The Life Cycle of a Box Jellyfish

The box jellyfish is the most dangerous, venomous marine animal known to man. It is known to have killed more than five dozen people, with many more suffering painful stings from this blue creature of the sea. The box jellyfish, also known as the sea wasp or marine stinger, lives and reproduces primarily in and around the waters of Australia, the Indo-Pacific area, as well as Southeast Asia.

Learning facts and habits of box jellyfish can be difficult

Belonging to the class Cubozoa, the box jellyfish has many characteristics of a true jellyfish, but is not a true jellyfish. The color of the box jellyfish is blue, which often makes them virtually invisible in the water. Their transparency in the ocean is a primary reason that many people had previously been unable to determine what stung swimmers, injuring or killing them.

With clusters of eyes on each side, the box jellyfish is capable of detecting light and has some vision.

Two species of box jellyfish are the most well-known. The first is the one that is usually referred to when describing the box jellyfish, the Chironex fleckeri, which is the largest. Box jellyfish can grow to a diameter of 25 to 35 cm across, with its tentacles averaging as much as 3 meters in length. With up to 60 tentacles on each box jellyfish, which some sources say contains “thousands” of stinging cells, while other sources, such as “Reefed” say there are “millions,” a sting from a Chironex fleckeri box jellyfish can cause cardiac arrest within minutes.

The second species of most well-known box jellyfish is the Carukia barnesi, commonly called the Irukandji. This species is a smaller box jellyfish, measuring only “thumbnail size,” according to the Outback Australia Travel Secrets article, “The Australian Box Jellyfish.”  

One difference between the box jellyfish and other species of jellyfish is that the box jellyfish can actually swim. It can swim at a speed of about 3 to 4 knots as they propel themselves forward, whereas other jellyfish just drift in the water.

The box jellyfish has a short life span

Box jellyfish reach sexual maturity at around two months of age. The Department of Zoology at the University of Michigan explains that box jellyfish breed once a year from late summer to early fall. Different species of box jellyfish may mate differently. Some box jellyfish may mass spawn as other species of jellyfish, where the males and females release sperm and eggs into the water without having any physical contact. Fertilization usually occurs after the mass spawning of the jellyfish with the male releasing his sperm into the water through his mouth. The sperm are fertilized after the female swallows the sperm.

However, the article “Scientists Unravel Evolution of Highly Toxic Box Jellyfish,” reveals that a recent study has uncovered some interesting characteristics about this venomous creature. Study co-author, Cheryl Lewis Ames has documented at least one of the box jellyfish species, the Copula Sivickisi, “that exhibits a courtship of sorts where a male and female interact one on one to mate.” This “complex mating ritual” is considered unique amongst jellyfish and their kin. According to the article, their vision may actually have something to do with the evolution of the mating behaviors of the box jellyfish.

Soon after fertilization occurs, the larvae or planulae leave the female through her mouth into the water. They attach themselves to a hard surface, such as rocks, where they will mature. After attaching itself, the planulae will develop into a polyp, which will feed on microscopic organisms, while it continues to develop until it reaches juvenile medusa, a free-swimming tiny jellyfish.

The parent box jellyfish die soon after spawning, living only for several months to a year, which means that adult box jellyfish have no relationship with, nor participate in the upbringing of their young.