A Portuguese man-of-war is not one animal

Physalia is a siphonophore: a colony of specialised individuals — the float, the stinging tentacles, the feeding parts, the reproductive parts — budded from one larva and unable to live apart.

A siphonophore starts as one fertilised egg and then buds a string of zooids that share a circulation and a fate. In the man-of-war the top zooid is the pneumatophore, a float filled with gas, with a crest that acts as a sail. Below it hang gastrozooids that digest, dactylozooids that carry the tentacles and the nematocysts, and gonozooids that reproduce. Each is an individual in the taxonomic sense — a modified polyp or medusa — and none of them is a viable animal on its own. The sting, which is genuinely dangerous to a swimmer, belongs to the tentacle people. The sail belongs to someone else. The meal is shared through the colony.

Calling it a jellyfish is the error the surface invites, because both are gelatinous and both sting. Jellyfish are single organisms. This is a colony that has gone so far into division of labour that it occupies the ecological slot of a single predator. A beach covered in blue floats is a beach covered in wrecked colonies, not in fish, and not in one creature that decided to come apart. It was never one creature. It was a crew.