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Are Jellyfish Dangerous? Everything You Need to Know

Jellyfish, also known as sea jellies, are among the few marine animals whose physical appearance does not exactly highlight their capabilities. While they look light and easy to trample, facts confirm that jellyfish are top predators. They know how to hunt and catch prey.

Jellyfish are often considered dangerous to humans, with most claims focused on the severity of their venom and the possibility of them being fatal. This article will consider the reality of these claims and whether jellyfish can be dangerous and aggressive to us. 

Are Jellyfish Dangerous?

All jellyfish pose a level of danger to humans. They can all sting and do so with precision. Most jellyfish stings will cause an instant burning and itching sensation similar to a bee. You will feel the worst pain in the first few hours after a bite. The pain will naturally subside in the next couple of hours.

Some jellyfish are, however, venomous, and their bite can trigger a range of non-fatal side effects like illness, irritation around the stung area, and throbbing pain that could last a few weeks. Box jellyfish or cubozoans possess enough venom to cause human mortality.

Not all box jellyfish can kill humans, which explains why jellyfish attacks annually are astronomically higher than the number of deaths recorded. There are approximately 150 million attacks on humans by jellyfish annually, with 100 leading to death.

Jellyfish attacks are quite common. However, they will not attack you if you do not touch them. Brushing against a jellyfish during a swim is an invitation for a sting.

Are Jellyfish Aggressive?

Jellyfish are not aggressive toward humans. They prefer to stay away from us and will never attack us unprovoked. Jellyfish only sting if we touch them in the ocean.

When touched, they do not back down from a threat and will instinctively react with a sting. So a jellyfish will only sting you if you mistakenly touch or brush its tentacles. The pain from a sting is immediate and causes a burning sensation similar to a bee.

Also read: What Animals Eat Jellyfish? All About Jellyfish Predators

Jellyfish tentacles

Are Jellyfish Poisonous or Venomous?

A good number of jellyfish are poisonous, and they effectively use their venom to take down prey and kill them. Their long tentacles inject the venom from their tons of microscopic stingers. Despite this, jellyfish venoms are rarely life-threatening.

If bitten by a jellyfish, you may experience mild symptoms like fever or suffer more severe illness. Typically, it is advised to avoid jellyfish as their stings can be painful, whether they are venomous species or not.

How Do Jellyfish Sting You?

Jellyfish will sting you if you touch its tentacles, the appendages it uses for stinging. The tentacles house thousands of microscopic barbed stingers that have tiny bulbs which in turn carry the venom.

When you brush against a jellyfish, the stingers will send thousands of microscopic venoms through the tentacles into your body.

A venomous bite will likely only trigger mild symptoms. However, if a dangerous box jellyfish bites you, you will need to contact medical help immediately.

What Does a Jellyfish Sting Feel Like?

Jellyfish stings create a prickling, burning, stinging pain that is similar to that of a bee. The stung area of the skin will evidently have a print of thousands of stingers called nematocysts. You will feel the worst if the sting is in the first two hours before getting significant relief.

Jellyfish with long tentacles

How Long Does a Jellyfish Sting Last?

The sensation from a jellyfish sting can last for a few weeks, but the worst of the pain is after the first few hours. The first two hours of a jellyfish bite are the most painful, with the burning consistent.

You will experience an obvious reddish, swollen welt around the bitten area. The pain will start to subside as time goes on, with occasional itching that could last for up to a week.

What Part of the Jellyfish Stings You?

Jellyfish sting with thousands of stingers in their tentacles. While the tentacles are what you see when you feel the burning pain of a sting, the thousands of stingers in these tentacles inflict the real pain.

The stingers also pass venom if you are stung by a poisonous jellyfish. The stingers will leave tins of small marks that form several lines of welts in the stung area of your skin.

Side Effects of Jellyfish Sting

  • A jellyfish sting can cause a prickling, burning, stinging pain for up to two hours.
  • The stung area will form welts or tentacle prints on the skin, which will be evident for a few weeks.
  • Mild to severe itchiness for a week or a few weeks after being stung.
  • Swelling around the region of the string.
  • The pain may cover an entire leg or arm if the jellyfish is poisonous.
  • Feverish symptoms and severe illness if the jellyfish have high venom toxicity.

What Happens If You Get Stung by a Jellyfish?

The most obvious sign after being stung by a jellyfish is the rush of pain and tentacle print that appears on the skin area. You will eventually feel a range of symptoms two hours after the bite.

Some signs you may notice include severe itchiness, systemic or full-body illness, weakness, and a range of feverish conditions that may require medical attention.

Pink jellyfish

Can a Jellyfish Kill You?

Only the box jellyfish has been confirmed to have enough toxicity to kill a human. However, only a few select box jellyfish species can kill an adult human.

Realistically, most jellyfish cannot kill a human, whether venomous or not. They may be able to trigger non-fatal side effects like swelling and reddish marks. Some may also cause illness, but that is the worst effect they can trigger.

You will eventually recover from the illness and feel better with time.

Frequently Asked Questions

What is the Most Dangerous Jellyfish?

The Australian box jellyfish is the most venomous jellyfish. Its sting is life-threatening and triggers several severe symptoms that could lead to death in several minutes. The Australian box jellyfish venom can cause Cardiac arrest, paralysis, and death within a few minutes.

How Fast Can a Jellyfish Kill You?

Jellyfish’s high venom toxicity can kill a human between 4 minutes to up to 48 hours. The Australian box jellyfish, which is the most venomous fish in the ocean, has a fatal toxicity that can kill a grown adult within 1 to 8 minutes.

The Irukandji jellyfish, another highly poisonous sea jelly, can kill an adult human within 48 hours due to delayed symptom manifestation after a sting.

Can Jellyfish Sting When Dead?

Yes, jellyfish can still sting even at death. At death, the nematocysts’ cell structure is maintained for a long time and automatically attacks any object, person, or animal that brushes it. Even floating tentacles separated from jellyfish can still sting and possibly pass venom for up to 2 weeks. Jellyfish are dangerous and are not friendly animals.

Can Jellyfish Sting Each Other?

Jellyfish do not sting each other. Each jellyfish has chemicals that serve as cues to each other so they are not mistaken as threats or prey. They are one of the few animals that are not cannibalistic because they never sting themselves.

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