Printer Friendly

Weird Science: Deadly Box Jellyfish

SF Fig. 3.3. Irukandji box jellyfish (Malo sp.) in glass vial

Image courtesy of GondwanaGirl, Wikimedia Commons

The venom of Irukandji box jellyfish (Malo spp.), the smallest jellyfish in the world with an average size of only one centimeter, have been proven fatal to humans (SF Fig. 3.3). Although the main bell of the box jelly is about the size of a sugar cube, its stinging tentacles can stretch for one meter (SF Fig. 3.4) The venom of Irukandji jellies, which are found off the coast of Australia, acts on the nervous system and paralyzes the lungs and heart. Some parts of the body are also more susceptible than others to stings. The many nerve endings in our face and lips mean stings to those locations are more painful than they would be elsewhere.

Image caption

SF Fig. 3.4. Scale illustration of Irukandji box jellyfish (Malo sp.)

Image copyright and source

Image courtesy of anynobody, Wikimedia Commons


Cnidarian venom is a protein. The best way to treat a sting is to break down the protein chemically with a “sting kill” medication or meat tenderizer. Because heat also helps to break down proteins, hot water can be used on a sting. Some people develop an allergic reaction to the venom after repeated stings. It is important to seek medical help for a sting victim who faints or shows signs of unusual swelling or breathing distress.


Cnidarians can capture and digest animals ranging in size from small plankton to rather large organisms, such as small reef fish. After a cnidarian stings and captures its prey, the tentacles work together to move it into the mouth. The prey is swallowed into the gastrovascular cavity and digested. Endoderm cells produce digestive chemicals called enzymes, which break the chunks of food into tiny particles. The cells then engulf the particles and further digest them into nutrient molecules. The cnidarian expels indigestible material through the mouth, which serves the gastrovascular cavity as both entrance and exit.

Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.