Life Cycle of the Box Jellyfish

Of the almost 30 species ofjellyfish, only a few life cycles are known. The life cycle of the box jellyfish, Chironex fleckeri, was only recently documented in the 1980’s. This jellyfish, also known as the Sea wasp, has an almost world-wide distribution. They can be found along the coastal waters of south eastern Asia, the Gulf of Mexico, and of course Australia. Sometimes described as being pale blue in color, the are transparent when looking for them in the water.


Box jellyfish, also called the killer jellyfish, can grow to be as large as a basketball and have as many as 60 tentacles reaching a length of 15 feet. They have a cube, or box-shaped body or ‘bell’ called an umbrella. One opening or mouth in found inside the bell. Some have one tentacle at each corner of the bell, while others have numerous tentacles. The bell also has four dark spots around the outside, a form of primitive eyes. These eyes  can only distinguish brightness, while not actually being able to see. They do keep the jellyfish from running into things as it floats along with the currents. Surprisingly, these jellyfish can move at will too. They have been known to move 10-20 feet a minute. The sting of this jellyfish is also lethal to humans. An adult can die from the sting in as fast as 3 minutes. It is said that the venom in one adult sea wasp can kill up to 60 adults.

Diet and Life span

Small fish, crustaceans and plankton make up the diet of box jellies. Because their life span is not long, they eat almost constantly. The life span of the jellyfish that have been studied over the past several years varies from a few hours to several months. It hs been found that most coastal waters jellyfish live only 2-6 months. This explains their need to feed constantly sothat they can reach adulthood quickly in readiness to reproduce.


It was thought that the box jelly bred asexually, but research has found that there are males and females. They spawn by letting loose masses of sperm and eggs that mix in the waters. The sperm and eggs form up to produce a ‘planula’, or larval form. This planula free floats on the tides for several days before winding up inland in the coastal creeks. There, they eventually sink to the bottom of the creek bed and forming into a polyp, attach thereselves to the rocky bottom. The polyps feed on plankton and grow very quickly. Eventually, they turn into a miniature jellyfish, or ‘medusa’. It takes several days for the Medusa’s to drift down to the mouth of the creeks, and eventually back out into the ocean. It is at this time that people are likely to come into contact with them. They are more prolific in Australia’s wet season, November through May of the year.

Of interest is the observations made over the last several years about the varying numbers from season to season of the box jellyfish. Researchers have noted that in 1999, a count was made in a selected area along the coast of Australia, and a total of 272 box jellies were counted. The following year, the number was zero. It was suggested that our changing weather patterns are to blame.