Australian box jellyfish

Box jellyfish live in warm, shallow seas in the north of Australia.

They like calm water near beaches, river mouths and mangroves. In the warm, wet months there are more of them near the shore.

Box jellyfish live in shallow, tropical waters along Australia's northern coasts: from Queensland, across the Northern Territory, to northern Western Australia.

Their babies grow up in rivers and creeks that flow into the sea. When they become young jellies, they move out toward the coast. That is why there are more of them near beaches during the warm, wet months, the time people in northern Australia call stinger season, which usually runs from November to May.

Surf Life Saving Queensland gives the distribution as shallow tropical Australian waters north of Agnes Water in Queensland, all Northern Territory waters, and Western Australia south to Exmouth. A 2002 letter in the Medical Journal of Australia gives Broome to at least Gladstone. Animal Diversity Web also mentions Southeast Asia; this page maps only Australia, where the species is well documented.

The polyps are thought to live some distance up estuaries, and young medusae are washed out of creeks at the start of the season (Gordon and Seymour, 2012). Medusae typically appear along the far north Queensland coast in December, sometimes as early as October, and Surf Life Saving Queensland notes that the stinger season typically runs from November to May.

Box jellyfish eat small fish and prawns.

Their tentacles catch the food. Then the tentacles pull it up to the jelly's mouth.

Adult box jellyfish hunt in shallow water, mainly for small fish and prawns. Young ones eat mostly tiny shrimp.

Their tentacles are covered in millions of microscopic stinging capsules called nematocysts. Each one works like a tiny spring-loaded needle that fires when touched. A box jellyfish cannot chase fast fish, so its sting must stop them very quickly. The tentacles then reel the prey up to the mouth.

Animal Diversity Web reports that adults feed mainly on small fish and prawns in shallow water, and that juveniles feed mostly on shrimp, especially Acetes australis; Australian Geographic gives a diet of mostly fish and sometimes crustaceans.

Each tentacle carries millions of nematocysts. Because each releases only a minute dose, the jellyfish discharges as many as possible and draws captured prey toward the bell and other tentacles. Australian Geographic explains that although box jellyfish can swim against currents and steer by pulsing the bell, they are not fast enough to pursue prey, so their venom acts quickly on fish.

Box jellyfish swim slowly in the day.

They can rest on the sea floor. When the sea is rough and stormy, they sink down to calm water.

Box jellyfish are busy swimmers, but they also rest. During the day they usually swim slowly, and they swim faster at night. Unlike most jellyfish, they can rest on the sea floor without moving, and when the sea gets rough they sink down until it is calm again.

Few animals eat box jellyfish because of their stings. Green sea turtles are a known predator: their thick skin protects them from the stinging cells.

ADW reports slower swimming by day than at night, rest periods on the sea floor that may balance the energy spent swimming, and sinking to the bottom in rough seas or moving to deeper, calmer water during storms. Gordon and Seymour (2012) found more juveniles along the coastline and larger medusae in estuarine populations, and noted that medusae did not appear to accumulate along the coast.

ADW names green turtles (Chelonia mydas) as a known predator, unaffected because the venom does not penetrate their thick skin, though jellyfish are not their main food.

Box jellyfish are not in danger.

Their sting is very strong. In northern Australia, people swim at beaches with lifeguards, nets and special suits. Never touch a jellyfish. Tell a grown-up.

The Australian box jellyfish has not been assessed for the IUCN Red List, and there are no special efforts to protect it. It is a natural part of tropical Australian seas.

Its sting is extremely dangerous, so people in northern Australia take care during stinger season. Some beaches have stinger nets that keep box jellyfish away, and swimmers can wear special stinger suits that the stinging cells cannot get through. Lifeguards help too. If you visit, always follow their advice.

Chironex fleckeri has not been evaluated for the IUCN Red List (GBIF's Red List copy: Not Evaluated; ADW: no special status). Surf Life Saving Queensland classes it among the dangerous tropical marine stingers; its sting causes immediate severe pain and whip-like marks and can be life-threatening, and antivenom is held at hospitals and ambulance stations in tropical coastal areas.

Prevention relies on stinger nets at some beaches and suits made of a material that nematocysts cannot penetrate (Australian Geographic), lifeguard help, and avoiding the water during the stinger season. Research on its venom, ADW notes, has led to an antivenom and to studies of why it affects the heart so strongly.