Comb jellies provide a theatrical example of insidious species at work. The American comb jelly (Mnemiopsis leidyi), sometimes called the warty search jelly, has been spreading to foreign habitats intended for 26 years. Resident to the Atlantic Ocean, they first appeared in the Black Sea in 1982. They had stowed missing in a ship’s ballast water, which is used for stabilization. When the water was dumped, the species keenly took up residence in the area.

Jellies eat through filtering food from water. In their stable search for grub, small species resembling American comb jellies sift through roughly a gallon of seawater every day, says Keith Bayha, a marine natural scientist at the University of California at Merced. This caused a whole collapse of local fisheries specializing in anchovies and sardines fish to feed on the similar plankton the jellies eat. To add slight to injury, the jellies were devouring not now the fish’s food, but their eggs and young as well.