The sting of a Chironex fleckeri box jellyfish, which live around Australia and the Philippines, can kill you within three minutes—and Australia's seen an increase in jellyfish numbers lately. In Sweden and Israel, vast numbers of jellyfish have caused trouble at nuclear and coal power plants this year. The populations of all kinds of jellyfish are growing, Mother Jones reports, and it may be due in part to climate change; jellyfish like warm water. What's more, they could be helping the oceans get even warmer, since carbon-releasing bacteria feast on their droppings. Meanwhile, overfishing is killing jellyfish predators.
About 150 million people suffer jellyfish stings yearly; hundreds of thousands of those are in the Chesapeake Bay and Florida. Fortunately, most aren't going to kill you. But about 50 people per year may die from the stings, an expert notes. Brushing against a "trigger hair" on a jellyfish cell prompts a venom sac to shoot out. Even a broken-off tentacle can sting you. If you get stung, try removing leftover pieces of tentacle with tweezers or a stick—not your fingers—and then washing the area with seawater. The UN has called on scientists to help fight the jellyfish scourge, Haaretz notes. Most efforts thus far haven't been fruitful, but an Israeli scientist may be onto something: Their proteins, he says, could help make bandages and other medical products. Another option? Robots. (Read more jellyfish stories.)