I’m very regimented/vigilant in monitoring my dog My Guy’s food intake. I want him to live a long, healthy life! I want him to hop around with the ease of a Middle Earth elf! It’s just a no-brainer to me. When it comes to extending this ethos to my own health however… sigh, the struggle is real. (See: my long-documented love affair with chips.) In short, while I myself eat like an animal, I make sure my animal eats the food that his body needs to thrive. Tourists on the Rock of Gibraltar have a different approach, apparently. The visiting humans leave so much junk food behind that it’s prompted a whole new behavioral pattern in the local Barbary macaque population: the monkeys are eating mud to treat their junk food-induced indigestion! A research team just published their findings in Scientific Reports after observing 230 macaques indulge in their new culinary routine.
The practice of eating dirt, known as geophagia, is uncommon in the monkey species. Although local officials routinely feed the monkeys at the Mediterranean destination seeds, fruits, and vegetables, visitors to the area are known to offer the monkeys snack foods, including chips, candy, and even ice cream. The research team highlighted in their findings that the mud-eating behavior peaked during the holiday seasons each year, at the same time tourist levels were at their highest.
Dr. Sylvain Lemoine, a primate behavioral ecologist at the University of Cambridge, explained that the monkeys are most likely rebalancing their gut microbiomes after consuming salty, fatty foods.
“We think that eating this junk food disrupts the composition of the microbiome, and we know that bacteria and minerals in soil can help recompose the microbiome and alleviate the negative effects,” Lemoine told The Guardian. “We think there’s a protective effect of the soil.”
Lemoine highlighted that eating mud may allow the monkeys to continue eating junk food despite its negative effects. “The emergence of this behavior in macaques is both a functional and cultural one, like nutcracking in chimps, except it is driven entirely by proximity to humans,” added Lemoine.
Between August 2022 and April 2024, researchers counted 46 “geophagic events” (performed by 44 individual monkeys) after 31 days of observation, averaging about 12 events per week. Experts compare this geophagy frequency to that of lemurs and chimpanzees, who ingest dirt for mineral intake and to ease plant toxins.
The macaques also have a preference for specific soils, with 84% of the events involving monkeys eating red clay, or “terra rossa.” One particular troop enjoyed “tar-clogged soil collected from potholes in asphalt roads,” which made up 70% of that group’s events.
Despite heavy discouragement from local authorities, macaques are unlikely to reduce their junk food consumption, given the popularity of the tourist attraction and their history of interacting with humans dating back to the 18th century.
“Gibraltar’s macaques are deeply entwined with human history, offering a striking example of a human-primate interface,” explained Lemoine. “The range of human interaction across Gibraltar’s macaque groups creates a natural experiment for understanding how anthropogenic landscapes affect primate behavior and culture.”
“Gibraltar’s macaques are deeply entwined with human history, offering a striking example of a human-primate interface.” Oh dear, we’re about to get $172 vials of GOOP Mud, aren’t we? It’s no less than we deserve for getting the macaques hooked on our crap food! The bottom line I always hit with me vs My Guy, is that I can treat my body however horribly I want to, but I’m gonna do right by my dog. We have not done right by these monkeys. Can I honestly say I wouldn’t ingest mud in order to keep living a life of exorbitant french fry consumption, or that I haven’t done so already? That’s not the point! The point is don’t litter, put your trash in the proper receptacles — think of the macaques! They’re eating mud because of us. MUD!
Monkeys at Tourist Destination Ingest Mud to Combat Tummy Issues Caused By Eating Junk Food, Researchers Say https://t.co/bOdX8WyGbV
— People (@people) April 23, 2026
Photos credit: Sebastian Wasek/Avalon, Mike Lane/Avalon, Wolfgang Kaehler/Avalon, Keith Mayhew/Avalon, David Osborn/Avalon