Portuguese Man-of-War (Bluebottle)

Portuguese man-of-wars are free-floating cnidarians with blue gas-filled bladders and long tentacles that drift on the surface of the ocean. Contact with a man-of-war’s tentacles can cause intense pain and other, systemic symptoms.

There are two species in the genus: Physalia physalis (known as Portuguese man-of-war) in the Atlantic, and Physalia utriculus (known as bluebottle) in the Indo-Pacific. These animals are easily recognized; if you see a blue, purple or pinkish gas-filled bladder with blueish tentacles, you can bet it is a specimen of Physalia.

Although a Portuguese man-of-war appears to be a single creature, it is actually a colony made up of four types of polyps.

The Atlantic (P. physalis) species is typically a bit larger than its Australian counterpart (P. utriculus), with the gas bladder (pneumatophore) rarely exceeding a foot (30 centimeters) and its tentacles (dactylozoids) commonly 33 feet (10 meters) long and possibly extending up to 100 feet (30 meters).

Although many people think these animals are a species of jellyfish, Portuguese man-of-war belong to the order Siphonophora, a class of hydrozoans. Despite their resemblance to jellyfish, these animals are more closely related to fire coral and stinging hydroids than to true jellyfish.

Mechanisms of Injury

These animals contain cnidocytes capable of delivering a potent proteic neurotoxin capable of paralyzing small fish.

Approximately 10,000 people are stung by cnidarians each summer off the coasts of Australia, and the vast majority of these stings are by Physalia species. In fact, man-of-wars cause the most cnidarian envenomations leading to emergency evaluations globally. The risk may not be so great for divers, however, as most Physalia stings occur on beaches or on the surface of the water rather than while submerged. Certain regions are known to have seasonal outbreaks, but incidence is highly variable between regions.

Signs and Symptoms

Physalia stings cause red welts accompanied by swelling and moderate to severe pain. These local symptoms last for two to three days. Systemic symptoms are less frequent but potentially severe. They may include generalized malaise, vomiting, fever, an elevated heart rate at rest (tachycardia), shortness of breath and muscular cramps in the abdomen and back. Severe allergic reactions to the man-of-war’s venom may interfere with cardiac and respiratory function, so divers should always seek a prompt professional medical evaluation.


  • Always look up and around while surfacing. Pay special attention during the last 15 to 20 feet of your ascent, since this is the area where you are most likely to encounter cnidarians and their submerged tentacles.
  • Wear full-body exposure suits regardless of water temperature. Mechanical protection is the best way to prevent stings and rashes. Even thin rash guards or dive skins are usually sufficient to prevent direct contact with most cnidarians.
  • In areas where these animals are known to be endemic, a hooded vest may be the best way to protect your face, ears and neck.

First Aid

  • Avoid rubbing the area.
    • Cnidarian tentacles are like nematocyst-coated spaghetti, so rubbing the area or allowing the tentacles to roll over unaffected skin will significantly increase the affected surface area and the envenomation process. NOTE: Initial pain may be intense. Though life-threatening complications are rare, monitor circulation, airway and breathing, and be prepared to perform CPR if necessary.
  • Remove the tentacles.
    • Carefully remove the man-of-war’s tentacles to avoid further envenomation using tweezers or gloves. NOTE: If you do not have access to tweezers or gloves, the keratin layer of the skin on your fingers is likely thick enough to protect you. Keep in mind, however, that after removal your fingers may contain hundreds or thousands of unfired nematocysts, so pretend you have been handling hot chili peppers that could cause painful blisters anywhere you touch; so treat your fingers according to the following instructions.
  • Flush the area with seawater.
    • Once the tentacles and any remnants have been removed, use a high-volume syringe to flush the area with a powerful stream of seawater. The purpose of this is to remove any remaining unfired nematocysts. Never use fresh water since this will cause unfired nematocysts to fire (via osmotic lysis).
  • Apply vinegar.
    • White household vinegar (or a mild acetic-acid solution of 2 to 5 percent in water) tends to stabilize unfired nematocysts. Vinegar will not do anything to the venom already injected, so it is only used as a rescue technique to prevent further envenomation from unfired nematocysts.
  • Apply heat.
    The application of heat has two purposes: 1) It may mask the perception of pain, and 2) it may assist in thermolysis. Since we know the venom is a protein that has been micro-inoculated superficially, application of heat may help by denaturing these toxins.
    • Immerse the affected area in hot water (no hotter than 113°F/45°C) for 30 to 90 minutes. If you are assisting a sting victim, test the water on yourself first to assess heat level. Do not rely on the victim’s assessment of a hot but tolerable temperature, as intense pain may impair their ability to evaluate safe heat levels. If you cannot measure water temperature, a good rule of thumb is to use the hottest water you can tolerate without scalding. Note that different body areas have different tolerance to heat, so test the water on yourself on the same area where the diver was injured.
    • Repeat as necessary.
    • If hot water is not available, apply a cold pack or ice in a dry plastic bag.
  • Always seek a professional medical evaluation.
  • Continue monitoring.
    • Continue monitoring the diver until a higher level of care has been reached. Injuries involving species of Physalia tend to cause intense systemic symptoms. Shock might result from substantial envenomations or in smaller victims.

Vinegar and Physalia Species

Use of vinegar is controversial with Physalia spp. Though the use of vinegar has traditionally been recommended, several studies both in-vivo and in-vitro show massive nematocyst discharge upon pouring vinegar over certain species of cnidarians, including Physalia. Still, the most current American Heart Association guidelines (AHA 2015) recommend application of vinegar for all jellyfish — including Physalia spp.

If you choose to apply vinegar, you can optimize application and reduce waste by using spray bottles. Generously spray the area with vinegar for no less than 30 seconds to neutralize invisible remnants. Pick off any remaining tentacles.

Implications in Diving

For the Diver

For the Dive Operator

For the Physician

  • Administer first aid treatment as described above.
  • Seek a professional medical evaluation. Any doctor should be able to help, regardless of any dive medicine knowledge or training.
  • A return to diving may be considered if a physician determines that the injury is closed and there are no unacceptable risks of infection.
  • As the leader of the expedition, you have a duty of care if the injured person was hurt during your trip.
  • Provide first aid treatment as descried above.
    • There are many folkloric first aid treatments proposals; use common sense, and refrain from attempting any scientifically unsound solutions. Remember you might be liable.
  • Make sure you have your customers evaluated by a medical professional.
  • Don’t worry about finding a doctor with dive medicine experience; any doctor should be able to help.
  • Treatment is usually symptomatic, with an emphasis on pain management. Do not hesitate to manage the symptoms aggressively. Pain can be significant to extreme. Shock is possible with significant envenomations and in small victims. Physalia spp tend to cause systemic symptoms beyond those expected at the area of contact.
  • Corticosteroids may or may not be effective.
  • Venoms from these hydrozoans are known to have dermonecrotic and hemolytic effects. Monitor accordingly.

For additional information about marine life injuries, check out the Hazardous Marine Life Medical Reference Book.