Hazardous Marine Life

Hazardous Marine Life

Portuguese Man-of-War

Portuguese man-of-wars are free-floating cnidarians characterized by 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.

Biology and Identification

There are two species for the genus: Physalia physalis in the Atlantic and Physalia utriculus in the Indo-Pacific. The Atlantic man-of-war may reach slightly larger dimensions, with the gas bladder rarely exceeding one foot (30 centimeters) and tentacles averaging 33 feet (10 meters) and possibly extending up to 165 feet (50 meters).

Though many people mistake the Portuguese man-of-war for a species of jellyfish, this genus belongs to the order Siphonophora, a class of hydrozoans. What we see as a single specimen is actually a colony composed of up to four different types of polyps. Despite its resemblance, these animals are more closely related to fire coral than to jellyfish.

The Portuguese man-of-war is easily recognizable; if you see blue tentacles, you can bet they belong to Physalia.

Risk to Humans

The man-of-war's polyps contain cnidocytes delivering a potent proteic neurotoxin capable of paralyzing small fish. For humans, most 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, 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 timely professional medical evaluation.


Approximately 10,000 cnidaria envenomations occur each summer off the coasts of Australia, the vast majority of which involve Physalia. In fact, man-of-wars cause the most cnidarian envenomations prompting emergency evaluation 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.


  • Always look up and around while surfacing. Pay special attention during the last 15-20 feet of your ascent, since this is the area where you may find cnidarians and their submerged tentacles.

  • Wear full-body wetsuits regardless of water temperature. Mechanical protection is the best way to prevent stings and rashes.

  • In areas where these animals are known to be endemic, a hooded vest may be the best way to protect your neck.

First Aid

  1. Avoid rubbing the area. Cnidarian tentacles are like nematocyst-coated spaghetti, so rubbing the area or allowing the tentacles to roll over the skin will exponentially increase the affected surface area and, therefore, 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.

  2. Remove the tentacles. You must take great care to remove the man-of-war's tentacles to avoid further envenomation. Those distinctive blue tentacles are quite resistant to traction, so you can remove them fairly easily with some tweezers or gloves.

    NOTE: If you do not have access to tweezers or gloves, 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 even thousands of unfired nematocysts, so pretend you have been handling hot chili peppers that cause blisters anywhere you touch, and treat your fingers as recommended from the next step on.

  3. Flush the area with seawater. Once the tentacles and any remnants have been removed, using a high-volume syringe flush the area with a powerful stream of seawater to remove any remaining unfired nematocysts. Never use freshwater since this will cause unfired nematocysts to fire.

  4. Apply heat. Immerse the affected area in hot water (upper limit of 113°F/45°C) for 30 to 90 minutes. If you are assisting a sting victim, try the water on yourself first to assess tolerable heat levels. Do not rely on the victim's assessment, as intense pain may impair his ability to evaluate tolerable 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 the same area where the diver was injured. Repeat if necessary. If hot water is not available, apply a cold pack or ice in a dry plastic bag.

    NOTE: 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 superficially inoculated, application of heat may help by denaturing the toxin.

  5. Always seek an emergency medical evaluation.

  6. Continue monitoring the patient until a higher level of care has been reached.

Vinegar Application

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 household vinegar over certain species of cnidarians, including Physalia. Still, the most current American Heart Association guidelines (AHA 2010) recommend application of vinegar for all jellyfish, including Physalia spp. If anything changes, DAN will let you know.

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