"The sheer size of them, individually, makes them fairly spectacular," Graham said. Spectacular, perhaps, to scientists, but perilous to villagers along the Japanese coast who have seen the destructive habits of these colossal creatures in the past. They had giant-jellyfish invasions in 2005 and 2007, and because they've recently been spotted in the Sea of Japan, they're bracing for another, potentially harmful wave this summer.

The jellyfish destroy fishermen's nets, getting trapped in them, tearing holes and ruining catches.

Fishermen often use expensive mazelike nets that stretch for hundreds of kilometers. When swarms of giant jellyfish tear them, the result is devastating.

"Communities of fishermen and these fishing villages own these nets," Graham said. "When these nets get wiped out, it actually has this economic devastation for an entire community."

The good news is that previous attacks have prompted Japan to put in place a warning system for fishermen. While they