The practice of eating earth, known as geophagy, is a widespread and ancient behavior observed across the animal kingdom. This intentional consumption of soil, clay, or other earth-like substances is a targeted biological strategy. Animals engage in geophagy as a form of self-medication or nutritional supplementation to overcome challenges in their natural diets and environments. The motivation behind this action is complex, serving multiple purposes related to survival and physiological maintenance.
Defining Geophagy and Common Animal Examples
Geophagy is defined by the deliberate ingestion of earth or soil-like materials, which often includes specific mineral-rich clays, chalk, or even termite mound materials. This behavior is distinct from the accidental ingestion of dirt that occurs during feeding. Animals often travel considerable distances to access certain mineral licks or exposed clay banks, indicating a targeted search for specific soil compositions. In the Amazon rainforest, macaws and parrots gather at specific riverbank cliffs, known as clay licks, to consume mineral-rich soil layers. African elephants use their tusks to dig and scrape soil from geological formations, creating large treeless areas called “licks.” Primates, including chimpanzees, have also been observed consuming clay to supplement their diets.
Nutritional Deficiencies Driving Geophagy
One of the primary drivers for geophagy is the need to supplement essential minerals that are often scarce in an animal’s regular diet. Herbivores, in particular, frequently consume plants that are low in macro-minerals like sodium, a nutrient necessary for nerve and muscle function and for maintaining the body’s fluid balance. In many forested regions, the available vegetation is naturally sodium-poor, making mineral licks a vital source of this element. Studies on parrots in the southeastern Peruvian Amazon show that the soils they selectively consume have significantly higher sodium content compared to the surrounding earth. This targeted consumption suggests a direct physiological response to a sodium deficit. Geophagy can also be a targeted response to deficiencies in other elements, such as calcium or phosphorus. For instance, cattle experiencing low phosphorus levels have been observed engaging in soil consumption to correct this deficiency.
The Role of Earth in Detoxification and Digestion
Beyond nutritional supplementation, geophagy serves a protective function, particularly for animals whose diets include naturally toxic plants. Certain types of clay, such as kaolinite, act as natural adsorbents in the digestive tract. These clays have a structure that allows them to bind to positively charged compounds, including plant toxins like tannins and alkaloids. When an animal ingests these specific clays, the toxins are bound to the clay minerals within the gut and are safely passed through the digestive system without being absorbed into the bloodstream. This mechanism allows animals like parrots to consume seeds and unripe fruits that contain protective plant chemicals. In addition to toxin binding, the ingestion of soil can aid in mechanical digestion by providing grit, which helps to break down tough plant matter in the stomach. The presence of clay may also help to regulate stomach acidity or act as an anti-diarrheal agent, aiding overall digestive health.
Potential Health Risks of Soil Consumption
While geophagy offers clear benefits, the practice is not without risks, as soil can contain various contaminants. One significant danger is the ingestion of parasites, specifically helminth eggs, which can remain viable in the soil for extended periods. Animals that consume topsoil, especially in areas contaminated by feces, face a higher risk of parasitic infection. Furthermore, the earth can contain elevated concentrations of heavy metals, such as lead, mercury, and arsenic, which can be toxic if consumed regularly. Ironically, the very binding properties of the clay that help neutralize toxins can also pose a problem by binding to beneficial nutrients and pharmaceuticals, potentially reducing their absorption in the gut.