Box jellyfish are a curious breed. For one thing, they have two dozen eyes, most of which have lenses, corneas and irises. In other words, they can see. The anatomy of a regular jellyfish only allows them to distinguish light from dark. Box jellyfish also have a more advanced nervous system then their cousins, allowing them to quickly avoid, and engage, objects.
Here's what might be the worst part: unlike other species of jellyfish who wait for their meals, box jellyfish swim as they actively hunt their prey, which is mainly shrimp and small fish. They propel through the water at 4 miles per hour (6.43 kilometers per hour) by opening and shutting their bell-shaped heads, like an umbrella in a rainstorm.
Dr. Angel Yanagihara, a marine biologist at the University of Hawaii at Manoa, and the world's foremost expert on box jellyfish, says that the box jellyfish does not release venom like a rattlesnake. Instead, when a box jellyfish stings, it releases a "digestive cocktail" that helps the creature catch and digest its meals. In humans, however, Yanagihara says that digestive cocktail acts like a "molecular buckshot...causing holes in all our cells." A person's heart can stop in as little as five minutes. Yes, you don't want to experience a box jellyfish sting.
Box jellyfish are among the oldest animals on the planet, dating back at least 600 million years, surviving several mass extinctions. Box jellyfish numbers, as those of all jellyfish, are growing, exacerbated by warming oceans, and oxygen-depleting fertilizers that eventually find their way into the water. They are most active between November and April (jellyfish season).
"We're a greater threat to them, than they are to us," says Yanagihara, who has experienced a box jellyfish sting several times and survived.