No vacation to one of Hawaii’s islands is complete without swimming or snorkeling in the stunning waters of the Pacific Ocean. With fantastic visibility and comfortable water temperatures, you can enjoy seeing stunning corals, reef fishes, sea turtles, and even manta rays.
However, jellyfish are found in Hawaii’s waters, and some can sting.
We will take you through the different types of jellyfish in Hawaii. You’ll discover which ones you need to be wary of and what to do if you should be unlucky enough to experience a jellyfish sting.
Mostly there’s nothing to worry about, as millions of people enjoy the waters around the Hawaiian islands each year without incident.
What Kind of Jellyfish Are in Hawaii?
If you’re wondering, “are there jellyfish in Hawaii?” the answer is yes. You’ll find jellyfish in almost all of the world’s oceans, including the waters around Hawaii.
There are almost 1,800 different animals that scientists class as jellyfish, and in Hawaii, we only see a few of them. Jellyfish are relatives of such diverse sea animals as sea anemones and corals, and many of them use a sting to catch their food.
The kinds of jellyfish found in Hawaii include probably the most common jellyfish, the harmless moon jellyfish.
You’ll usually see the spotted jellyfish in shallow waters, including lagoons and harbors, and it’s another which doesn’t sting.
The jellyfish of Maui, Oahu, and the other islands that cause the most concern are the different types of box jellyfish. These mostly transparent jellies can give a potent sting, so they are best avoided. Luckily, the box jellyfish calendar can predict their appearance in the ocean as they typically appear about eight to ten days after a full moon.
Hawaii also receives visits from the Portuguese man o’ war. Although these aren’t technically jellyfish, they look like one to most people. You should treat their long stinging tentacles with the utmost respect and stay well away.
Finally, we’ll be looking at stinging sea lice, which are tiny jellyfish larvae.
You don’t need to be overly concerned about jellyfish when visiting Hawaii. Use common sense, and don’t touch anything in the water or on the beach that could sting you. Always follow the instructions given by warning signs and flags.
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5 Types of Jellyfish in Hawaii
There are five main types of what are commonly called jellyfish seen in Hawaiian waters. We will look at how to identify them, where you might see them, and consider how concerned you need to be if you encounter one.
If you want to be guaranteed to see jellyfish for yourself, you can see many of these species in the Waikiki Aquarium in Honolulu.
1. Moon Jellyfish (Aurelia aurita)
You don’t need to worry if you come across moon jellyfish in Hawaii as they are harmless to humans.
What Do Moon Jellyfish Look Like?
Adult moon jellyfish measure up to 25–40 cm (10–16 in) in diameter. Their translucent bodies are often purple-colored, but you may also see them having a blue, yellow, or white shade.
Moon jellyfish are pretty easy to identify thanks to the distinctive four, five, or six small pink or purple circles that can be seen inside their bodies.
The moon jellyfish is round in shape and relatively flat. They curve towards their base at the edges, so they look like a small frisbee.
Underneath, moon jellies have a collection of very short tentacles, which they use to trap their microscopic plankton food.
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Where Might You See Moon Jellyfish?
Moon jellyfish drift along at the water’s surface, carried by the current. You’ll often find them in coastal waters, and they may collect in bays, lagoons, or harbors. It’s normal to see them together in large numbers as they feed.
Moon jellyfish often get washed onto Hawaii’s beaches, particularly in rough weather, allowing seabirds to enjoy a leisurely meal.
Do Moon Jellyfish Sting?
No, moon jellyfish won’t sting you. Although moon jellyfish have nematocysts on their tentacles to capture prey, it’s doubtful that you’ll feel anything if you come into contact with one. If you are very sensitive, at most, you’d possibly feel something like a minor bee sting.
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2. Spotted Jellyfish (Mastigias papua)
You might also hear this relatively small jellyfish called the lagoon jelly, golden medusa, or Papuan jellyfish.
What Do Spotted Jellyfish Look Like?
Spotted jellyfish have small white spots on their yellow-brown tinted bell.
The average size for fully-grown spotted jellyfish is between two and seven centimeters / 0.8–2.8 inches in diameter and three to ten centimeters / 1.2–3.9 inches long.
Where Might You See Spotted Jellyfish?
The spotted jellyfish has symbiotic algae living in its tissues that use sunlight to make food. For this reason, spotted jellyfish are usually seen in groups during the day in shallow water lagoons over sandy-bottomed shorelines, where they will swim to stay in the best sunlight.
Do Spotted Jellyfish Sting?
No, spotted jellyfish won’t sting you. Because they have evolved to use sunlight for virtually all their food requirements, they have almost completely lost their need to sting.
3. Box Jellyfish (Cubozoa)
You may have heard horror stories about box jellyfish and want to know are there box jellyfish in Hawaii. The answer is yes. However, luckily the famously dangerous Australian box jelly (Chironex fleckeri), also known as the sea wasp, is NOT found here.
There are three species of box jellyfish found in Hawaiian waters: Carybdea rastonii, Carybdea sivickisi, and Alatina alata.
Alatina alata is the largest of the three Hawaiian box jellies, but its body still only reaches between 2.5 – 7.5 centimeters / one to three inches tall.
What Do Box Jellyfish Look Like?
Box jellyfish are relatively small and get their name from their square, box-like bodies.
Although their bodies are small, box jellyfish can have four relatively long tentacles that trail behind them for up to one meter / three feet when they swim.
Box jellyfish are almost completely clear and are very hard to see in the ocean.
Where Might You See Box Jellyfish?
You’ll usually find box jellyfish in shallow waters, and it is relatively common to see them at some of the more popular beaches.
However, you can plan your beach day as the arrival of the box jellyfish can be predicted with reasonable accuracy.
Box jellyfish spawn a few nights after a full moon in the open ocean beyond the reefs. High tides eventually carry the jellyfish over the reef and into shallower waters, where they get trapped. Beach visitors then find box jellyfish in the shallows, often in considerable numbers.
By checking the jellyfish calendar, you can determine when large numbers are predicted. Usually, this is eight to ten days after a full moon, particularly on the south-facing Hawaii beaches. The jellyfish invasion usually lasts for about five days.
It’s worth knowing that rough or windy weather can push box jellyfish in more quickly to the shore, and you may see them earlier than the box jellyfish calendar predicts.
The most common beaches to see box jellyfish include the north shore at Waimea Bay and the south shore beaches (Waikīkī, ala Moana, and Hanauma Bay). They can also be expected on Oahu’s south-facing beaches, the western or leeward beaches (Makaha and the Waianae Coast), and the eastern or windward coast at Kailua.
Do Box Jellyfish Sting?
Box jellyfish have a painful sting. However, fortunately, they are only very rarely fatal.
The long tentacles are covered in microscopic stinging cells, and if you are unlucky enough to contact them, you will know it straight away.
The jellyfish stings when the cells are activated by contact. The stinging cell fires a barbed thread that can pierce your skin. This delivered the box jellyfish venom, which causes an instant burning sensation. Barbs that don’t penetrate the skin can remain on its surface and sting you later when administering first aid.
You can help prevent the risk of getting stung by avoiding swimming when there are warnings. Take the time to look carefully at the water before getting in and try to see if there are shapes or shadows that may be box jellies.
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4. Portuguese Man O’ War (Physalia physalis)
The Portuguese man o’ war isn’t actually a jellyfish. It’s something called a marine hydrozoan. However, as for most people, it looks and behaves just like one, we can treat it as a jellyfish for this article.
Portuguese Man o’ war encounters are relatively common in Hawaii, and as they deliver a painful sting, it’s essential to be aware of what they look like and where you may see them.
You may also hear them called blue jellyfish or blue bottles in Hawaii, so they’re talking about the same thing if someone mentions those names.
What Does a Portuguese Man O’ War Look Like?
The man o’ war stays afloat thanks to an unusual gas-filled sack unlike a jellyfish. These bladders are translucent blue, purple, pink, or mauve colored, so they are reasonably difficult to see against the ocean as they move on the surface pushed along by the wind.
The sail bubble can be as tall as 15 centimeters / 6 inches and about 9 to 30 centimeters / 3.5 to 12 inches wide. Hidden below the surface are huge tentacles which can be as long as 10 and 30 meters / 30 to 100 feet.
Where Might You See a Portuguese Man O’ War?
You’ll usually find the man o’ war on south-facing beaches where the winds carry them toward the shore. However, it’s always good to check the water before you get in, no matter where you are during the bluebottle season.
Does a Man O’ War Sting?
When activated by touch or chemical cues, the man o’ war can send stinging cells into the water from its tentacles that can penetrate human skin and give a nasty sting. It’s common for multiple stingers to remain on the skin’s surface with the tentacle’s sticky remains. It’s essential to take care when administering first aid not to activate these and worsen the problem.
You should be aware that even seemingly dead animals washed onto the beach can still sting you, so handling one without protection is not a good idea.
Man o’ war stings can cause breathing and cardiac difficulties, fever, shock, and even death if left untreated. Immediate first aid and emergency medical attention are needed in the event of any sting.
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5. Sea Lice (Jellyfish Larvae)
In Hawaii, what are called sea lice are actually jellyfish larvae known for occasionally making swimming and snorkeling very uncomfortable.
What Do Sea Lice Look Like?
Sea lice are tiny, so you’re not going to see them in the water. Check local information and ask lifeguards if they are a problem before swimming.
Where Might You Find Sea Lice?
Sea lice can appear anywhere, but they are probably most common on the leeward beaches during the summer.
Do Sea Lice Sting?
Unfortunately, sea lice can deliver toxin and sting similar to other jellies. It’s common to experience a burning rash that can be itchy and painful for several days.
Many people consider that wearing baggy clothing like t-shirts while swimming makes it more likely to get stung as the sea lice get trapped inside, making a sting more likely.
Avoid baggy swimwear and wear reef-safe sunscreen, which can act as a barrier to reduce the risk of being stung. Shower immediately after swimming and change out of your bathing suit straight away.
If you feel a reaction, make sure that you thoroughly wash your bathing suit in detergent before wearing it again.
Sea lice aren’t so common that they ruin the enjoyment of the millions of people that swim every year in Hawaii’s waters. However, if you do suffer an unknown rash or itchiness after swimming, they could be the cause.
Are There Dangerous Jellyfish in Hawaii?
At certain times, large numbers of stinging jellyfish, including box jellies and the man o’ war, can be pretty common.
Both of these can cause painful stings and irritating rashes that require medical attention.
Fortunately, you won’t find the world’s most dangerous box jellyfish in Hawaii.
The three species that are seen can have an uncomfortable sting, but they are generally not considered deadly.
You can use the box jellyfish calendar to predict when you are more likely to encounter them and plan your swimming accordingly.
What Do You Do if You Get Stung by a Jellyfish in Hawaii?
Ma o’ war and box jellyfish stings need immediate first aid and medical treatment. If you’re in doubt of what to do, call emergency service for assistance.
First Aid Treatment for Jellyfish Stings
Box Jellies and Man O’ War Stinging Cells
Follow these steps to treat man o’ war and box jellyfish stings:
1. Carefully spray the area with white vinegar to reduce venom activity.
2. Gently remove the remaining tentacles using tweezers, gloves, a plastic bag, a towel, or anything else you have to protect your bare fingers. Take care not to scrape or rub the tentacles as this can cause more venom to be released.
3. Wash the affected area with large amounts of white vinegar.
4. Place a hot compress on the wound or immerse it in hot water. Applying heat may help to relieve pain.
5. Monitor the victim carefully and get immediate medical attention if they have any difficulty breathing, anaphylactic shock, an irregular heartbeat, altered levels of consciousness, or begin to feel unwell in any way.
If you think you’ve been stung by sea lice, wash the affected area with large amounts of vinegar.
Applying hydrocortisone cream and taking antihistamines, including Benadryl, can help reduce irritation and itching.
If symptoms worsen or you start to feel unwell, seek emergency medical assistance.
Of all the types of jellyfish in Hawaii, some are relatively safe, and some can cause nasty stings.
Always check local information before going in the water to see if there is a higher than average risk. Carry a first aid kit with you and keep updated with current jellyfish sting treatment recommendations.
The chance of getting stung by a sea jelly on your Hawaii vacation is really quite small, so long as you’re sensible.
British-born Dan has been a scuba instructor and guide in Egypt's Red Sea since 2010.
Dan loves inspiring safe, fun, and environmentally responsible diving and particularly enjoys the opportunity to dive with sharks or investigate local shipwrecks.
When not spending time underwater, Dan can usually be found biking and hiking in Sharm's desert surroundings.