Ants are social insects found across nearly every terrestrial habitat, exhibiting an enormous range of feeding behaviors. While many species are omnivorous scavengers or predators, a significant portion of the ant world relies on plant material for survival. The nature of this consumption varies dramatically, ranging from indirect cultivation to the harvesting of specialized plant parts. Understanding these dietary habits requires looking at the highly evolved partnerships and specialized foraging strategies they employ.
True Plant Eaters and Fungus Farmers
The most dramatic example of ants relying on plant matter involves the fungus-growing ants of the Attini tribe, such as leaf-cutter ants (Atta and Acromyrmex genera). These ants are not true herbivores because they lack the enzymes to break down cellulose in fresh leaves. Instead, they operate as sophisticated agriculturalists, using plant material as a substrate to cultivate a specific fungus, primarily from the genus Leucoagaricus.
The ants meticulously cut leaves, carry them back to their nests, and chew them into a pulp to create a nutrient-rich garden. The fungus breaks down the tough plant fibers, effectively handling the ant’s digestion process. The ants and their larvae then feed exclusively on specialized nutrient-rich growths called gongylidia produced by the fungus. This mutualistic system represents a highly specialized form of indirect herbivory that sustains millions of ants across the Americas.
Lower-attine species use materials like insect feces, dead wood, and detritus to grow their fungi. Higher-attines shifted to using fresh plant tissue, allowing for industrial-scale agriculture that makes them dominant herbivores in many Neotropical ecosystems. Workers of the leaf-cutter species also ingest some plant sap released during cutting, providing a quick source of carbohydrates.
Consuming Plant Secretions and Seeds
Many ant species consume substances produced by plants that are not structural tissue, often to satisfy their high demand for sugars. One common energy source is nectar, collected directly from flowers (floral nectar) or from specialized glands outside the flower (extrafloral nectaries). These sugar-rich secretions provide the necessary carbohydrate fuel for the colony.
A significant portion of the ant diet is derived indirectly from plants in the form of honeydew, a sugary waste product excreted by sap-sucking insects like aphids, scale insects, and mealybugs. Ants engage in trophobiosis, or “farming,” protecting these insects from predators in exchange for the honeydew. The ants stroke the aphids to encourage the release of the sweet droplet.
Beyond sweet secretions, many ants, particularly in arid regions, are primarily granivores, meaning they consume seeds. Harvester ants from genera like Pogonomyrmex and Messor collect seeds and store them in underground chambers called granaries. They consume the nutrient-rich seed kernel directly, making the seed a primary food source for adults and larvae. This behavior is a direct instance of ants consuming plant tissue.
Ecological Relationships with Plants
The interaction between ants and plants extends beyond simple consumption into complex ecological partnerships that benefit both organisms. One such mutualism is myrmecochory, or seed dispersal by ants. These plants produce seeds equipped with an elaiosome, a fleshy, lipid and protein-rich appendage that serves as a food reward for the ants.
Ants carry the entire seed back to their nest, consume only the elaiosome, and then discard the viable seed in a nutrient-rich waste area or midden. This acts as a favorable site for germination. This process moves the seed away from the competition of the parent plant and protects it from seed predators and fire.
Plants also recruit ants for defense in what is known as defensive mutualism. Many plants, known as myrmecophytes, have evolved specialized structures to house and feed ant colonies. They provide shelter in hollow thorns or stems (domatia) and food like extrafloral nectar or protein-rich Beltian bodies. In return, the resident ants aggressively patrol the plant, defending it against herbivores and clearing competing vegetation.