Ants are one of the most successful and diverse insect groups on Earth, adapted to nearly every terrestrial environment. Whether ants consume plant leaves is nuanced, depending entirely on the species and its specific foraging behavior. The vast majority of ant species do not directly feed on leaves, but there are notable exceptions that rely on plant material. Furthermore, many common ant species cause significant damage to plants not by eating them, but through indirect, symbiotic relationships with other garden pests.
The General Ant Diet
The diet of most ant species is highly varied, which is a major factor in their ecological success across diverse habitats. Most ants are generalist omnivores, consuming a mix of sugary liquids and protein-rich substances. Foraging workers scavenge dead insects and other arthropods for protein, which is important for developing larvae within the colony.
Adult ants primarily rely on carbohydrates found in sugary sources like flower nectar and plant sap to fuel their constant activity. Certain species, known as harvester ants, have specialized diets focused on collecting and storing seeds, acting as important dispersal agents for many plant species. This dietary profile confirms that for most ants, fresh leaf material is not a preferred or viable food source.
The Specialized Behavior of Leaf-Cutter Ants
The most famous exception to the general rule are the leaf-cutter ants, belonging primarily to the genera Atta and Acromyrmex, found throughout Central and South America. These ants are notorious for carrying pieces of freshly cut foliage back to their underground nests. It is a common misconception that they are chewing and swallowing the leaves they harvest.
Instead, the ants use the masticated leaf material as a nutrient-rich substrate to cultivate an obligate symbiotic fungus, Leucoagaricus gongylophorus. The ants lack the digestive enzymes necessary to break down the complex polymers in the leaves themselves. The fungus acts as an external digestive system, converting the plant matter into specialized, nutrient-rich swellings called gongylidia, which the ants then consume as their primary food source. This sophisticated agricultural system makes the leaf-cutter ant one of the world’s dominant herbivores.
Indirect Damage Through Pest Farming
A more common reason gardeners notice ants on their plants is that the ants are actively farming sap-sucking insects. Ants engage in a mutualistic relationship with pests like aphids, scale insects, and mealybugs. These soft-bodied pests insert piercing mouthparts into the plant tissue and feed on the sugar-rich sap flowing through the plant’s vascular system.
The pests must consume large quantities of sap to obtain sufficient nitrogen, leading to the excretion of a sugary waste product called honeydew. The ants consume this honeydew, often stimulating its release by stroking the pests with their antennae, a behavior known as “milking.” In return for this sweet reward, the ants aggressively protect their “herd” from natural predators, such as ladybugs and parasitic wasps.
The actual damage to the plant, including wilting, yellowing, and stunted growth, is caused by the pests drawing out the plant’s fluids. The presence of ants facilitates this damage by allowing pest populations to explode unchecked. Furthermore, excess honeydew drips onto the leaves and fosters the growth of sooty mold. This black fungus blocks sunlight and reduces the plant’s ability to photosynthesize.