Invasive species that spread through water are always difficult to deal with, zebra mussels, flying carp, and millfoil are all well-known examples here in the Midwest. Imagine, though, an invasive species spreading through the ocean, taking advantage of changing conditions to ruin life for everything else.

No need to imagine it. They’re already here.

They’re known as “cockroaches of the sea,” and swarms of supersized jellyfish are growing even larger and more menacing as Earth heats up, the AP reports. The hardy scavengers benefit from almost anything that hurts other ocean dwellers — sort of bizarro-world canaries in the coal mine — and some scientists are worried climate change could be their key to world domination. Overfishing has already obliterated many of their top predators, and pollution has helped proliferate the plankton they eat, but marine biologists have also begun noticing strong correlations between warmer ocean temperatures and exploding jellyfish populations.