The sea wasp is a box jelly with extremely potent and painful venom that has been known, in extreme cases, to kill people in as few as three minutes. The sea wasp’s small body is less of a concern than the tentacles, which reach up to 10 feet (3 m) long. Each of the 60 tentacles hanging down from the sea wasp’s body is covered with specialized stinging cells, called cnidocytes.
Using these stinging cells, the sea wasp hunts small fishes and pelagic invertebrates like swimming crabs or prawns. The cnidocytes are also the source of the powerful sting, and the stories of deaths caused by the sea wasp almost always involve a person being wrapped in multiple tentacles, with stings covering much of the body.
There are multiple, cryptic species in the genus Chironex, so the exact range of the sea wasp is unknown. It is particularly common off the northern coast of Australia, where beachgoers are often stung, prompting a massive campaign by the tourism industry to install nets off of main swimming areas to keep the sea wasps out. Though their stinging tentacles provide them with a means of capturing prey, they do not provide these jellies with sufficient predator defense. They are a favorite prey of leatherback turtles and some other pelagic predators. Among the jellies, the box jellies are known for having some of the most complex eyes. Recent lab studies imply that sea wasps can discern some colors and may even be able to generate three-dimensional images, but the latter has not been confirmed, as they have no brain or central nervous system.
Like many jellies, sea wasps have an interesting life cycle that includes a combination of sexual and asexual reproduction. Sexually mature sea wasps are the jellies (known as medusae), with stinging tentacles, with which we are most familiar. These adults reproduce via external fertilization, where females release eggs and males release sperm into the water column. Once the egg is fertilized, a larva hatches and lives in the pelagic environment for some time. As it grows, the larva searches for a suitable place in shallow water and eventually attaches to the sea floor where it grows into an upside down medusa known as a polyp. During the polyp phase, an individual buds off several clones of itself that swim away as medusae and eventually grow into sexually mature sea wasps. This alternation of sexual and asexual reproduction may be a means of quickly increasing numbers while preserving the importance of mixing genes with other individuals.
Sea wasps are not eaten by people, and there is not sufficient data to determine their population trends. However, anecdotal data implies that their numbers are likely stable or increasing and that human activity is not a threat to this species’ survival.