Australian Box Jellyfish Facts | Nature’s Deadliest Creature

The northern Australian box jellyfish (Chironex fleckeri) is truly nature’s deadliest marine invertebrate. Its highly venomous sting causes a human death in as little time as 3 to 5 minutes. If a human is stung by C. fleckeri he must immediately seek medical attention before it is all too late. The C. fleckeri has a large transparent bell which is nearly the size of a human head. ‘Sea wasp’ is the other name of Australian box jellyfish. Like its name, the jelly occurs in the coastal waters of northern Australia including New Guinea to as far north as Vietnam. During the winter season (especially from March to June) the C. fleckeri is quite common however larger species may show up as later as in September or November.

The long thread-like tentacles of the Australian box jellyfish poses a serious threat to most other animals as well as humans. These tentacles are packed with millions of explosive cells (known as nematocyte). On contact extremely powerful venom is discharged along with these nematocysts. A namatocyte or cnidocyte do not only serve as a defense against predators it is also useful in capturing prey. The jelly is named after Hugo Flecker, the first radiological doctor who discovered the species when he found a 5-year-old child died of its sting in January 1955.

Australian Box Jellyfish Facts

Physical Appearance

  • Cubozoans are collectively known as box jellyfish. The largest species of cubozoans is the Australian box jellyfish. Prominent among its physical characteristics are bell and tentacles. The box jellyfish bell is too transparent to be identified in its natural habitat.

Jellyfish Bell

  • The bell grows nearly the size of a human head or a basketball. The bell of a largest specimen measured up to 30 cm in diameter. The specimen was found in Queensland.
  • The bell has four corners each of which drops 15 long tentacles. It has pale blue appearance and possibly faint markings. This is not what makes jellyfish dangerous. It is the characteristic feature of being transparent underwater that virtually makes it impossible to see in its natural habitat.
  • Swimmers find it difficult to observe the Australian box jellyfish. The specimens in Darwin do not seem to be as large for their bell grows only 14 centimeter in diameter.
Australian Box Jellyfish
Australian Box Jellyfish Tentacles are quite visible. Image Credits

Jellyfish Tentacles

  • The Australian box jellyfish possesses 60 tentacles whereas other species have 40 – 50 tentacles. The tentacles are not so obvious when the jellies are swimming because they contract their tentacles.
  • The length of the tentacles during swimming contracts to about 15 cm while diameter up to 5 mm. Like most other jellies, the Australian box jellyfish is an active hunter. When the hunt is on, the jellyfish extends its tentacles for as long as 3 meters.
  • Millions of cnidocytes are joined with jellyfish tentacles. These cells become activated when jellies release poisonous chemical. fleckeri is diurnal and it is known to sleep on the ocean floor at night. Scientists are still trying to figure out the sleep theory of the Australian jellyfish.

Jellyfish Eyes

  • As in a typical box jellyfish, the Australian subspecies possesses 24 eyes. Studies show that the jellyfish eyes are capable to form images but scientists aren’t sure if it can recognize an object. Moreover, it is uncertain as to how the jellyfish makes sense of everything it touches or observes since it lacks central nervous system. That is to say that brainless animal doesn’t do anything senseless.

Geographic Range

  • Like other jellyfish, the Australian box jellyfish is a pelagic species which means it neither dive deep nor does it swim near the shore. It occurs in the coastal waters of northern Australia as well as New Guinea, Gulf of Carpentaria, Bustard Heads, to as far north as Vietnam.
  • Still the researchers are unable to observe the entire distribution of fleckeri outside Australia. In Australia jellies mostly inhabit the northern coasts of Agnes Water and Exmouth.
Australian Box Jellyfish facts
Australian Box Jellyfish stretches its tentacles during hunting.

Australian Box Jellyfish Habitat

  • The Australian box jellyfish makes home in freshwater habitats including creeks, river mouths, and estuaries where it can easily find small fish and shrimps to prey on. fleckeri do not occur in coral reefs and areas which are abundant in seagrass and weed.

Australian Box Jellyfish Sting

  • The Aussie jellyfish is quite infamous for its highly potent sting that can cause human death in just few minutes. The sting may be moderately felt but the pain is intense. The larger specimens are more dangerous than the smaller ones.
  • If a person is stung by a fleckeri he must seek medical treatment immediately. One of the effective first-aid methods is to use vinegar or ice packs. This can reduce the intense pain straightaway. The Australian jellyfish venom is so powerful that it might not give you an opportunity to get to the nearest hospital. Therefore first-hand treatment is vital before seeking medical attention.
  • During the summer months, the fleckeri occurs in large numbers in northern Australia. Days later they will move to the estuaries to breed.

Australian Box Jellyfish facts Australian Box Jellyfish Behavior

  • The Australian box jellyfish shows different movement patterns in different times. It all depends on the physical and biological factors.
  • In the coastal habitats the jellies move quite frequently during day and night. However in the estuarine habitats, they are relatively more active at night than at daytime. Besides, in the coastal habitats jellies travel at the same pace no matter how fast the tide is.
  • Other conditions include wind speed or unusual wave turbulence. Box jellyfish normally hesitates to go into the high turbulent areas. As such they fancy living in sheltered bays.
  • Tidal currents are likely to determine the travel direction of fleckeri.
  • The Australian box jellyfish becomes less restive in the mid to late afternoon. During this time the animal lies on the ocean floor in a statue-like posture. It will either stretch its delicate tentacles or retract them inside the bell.

Feeding Ecology and Diet

  • The movements of fleckeri are primarily determined by the availability of prey. The jellies will gather in large numbers where prawns and fish are abundant.


  • All the cnidarians are thought to share certain adaptation characteristics. One such feature is radial symmetry. The radial symmetry is a trait that allows jellies to observe animals in almost all directions at the same time. This is useful adaptation in that it helps the box jellyfish to defend as well as to capture its prey.
  • The Australian box jellyfish have evolved to possess photoreceptors however it is unable to identify colors of light. The fleckeri is capable to distinguish dark and light objects which is probably an adaptation to avoid predators.
  • Although the jellyfish eyes cannot form images yet it helps the animal to detect motion.
  • The Australian box jellyfish is known to detect vibrations. This ability allows jellyfish to spot its prey as well as to detect predator’s movement.

Read more : Box Jellyfish Facts for Kids


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