Irukandji jellyfish

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Malo kingi in a clear plastic vial.

Irukandji jellyfish (/ˌɪrəˈkæni/ IRR-ə-KAN-jee) are any of several similar, extremely venomous species of box jellyfish. With an adult size of about a cubic centimeter (1 cm3), they are both the smallest and one of the most venomous jellyfish in the world. They inhabit the northern marine waters of Australia. They are able to fire their stingers into their victim, causing symptoms collectively known as Irukandji syndrome. There are about 16 known species of Irukandji, of which Carukia barnesi, Malo kingi, Malo maxima, Malo filipina and Malo bella are the best-known.[1][2][3]

The symptoms of Irukandji syndrome were first documented by Hugo Flecker in 1952.[4] They were named after the Irukandji people, whose country stretches along the coastal strip north of Cairns, Queensland.[3][5] The first of these jellyfish, Carukia barnesi, was identified in 1964 by Jack Barnes; to prove it was the cause of Irukandji syndrome, he captured the tiny jelly and allowed it to sting him, while his 9-year-old son and a lifeguard observed the symptoms (and then rushed him to the intensive care unit).[6] Australian toxinologist Jamie Seymour made a documentary about the jellyfish called 'Killer Jellyfish'.[3][7][8]

In 2015, North Queensland researchers discovered evidence that Irukandji jellyfish actively hunt prey.[9][10]


The Irukandji jellyfish exists in the northern waters of Australia. The southern extent of the Irukandji's range on Australia's eastern coast has been gradually moving south.


A scale illustration of an Irukandji jellyfish and its tentacles. Below the jelly's medusa bell are two polyp forms of the species.

Irukandji jellyfish are very small, with a bell about 5 millimetres (0.20 in) to 25 millimetres (0.98 in) wide (or wider) and four long tentacles, which range in length from just a few centimetres up to 1 metre (3.3 ft) in length.[11]

Malo maxima mature irukandji typically have halo-like rings of tissue around their four tentacles. Apparently, it is the mature Irukandji that are highly venomous (in all species). Apparent Malo maxima juveniles have been identified without the halo-rings, and without gonads, and have demonstrated far weaker toxicity in stinging researchers.[3] The stingers (nematocysts) are in clumps, appearing as rings of small red dots around the bell and along the tentacles.[11]

The Irukandji's small size and transparent body make it very difficult to see in the water.[3]

Very little is known about the life cycle and venom of Irukandji jellyfish. This is partly because they are very small and fragile, requiring special handling and containment.[citation needed] Their venom is very powerful. They were erroneously blamed for killing 5 tourists during a 3-month period in Australia.[12] In fact, no evidence exists to suggest that any of the five victims displayed two universal features of Irukandji syndrome: delayed onset (5-40 min to illness and 2-12 hrs to death) and highly visible distress (vomiting, difficulty breathing, extreme pain, etc).[13] Researchers conjecture that the venom possesses such potency to enable it to quickly stun its prey, which consists of small and fast fish. Judging from statistics, it is believed that the Irukandji syndrome may be produced by several species of jellyfish, but only Carukia barnesi and Malo kingi have so far been proven to cause the condition.[3][14]


Unlike most jellyfish, which have stingers only on their tentacles, the Irukandji also has stingers on its bell. Biologists have yet to discover the purpose of this unique characteristic. The hypothesis is that the feature enables the jellyfish to be more likely to catch its prey of small fish.[3]

Irukandji jellyfish have the ability to fire stingers from the tips of their tentacles and inject venom.[15]

Irukandji jellyfish's stings are so severe they can cause fatal brain hemorrhages and on average send 50-100 people to the hospital annually.[16]

Robert Drewe describes the sting as "100 times as potent as that of a cobra and 1,000 times stronger than a tarantula's".[17]

Irukandji syndrome[edit]

Irukandji syndrome is produced by a small amount of venom and induces excruciating muscle cramps in the arms and legs, severe pain in the back and kidneys, a burning sensation of the skin and face, headaches, nausea, restlessness, sweating, vomiting, an increase in heart rate and blood pressure, and psychological phenomena such as the feeling of impending doom.[18] The syndrome is in part caused by release of catecholamines.[11] The venom contains a sodium channel modulator.[11]

The sting is moderately irritating; the severe syndrome is delayed for 5–120 minutes (30 minutes on average). The symptoms last from hours to weeks, and victims usually require hospitalisation. Contrary to belief, researchers from James Cook University and Cairns hospital in far north Queensland have found that vinegar promotes the discharge of jellyfish venom. "You can decrease the venom load in your victim by 50 per cent," says Associate Professor Jamie Seymour from the Australian Institute of Tropical Health and Medicine at the university. "That's a big amount, and that's enough to make the difference, we think, between someone surviving and somebody dying."[19] However, other research indicates that while vinegar may increase the discharge from triggered stingers, it also prevents untriggered stingers from discharging; since the majority of stingers do not trigger immediately, the Australian Resuscitation Council continues to recommend using vinegar.[20]

Treatment is symptomatic, with antihistamines and anti-hypertensive drugs used to control inflammation and hypertension; intravenous opioids, such as morphine and fentanyl, are used to control the pain.[19] Magnesium sulfate has been used to reduce pain and hypertension in Irukandji syndrome,[21] although it has had no effect in other cases.[22]

Irukandji jellyfish are usually found near the coast, attracted by the warmer water, but blooms have been seen as far as five kilometres offshore. When properly treated, a single sting is normally not fatal, but two people in Australia are believed to have died from Irukandji stings in 2002 during a rash of incidents on Australia's northern coast attributed to these jellyfish[3][23][24][25]—greatly increasing public awareness of Irukandji syndrome. It is unknown how many other deaths from Irukandji syndrome have been wrongly attributed to other causes. It is also unknown which jellyfish species can cause Irukandji syndrome apart from Carukia barnesi and Malo kingi.[26]


  1. ^ Gershwin, Lisa-Ann (2007). "Malo kingi: A new species of Irukandji jellyfish (Cnidaria: Cubozoa: Carybdeida), lethal to humans, from Queensland, Australia". Zootaxa. 1659 (1659): 55–68. doi:10.11646/zootaxa.1659.1.2. Retrieved 2010-07-23.
  2. ^ Li, R. (2011). "The pharmacology of Malo maxima jellyfish venom extract in isolated cardiovascular tissues: A probable cause of the Irukandji syndrome in Western Australia". Toxicology Letters. 201 (3): 221–9. doi:10.1016/j.toxlet.2011.01.003. PMID 21237252.
  3. ^ a b c d e f g h Crew, Becky, "The Smallest and Deadliest Kingslayer in the World," October 7, 2013, Scientific American blog, retrieved Nov. 6, 2016
  4. ^ Pearn, J. H. (1990). "Flecker, Hugo (1884–1957)". Australian Dictionary of Biography, Volume 14. Melbourne University Press. pp. 182–184. ISBN 978-0-522-84717-8. Retrieved 2013-10-01.
  5. ^ Flecker, Hugo (1952-07-19). "Irukandji sting to North Queensland bathers without production of weals but with severe general symptoms". The Medical Journal of Australia. 2 (3): 89–91. doi:10.5694/j.1326-5377.1952.tb100081.x. ISSN 0025-729X. PMID 14956317.
  6. ^ Gussow, Leon (April 2005). "The Amazing and Bizarre Discovery of Irukandji Syndrome : Emergency Medicine News". Emergency Medicine News. 27 (4): 44. doi:10.1097/00132981-200504000-00037.
  7. ^ Barnes, J. (1964). "Cause and effect in Irukandji stingings". Med J Aust. 1 (24): 897–904. doi:10.5694/j.1326-5377.1964.tb114424.x. PMID 14172390.
  8. ^ Li, Ran; Wright, Christine E.; Winkel, Kenneth D.; Gershwin, Lisa-Ann; Angus, James A. (Mar 2011). "The pharmacology of Malo maxima jellyfish venom extract in isolated cardiovascular tissues: A probable cause of the Irukandji syndrome in Western Australia". Toxicol Lett. 201 (3): 221–9. doi:10.1016/j.toxlet.2011.01.003. PMID 21237252.
  9. ^ Branco, Jorge (2015-06-05). "Deadly irukandji jellyfish catch their food like a human fisher". Brisbane Times. Retrieved 2018-06-04.
  10. ^ "Irukandji jellyfish actively hunt prey researchers find". ABC Far North Qld. 2015-06-03. Retrieved 2018-06-04.
  11. ^ a b c d Tibballs, J. (December 2006). "Australian venomous jellyfish, envenomation syndromes, toxins and therapy". Toxicon. 48 (7): 830–59. doi:10.1016/j.toxicon.2006.07.020. PMID 16928389.
  12. ^ "Fifth tourist in 3 months dies while snorkeling at Great Barrier Reef". Fox News. The Sun. 3 February 2017. Retrieved 28 June 2017.
  13. ^ {{Gershwin, L., A. J. Richardson, K. D. Winkel, P. J. Fenner, J. Lippmann, R. Hore, G. Avila-Soria, D. Brewer, R. J. Kloser, A. Steven and S. Condie. (2013). Biology and ecology of Irukandji jellyfish (Cnidaria: Cubozoa). Advances in Marine Biology 66: 1-85.}}
  14. ^ Barnes, J. H. (1964-06-13). "Cause And Effect In Irukandji Stingings". The Medical Journal of Australia. 1 (24): 897–904. doi:10.5694/j.1326-5377.1964.tb114424.x. ISSN 0025-729X. PMID 14172390.
  15. ^ Killer Jellyfish, Oasis
  16. ^ Predicting deadly Australian jellyfish movement, Australian Geographic, 13 May 2014
  17. ^ Drewe, Robert (1 November 2015). The Beach: An Australian Passion. National Library of Australia. ISBN 9780642278807 – via Google Books.
  18. ^ Carrette, Teresa; Seymour, Jamie. "Jellyfish responsible for causing Irukandji syndrome" (PDF). James Cook University. Archived from the original (PDF) on 2011-06-08. Retrieved 2011-10-02.
  19. ^ a b Greenland, P.; Hutchinson, D.; Park, T. (March 2006). "Irukandji Syndrome: what nurses need to know". Nursing and Health Sciences. 8 (1): 66–70. doi:10.1111/j.1442-2018.2006.00255.x. PMID 16451431.
  20. ^ Wilcox, Christie (9 April 2014). "Should We Stop Using Vinegar To Treat Box Jelly Stings? Not Yet—Venom Experts Weigh In On Recent Study - Science Sushi". Science Sushi. Retrieved 28 June 2017.
  21. ^ Corkeron, M.; Pereira, P.; Makrocanis, C. (October 2004). "Early experience with magnesium administration in Irukandji syndrome". Anaesthesia and Intensive Care. 32 (5): 666–9. doi:10.1177/0310057X0403200510. PMID 15535491.
  22. ^ Little, M. (August 2005). "Failure of magnesium in treatment of Irukandji syndrome". Anaesthesia and Intensive Care. 33 (4): 541–2. PMID 16119507.
  23. ^ Fenner, Peter J.; Hacock, John C. (2002-10-07). "Fatal envenomation by jellyfish causing Irukandji syndrome". The Medical Journal of Australia. 177 (7): 362–3. doi:10.5694/j.1326-5377.2002.tb04838.x. ISSN 0025-729X. PMID 12358578.
  24. ^ "Hope for lethal jellyfish cure". BBC News. 2003-01-31. Retrieved 2010-05-05.
  25. ^ Lewis, Wendy (2007). See Australia and Die. New Holland Publishers. ISBN 978-1-74110-583-4. Retrieved 2013-10-02.
  26. ^ Seymour, Jamie; Carrette, Teresa. "Identification of cubozoans responsible for causing Irukandji syndrome". James Cook University. Archived from the original on 2008-09-19. Retrieved 2011-10-02.

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