From the Arctic to the equator and on to the Antarctic, jellyfish plagues (or blooms, as they’re technically known) are on the increase. Even sober scientists are now talking of the jellification of the oceans. And the term is more than a mere turn of phrase. Off southern Africa, jellyfish have become so abundant that they have formed a sort of curtain of death, “a stingy-slimy killing field,” as Gershwin puts it, that covers over 30,000 square miles. The curtain is formed of jelly extruded by the creatures, and it includes stinging cells. The region once supported a fabulously rich fishery yielding a million tons annually of fish, mainly anchovies. In 2006 the total fish biomass was estimated at just 3.9 million tons, while the jellyfish biomass was 13 million tons. So great is their density that jellyfish are now blocking vacuum pumps used by local diamond miners to suck up sediments from the sea floor.