Scientists have identified a direct link between tourist feeding and soil consumption among Gibraltar’s Barbary macaques, with monkeys eating dirt to counteract digestive distress from junk food.
Tourist junk food disrupts monkey gut health
Researchers observed that macaques with the most contact with tourists consumed the most soil, particularly during peak holiday seasons, as a response to eating fatty, salty and sugary snacks like ice-cream, chocolate and crisps. The behaviour, known as geophagy, was absent in a group isolated from visitors, suggesting It’s a learned adaptation to human-provided food. Over two years, nearly a fifth of the monkeys’ diet came from tourist junk food, with those near the top of the Rock — where visitor density is highest — more than twice as likely to eat such snacks.
Soil may restore microbial balance after dietary disruption
Dr Sylvain Lemoine of the University of Cambridge hypothesises that the monkeys ingest soil to rebalance their gut microbiomes, which are disrupted by unhealthy tourist food, noting that minerals and bacteria in dirt can help alleviate digestive upset. The team recorded 44 monkeys eating dirt on 46 occasions, including three cases where soil consumption followed immediately after eating ice-cream, biscuits or bread. When visitor numbers dropped in winter, soil eating fell by over 30%, reinforcing the correlation between human activity and the behaviour.
Local feeding habits compound the issue
Both tourists and locals contribute to the problem, offering items ranging from salted peanuts and dried pasta to Coca-Cola and Magnum ice-creams, which the monkeys prefer over sorbet. While authorities provide daily rations of fruit, vegetables and seeds, uncontrolled feeding undermines these efforts and introduces dietary risks. The findings highlight how human-wildlife interaction, even when well-intentioned, can trigger physiological adaptations in animals seeking to mitigate harm.
Why do the monkeys eat soil?
Scientists believe the monkeys eat soil to soothe stomach upset and rebalance their gut microbiomes after consuming tourist junk food, which disrupts digestion.
Is this behaviour seen in all monkey groups on Gibraltar?
No, the behaviour was not observed in a group of macaques isolated from tourists, indicating it is linked to human contact and not a natural dietary habit.
