Killer whales live in the sea near Washington State in the United States. In 2025, scientists used a drone to watch them from the sky. They saw something new. A killer whale bit off a piece of kelp, a large seaweed.

Then two whales held the kelp between their bodies and rolled it. This was the first report of whales making a tool like this. They may do it to clean their skin or to become better friends.

Tool use is well known in land animals such as chimpanzees and crows, but it is much rarer in the sea. In 2025, researchers studying killer whales near Washington State reported something surprising. Using drone footage, they saw whales bite off pieces of bull kelp, a large seaweed, and roll them between their bodies with a partner.

The team called this behavior "allokelping." It was not rare: it was seen on 8 of the 12 days of observation and in all three groups of whales. Whales of all ages and both sexes took part, often with close relatives. The researchers think it may help the whales build social bonds or keep their skin healthy.

While tool use has been widely documented in land animals, reports from marine mammals are scarce, and those that exist mostly involve foraging, such as dolphins using sponges to search the seabed. A 2025 study in Current Biology describes something different. Researchers from the Center for Whale Research and the University of Exeter used drones to film the endangered southern resident killer whales in the Salish Sea. They observed whales biting off short lengths of bull kelp stalk, placing them between their own body and a partner's, and rolling them back and forth.

The team named the behavior "allokelping." It occurred on 8 of the 12 days of observation, in all three pods, and across ages and sexes, with partners tending to be close maternal relatives or whales of similar age. Because the whales modified the kelp before using it for mutual body care, this is considered the first report of tool manufacture for social grooming in cetaceans. However, the suggested functions, strengthening social bonds and removing dead skin, remain hypotheses, and only one population was observed, so it is unclear whether other killer whales do the same.