Watch sharks use manta rays to scratch itches

Galapagos sharks have been observed using manta rays as living scratching posts to remove parasites, according to two new studies published in recent months. The behavior was documented at three dive sites off Mexico’s Revillagigedo archipelago between December 2024 and January 2026.

Scientists watched the sharks rubbing their snouts and gill regions against the top and bottom surfaces of manta rays. These areas are known hotspots for sea lice, which strongly suggests the mantas were being used as a tool for scratching unreachable itches.

The manta rays—large, gentle animals with no real defenses besides their size—mostly tolerated the rubbing from juvenile sharks. In those cases, the mantas barely reacted, only shuffling slightly. But when adult sharks approached, the mantas went into flight mode, rolling backward and trying to escape.

Researchers are confident the behavior isn’t hostile. The sharks weren’t trying to bite.

A total of eight such shark-manta encounters have been documented by two separate groups of researchers. Their findings were published in Marine Biodiversity and Environmental Biology of Fishes.

“The sharks know that the surface of the manta is like sandpaper, so it’s a good surface to remove those parasites,” said Mauricio Hoyos, a co-author of one study and director of the marine conservation nonprofit Pelagios Kakunjá.

Shark skin, like that of manta rays, is made up of dermal denticles—small, tooth-shaped scales that are sharp and rough. Marine ecologist Jane Vinesky, lead author of the same study and a Ph.D. student at Pelagios Kakunjá, explained that this roughness is exactly why the rays make good scratching surfaces.

Typically, sharks with parasite problems visit cleaning stations, where small cleaner fish pick off parasites. But those stations can get crowded. Hoyos said competition at cleaning stations might be driving some sharks to try alternative strategies.

Gregory Skomal, a marine biologist who heads the Massachusetts Shark Research Program and was not involved in either study, has seen smaller fish use sharks as exfoliators to scrape off parasites. He described the newly observed shark-manta interaction as “unique and exciting.”

It’s unclear how sharks first learned this behavior. Hoyos wonders whether they got the idea when smaller fish scratched their own itches on the sharks first. Skomal suspects individual sharks simply tried it one day, found it worked, and kept doing it. “In the world of sharks,” he said, “a lot of what they do involves trial and error.”

Previously, Galapagos sharks were spotted scratching their snouts and gills on whale sharks, which also have rough skin. The new observations add manta rays to the list of surfaces sharks use for parasite removal, though the interaction appears to be more complex given the mantas’ mixed reactions.