Spider Monkeys Invent Medicated Body Scratcher

July 31, 2009 -- Wild spider monkeys now have a new tool under their proverbial belt: a body scratcher that may release medicinal compounds, according to a study published in the latest issue of the journal Primates.

The study is the first to report this spider monkey scratcher. Lead author Stacy Lindshield told Discovery News that two other instances of the use of objects as tools by the social monkeys have been documented.

"Spider monkeys have been observed rubbing crushed and chewed leaves on their bodies," said Lindshield, a researcher in Iowa State University's Ecology and Evolutionary Biology Graduate Program.

She explained that the smelly practice may "play a role in olfactory communication."

"Second, spider monkeys are known to break off branches and drop them on or near human observers," she added, "so it's not a good idea to be directly beneath these guys!"

She and co-author Michelle Rodrigues collected observational data on wild spider monkeys at El Zota Biological Field Station in northeastern Costa Rica. They documented three instances where the monkeys used the scratcher tool.

WATCH VIDEO: Chimpanzees in the Congo were recently recorded using a new kind of tool to scoop up termites.

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The first to scratch was an adult female. Holding a small, leafy branch in her hand, she scratched her chest and abdominal regions.

The second, another adult female, used a detached stick lacking side branches and leaves to scratch her left side. She chewed the tool tip between bouts.

The third individual, a juvenile female, first chewed the distal tip of a stick before scratching the underside of her tail and her genital region.

The scientists think that by modifying the scratcher tip, the monkeys could be providing "more relief and comfort during scratching." The chewing alteration could "also be related to the chemical properties of the selected plant, as research on fur-rubbing and self-medication indicates that some primates select plants or invertebrates with chemical properties for this reason."

Like a human slathering on scented ointment, the plants may then be providing soothing compounds. Since the monkeys aren't just scratching hard-to-reach spots, they could also be stimulating their own scent production glands, which are involved in nose-detecting communication.