In a surprising new study, scientists have observed killer whales using marine plants—mostly kelp—as tools for social grooming. The findings, published in Current Biology, mark one of the clearest examples yet of non-human animals using natural objects for mutual care and bonding.

Between 2001 and 2022, researchers recorded 84 instances of orcas interacting with seaweed across three different populations: the Northeastern Pacific, the North Atlantic, and the Southern Ocean near sub-Antarctic Marion Island. These interactions were not random. The whales consistently draped or passed kelp and other macroalgae across one another’s bodies, particularly along the dorsal fin, pectoral fins and tail flukes.

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Social tool use

Dr Andrew Trites from the University of British Columbia explained that the behaviour is likely a form of social grooming rather than play or self-grooming. “This is one of the few examples of marine mammals using tools on each other,” said Trites. The interactions appeared calm and cooperative, suggesting a social function beyond hygiene.

Tool use among animals is often associated with solitary activities like foraging. The observed kelp-grooming, however, may represent a rare case of “socio-tool use”—when one animal uses an object on another for social benefit. Similar behaviours have been seen in some primates and elephants but are virtually unheard of in marine mammals.

Next steps

Researchers plan to investigate whether the kelp provides a physical or chemical benefit—such as removing parasites or soothing skin—as well as the cultural transmission of this behaviour across pods. The study raises new questions about intelligence, cooperation and innovation in orca societies