Jellyfish can pack a wallop!

If you have ever been swimming in the ocean and felt a burning pain somewhere on your exposed skin, there is a good chance that you were just stung by a jellyfish! Some species are quite small and your first inkling that they are there is when you are stung! In Guam (and other parts of the world as well) jellyfish can be a threat to swimmers, scuba divers, and other water sports enthusiasts. Encounters with most jellyfish fall somewhere between mild discomfort to excruciating pain. In a handful of species even death may occur.

“Jellyfish” is the common name associated with the medusa phase of the sub-phylum Medusozoa which make up the majority of the species within the phylum of Cnidaria. There are four classes which include Scyphozoa, Cubozoa, Hydrozoa, and Staurozoa. Most jellyfish are free swimming marine animals with a shape like a bell or upside down bowl with trailing tentacles. The tentacles are armed with stingers called nematocysts that they use to capture prey and/or as a defensive mechanism. It’s thought that interaction with chemicals on the skin is what causes the nematocysts to fire and inject venom.

Another member of the phylum Cnidaria, the Physalia utriculus, also known as the Indo-Pacific Man-of-War, is also spotted in Guam waters (and of course, throughout the Indo-Pacific region). It has a smaller float than the Portugese Man-of-War and only a single tentacle. The Physalia utriculus is not a true jellyfish, but a siphonophore. It is made up of medusoid and polypoid zooids. These are tiny animals that are connected to each other and perform the same functions as organs or tissues do in multicelluar organisms. A gas sac keeps it afloat and it is at the mercy of wind, waves, and current. They look like a small blue bubble floating in the water. Just remember that long tentacle hanging beneath it will sting you!

In Guam, box jellyfish seem to gather approximately 9 days after a full moon. This likely has an association with the reproductive cycle. Although not of the deadly variety, they still can pack a painful sting. These jellyfish are normally 3-6 inches long, with a four-sided, transparent bell. They have four tentacles, one on each corner of the bell.

Washed up man-of-war and box jellyfish under moist conditions can still sting for weeks, so keep an eye out when walking on the beach. As a scuba diver, my primary protection is to minimize exposed skin by wearing a dive skin and hood if I am expecting them in the water. Most divers wear a rash guard as a minimum.

For first aid, use something to scrape any parts of the tentacle that have stuck to the skin off or use tweezers if you have them. Do this carefully as they can still sting! The usual advice is to rinse liberally with saltwater. Vinegar if you have it may help. Soaking in very hot water (no more than a 113F) can help break down the toxin. Soak for at least 30-45 minutes. An analgesic like aspirin can help with pain and a hydro-cortisone cream or oral antihistamines can help with itching and swelling.

If there is a sign of a severe reaction such as intense pain, difficulty breathing, swallowing, chest pain, nausea, vomiting, numbness then go to the emergency room immediately. Getting stung in the face, around the eyes (more applicable to swimmers than divers), or in the mouth, especially if any of the tentacles get in the mouth causing swelling of the lips and tongue, then see a doctor immediately.

For most jellyfish stings first aid and following up by treating the welts with ice packs (for swelling) and antibiotic cream for infection while they heal should be enough.

Currently in Guam box jellyfish are expected July 8th-11th according to Brent Tibbatts, a fisheries biologist with the Guam Department of Agriculture. Box jellyfish are expected in shallow waters around Merizo, Piti, Tumon, Pago and Talofofo. Expect the Indo-Pacific Man-of-War to be seen on the north and east coast of Guam where prevailing winds and current pushes it onshore. Sightings should be reported to the Department of Agriculture by calling 735-0289 or by email at