These enormous jellyfish can grow up to 90cm across, weigh as much as an average 11-year-old child and are washing up on our shores in droves.
But don’t worry – they won’t hurt you... much.
Barrel jellyfish have been spotted on Fleetwood Beach in recent days as the warm weather brings them closer to the coast.
Anyone who spots one on the beach is warned not to touch it but the jellyfish are not considered dangerous to humans.
The creatures – the largest jellyfish found in this country – have a weak sting that experts say is similar to that of a nettle.
Ken Harcombe, of the Rossall Point watch tower, which looks our over the sands, said they have been getting reports of jellyfish in the area.
In summer and autumn they may swarm off the coast, sometimes washing up in large numbers.
He added: “We were sent a photograph of a jellyfish in front of the tower.
“I believe it was quite big, about two feet across.”
In recent weeks, swarms of the creatures have been reported off the South coast but now they are being spotted up North too.
The route to the Wyre Light in recent days has been littered with dozens of jellyfish, including a handful of “massive” barrel jellyfish, according to one person who recently made the trip.
Fleetwood Coastguard posted some pictures of them on Facebook, warning people to “be careful”.
The post read: “One of our crew has just taken these photos of some barrel jellyfish that are coming ashore on Fleetwood beach.
“These are the largest jellyfish in UK waters and can grow up to 90cm.
“Be careful if you’re out on the beach this weekend.”
According to Buglife, a charity dedicated to the conservation of invertebrates, they are “gentle giants”.
Its website adds: “Several jellyfish visit UK waters. The Barrel jellyfish is our largest, with a diameter of up to 90cm and weights of up to 35kg.
“In summer and autumn they may swarm off the coast, sometimes washing up in large numbers.
“These giant jellyfish swarms cause quite a stir. However they are gentle giants.
“Barrel jellyfish feed entirely on tiny plankton, so their sting is too weak to hurt humans.”