Venomous Jellyfish You Never Want to Meet

Snorkeling and scuba diving in the world’s waters may give you a rare opportunity to see a jellyfish you never wanted to see in the first place. That’s right: the deadly variety. Those particular species are capable of sending fear rushing down your spine and inciting maximum efforts to separate yourself from their vicinity. Do you know of these jellyfish and how to identify them? We’ve got some answers for you!


Jellyfish details


We love jellyfish. And why wouldn’t we? These incredible creatures benefit ocean ecology by preventing zooplankton and small fish species overpopulation. Their varieties number in the thousands (some scientists speculate there could be as many as 300,000 undiscovered species) and have inhabited our oceans for 500 to 700 million years. They are regarded as one of the oldest animals on earth. In fact, they are the first known animal to have a nervous system.


Jellyfish tentacles and venom


All jellyfish tentacles sting once you come into contact with them (they also use their tentacles on prey). These fascinating appendages were engineered by nature to deliver toxin with microscopic, barbed stingers. The stingers have tiny bulbs of venom called nematocysts and a coiled, sharp tube to deliver with utmost efficiency. Most jellyfish stings are harmless to people. But there are the more dangerous types we should all avoid.

A majority of deadly venomous jellyfish have transparent bodies, which makes them more difficult to see. Jellyfish won’t approach you on purpose. You’re more likely to brush up against them or accidentally step on one, made all the more likely when they are nearly invisible.

The good news is they inhabit specific areas of the oceans such as Australian and Indo-Pacific waters. There are 70 known venomous jellyfish which can be a danger to humans. You can plan ahead if you know you’ll be snorkeling or diving in those areas by bringing a first aid kit and using a buddy system.


Jellyfish to avoid during snorkeling or scuba diving (or any ocean activity for that matter)


While we don’t have time to go through an entire detailed list of the 70 known dangerous jellyfish, we can point to a few that are near or at the top.


Chironex Fleckeri (Sea Wasp)


The sea wasp is the largest box jellyfish. It is known as the most venomous jellyfish in the world. It also owns the title of most venomous sea creature! Its bell grows to basketball size, while its 15 tentacles can stretch to three meters long. The sea wasp bell is transparent with a blue hue, and markings that some say resemble a human skull. 


  • Found in Northern Australia coastal waters and throughout the Indo-Pacific
  • Its venom can cause death within 5 minutes
  • Victims can experience cardiac arrest or drown before leaving the water
  • Sea Wasps hunt during the day and rest on the ocean floor at night





Size doesn’t matter with this little dude. If you thought deadly stinging barbs on tentacles were bad enough, think again. This tiny but deadly box jellyfish has stinging cells on its bell-shaped form in addition to its tentacles. Irukandji can fire its stingers into its victims. Its venom is highly potent, leading to what is known as Irukandji Syndrome in humans. 

Image: "File:Irukandji-jellyfish-queensland-australia.jpg" by GondwanaGirl 04:29, 6 January 2009 (UTC) is licensed with CC BY-SA 3.0. To view a copy of this license, visit


  • Found in Australian northern waters
  • Its sting can cause Irukandji Syndrome within 5 – 40 minutes, and death in 2 – 12 hours
  • Irukandji Syndrome causes headaches, muscle aches, abdominal pain, hypertension, and more
  • Victims must be hospitalized quickly or they could die
  • Pain from the Irukandji Syndrome is so severe that patients have begged doctors for death


Chiropsalmus Quadrumanus


There has not been much taxonomic research on the chiropsalmus quadrigatus, despite being known as dangerous to adults and especially children. Its rather small size at five inches may seem unimposing. But the thirteen-foot-long tentacles can deliver venom capable of causing cardiac dysfunction and respiratory depression in humans. The extremely painful sting can cause a rash lasting for several months.


  • Known as the “four handed box jellyfish”
  • Located in the Pacific Ocean, Gulf of Mexico, and western Atlantic Ocean
  • Outer tentacles have a pink tint and the inner tentacles are yellowish-white
  • Prefers warm, open seas and are seldom seen near the surface



A majority of jellyfish are harmless to humans. Their incredible, otherworldly shapes and colors contribute to the allure of our oceans with fathomless beauty. We’d love to see your jellyfish encounters (hopefully the safe kind!). Share your photos and stories with us in the comments below!



Show your love for jellyfish with SlipIns Sea Legs 50+ UPF sun protective leggings! Our Jammin’ Jellies design features gorgeous jellyfish colors in a comfortable 4-way stretch fabric. They’re perfect for all water sports! And bonus: They’re not see through, wet or dry.



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