A species of monkeys in Indonesia has been observed using stones as sex toys, a new study revealed.
Researchers made the conclusion after studying the activity of over 170 long-tailed macaques living at the Sacred Monkey Forest Sanctuary in central Bali between 2016 and 2019.
According to the paper published in the biology journal Ethology, both male and female monkeys, regardless of age, tapped and rubbed stones on their genitals for pleasure. The study, which builds on lead author Camilla Cenni’s previous research, hypothesized that these monkeys did use stones to masturbate.
Based on their observations, young males were more likely than older males to use the stones for sexual stimulation, which often resulted in a sexual physiological response, such as an erection. The use of stones has also been linked to other sexual behaviors, including mounting.
Cenni, a Ph.D. student at the University of Lethbridge in Canada, had previously studied the behavior in male monkeys back in 2020.
The recent experiment involved observing female monkeys. One difference the scientists observed among the female monkeys was their selectiveness in choosing stones to rub and tap against.
Previous studies have established that monkeys also use stones to assist with obtaining food. According to Cenni, their recent findings showcase the animals’ ability to use stones beyond just survival.
“When we talk about tool use in animals, we normally think about survival-dependent instances,” Cenni was quoted as saying. “There is an increasing number of studies that are suggesting that using objects as tools doesn’t have to be a matter of survival. This is clearly an example.”