A Gibraltar monkey
A new study indicates that Gibraltar monkeys learned to eat dirt to alleviate gastrointestinal discomfort caused by excessive consumption of sweet and savory foods offered by tourists.
Eating dirt to digest “junk food”? The Gibraltar monkeys discovered that it works.
Groups of these primates – the only free-ranging population of monkeys in Europe – have been scientifically observed for the first time to regularly resort to “geophagy”the intentional ingestion of land, says a statement about the work from the University of Cambridge, in the United Kingdom, released this Wednesday.
Researchers monitoring groups of monkeys on the Rock of Gibraltar, in the south of the Iberian Peninsula, also known as Barbary macaques, recorded cases of geophagy and discovered that “animals in frequent contact with tourists eat much more land”, and “Land ingestion rates are higher during the high season”.
“During a total of 98 days of observation, between the summer of 2022 and the spring of 2024, scientists recorded 46 ‘events’ of soil ingestion in 44 different animals”, states the statement, adding that “three cases of geophagia were observed immediately after an animal had consumed tourist food: ice cream (7 minutes before), cookies (48 minutes before), bread (6 minutes before)”.
According to scientists, chocolate, snacks and ice cream offered or stolen (something this type of monkey really likes to do) to tourists – a substantial part of the diet of some Gibraltar monkeys – alter the “composition of the gut microbiome” of animals and have led to changes in their behavior.
“Eating earth can help rebalance the stomach from monkeys, providing bacteria and minerals missing from processed foods”, being “probable that help coat the intestine and soothe or prevent irritation caused by excess sugar and fat”, they say.
“The foods brought by tourists and consumed by Gibraltar monkeys are extremely rich in calories, sugar, salt and dairy products”, he says. Sylvain Lemoinewho led the study, in March at Scientific Reports.
“This is completely different from the foods typically consumed by the species, such as herbs, leaves, seeds and, occasionally, insects”, adds the primatologist from the Department of Archeology at Cambridge.
There is a vast menu of lands
Scientists recorded not only when and where the animals ingested soil, but also the types of soil and the social context, concluding that this is a socially transmitted behavior, given that different groups have preferences for certain types of soil.
According to the study, around 30% of geophagy cases occurred in groups, with several animals eating dirt together from the same rocky outcrop, and 89% of all incidents occurred in the presence of other monkeys who often watched them.
The monkeys clearly preferred certain types of soil, with most seeking out the “terra rossa” or red clay found in Gibraltar, which represented 83% of all geophagy episodes.
Lemoine, founder of the Monkeys of Gibraltar Project, says researchers believe “the monkeys started eating soil to protect the digestive system from the high energy and low fiber content” of junk food.
“The consumed soil acts as a barrier in the digestive tractlimiting the absorption of harmful compounds. This can alleviate gastrointestinal symptoms, from nausea to diarrhea. Soil can also provide beneficial bacteria that help with the intestinal microbiota”, he explains.
An average of 12 soil ingestion “events” were observed per week, considered a high value among the geophagy frequencies already recorded in primates, comparable to that of chimpanzees and lemurs, which eat soil to obtain minerals and protect themselves from plant toxins.
There are around 230 monkeys in Gibraltar, distributed in eight stable groups that inhabit different areas of the Rock.
Local authorities provide fruit, vegetables and water daily at designated food points and vvisitors are prohibited from feeding them. However, many do so and the animals often look for and steal food brought by tourists.
During the observation period, almost a fifth (18.8%) of all food consumed by the monkeys was junk food brought by tourists and the three groups of monkeys that live at the top of the Rock, one of the places with a large concentration of people, were responsible for more than two thirds (72%) of all cases of soil ingestion.
A group that had no contact with tourists or access to human food was the unique in that researchers observed no soil consumption.
Geophagy also happens in humans
In some human cultures, geophagy is common, often associated with the ingestion of nutrients during food production. pregnancybut in this case the researchers did not find an increase in the monkeys’ soil intake during pregnancy or lactation, suggesting that it is not driven by a need for supplementation.
“The emergence of this behavior in monkeys is both functional as cultural (…), but it is idriven entirely by proximity to humans”, points out Lemoine.
