and sperm, with fertilised eggs going on to form new colonies. These animals are anchored to the sea surface by a highly modified zooid which forms an air sack, filled with a mixture of carbon monoxide defused from the zooid and nitrogen, oxygen and argon from the atmosphere, which are brought into the sack through osmosis.

Portuguese Man o' War produce an extremely strong venom, for both capturing food and defending the colony, and which is capable of causing extremely painful stings, and sometimes death, in Humans, for which reason people are advised to be extremely cautious on beaches where these animals wash up, not just of entire animals but also detached tentacles, which are less visible but still capable of stinging.

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