Bluebottle: Physalia utriculus

The Australian Bluebottle, Physalia utriculus, is not a single jellyfish. It is a colonial siphonophore: specialised connected zooids form the float, feeding, stinging and reproductive parts. [1] It is also known as the Pacific Man-of-War or Indo-Pacific Man o’ War. “Portuguese Man-of-War” is sometimes used loosely, but can create confusion with the related Atlantic species Physalia physalis. [1]

WildGuardian’s MEDIUM label reflects the usual risk of a painful sting, not a licence to handle one. Do not touch a Bluebottle in the water or on the beach. A stranded tentacle can still sting.

Recognition and limits

A Bluebottle has a blue, bottle- or pear-shaped gas float, sometimes edged with green or pink, and a trailing stinging tentacle. The Australian Museum gives a float size of about 2–15 centimetres. [1] The float can be very conspicuous when an animal washes onto wet sand, but its tentacle may be much harder to see.

A blue float and trailing tentacle are useful clues, not a reason to pick an animal up. On a beach, keep clear and warn children and pets. In the water, do not approach a floating colony to identify it. Unknown jellyfish or stingers in northern Australia require a more cautious response because box jellyfish are possible. [2]

Where Bluebottles occur

Bluebottles are open-water drifters in the Indian and Pacific oceans. In Australia they are often encountered on the east coast in summer and in southern Western Australia during autumn and winter. [1] Their arrival on beaches is driven by wind, currents and tides rather than a fixed location-by-location calendar.

They are more likely to strand on exposed ocean beaches after strong onshore north-easterly winds and are less common in sheltered water. [1] That is why several Bluebottles may suddenly appear after a weather change even if none was seen the day before.

The colony feeds on larval fish, molluscs and small crustaceans. Stinging cells on the tentacle capture prey and pass it to feeding zooids. [1] The tentacle’s role in feeding is also why direct contact is the relevant human hazard.

Safer beach choices

Follow beach warnings, stay out of water where Bluebottles are visible in the shallows or washed up along the sand, and choose patrolled beaches where possible. The National Health and Medical Research Council advises avoiding direct contact with venomous aquatic organisms and using warnings where hazards are known. [3]

Wear suitable footwear on beaches where washed-up marine life is present, but do not rely on shoes or a glance at the water to make an unidentified jellyfish safe. Do not touch a washed-up Bluebottle to remove it; alert a lifeguard or beach manager if assistance is needed.

Bluebottle sting: correct first aid

A Bluebottle sting is treated differently from a tropical box-jellyfish sting. Healthdirect advises rinsing the sting with seawater, not fresh water, and removing tentacles by hand or with seawater. [2] Then immerse the affected limb in hot water at about 45 °C for 20 minutes, taking care not to burn the person. A hot shower or running hot water may be used if immersion is not possible. [2]

Do not use vinegar for a Bluebottle sting. Healthdirect says vinegar may increase pain. [2] Seek medical care for severe or persistent pain or other concerning symptoms. Call 000 for urgent medical help.

In northern Australia, do not assume an unknown jellyfish sting is a Bluebottle sting. Healthdirect advises treating an unknown sting north of Bundaberg in Queensland and Geraldton in Western Australia as a possible box-jellyfish sting. [2]

Frequently asked questions

Is a Bluebottle a jellyfish?

It is often called a jellyfish, but it is technically a colonial siphonophore rather than a single jellyfish. [1]

Can a Bluebottle on the beach still sting?

Yes. Keep clear of beached animals and tentacles. [1]

Should I use vinegar for a Bluebottle sting?

No. Rinse with seawater, remove tentacles and use tolerably hot water. Healthdirect says vinegar can increase Bluebottle-sting pain. [2]

What if I do not know what stung me in northern Australia?

Treat it as a possible box-jellyfish sting and follow local emergency guidance rather than assuming it was a Bluebottle. [2]

References

1. [1] Bluebottle — Australian Museum
2. [2] Jellyfish stings — Healthdirect Australia
3. [3] Guidelines for Managing Risks in Recreational Water — NHMRC