Box jellyfish are simple animals. They have an almost cubical body (called the bell) and groups of trailing tentacles grow from fleshy extensions at each of the four corners of the bell - see Figure.

The trailing tentacles present the danger to man. These can extend several metres behind an adult box jellyfish, and can number as many as sixty in a fully mature animal.

Chironex, largest of the Box jellies

Box jellyfish are able to manoeuvre to avoid obstacles if they have enough time to react. They can see (poorly) with simple eyes.

They react to the "taste" of food; prawns, small fish etc. Once contact is made with a potential food source, some of the stinging cells will fire and the muscles in the tentacles will contract.

This knowledge forms the basis of two approaches which can be taken to reduce the problem of stings

• Covering the skin provides a physical and probably "tasteless" barrier to the stinging cells
• Pouring vinegar onto a sting prevents the firing of additional venom into the victim.

Box jellyfish have been found on tropical shores from Darwin, through the Gulf of Carpentaria and down the east coast of Queensland as far south as Gladstone. It is also probable that they are to be found in the tropical waters of Western Australia.

They are most troublesome in shallow waters and appear to prefer beaches, which have some fresh or brackish water input. They are often found around the mouths of creeks, and some fatalities have occurred kilometres inside the mouths of rivers with substantial tidal inflow.

When are Box Jellyfish around?
Current knowledge indicates that November to April are the most dangerous months in the Port Douglas to Gladstone stretch of coast. North of Port Douglas, the season appears to lengthen.

How visible are they?
Although relatively large, box jellyfish are virtually invisible. Even in crystal clear water, they are difficult to see. In our coastal waters they are nearly impossible to see, especially when there are surface waves.

These are not like other jellyfish, which can be seen from the beach or a boat. Even trained observers often find them extremely difficult to find. Never assume that there are no box jellyfish present because they 'have not been seen'.

There are a number of precautions, which will lessen the risk of a major sting from box jellyfish. The more precautions you take, the fewer problems should occur.

Cover up your body
A box jellyfish has simple tastes and we "taste" acceptable. Lethal stings require lots of tentacle and skin contact. Wearing body cover minimises the amount of exposed skin.

Any body cover which clings to the skin will give good protection. The most important feature of any cover is that it fits firmly at ankles, wrists, waist and neck, because it is vital that no long tentacles can sweep against the skin through any openings.

Specially made stinger suits of lycra material give neck to ankle protection. However, other clothes can be used to good effect, high necked skivvies with pantyhose, jeans or exercise tights which are close fitting at the ankles.

As an interim measure lifesavers sometimes use two pairs of pantyhose, with the feet cut out. One pair is worn conventionally, the other pair is reversed and the swimmers arms are protected by the pantyhose legs, with a small hole being made at the crotch seam for the swimmer's head.

Swim at protected beaches
Some beaches have stinger nets installed and these provide protection from large box jellyfish. Newer models with fine mesh also protect against another tiny stranger (Irukandji) which can also cause a swimmer to have a severe reaction to the sting.

Avoid sudden movement
Box jellyfish can see objects in the water and can move quite quickly to avoid them. Running, splashing violently, and diving causes the water to swirl around a swimmer, with the risk of bringing the tentacles into contact with the skin.

When we move quickly through the water, we do not allow the box jelly time to take evasive action. Most stings occur because people blunder into the jellyfishes' tentacles.

Avoid dangerous situations
Some places and weather conditions are particularly hazardous. The mouths of fresh or salt water creeks are particularly attractive to box jellyfish. Glassy still waters or gentle ripples on the beach may bring box jellies very close inshore to search for prawns and fish.

Always cover up when going even a short distance between a boat and the shore, or when swimming from the shore, as most stings happen in these situations.

Carry First Aid materials and know emergency treatment
If someone is stung by a box jellyfish, the sting should be flooded with vinegar (use at least two litres). It won't help the pain, which is the result of some of the stinging cells firing through the skin, but it will prevent any undischarged stinging cells from releasing their venom, and so lessen the risk of a fatality.

With a major sting, medical help is urgently required. If the victim stops breathing or their heart stops artificial respiration and heart massage (CPR) is vital and should take precedence. To review CPR procedures look at our web pages Emergency techniques

If you are far from help, flood the sting with vinegar. If you know how to immobilise a limb with splints and pressure bandages, it will help as swimmers are usually stung on the legs. Pressure bandages keep the venom confined to the skin until the victim can be given expert medical attention. There is an antivenom available, which must be administered by trained medical personnel.

The Marine Stinger Book, published by the Surf Life Saving Association of Australia is a useful source of further information.