Gibraltar’s Monkeys Eat Soil to Counteract Junk Food from Tourists

Gibraltar’s famous macaques have learned to eat soil to settle their stomachs after consuming junk food from tourists, according to a new study published in Scientific Reports on April 22, 2026.

Researchers from the University of Cambridge observed Barbary macaques on the Rock of Gibraltar engaging in geophagy, the intentional consumption of soil, dirt, and clay, as a response to gastrointestinal distress caused by eating sugary, fatty, and salty snacks provided by visitors. The behavior was most common among monkeys with frequent contact with tourists and peaked during the holiday season.

The study found that macaques living near tourist areas consumed significantly more soil than those in isolated groups with little human interaction. Scientists believe the soil may act as a protective lining in the gut, helping to prevent irritation from excessive intake of processed foods like chips, chocolate, ice cream, and candy.

While the exact mechanism is not yet proven, researchers suspect the clay and minerals in the soil bind to irritants or coat the digestive tract, reducing inflammation and nausea. Similar self-medicating behaviors have been documented in other animals and humans, but What we have is the first formal observation of geophagy in Gibraltar’s macaque population.

Approximately 230 Barbary macaques live in eight distinct groups across Gibraltar. Although local authorities provide daily rations of fruit, vegetables, and seeds, tourists routinely feed them human junk food despite warnings and fines. The researchers noted that the soil-eating behavior appears to be a learned adaptation to the changing dietary pressures of living in an anthropogenic landscape.

The findings highlight how wildlife can develop novel behaviors in response to human activity, though scientists caution that such adaptations do not eliminate health risks. Long-term consumption of high-calorie, low-nutrient foods may still lead to obesity, diabetes, or other metabolic issues, even if soil intake offers temporary relief.

Further research is needed to analyze the chemical composition of the soil consumed and its precise effects on the macaques’ gut microbiome and intestinal health. For now, the behavior stands as a clear example of how animals adjust to human-altered environments in ways that reflect both resilience and vulnerability.