Look out below.

• Position: News & Trends - Brief article

This monstrous glob is called a Nomura's jellyfish, a species that first invaded the Sea of Japan in 2005 and refuses to go away. They can grow as big as 6 feet wide and weigh more than 450 pounds-about as heavy as a male lion. This year, the jellyfish population has ballooned to 100 times its normal size, causing problems for Japanese fishermen: The jellyfish get swept up by fishing nets and their...