Gibraltar’s Famous Monkeys Are Eating Dirt, Likely to Alleviate Stomach Aches From Munching on Tourists’ Junk Food

The British territory’s Barbary macaques are the only wild monkeys in Europe. But many are consuming human snacks high in calories, sugar, salt and dairy, and low in fiber

Sara Hashemi | Daily Correspondent

April 23, 2026

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Move over, Tums. Monkeys in Gibraltar seem to have found an unusual health hack to deal with upset stomachs. The British territory’s famous macaques have learned to eat dirt to help with digestion issues caused by eating snacks given by—or stolen from—tourists, researchers report in a study published March 19 in the journal Scientific Reports.

The work “sheds light on the adaptability of these primate populations living in highly anthropogenic landscapes,” says study co-author Sylvain Lemoine, a primate behavioral ecologist at the University of Cambridge in England, to Ed Cara at Gizmodo.

About 230 Barbary macaques live on Gibraltar, located at the southern tip of the Iberian Peninsula, bordering Spain.  They’re the only wild monkeys currently residing in Europe, and they were likely introduced by humans long ago.

The animals have divided themselves into eight stable groups that live on different areas of the territory’s well-known mountain, the Rock of Gibraltar. Tourists flock to see the monkeys, and that contact with humans leads to them feast on ice cream, bread, cookies and other snacks that are calorie-rich but fiber-poor—even though they’re fed fruit and vegetables every day by local authorities.

Signs all over the Rock say not to hand out meals to the creatures, but the rules are not well-enforced. Tour guides even offer meals directly to the macaques, encouraging tourists to do it too, wrote BBC Discover Wildlife’s Arnold Monteith.

In 2022, Lemoine and his colleagues began conducting a long-term study of the monkeys’ behavior and ecology, per Gizmodo. That’s when they noticed the animals regularly munching on dirt, a practice known as geophagy.

Across nearly 100 observation days from August 2022 to April 2024, the researchers witnessed 44 monkeys eating soil a total of 46 times. They also found that junk food made up almost one-fifth of the examined macaques’ diets.

A relationship emerged between how much dirt the creatures ate and how frequently they interacted with humans. Macaques near the top of the Rock—an area that sees a lot of tourism—ate the most junk food, as well as the most dirt. Sometimes they even chowed down on soil right after eating a tourist treat. On the other hand, a group that did not have prolonged contact with tourists was never seen engaging in geophagy.

When tourist numbers dropped in the winter, the macaques were 40 percent less likely to eat human food and 31 percent less likely to eat soil than in the summer, the team found.

“We think the macaques started eating soil to buffer their digestive system against the high-energy, low-fiber nature of these snacks and junk foods, which have been shown to cause gastric upsets in some primates,” Lemoine says in a statement. “The consumed soil acts as a barrier in the digestive tract, limiting absorption of harmful compounds. This could alleviate gastrointestinal symptoms from nausea to diarrhea.”

Research suggests that geophagy serves many purposes connected to detoxification and supplementing their diets with important minerals, Paula Pebsworth, a primatologist at the University of Texas at San Antonio who was not involved in the study, tells Ian Sample at the Guardian.

Lemoine and his colleagues doubt that the monkeys are eating dirt to help with mineral supplementation. If that was the cause, they should have seen pregnant and lactating animals increase their soil intake, which wasn’t observed.

Pebsworth says it is plausible that the macaques are engaging in the strange practice to help them digest all the human food, and notes that the practice has been documented at Japan’s Arashiyama Monkey Park. “However, while geophagy may serve as a coping mechanism, a more effective management approach is to reduce or eliminate the provisioning of human foods,” she tells the Guardian.

Sara Hashemi | Read More

Sara Hashemi is a science writer and fact-checker currently based in New York City. Her work has appeared in Sierra, The Body, Maisonneuve magazine and more.