pink coral image with fish

Sea Wasp

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Sea Wasp from northern Australia

Sea Wasp

Species - Chironex Fleckeri

Synonyms - Box Jellyfish, Fire Medusa, Indringa.

An American author named Mayer who was speaking about some of the stinging Cubomedusae found in the Caribbean waters of Central America coined the name Sea Wasp.

In Australia it is more commonly known as the Box Jellyfish.

Yet of all the types described none are as venomous as the Indo-Pacific Box Jellyfish. It is claimed to be the most venomous marine animal known.


The Box Jellyfish has a shape of a bell or cuboid with four distinct sides, as in a box, hence the local name - Box Jellyfish. From each of four corners of the cube, or bell measuring up to 20 cm along each side, the Box Jellyfish projects into pedaliums, each of which may contain up to as many as fifteen tentacles each 3 metres in length.

Box Jellyfish are pale blue and transparent and are difficult to see, even in clear ocean waters they are almost invisible, and for years it wasn't known what was actually causing such excruciating pain often followed by death. It was first thought to have been the Portuguese man-of-war, but as most stings from the Portuguese man-of-war are usually accompanied by a sighting it became obvious that it was probably something else. As death occurred sometimes within 2 to 3 minutes, researchers began to search for another culprit.

Box Jellyfish Season

The Box Jellyfish season across the top of northern Australia starts with the onset of the wet season, usually around October and lasts until April. Further south along the northern Queensland or northern Western Australian coast the season is usually from November to March. The Box Jellyfish sometimes appear further south and sometimes a few weeks beyond the official close of season before disappearing until the next wet season.

Always check with local authorities for advice before swimming in the ocean; otherwise wear fully protective clothing. Never swim on your own in isolated areas. If you are stung, your chance of survival or even getting yourself to the shore is virtually zero. The pain has been described as so excruciating that you will probably go into shock and drown, even before the full affect of the venom takes place.


Box Jellyfish prey on small crustaceans and small fish. They appear to travel towards the shore in calm weather on a rising tide and congregate near the mouths of creeks and rivers following rain. It is thought that after rain, food is washed down these watercourses to the waiting Box Jellyfish.

For mobility, the Box Jellyfish contracts with a jet-like motion, shooting itself along up to speeds of 4 knots. It is presumed to have eyes connected to a nerve ring and the creature can take evasive action or move towards its prey.

The Box Jellyfish uses its tentacles to kill its prey. If a swimmer makes contact with the Box Jellyfish's tentacles, perhaps only 6 or 7 metres of them, death may result! Children may die after even less contact. The severity of the sting is relative to the size of the Box Jellyfish, the sensitivity of the victim's skin, and the amount of tentacle that has come into contact.

A very large Box Jellyfish has tentacles that, if placed end to end, would measure more than 60 metres, so it is not unusual for a rescuer to inadvertently become entangled in another section of the tentacles and suffer the same fate. Sometimes the victim somehow manages to get ashore only to die within a few minutes as friends look helplessly on.


Dangerous Marine Animals of the Indo-Pacific Region, (Diving Centre Monograph on identification first aid and medical treatment) 2nd reprint, Wedneil Publications (Newport, 1978), Dr. Carl Edmonds.

Sea Wasps (Scyphozoa: Cubomedusae) in the Northern Territory, Northern Territory Naturalist, vol 1, no. 1 (Darwin, 1978). Dr. D.L. Grey.

Compiled by Barry Tobin