By Shivali Best For Mailonline

Published: 06:01 EDT, 16 August 2022 | Updated: 15:57 EDT, 16 August 2022

Every year, thousands of visitors flock to Bali's Sacred Monkey Forest Sanctuary to see long-tailed macaques in their natural habitat.

But visitors could get more than they were bargaining for, according to a new study.

Researchers from the University of Lethbridge have revealed how the monkeys – both male and female – frequently use stone tools as sex toys to pleasure themselves.

Researchers from the University of Lethbridge have revealed how monkeys in Bali's Sacred Monkey Forest Sanctuary – both male and female – frequently use stone tools as sex toys to pleasure themselves (stock image)

Previous research suggested primates masturbate as a way to clear out low-quality sperm before they mate.

However, in this case, the male Balinese macaques were not using their sex toy to ejaculation.

Instead, researchers believe the monkeys use the sex toys for pleasure. 

Dr Cyril Grueter, an Associate Professor of Primatology at the University of Western Australia, who was not involved in the study, said: 'It doesn't need to provide a function other than self-reward. 

'As long as a behaviour doesn't negatively affect an individual's fitness, it may not be weeded out.'

Previous studies have shown that several other non-human primates practice masturbation using a range of tools.

For example, in 2018, researchers spotted a wild male chimpanzee using a discarded plastic bottle to pleasure himself.

And in 2016, a male chimpanzee in Tanzania was spotted masturbating with a piece of fruit.

However, until now it has been unclear whether or not long-tailed macaques also practice tool-assisted masturbation.

In the new study, researchers studied video footage captured of long-tailed macaques in the Sacred Monkey Forest Sanctuary from 2016-2019.

In the videos, they spotted hundreds of examples of monkeys rubbing or tapping stones on their genitals while in a seated position.

The males played with the stones more when their penises were stretched out with one hand or erect, which suggests that the action was for sexual pleasure, according to the researchers.

However, it was harder to understand whether the females were rubbing the stones for sexual pleasure of not.

They tended to choose rougher stones to apply to their genitals, which the researchers suggest could provide greater stimulation than smooth stones.

Previous research has suggested that primates masturbate as a way to clear out low-quality sperm before they mate.

However, in this case, the male Balinese macaques were not using their sex toys to ejaculate.

Instead, the researchers believe the monkeys simply use the sex toys for pleasure.

Speaking to New Scientist, Dr Cyril Grueter, an Associate Professor of Primatology at the University of Western Australia, who was not involved in the study, said: 'It doesn't need to provide a function other than self-reward.

Previous research has suggested that primates masturbate as a way to clear out low-quality sperm before they mate. However, in this case, the male Balinese macaques were not using their sex toy to ejaculation. Instead, the researchers believe the monkeys simply use the sex toys for pleasure (stock image)

'As long as a behaviour doesn't negatively affect an individual's fitness, it may not be weeded out.'

The fact that the monkeys are regularly fed by visitors to the sanctuary could also encourage the behaviour, according to Dr Grueter.

'These monkeys get food handouts from people and thus have to spend less time foraging for natural foods,' he added.

'This frees up time in their activity schedule that can be devoted to non-essential activities, such as masturbation with sex toys.'

Macaque monkeys on a remote island get by with a little help from their friends, according to a new study — in fact, monkeys with 'best friends forever' have the greatest chances of survival.

Scientists at the University of Exeter found female macaque monkeys on an island near Puerto Rico were 11 per cent less likely to die in a given year.

The team observed a series of social connections in 319 adult female monkeys over seven years, including time spent together and time grooming each other's fur.

Monkeys with many connections with different friends was also linked with survival rates, scientists concluded. 

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