Many animals across diverse ecosystems rely on grass as a primary food source. This widespread feeding strategy, found from vast plains to backyard lawns, is integral to maintaining the balance of grasslands and other environments globally.
Defining Grass Eaters
Animals that primarily eat grass are known as grazers. These herbivores specialize in consuming “true” grasses from the Poaceae family. This differentiates them from browsers, which feed on leaves, twigs, or fruits from shrubs and trees. For grazers, grass constitutes a significant portion of their diet.
Diverse Examples of Grass-Eating Animals
Many animals across various classes thrive on a grass-based diet. Large terrestrial mammals include domesticated cattle, sheep, and horses. Wild counterparts include zebras in African grasslands, and bison and pronghorn antelope on North American prairies. Hippopotamuses, despite their semi-aquatic nature, emerge at dusk to graze on grasses. Kangaroos, such as the red kangaroo, are also grass-eating marsupials.
Smaller mammals also eat grass. Rabbits and guinea pigs are known for their grass-heavy diets. Capybaras, the world’s largest rodents, graze extensively on grasses and aquatic plants in South American wetlands.
Birds and insects also consume grass. Canada geese graze on various parts of grass. Other grass-eating bird species include house sparrows, pigeons, and starlings, which forage in urban green spaces. Grasshoppers are graminivorous insects known for consuming large amounts of grass. Armyworms, cutworms, and sod webworms are insect larvae that feed on grass blades.
Physical Adaptations for Grazing
Consuming and digesting tough, fibrous grass requires specialized adaptations. Many grazers possess dental structures like wide mouths and broad, flat molars for grinding plant material. Strong incisors clip grass blades close to the ground. Grass contains abrasive silica, so grazer teeth often have high crowns that continually erupt to compensate for wear.
The digestive systems of grass-eating animals are adapted to break down cellulose, a complex carbohydrate abundant in grass, which most animals cannot digest directly. Ruminants, such as cattle, sheep, and deer, have a multi-chambered stomach. In the rumen, symbiotic microbes ferment the grass, breaking down cellulose and producing volatile fatty acids that serve as the animal’s main energy source. Ruminants also regurgitate partially digested food, known as cud, to re-chew it, aiding digestion.
Other grazers, like horses, rhinos, and rabbits, are hindgut fermenters. These animals have a single-chambered stomach, and cellulose fermentation occurs in their enlarged cecum and large intestine. While less efficient at nutrient absorption than ruminant digestion, hindgut fermentation allows for faster processing of large quantities of forage. Rabbits exhibit coprophagy, re-ingesting specialized droppings for additional nutrients.