They can leave swimmers and surfers cowering on the beaches, clog fishing nets and have even caused nuclear reactors to shut down.
Swarms of jellyfish regularly cause disruption to seaside economies and there are fears that in some places they are becoming more common.
Now scientists at the Korea Advanced Institute of Science and Technology in Daejeon, South Korea, have developed “jellyfish terminator” robots that can patrol the coastline.
The machines, known as the Jellyfish Elimination Robotic Swarm, or JEROS, use on-board cameras to visually detect jellyfish swimming in the water.
The robots float on the surface of the water and use submerged nets to suck up the jellyfish as they travel and then a propeller shreds them into pieces.
The scientists, who began work on the project in 2009, have now conducted full tests of their robots in the ocean.
Videos posted online show the robots swimming in formation and then shredding jellyfish underwater.
While jellyfish tentacles can still sting even when shredded, they can be prevented from swimming into areas where they may pose a problem for human activities.
The robots, which travel through the water at around 4 knots (4.6mph), could also help control jellyfish breeding, helping to prevent large swarms from forming.
According to Professor Myung Hyun, who led the team behind the project, the robots can remove 880lbs of jellyfish each per hour.
They have just finished conducting tests in the Masan Bay on the southern coast of South Korea with three prototype robots.
Writing in the journal Advances in Intelligent Systems and Computing, Professor Hyun said: “Recently, the increase in population of jellyfish is becoming a great menace to the oceans ecosystem, which leads to drastic damage to the fishery industries.
“The JEROS consists of an autonomous surface vehicle (ASV), a grid for jellyfish removal, and an autonomous navigation system.
“Once jellyfish are detected using a camera, the jellyfish removal scenario is started with generating efficient path to remove the jellyfish.
“Finally, the jellyfish is sliced up with the grid installed underneath the JEROS by following the generated path.
“The prototype of the system was implemented, and its feasibility was demonstrated through outdoor experiments and field tests.”
The researchers now intend to carry out further field tests while also focusing on ensuring the robots can stand up to waves and develop "cooperative jellyfish removal strategies".
Jellyfish swarms can cost coastal resorts millions in lost trade around the world as beaches are closed down.
Around Australia, box jellyfish cause particular problems as their stings can be deadly.
Swarms of jellyfish can at times stretch for hundreds of miles in the right conditions.
In South Korea, jellyfish are estimated to be responsible for around $300 million in damages and losses to fisheries.
On Sunday a swarm of jellyfish forced the Oskarshamn nuclear power plant in Sweden to shut down after clogging the pipes that bring in seawater to cool the plant’s turbines.