Discover the Most Dangerous Jellyfish Found in U.S. Waters

Vacationers at Daytona Beach, Florida were in for a nasty surprise over Memorial Day weekend. Upwards of 300 ocean goers were stung by jellyfish. The species responsible was likely the moon jellyfish, and although they have a painful sting, they are unlikely to cause serious harm. Lifeguards helped apply vinegar to stung individuals and reminded visitors that the tentacled creatures are capable of stinging even in death. This is a good reminder for summertime swimmers.

Luckily for those of us in the U.S., most jellyfish encountered in American waters will not cause serious harm. However, one species found along U.S. coastlines has the potential to be deadly. Do you know the most dangerous jellyfish found in U.S. waters? Are they common? Follow along to find out!

This post was updated on June 5, 2025 to include the recent surge of jellyfish stings at Daytona Beach.

What is the Most Dangerous Jellyfish in U.S. Waters?

The most dangerous jellyfish in the United States is the Alatina alata, also called the sea wasp. Another name for this jellyfish species is the winged box jellyfish. Previously, the species was named
Carybdea alata. This box jellyfish has a long range and a powerful sting. It was first recorded in 1830. Although box jellyfish are venomous and one of the most dangerous animals in the world, the Alatina alata‘s stings are rarely fatal. Instead, the stings leave an uncomfortable and burning rash for about 20 minutes. However, pain can continue for about 2 hours.

About the Sea Wasp

Jellyfish are unique creatures. Although the Alatina alata was only recorded in 1830, we’ve learned a lot about this jellyfish species. Follow along to learn more about the animal, including its size, range, diet, and potential predators.

Appearance and Size

So, what does a sea wasp look like? Sea wasps are transparent and smooth with a notable rounded tip umbrella. As their name suggests, they have four wing-like pedalia with pinkish-yellow tentacles. They are also about 25 centimeters long and about 1/2 to 1/3 as wide.

Distribution and Habitat

This box jellyfish species isn’t picky about its environment. However, they spend a lot of their time near shore waters. They also live in the deep sea. Sea wasps are found throughout the Pacific and Atlantic Oceans. In the United States, they are most often found on the eastern coast. Alatina alata are strong swimmers. They’ve been recorded in depths up to 3,500 feet. They’ve also been recorded and observed on the surface of the water.

Diet

Using their long tentacles, this jellyfish species consumes zooplankton. They also eat caridean shrimp and worms. Interestingly, in a study, researchers observed that most winged box jellyfish had empty stomachs.

Predators

Not a lot of animals are daring enough to try and hunt a winged box jellyfish. Their stings are painful. One of the only brave animals to eat box jellyfish is the green sea turtle. Green sea turtles have thick skin, so a sting doesn’t affect them.

The World’s Most Dangerous Jellyfish

The winged box jellyfish isn’t the most dangerous jellyfish in the world. Stings are, thankfully, rarely fatal. Instead, the world’s deadliest jellyfish is the Australian box jellyfish. Just one quick sting from this deadly marine animal is enough to cause paralysis and a heart attack! This species sports tentacles about 10 feet long, though they contract to about 5.9 inches long. Interestingly, these jellyfish also have 24 eyes. Unlike the winged box jellyfish, this species consumes small fish. They are most common in Australia and have been directly linked to about 64 deaths. Sometimes, the paralyzing stings can lead to drowning. Sadly, this risk is higher with small children.

What to do If you’ve Been Stung by a Jellyfish

At least 150 million people every year get stung by jellyfish; however, the majority of stings are mild and don’t result in hospitalization. Still, it’s a scary experience, and important to know what to do if you suspect you’ve been stung by a jellyfish.

Firstly, it’s important to remain calm. A lot of deaths in the ocean are a direct result of panicking, which leads to drowning. Treatment varies and depends on the species. If you’ve been stung by a jellyfish, experts recommend applying vinegar to the wound as soon as you get out of the water. Vinegar alleviates the stinging sensation and stops venom from releasing. You can also rub baking soda or salt water on the wound. However, if you’ve been stung by a box jellyfish, call 911, as you never know if your symptoms will be mild or severe.

Box jellyfish stings can cause tightness in the chest, nausea, and muscle spasms. When they sting, a red whipped-shape lesion is left behind. Sometimes, it blisters. You mustn’t rinse the sting with fresh water as this can spread the venom. Although movies have depicted using urine on a jellyfish sting, it’s not recommended.