When we think of dangerous animals, a bag of water without a brain may not seem like it should be on the list. But if ocean bathers hear “jellyfish!” they’ll stand at attention like meerkats, because jellies can pack a wallop.

Often gorgeous and often dangerous, jellyfish are a slippery mass of contradictions. Before the summer fades, we take a look at their squishy superpowers.

The main body of a jellyfish—its bell—is made of two thin layers of cells with non-living, watery material in between, says jellyfish biologist Lucas Brotz, a postdoctoral research fellow at the University of British Columbia in Vancouver.

This simple structure is a “neat evolutionary trick,” he says, that lets them grow big and eat more