Killer whales have been observed mutually grooming each other with a type of seaweed, the first known instance of a marine animal using tools in a way that was previously thought to be the preserve of primates such as humans.
A group of killer whales, which are also known as orcas, have been biting off short sections of bull kelp and then rolling these stems between their bodies, possibly to remove dead skin or parasites. The behavior is the first such documented mutual grooming in marine animals and is outlined in a new scientific paper.
