Gibraltar's Monkeys Eat Tourists' Junk Food. Then They Eat the Rock.
The Barbary macaques on the Rock of Gibraltar get fed a lot of junk. Tourists slip them M&Ms, Cornettos, chips, chocolate bars, bread. The monkeys take it. They also, researchers noticed, eat dirt.
Not randomly. The ones with the most tourist contact eat the most soil. Consumption peaks in summer when visitor numbers are highest. When tourists go home in winter, the soil eating drops 30 percent. The one group on the rock with no tourist access doesn't do it at all.
Researchers from Cambridge think the monkeys are self-medicating. Junk food disrupts the gut microbiome. Bacteria and minerals in soil can help restore it. The monkeys appear to have worked this out without anyone explaining it to them, which is not nothing.
The behavior is learned and transmitted within troops. Different groups favor different soils: most go for the terra rossa, the red clay found across Gibraltar. The Ape's Den troop prefers soil scraped from road potholes. Whether that particular workaround is doing them any good is an open question. The roads are busy and most of the vehicles still run on gas.
In three observed cases, monkeys ate soil within minutes of being given ice cream, biscuits or bread. Scientists clocked nearly a fifth of the macaques' total diet as tourist food during the study period. That's a significant operational problem with a low-tech solution that may or may not be introducing a different one.
Nobody's enforcing the "don't feed the monkeys" signs.
Read the full story at The Guardian, April 22, 2026
Hot Take: Self-medicating with roadside dirt because tourists won't stop handing you chocolate bars is a coping strategy. Not a good one, but the monkeys didn't create the problem.
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