How to Avoid Nasty Encounters with Jellyfish in Hawaii

Aug 11, 2021 | Marine Life in Hawaii

In Hawaii, about 8-10 days after a full moon, there is a higher probability of box jellyfish sightings on all leeward sides of Hawaii islands for three consecutive days.

Now, Hawaiian beaches and underwater adventures are great fun, but no one wants to be stung by a jellyfish. While none of the jellies in Hawaii are deadly, their sting burns badly, irritates the skin, and can ruin a vacation.

By knowing when the jellyfish are floating near the shore, you can better decide when to go swimming — or be better prepared when encountering one.

What Are Jellyfish?

“Jellyfish” (also known as “Sea Jelly”) is the common name for how Medusozoa look in their so-called “medusa stage,” which is their sexual (larvae-producing) life stage.

Technically, the correct term for jellyfish is “jellies,” as they are not actually fish.

Jellyfish have an umbrella-shaped body, and their tentacles can sting to protect themselves from predators.

Like humans, jellyfish are made up mostly of water. But jellies are composed of nearly 95% water. Humans consist of “just” 60% water.

Jellyfish have been around about three times as long as the first dinosaurs. Their oldest ancestors date back 500 million years; they might have lived up to 700 million years ago.

However, jellyfish don’t have a long lifespan; most jellyfish only live about a couple of months.

Jellies come in all different sizes, from as small as .4 inch (1 cm) in diameter and up to as big as about 6-8 feet (1,8-2,4 meters) in diameter with a length of about astonishing 70 feet (21 meters).

They live everywhere, from the Mediterranean to the Antarctic, at every ocean depth. They tolerate both shallow warm water and deep, dark, cold water.

Jellies eat other jellies, and hence, the biggest predator of jellies is its own kind. They usually leave their own specific species alone and eat other species of jellyfish.

For more fun facts about jellies, have a look here.

Back to top

How Do Sea Jellies Sting?

Some box jellyfish are known for their powerful venom that stuns or instantly kills prey, such as fish or shrimp. Stings from certain species can be harmful and extremely painful to humans and sometimes even fatal.

Most other species of jellyfish don’t pose a serious threat to humans.

Box jellyfish that are seen in Hawaii are not deadly.

The tentacles of a jellyfish are covered with hundreds of thousands of specialized cells; each cell harbors a capsule called a “nematocyst” or needle-like stinger.

When activated, this stinger shoots venom into prey or a predator (or a human) at the speed of 37 miles per hour (60 kilometers per hour). This is microscopic harpoon speed.

To a human, this sting feels like being poked with a bunch of needles. If hit close to the spine, some might feel like their limbs refuse to function properly or experience difficulty breathing.

Back to top

What Happens When You Get Stung

While fatalities from jellyfish are extremely rare, being stung by one can still ruin your vacation!

Also, most folks do not know an effective remedy, and applying a relief found on the internet could potentially intensify and lengthen the burning sensation.  

A Typical Jellyfish Sting Reaction

A typical jellyfish sting reaction

A typical jellyfish sting reaction

In most cases, reactions run the scope from not feeling anything to feeling extremely ill for several days and everything in between.

Most often, jelly stings result in immediate pain and red, inflamed, possibly throbbing, irritated markings on the skin.

In some severe cases, several hours after the initial sting, a person might experience nausea, vomiting, headache, muscle pain, weakness, drowsiness, difficulty breathing, or heart problems.

Symptoms often depend on a person’s age, health, size, time exposed to the stinger, and the size and type of jellyfish. If symptoms persist or exacerbate quickly, seek immediate medical treatment.

Extreme Reactions to Jelly Stings

In extremely rare cases, a sting can lead to high blood pressure, brain hemorrhage, and even death.

Most casualties from venomous box jellyfish stings happen within a matter of minutes from cardiac arrest. This type of box jellyfish would typically be found in Australia, not Hawaii.

While we still don’t completely understand the mechanism that leads to death, this article on shines a light on the science and the research behind it (Angel A. Yanagihara, Ph.D. from the University of Hawaii, is awesome!!).

What To Do When You Get Stung by a Jelly

There’s no actual proven remedy, and there are hundreds, if not thousands, of timeworn homemade treatments.

When you get stung by a jellyfish, first remove the tentacles or nematocysts from the skin without plucking or scraping. Use a towel or some cloth other than your fingers.

As to what to do next…

Many people swear by urinating on irritated skin (Please don’t!), while others insist on applying seawater (I don’t think so!) and baking soda, aloe vera juice, or hot water (NOT cold water or ice).

A recent study by researchers at the University of Hawaii concluded that some of these common recommendations are not that effective and might actually make the situation worse!

Their research suggests rinsing with vinegar after the sting to stop the jelly’s stinging cells from activating, then applying heat to slow down venom activity.

In our experience, HOT WATER definitely works (as much as you can stand it). For example, jumping into a hot tub brings fast relief, while cold water makes the nematocyst fire again.

If symptoms persist or get worse quickly, always seek immediate medical attention.

How Often Do People Get Stung by Jellyfish in Hawaii?

According to the Washington Post, studies and media reports estimate that the number of people who get stung hovers around 150 million stings per year worldwide.

However, as we know, most jellyfish stings aren’t fatal. Out of these 150 million, only a handful of people died from the jellyfish sting.

Fortunately, in Hawaii, the box jellyfish’s venom is less potent than their relatives elsewhere. Nonetheless, the sting is still painful.

Additionally, most folks do not know an effective remedy, and by doing the “wrong thing” they read on the internet, they could potentially intensify and lengthen the burning sensation.

Back to top

Varieties of Jellyfish Around Hawaii

Throughout the world, there are about 2,000 different documented varieties of jellyfish. Some scientists believe that there could be an additional 300,000 more jellies that have yet to be identified.

Ocean-goers around Hawaii encounter mostly “box jellies”, which are pretty predictable (see the calendar below); however, you will randomly encounter Man O’ Wars year-round around the shore. Most people get stung by these Man O’ War; they’re not technically jellyfish, but their sting is also painful.

Back to top

Why an Influx of Box Jellyfish?

Box Jelly influxes happen about 8 to 10 days after a full moon. This is when the box jellyfish’s mating habits are linked to tidal and lunar conditions.

When any jellyfish is sighted, lifeguards put up signs to warn people of their presence in the affected areas, but nevertheless, some people are eager to swim.

When high tides recede as dawn approaches, the box jellies appear inshore and often end up trapped along the beach. Or, strong onshore winds push jellies toward the beaches, and that’s when they really pose the biggest threat to swimmers.

Back to top

Box Jellyfish Arrival Dates Calendar for Hawaii

Check out the 2024 Manta Rays of Kona calendar with heartfelt stories about the magnificent gentle giants, including each month’s box jellyfish arrival dates. See when the jellies are expected along the leeward sides of all Hawaiian Islands during the day- or nighttime.



Back to top

How to Avoid Nasty Encounters with Jellyfish

There are four ways to avoid swimming into a group of jellyfish when you’re around Kona:

  1. If you booked a manta ray moonlight swim with us, we prepare the groups thoroughly and (almost) insist to have extra skin coverage — or (worst case scenario) we’ll cancel, abort or postpone to a safer day.
  2. If you’re planning your own trip and just want to go swimming around Hawaii, talk to the lifeguards for guidance.
  3. Look at the beach: If there are jellyfish on the beach, don’t go in the water because there will be far more jellyfish in the ocean.
  4. Use long-sleeved shirts and long pants, or a full wetsuit to reduce skin exposure.

Back to top

Swim Without Concern

At Manta Ray Advocates, we have lots of in-water experience and do our best to guide you without getting stung.

Click here to arrange a manta ray swim — we’ll make sure it isn’t when the jellies are floating about.

To fully prepare for swimming, snorkeling, and/or scuba diving with manta rays around Hawaii, download our ebook about how to prepare to swim with manta rays below!



Submit a Comment

Your email address will not be published. Required fields are marked *

More things you’ll love!

A Guide to the Different Types of Rays in Hawaii

A Guide to the Different Types of Rays in Hawaii

The Dark Side of Manta Ray Tourism: the Impact of Ecotourism on People, Mantas, and the Environment

The Dark Side of Manta Ray Tourism: the Impact of Ecotourism on People, Mantas, and the Environment

Swimming with manta rays: what you need to know before diving in

Swimming with manta rays: what you need to know before diving in

Do Manta Rays Smile? And What’s the Deal with Giggling Sting Rays?

Do Manta Rays Smile? And What’s the Deal with Giggling Sting Rays?

Preparing and Defogging your Snorkeling Mask (+ our Secret Solution)

Preparing and Defogging your Snorkeling Mask (+ our Secret Solution)

Full-Foot Fins or Open Heel Fins: Which Swimming Fins are Best?

Full-Foot Fins or Open Heel Fins: Which Swimming Fins are Best?

We participate in referral programs, and this website contains affiliate links. If you buy something after clicking a link on this website, we may get a commission – at no extra cost for you.

We only include products we love and wholeheartedly recommend. Read more here.

Free Downloads

Manta Ray Facts & Figures Ebook

Amaze your friends and family members with your knowledge of the gentle giants.


Guide to Swimming with Manta Rays

All the things you need to know before you embark on this adventure of a lifetime.


10 Tips for Marine Photography

Learn to capture life-changing moments underwater.


Pin It on Pinterest

Share This

Share this post with your friends!