I get by with a little kelp from my friend

THESE orcas are scratching each other's backs using a tool they made from seaweed especially for the job.

- Sam Hall

The astonishing behaviour was observed for the first time in footage recorded by drones. It shows several killer whales from three pods taking part in the mutual scratching sessions, from babies to oldies.

Individuals start by biting off a stalk of kelp and positioning it between themselves and another orca before rolling it between their bodies "for prolonged periods".

Scientists from the Centre for Whale Research (CWR), in collaboration with the University of Exeter, watched on in the Salish Sea, near the US state of Washington, and called it "amazing".