Grey whales have been spotted swimming up alongside boats and letting people pick the parasites off their heads.
Remarkable footage has captured the fascinating interaction off the west coast of Mexico, around 385 miles south of California, USA.
Whale watching captain Paco Jimenez Franco has spent the last 20 years observing the incredible creatures in Ojo de Liebre, a lagoon on the Pacific coast of the Baja Peninsula.
And he was recently filmed removing lice from a whale that was brushing up against the side of his small tourist boat.
He told US news outlet, The Dodo: ‘Once I removed the first one, she approached again so that I could continue to do so.
‘I have done it repeatedly, with the same whale and others. It is very exciting for me.’
The lice – also known as cyamid amphipods – are tiny crustaceans that live on the rough patches of a whale’s skin and eat algae.
It’s not known for sure whether they are harmful to whales, with some researchers believing they can be beneficial.
But Franco believes the fact the whales have returned time after time to have them taken off means it gives them some level of relief – an idea that some experts agree with, as the cyamids are likely irritating.
He said the same whale has repeatedly approached his boat for more ‘grooming’ and that she lifts her head from the sea and remains there long enough for him to remove plenty of lice.
Franco added: ‘The whales certainly don’t seem to mind when people pick them off, although you’d have to pick off hundreds to make much of a difference.’
Tourist Jerome Evangelio, who shared the video on Facebook, said the whale was voluntarily approaching the boat.
The post said: ‘The trust between the grey whales and boat captains at the calving lagoon of Ojo de Liebre in Guerrero Negro is something developed over the numerous encounters throughout the years.
‘This whale had no objections with our captain Paco picking whale lice off of its head.
‘Thank you Jordan Lightner for capturing this incredible moment during our adventure.’
Experienced British zoologist Mark Cawardine said he thinks grey whales have a ‘love-hate relationship with their whale lice’.
He told The Guardian: ‘They have very sensitive skin, and thousands of these little creatures holding on tight, or moving about, with their exceedingly sharp, recurved claws, must drive them nuts.’
Franco said his lice picking exercise began when a whale came very close to his boat, and he suspected it was seeking help to remove the crustaceans.
Ever since then, the same whale and others continue to return, which has only emphasised his appreciation for their astonishing nature.
He added: ‘I have learned, by seeing their behaviour, that there is a certain nobility in them. They’re incredible.’
Touching whales is mostly prohibited around the world, however it is allowed in designated regions along the Baja California coast when the whale initiates the interaction.
Grey whales can grow as big as 50ft long and weigh up to 41 tonnes, while they generally live between 55 and 70 years, although they have been known to live to the age of 80.