Science Facts

How Does Jellyfish Sting? – Causes & Faq

Jellyfish Sting

Jellyfish is a free-swimming umbrella-shaped marine animal that is not a fish at all. It’s because a fish is specifically centered around the anatomy of its backbone. Scientists discovered jellyfish fossils and rocks believed to be more than 500 million years old, making them older than most dinosaurs. It’s even possible that the jellyfish lineage goes even further to over 700 million years.

You’re swimming in the ocean when something brushes your leg. When the tingling sets in, you realize you’ve been stung by a jellyfish. How do these beautiful, gelatinous creatures pack such a painful punch? Jellyfish are soft because they are 95% water and are mostly made of a translucent gel-like substance called mesoglea.

They rely on thousands of venom-containing stinging cells called cnidocytes for protection and prey capture with such delicate bodies. Even baby jellyfish, the size of a pencil eraser, can sting. Larval jellyfish, ephyrae, look like tiny flowers pulsating in the sea. They become umbrella-shaped with a bell at the top and descending tentacles around the margin as they grow.

How does jellyfish sting?

Jellyfish skin absorbs oxygen through bodies which evades the need for lungs. Since they don’t have any blood coursing through their veins, there’s no need for a heart to pump it through the body. They can even split in half to create a second version of themselves. The largest species of jellyfish, the lion’s mane, has tentacles that can extend more than 100 feet, longer than a blue whale. These tentacles contain most of the stinging cells, although some species have them on their bells, too.

Each sting cell has a hollowed capsule called a nematocyst containing a tightly coiled, harpoon-like thread immersed in venom. The venom contains toxins that can affect gastrointestinal, cardiac, and neurological systems and cause allergic reactions.

Venom is ejected via a nematocyst, a whip-like hollow tubule. It lies coiled under high osmotic pressure. When mechanical or chemical stimuli activate an external trigger, the lid of the cell pops open, and seawater rushes in. It forces a microscopic barbed harpoon to shoot out, penetrate and inject venom into its victim.

A brush of skin with a tentacle is enough to set the sting mechanism of millions of cells in motion. The skin is a natural substance which when coming in contact with a stinging cell. A sensor collects it on the cell. The sensor then decides whether the contact is with another tentacle or a potential food source like skin. The sensor passes the information up to the cell’s body, triggering an enormous pressure buildup within the cell.

  • When the pressure reaches 200 atmospheres, the coil turned dark is fired and penetrates the skin at 40,000 G’s. A toxic dart then spreads the poison throughout the skin, much like a multi-headed poisonous arrow. This process is happening with millions of stinging cells. So you might guess inflammation and a great deal of pain.

Jellyfish tentacles have organelles in them called nematocysts. They’re like little hypodermic needles. Nematocyst discharge can occur in less than a millionth of a second. It makes it one of nature’s fastest biomechanical processes. Nematocysts can continue to fire even after a jellyfish has died. So it’s important to remove lingering tentacles stuck to the skin. Rinsing with vinegar will usually render undischarged nematocysts inactive. Seawater can also help remove residual nematocysts. But don’t use freshwater because any change in salt balance alters the osmotic pressure outside the cnidocyte. And it will trigger the nematocyst to fire.

  • A jellyfish hold 100 times more venom than the most dangerous Cobra on the planet.

Most jellyfish stings are a painful nuisance, but some can be deadly. An Indo-Pacific box jelly is also called a sea wasp. It releases venom, which can cause contraction of the heart muscles and rapid death in large doses. There’s an anti-venom, but the venom is fast-acting. Despite the impressive power in their tentacles, jellies aren’t invincible. Their stinging cells are no match for the armor of thick-skin predators, like the leatherback turtle and ocean sunfish.

These predators both have adaptations that prevent slippery jellyfish from escaping after they are engulfed: backward-pointing spines in the turtle’s mouth and esophagus and recurved teeth behind the sunfish’s cheeks. Even tiny lobster slipper larvae can cling to the bell of a jellyfish and hitch a ride, snacking on the jelly while they preserve their energy for growth. Small agile fish use the jellies as moving reefs for protection, darting between tentacles without ever touching them.

Nudibranchs, which are sea slugs covered in a protective slime. They can steal the jelly’s defenses by eating the cnidocytes and transferring them to specialized sacks for later use as weapons against their predators. Even humans might benefit from the sting of a jellyfish one day. Scientists are manipulating cnidocytes to deliver medicine, with nematocysts rarely 3% of the size of a typical syringe needle.

Why jellyfish sting?

Jellyfish are anatomically vulnerable. Their venomous sting acts as a defense and hunting mechanism when their tentacles encounter food or prey. They reach out and fire a harpoon-like structure from within their bodies that contain neurotoxic venom. When it comes to other marine life, it’ll paralyze their prey. But when it comes to humans, it’ll just really hurt. Jellyfish have enough venom to disable prey their size because humans are bigger. It has a less dramatic effect on bodies compared to small marine life. But that doesn’t mean it won’t hurt. Symptoms include intense stinging pain, itching rash, and raised welts.

  • In a word, some other progressive or after-effects of a jellyfish sting include nausea, vomiting, diarrhea, lymph nodes, swelling, abdominal pain, muscle spasms, or general numbness. In contrast, more severe reactions include difficulty breathing or death.

Their venom is meant to instantly kill or stun prey like fish or shrimp so that their struggle to escape won’t damage its delicate tentacles. What makes the jellyfish unique is its venom. According to NatGeo, they’ve developed the ability to move swiftly in water. They even have eyes with a sophisticated lens, retina, iris, and cornea, allowing them to see. Scientists aren’t sure exactly how to box jellyfish process what they see. Jellyfish stings are very rarely deadly. What is most dangerous is inaction or the wrong course of action.

Each year, about 150 million people around the world are stung by jellyfish. Sometimes large numbers of jellyfish are pushed close to shore by ocean currents, resulting in episodes of mass stingings. In contrast, many types of jellyfish are relatively harmless. Most stings only cause pain and red marks on the skin. Like the box jellyfish, some types are much more dangerous and cause whole-body and potentially life-threatening illnesses. These severe stings can cause vomiting, muscle spasms, fainting, difficulty breathing, and heart problems.

  • The box jellyfish is considered one of the most venomous and dangerous creatures in the world.

Different species of these cube-shaped jellies range in size from 5 millimeters to 3 meters long. Their sting can cause excruciating pain, heart failure, and death within minutes. An estimated 40 people die each year from box jellyfish stings. Some scientists believe this number may be closer to 500.

Frequently asked questions

Does peeing on jellyfish sting work?

With over 200 diverse species in temperate and tropical regions around the globe, these primitive creatures have been around for 600 million years of evolutionary history. While they may not have a brain, heart, or much social life, jellyfish are masters of chemistry. They use photoreceptor proteins to sense light, bioluminescent proteins to produce light. And toxins to knock the living daylights out of their prey and predators.

You’ve all heard the rumor that peeing on a jellyfish sting can make the pain go away. But does this icky old wives tale stand up to science? If you’re taking a trip to the beach, rest assured jellyfish will not seek you out. They only sting if you run into them. They’re covered in stinging cells called cnidocytes, which they’ve evolved to paralyze prey and deter predators.

The urine’s acidity supposedly denatures porin proteins. When your unconcentrated urine hits them, water will force its way into the cells to achieve a balance. This extra pressure is just what the nematocysts need to fire, injecting you with a brand new round of toxins.

The old wives tale is correct that an acidic solution might neutralize some toxins. But the amount of acid isn’t in urine. Pee is acidic, usually with a pH of around 6. It isn’t acidic enough to denature porins and prevent them from hole-punching cells. So urine and water don’t work.

How to treat a jellyfish sting?

Effective treatment of jellyfish stings depends on the species that stings you. But generally, if you’ve been stung, you should remove any attached tentacles with tweezers instead of scraping or rubbing them as the pressure releases their venomous capsules. Then soak the affected area in hot water or vinegar. Severe stings may require CPR, and if it was a box jelly, you might need an antivenom.

Recently, scientists have found a potential antidote to box jelly stings in the form of cholesterol medication. Though it has only been tested in mice, it could block pain, tissue death, and scarring for 15 minutes. To avoid getting stung in the first place, scientists have developed topical products that can prevent or reduce their severity. One study found that this type of cream prevented over 80 percent of jellyfish stings. You can also wear a protective suit or avoid the ocean during jellyfish season.

More Articles:


Klappenbach, Laura. “Ten Facts about Jellyfish”. Archived from the original on 26 February 2009.
Daley, Jason, “Take a Peek at the Mesmerizing ‘Cosmic Jellyfish'”. Smithsonian.
Isabelle Rodd, “Why jellyfish could be a ‘perfect food'”. BBC News.

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