Rarely seen when scuba diving here in Koh Tao, Box Jellyfish is a beautiful but highly dangerous invertebrate species. These deadly creatures may not look dangerous, but each box jellyfish carries enough venom to kill more than 60 humans. Of the 50 or so species of box jellyfish, only a few have venom that can be lethal to humans.
Box jellyfish, named for their cube-shaped body structure, have long trailing tentacles covered in biological booby traps known as nematocysts – tiny darts loaded with poison. People and animals unfortunate enough to be injected with this poison may experience necrosis of the skin, excruciating pain and, if the dose of venom is large enough, cardiac arrest and death within minutes of being stung.
Box jellyfish have traits that set them apart from other jellyfish. They are fast swimmers, notably box jellyfish can swim at maximum speeds approaching four knots; which is faster than most humans can swim. Whereas, most species of jellyfish float wherever the current takes them with little control over their direction.
Photo by: Huw Penson Photography
Their body structures are also complex. They have a well designed nervous system that enables them to move quickly, a brain-like structure, and twenty four eyes that can detect the difference between light and dark. Box Jellyfish can navigate around obstacles and swim swiftly to a desired location.
More box jellyfish appear during Thailand’s wet monsoon season, owing to the increased activity of the ocean and the changing winds that bring these jellyfish closer to the shoreline.
Learn more about marine animals and reef conservation at New Heaven Reef Conservation Program