Jellyfish are some of the most magical creatures on the planet, and some of the most deadly. If you look at them swimming around inside an aquarium tank, you may wish that you could reach out and touch one. Their thin, transparent skin and long tentacles are elegant as they flow through the water. Some types of jellyfish light up, putting on a light show for those who are watching.
However, they are also very, very dangerous. One type of jellyfish that is native to Australia is the size of a thumbnail yet has a toxin in its tentacles that is strong enough to kill a person. Moreover, the box jellyfish kills around 100 people around the world every year, making jellyfish responsible for more fatalities annually than sharks.
Some stuff about jellyfish falls into the category of being downright weird. They are actually a giant form of plankton and the oldest multicellular organisms on the planet. One type of jellyfish can revert from a mature, adult state back to an infant polyp state. Furthermore, a different kind of jellyfish emits a mucous that contains stinging cells.
That’s right, one type of jellyfish sneezes, and its snot can sting you. There are plenty more fascinating and strange facts about these creatures that seem to belong to the realm of mythology more than real life. However, they are real, and they won’t be going away anytime soon. They have been around for over 650 million years and are proliferating rapidly while other marine creatures are dying out!
To learn everything that you never even wanted to know about jellyfish, keep reading.
Well, as long as there is water. Jellyfish live in every single ocean of the world – the Atlantic, the Pacific, the Indian, and the Arctic Oceans. Oceans are made of saltwater, and animals that have adapted to living in seawater are unable to live in freshwater. So if you take a jellyfish from the ocean and put it into a freshwater lake, it will die.
But some types of jellyfish do live in freshwater! You may have thought that you could be safe from jellyfish stings if you go swimming in a lake or a river, but some freshwater bodies have jellyfish swimming through them.
Invertebrate means an animal that does not have a spine. Jellyfish do not have any bones, ears, brain, heart, feet, or legs. However, they do have a very basic nervous system that has receptors to detect vibrations, light, and chemicals in their immediate surroundings. These receptors enable them to navigate through the water.
Instead of a mouth, jellyfish have a digestive tube that protrudes from its body, through which they feed. In some types of jellyfish, this tube is surrounded by curly tentacles that look like ribbons; these tentacles are known as mouth arms or oral arms. To breathe, jellyfish do not need lungs or gills, as the skin on their bodies is thin enough that they can breathe through it.
Some jellyfish are so small that you can barely even see them. In fact, the smallest jellyfish are just the size of the eraser on a pencil! Their small size and transparent appearance help them hide from predators. However, not all jellyfish are small. Some jellyfish can have tentacles over 40 feet long!
The most giant jellyfish have bodies that are a whopping eight feet in diameter – about the height of a standard-size door. These monster-size jellyfish have tentacles that are 200 feet long, approximately the length of not one but two blue whales. The sheer size of the largest jellyfish is enough to keep some predators away.
If you experience an unhappy encounter with a jellyfish while enjoying an otherwise pleasant trip to the beach, there is a natural explanation why: the vast majority of jellyfish live in shallow coastal areas, where the water is warm. They aren’t looking to sting you; instead, you are in their territory!
Nevertheless, some jellyfish, especially the larger ones, live as deep as 30,000 feet under the sea. That is about five miles down! Moreover, while they typically live in warm waters, scientists have found some in subarctic areas, where the water is much, much water. Jellyfish, on the whole, are quite resilient and thrive in a wide variety of environments.
The two contenders for the smallest jellyfish are the creeping jellyfish and the Australian Irukandji. The creeping jellyfish has a body that can be as little as 0.5 mm to only a few millimeters in diameter. The Australian Irukandji is extraordinarily poisonous and only the size of a fingernail. Its stings can cause immense harm, and you won’t have any warning because these jellyfish are so tiny.
Nomura’s jellyfish is the largest in the world. While super-size jellyfish monsters are the stuff of nautical nightmares, the big ones seem to be quite rare. The Stygiomedusa gigantean, another of the super-size jellyfish, has only been seen 17 times in the past 110 years.
There Are Different Ways For Jellyfish To Reproduce
Some types of jellyfish reproduce asexually by splitting in half. Other breeds have both males and females engage in sexual reproduction. Some kinds of jellyfish are even hermaphroditic, meaning that they have both male and female reproductive organs.
The lifespan of jellyfish varies wildly, with some only living for a few hours and others living for many months. Some live for several years, and one species has been known to live for 30 years! Jellyfish who live in aquariums usually have longer lifespans than those that live in the wild, probably because they are very fragile.
Portuguese Man Of Wars are dreaded marine creatures whose tentacles have a poison powerful enough to kill fish and even humans. Their tentacles can be as long as 165 feet long, and though the more typical length is 30 feet, they are still fierce. They are responsible for thousands of stings every year, and because they usually travel together (sometimes in groups of 1000!), finding one Man-Of-War may lead to an entire beach getting closed.
Portuguese Man Of Wars look like jellyfish, but they are not. They aren’t even one species in particular but rather a combination of several different organisms that work together. One organism comprises the gas-filled bladder, which resembles the body of a jellyfish. The other organisms include the tentacles and other parts of the Man Of War.
You may want to believe that bottom feeders eat what is on the bottom of the ocean, but the reality is a little grosser. Bottom feeders consume out of the same orifice through which they excrete waste. Jellyfish fall into that category, meaning that they eat and poop through the same tube.
Jellyfish are carnivores, so through their feeding tube, they eat tiny animals, including crustaceans (which include shrimp and crabs), small fish, fish eggs, other jellyfish, and plankton. Yes, jellyfish are meat-eaters, though they don’t hunt their food. They passively eat through their oral tubes.
If you have ever had the misfortune of being stung by a jellyfish, you might be inclined to think that the toxins contained in the jellyfish’s tentacles are enough to deter any predators. But believe it or not, some animal species eat jellyfish!
Mostly large marine animals feast on jellyfish. These animals include tuna fish, swordfish, sharks, sea turtles, and Pacific salmon. Maybe they get stung on the inside but just don’t seem to learn their lesson about jellyfish. Alternatively, perhaps they have a built-in protective mechanism that prevents the jellyfish from hurting them.
Jellyfish Have Been Around For a Very, Very Long Time
Jellyfish are actually the oldest multi-organ animal that is still around today! They have been swimming around in the oceans for upwards of 650 million years, making them older than sharks, dinosaurs, even cockroaches!
The longest-living jellyfish are probably the Turritopsis nutricula, what some people refer to as the “immortal jellyfish.” This species can use a cellular process known as transdifferentiation to revert from a mature adult stage back to being a polyp. In other words, instead of dying of old age, it continually cycles back to being an infant.
The hard outer shell of crabs makes them impervious to the stings that could kill a creature of similar size. Perhaps just to flaunt their resilience to other sea creatures, some types of crabs actually hitch rides on jellyfish and even feed on the food particles on the tentacles!
Hopefully, these marine hitchhikers know better than to venture too near the jellyfish’s feeding tube, as crustaceans are a part of the jellyfish’s diet. And hopefully, the crabs know enough not to try to eat the jellyfish, because that hard shell won’t protect them from a poisonous sting on the inside!
Fish have gills. Jellyfish do not. They are a complex form of plankton that is part of the Cnidaria (“stinging nettle” family. To ease some of the confusion about whether jellyfish are real fish, some aquariums are encouraging people to refer to them as “sea jellies” or just “jellies.”
There are thousands of types of jellyfish, with 2000 different species having already been discovered. Some scientists estimate that as many as 300,000 jellyfish species have not yet been found! Only 70 of the known species can hurt people; most species either harm other marine life or live so far from coastal areas that they are unlikely to encounter humans.
There are two ways that jellyfish move around. One is by taking water into their bodies and then squirting it out behind them. This movement creates a water jet that propels them forward. Another way that they move is by floating with the water currents. This is also how Portuguese Man Of Wars move around – they float instead of propelling themselves or swimming.
If you want to watch jellyfish swim, visit an aquarium that has a jellyfish tank. You will probably see moon jellyfish, which are the most common kind in North America. By the way, if you encounter a moon jellyfish while out swimming in the ocean, the sting won’t be poisonous. It will probably give you a rash but won’t cause any severe health issues.
Jellyfish are remarkably resilient and can live and thrive in habitats that are not native to them. The shipping industry, in particular, has been responsible for inadvertently transplanting jellyfish into different parts of the globe; this happens when jellyfish polyps latch onto a ship that is traveling across the ocean or when ballast water containing jellyfish is released.
Jellyfish are able to reproduce in their new environments so rapidly that they can disrupt marine ecosystems. In 1982, comb jellyfish entered the Black Sea for the first time. Within a mere eight years, there were 900 million tons of them in the water! They have caused hundreds of millions of dollars of losses to the fishing and tourism industries around the Black Sea.
A jellyfish bloom is a group of jellyfish that swim around together. Much like a school of fish, or any group of animals that can survive better in a community rather than with each on his or her own, jellyfish blooms enable them to adapt better to their environments.
Some blooms can have millions of jellyfish. Near Japan, massive jellyfish – each the size of a refrigerator – have been known to come together in blooms of 500 million or more! You probably don’t want to be heading to the beach with those kinds of jellyfish blooms around. Environmental degradation may be increasing the size of jellyfish blooms as well as the number of them and cause them to take over other habitats.
Ocean Degradation May Be Increasing Jellyfish Populations
“Dead zones” are areas in the ocean where there is either so much pollution or so little oxygen that only a few marine creatures can live there. Jellyfish can live in dead zones, so the increase in dead zones in the world’s oceans means that jellyfish are reproducing at a rate much faster than other marine life.
While this may sound like good news for jellyfish, it is terrible news for ecosystems. Marine ecosystems, in particular, have very delicate balances, and any disruption at all can cause a chain reaction of species dying off. Jellyfish may find that they lose their food sources because they are increasing so rapidly, while humans are causing so much degradation of the oceans.
Jellyfish may be pretty to look at – at least if you are on the other side of a glass – but they can cause much harm. People in Japan are very much aware of how much harm jellyfish can cause, and not only because of the massive blooms of super-size jellyfish.
A while back, a giant jellyfish, known as Nomura’s jellyfish, got stuck inside the cooling system of a nuclear reactor in Japan. Nuclear reactors are usually located near water so that the water can cool the systems down and prevent them from overheating. When this giant jellyfish got stuck inside the nuclear reactor, it had to be temporarily shut down.
Not that humans eat jellyfish, at least not usually (although they are a delicacy in some Asian countries). Some industries harvest jellyfish because they can be used to make collagen. Collagen is a protein that can be found in some cosmetics and beauty treatments, and it is also helpful for relieving the symptoms of rheumatoid arthritis.
However, on the whole, beyond being pretty to look at, jellyfish and humans don’t mix well at all. Jellyfish stings affect about 150 million people around the world every year; if you live near a coastal area, you or someone you know has probably been stung. Approximately half a million people swimming in the Chesapeake Bay are stung by jellyfish each year, along with 200,000 people in Florida.
Jellyfish blooms may be helpful for jellyfish trying to navigate the murky ocean depths, but they have been harmful to other species. In 2007 in Northern Ireland, a jellyfish bloom that entered a salmon farm killed more than 100,000 fish. The problems associated with jellyfish blooms will likely get worse as they continue to proliferate.
These problems are not only because of humans encroaching on marine habitats but, even more so, because of how human activity has been degrading the planet. While oceanic dead zones cause many animals to die off, they are places where jellyfish thrive. Jellyfish are proliferating precisely because the conditions we are creating are better for them.
Medusa was the creature in Greek mythology who had snakes for hair and would turn anyone who looked at her into stone. Because of the snake-like tentacles that emerge from the “head” of a jellyfish, a mature jellyfish is known as a medusa.
An infant jellyfish is known as a polyp. You may not even recognize a polyp as a jellyfish, not that you would see it anyway. But some jellyfish skip the polyp stage altogether, as they reproduce by splitting in half. These jellyfish are born as fully formed medusas and can start stinging right away.
Jellyfish don’t sting because they are angry. Inside each of their tentacles are cells known as cnidoblasts, and inside of the cnidoblasts are tiny things called nematocysts. Inside of the nematocysts is a coiled-up thread that stings. But a jellyfish doesn’t sting something because it chooses to release one of those threads.
When something becomes tied up in the jellyfish’s tentacles, pressure builds up inside of the nematocysts. That pressure causes the stinging threads inside of them to uncoil, much like a spring-loaded mechanism getting released. Remember that fun fact next time you watch SpongeBob SquarePants.
There is a popular myth that urine helps calm down jellyfish stings, but that is simply false. If you or someone else is stung by a jellyfish, the best course of action is to get out of the water immediately and apply saltwater to the sting. Saltwater will kill the stinging cnidoblasts, but freshwater will reactivate them and cause more harm.
If you have a credit card available, scrape it across the wound to remove the stinging cells. Moreover, completely disregard the popular advice about how to alleviate jellyfish stings. Meat tenderizer, urine, and vinegar will do nothing to help and can make the sting much, much worse.
One of the most poisonous types of jellyfish is the Australian Irukandji. Tourists flock to Australia every year to enjoy its sandy beaches and clear ocean water, but they are often unaware of the jellyfish dangers lurking just below the surface.
In 2002, an American tourist to Australia was swimming in the Great Barrier Reef, an ecosystem that is full of jellyfish. An Irukandji stung her, and she died from the poison. The Irukandji is a contender for the smallest type of jellyfish, being just the size of a fingernail. Yet its tentacles are three feet long and are full of poison that can severely harm or even kill humans.
Most jellyfish are easily recognizable by their sphere-like bodies, but curiously enough, some have a box-type body that looks more like a cube. These box jellyfish are incredibly poisonous; in one type of box jellyfish, there is enough poison to kill sixty humans!
In fact, more people die from jellyfish stings each year than from shark attacks. Most jellyfish stings are painful but relatively harmless. However, some are extremely poisonous and can cause life-threatening problems. If you are at the beach and the lifeguard orders people out because of jellyfish, make sure you follow directions. Staying in the water may be the last decision you ever make.
Jellyfish are composed of 95% water. Once they leave the water, their bodies collapse, and they immediately die. So if you see a gelatinous blob lying on the beach, it is most likely a dead jellyfish. Don’t touch it, in any case. Even a dead jellyfish can still sting. Alert the lifeguard so it can be removed safely.
And next time you plan a trip to the beach, make sure that the people in your group are aware of the dangers that jellyfish pose. They may be pretty to look at, but they are incredibly dangerous. Box jellyfish, in particular, kill as many as 100 people around the world every single year, and the uncoiling of jellyfish tentacles is one of the fastest reactions in nature.
You Can Get Stung By A Jellyfish Without It Touching You
If this isn’t the stuff of a jellyfish horror story, then I don’t know what is. A jellyfish tentacle that becomes separated from the body can still sting, as the reactions within the cnidoblasts that cause the nematocysts to release their poison can even happen.
However, there is another reason why jellyfish can sting you without even touching you: some kinds of jellyfish emit a type of mucous that is lined with cnidoblasts. That’s right, your happy day at the beach can get cut short because you accidentally swam into some jellyfish snot.
Most jellyfish have a body that propels them through the water. Upside-down jellyfish, though, live their lives anchored to the ocean floor with their tentacles pointing upwards. They don’t swim around and have to eat whatever makes the unfortunate decision of coming their way.
The tentacles of upside-down jellyfish are, on the whole, much shorter than those of the “right-side-up” ones. As such, they look more like plants growing out of the ocean floor than jellyfish swimming around. You may not even know if you are encountering an upside-down jellyfish until you feel its sting because you may think that it is nothing more than a plant.
A Sting By Jellyfish Snot Probably Won’t Cause Much Harm
The upside-down jellyfish that sting by sneezing all over the place is not nearly as poisonous as some of the more deadly types, such as box jellyfish and the Australian Irukandji. If you accidentally tread into an area with jellyfish snot, you will probably feel some stinging and may have some redness and swelling afterward.
But the wound is most likely superficial, and the pain will be temporary. Use a credit card to scrape off the top of any red areas on your skin and have someone pour on saltwater. Furthermore, for the love of all things bright and beautiful, do not ask anyone to pee on you!
In most types of jellyfish, the cnidoblasts, which contain the stinging poison, are confined to the tentacles. Touching the top of a jellyfish body won’t usually hurt you – at least not until one of the limbs zaps out and gets you. However, we would certainly urge people to avoid ever touching any part of a jellyfish, whether it seems to be poisonous or not.
But in certain types of upside-down jellyfish, the mucous that is emitted contains little blobs called cassiosomes; inside the cassiosomes are the cnidoblasts, with their nematocysts and spring-loaded poisonous threads inside. That reason explains why it causes stings.
The Phenomenon Of Stinging Snot Was First Documented In 1908
Researchers who study jellyfish wanted to understand the phenomenon of people getting stung when swimming in areas that have upside-down jellyfish, even though they don’t touch any of the tentacles. They pored over studies conducted on jellyfish to find whatever information they could.
They stumbled upon a publication from 1908, written by the zoologist Henry Farnham Perkins. He recognized the jellyfish mucous that was causing people to experience stings and concluded that they might be parasites. However, he acknowledged that he was entirely in the dark and did not know what in the mucous was causing people to get stung.
Researchers who were looking into the stinging nature of jellyfish snot published their findings in the February 13, 2020 edition of Communications Biology. They documented their results and showed why swimmers who are in the vicinity of upside-down jellyfish might feel burning sensations on their skin.
They also showed that the cassiomes, which contain the jellyfish poison, can actually live outside of the jellyfish snot for up to 10 days. They are wholly independent and capable of inflicting pain on anyone who ventures near them while remaining completely invisible. So yeah, poisonous jellyfish snot. What else is new?
This Method Of Stinging May Help Upside-Down Jellyfish Find Food
Studies conducted to understand the cassiosomes in a lab dish showed that the little blobs zip and zoom around. One researcher, Cheryl Ames, said that they move around like a Roomba vacuum cleaner, looking for debris to devour.
The poison inside the cassiosomes is capable of paralyzing brine shrimp, which then dies shortly afterward. So there may be a purpose to this jellyfish snot – causing the shrimp that the jellyfish feeds on to enter its range so that it can eat them. It may be gross, but certainly, one way to get your dinner.
“65 Stinging Jellyfish Facts,” by Karin Lehnardt. Fact Retriever. October 4, 2019.
“Ouch! Jellyfish snot can hurt people who never touch the animal,” by Erin Garcia de Jesus. Science News For Students. February 27, 2020.