Portuguese man o' war

The Portuguese man o' war (*Physalia physalis*) is a colonial marine siphonophore, not a true jellyfish.

The Portuguese man o' war (*Physalia physalis*) is a colonial marine siphonophore, not a true jellyfish. It floats on the ocean surface using a gas-filled bladder and is known for its long, venomous tentacles and painful sting. Portuguese man o' wars are occasionally reported on Canadian Atlantic coastlines when warm currents or wind patterns carry them northward, making them a beach safety concern for Canadian swimmers and shoreline visitors.

Classification and biology

The Portuguese man o' war is a siphonophore in the class Hydrozoa, meaning it is a colonial organism rather than a single animal. Its body is made up of specialized zooids that perform different functions such as flotation, feeding, and reproduction. It is often mistaken for a true jellyfish, but it is more closely related to other cnidarians such as hydroids.

Habitat and distribution

This species occurs in tropical and subtropical waters across multiple oceans and typically drifts at the sea surface. It is commonly transported by winds and currents and may strand on beaches far from open water. Large aggregations may form, with groups sometimes numbering more than 1,000 individuals.

Feeding and sting

The Portuguese man o' war uses long tentacles equipped with venomous stinging cells to capture small fish and other prey. It feeds on small fish, crustaceans, plankton, and other small marine organisms. Its sting can be very painful to humans and can cause welts or allergic reactions.

Common identification

It is recognized by a floating, balloon-like gas bladder, often blue to purple in colour, with tentacles trailing below. The sail-like structure gave rise to its common name. It is often mistaken for a jellyfish, but it is a siphonophore.