Blue, mysterious and arriving by the millions: the alien-like creatures blanketing US beaches

Masses of ephemeral organisms known as by-the-wind sailors' wash up in a blue tide' on the west coast most years but warmer winter seas could be increasingly their numbers

From Oregon to California, blankets of alien-like blue creatures are washing up on rocky beaches. They are Velella velella, tiny colonies of organisms with a sombrero-esque fin sticking out the top and tentacles dangling down.

Millions have been spotted along the US west coast this spring, much to the surprise and delight of beachgoers who have gleefully posted footage on social media. Some call it a blue tide" and it happens most springs - but not always to the same degree of abundance.