A study recently published in PLOS One suggests that Indonesia’s crested black macaques have learned to use stones as sex toys, making them the first non-human primates observed using a stone tool in the context of sexual behavior.
Researchers say the rare behavior seen only in Sulawesi crested macaques is unusual
Researchers studying Indonesian macaques have made a new discovery that suggests that the monkeys use stones as sex toys. Studying primates is hard since many of them are just endangered populations and difficult to access. However, in Sulawesi crested macaques, the researchers found a rare behavior in sexually mature male monkeys using small stone tools (called lithophiles) to stimulate themselves anally with surprising frequency. While these crested macaques are native to Indonesia and other areas of Asia, the study was only possible due to the accidental importation of Indonesian females into French Guiana by 19th-century American zoologist Walter Rothschild.
Macaques have been seen using moss-covered river cobbles as well as rounded river rocks about an inch (2.5 cm) across
Tool use has long been thought to be limited to humans. But scientists have found that chimpanzees in West Africa crack nuts by placing them on a stone and bashing them with another rock. In Southeast Asia’s Gunung Palung National Park, orangutans shake rattan palms over the water until they drop hard, nutritious seeds onto the ground. And now Indonesian macaques are raising the bar by apparently using stones as sex toys to complete their complex sexual behavior.
Using stones as sex toys were previously thought to be exclusive to humans. But studies have revealed macaques also employ tools during sexual encounters. In fact, they are one of only three non-human primate species (the others being chimpanzees and orangutans) that use tools in any capacity whatsoever.
The authors said this suggested that sexual pleasure could be a motivating factor
The monkeys are provided with a range of objects, including both natural and artificial stones. Males would masturbate by rubbing the stone along their penis. The use of the stone has not been reported before, study author Professor Agustin Fuentes told New Scientist. We think this might be because either it’s too difficult to observe or people just haven’t looked for it. He said that sexual pleasure could be a motivating factor in this behavior among the Indonesian population. The possibility that they use stones as sex toys might seem surprising at first, he added. But when we considered everything else these animals do with leaves and other objects it seems completely within reason.
Other primates are known to use tools but their targets tend to be food related
Tool use in animals is uncommon and not very well studied, according to the study. But other primates are known to use tools. Specifically, New Caledonian crows will use sticks to extract insects from logs and wild chimpanzees would presumably eat the termites that they would stir with a twig (marshmallows are also good). On some occasions, these actions can be creative – but their targets tend to be food related. The monkeys of Sulawesi Island were another group of creative tool users among primates; they would shake branches with nuts on them until the nut fell off and then eat them when they did. However, in the case of Indonesian monkeys using stones as sex toys is an entirely new example of creative tool use in animals.
While it was possible the monkeys used the objects sexually due to local availability, researchers think they probably picked them up because they felt good when they touched them
Monkeys in Indonesia use stones as sex toys, a study suggests, in a new example of creative tool use in animals. However this does not mean the monkeys were engaging sexually because of the local availability of objects; instead, it’s more likely they picked them up because they felt good when they touched them. In a study published recently on primates’ use of objects to complete simple tasks- a new line of research that is starting to show the great versatility and inventiveness that nonhuman primates possess- researchers found that female macaques and long-tailed macaques had obsessively collected and stored thousands of smooth river stones near their daybeds.