Thousands of jellyfish colonies, known as by-the-wind sailors, have been washed up on Malta and Gozo’s shores by last week’s strong winds.

The blue creatures have been spotted carpeting beaches, mostly on the east coach, in areas such as Baħar iċ-Ċagħaq.

There have also been sightings on Xwejni, Xlendi and Dwejra in Gozo and Golden Bay, Sliema and Marsascala in Malta. 

But for those who want to see them, there's a warning: they emit a foul stench of rotting fish. 

“When they die they lose their beautiful indigo colour and they look like plastic,” said marine biologist Alan Deidun. 

A rock pool full of jellyfish at Baħar iċ-Ċagħaq. Photo: Jonathan Borg

Known by the scientific name velella velella and the Maltese name Qluh, each by-the-wind sailor is not one jellyfish - but is made up of a colony of many polyps that are stuck to what looks like a sail, says Deidun.

The polyps feed on plankton and are connected by a canal system through which they share their nourishment. The “sail” is a flat disc made of chitin - the same substance insect wings are made of, he said.

Deidun explained that these colonies are very normal in Maltese waters at this time of year. Last year the cold winter kept them away, however they usually sail through Malta’s seas as they drift across the west Mediterranean lighting up the sea with their indigo sails.

A closer look at the by-the-wind sailor beached jellyfish. Photo: Jonathan Borg

This year the strong eastern winds that blew over Malta last week pushed them towards the east coast of Malta causing them to get beached and die.

“When they die they lose their beautiful indigo colour and they look like plastic,” he said adding that they emit a foul stench of rotting fish.

Deidun added that there is another interesting fact about these jellyfish colonies, which have a very mild sting that some people don’t even feel.

The by-the-wind sailor jellyfish before they lost their indigo colour. Photo courtesy of Spot The Jellyfish Campaign

As they sail across the open seas they often carry a traveller – an innocuous snail species, scientifically named Janthina, that feeds on them, said Deidun who coordinates the Spot the Jellyfish campaign.

When the snail latches on to the jellyfish it is often tiny and it grows as it buffets and travels the seas…the snail on the sail.