They are 6ft wide and weigh 450lb (200kg), with countless poisonous tentacles, they have drifted across the void to terrorise the people of Japan. Vast armadas of the slimy horrors have cut off the country’s food supply. As soon as one is killed more appear to take its place.

Finally, the quarrelsome governments of the region are banding together to unite against the enemy.

Echizen kurage is not an extraterrestrial invader, but a giant jellyfish that is devastating the livelihoods of fishermen in the Sea of Japan. Nomura’s jellyfish, as it is known in English, is the biggest creature of its kind off Japan and for reasons that remain mysterious its numbers have surged in the past few months.

The problem has become so serious that fishery officials from Japan, China and South Korea are to meet this month for a “jellyfish summit” to discuss strategies for dealing with the invasion. Japan’s ruling Liberal Democratic Party has formed a jellyfish countermeasures committee and fishermen are at work on technology to keep the marauders out of their nets.

The problem first became obvious in the late summer when fishermen chasing anchovies, salmon and yellowtail began finding huge numbers of the jellyfish in their nets.

Often the weight of the echizen kurage broke the nets or crushed the fish to death; those that survived were poisoned and beslimed by their tentacles.

Fishermen on the northern tip of Honshu, Japan’s main island, were forced to suspend work at the height of the lucrative salmon season.

In Akita prefecture some communities saw their incomes fall by 80 per cent. The gizzard shad fishers of South Korea have also been plagued by the Nomura’s.

In some places jellyfish density is reported to be a hundred times higher than normal. Worst of all, no one yet understands why. One theory is that global warming is heating up the seawater and encouraging jellyfish breeding.

Some observers blame heavy rains in China over the summer, which flowed out from rivers and propelled abnormal numbers of jellyfish towards Japan. Nutrients in its river water may have given them extra zip — or overfishing has allowed the growth of the populations of plankton on which the jellyfish feed.

Screens and meshes have been designed that allow fish through but keep out anything bigger, and a web of metal wires can be placed inside a net to chop the jellyfish to pieces.

In the meantime locals are making the best of it — rather than just complaining about jellyfish they are eating them.

Jellyfish are an unusual ingredient of Japanese cuisine but are much more prized in China. Coastal communities are doing their best to promote jellyfish as a novelty food, sold dried and salted.

Students in Obama have managed to turn them into tofu, and jellyfish collagen is reported to be beneficial to the skin.

SEA MONSTERS

• The most poisonous jellyfish is the Australian sea wasp, or box jellyfish, with enough venom to kill 60 people. Wearing tights is an effective defence
• The largest jellyfish ever found was a lion’s mane, with a bell 2m (7ft) across, and tentacles extending more than 35m
• The notorious Portuguese man o’war is not a jellyfish at all but a collection of different organisms including stinging tentacles
• Jellyfish have both male and female characteristics. A group releases sperm and eggs which mix in the water
• A collection of jellyfish is known as a smack

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