Why Do Ants Eat Plants?

Ants are often harvesting leaves for someone else.

The idea that ants eat plants is a common misconception. Ants lack the ability to digest plant material, but they do use plants and their leaves for other reasons. Some species can often be seen harvesting leaves and giving the impression that they're harvesting food, but what these ants do with plants is far more complex than simply taking a meal back to the colony. Does this Spark an idea?

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Colony Construction
- Ants can be an early warning sign of plant disease.
  
  Some ants are known to build their homes within tree trunks both living and dead. Carpenter ants are the most common of these types of ants, and will chew tunnels through the heartwood of the tree to hollow out passages and chambers for the colony. This wood does not get eaten, however; instead, it is removed from the newly constructed colony and deposited outside of the nest. The resulting pile of chewed wood is one of the telltale signs of a carpenter ant colony. The actions of these ants do not harm the plants they choose for their nests. Instead, the presence of an ant colony can be an indication that something is already wrong with the tree, as they will tend to choose sites with soft or decaying wood that is easy to chew through.
Feeding Herds
- Plant leaves are collected but not eaten.
  
  While ants can't eat plant material themselves, some varieties will harvest leaves and other plant material to feed herds of aphids they raise back in the nest. What the ants do eat is the sweet secretions that these aphids give off. The ants will construct tunnels and rooms around the aphids, and return to the nest with pieces of leaves for the aphids to eat -- raising and harvesting them much like a farmer raises and milks dairy cows. Other types of ants, such as leaf-cutter ants, will harvest leaves in a similar fashion and return them to the nest not for aphids, but as food for fungi. The fungi in the nest absorbs and breaks down the leaves, reproduces, and the ants in turn feed on the fungi.
Nest-making
- Even scorpions can become a meal for weaver ants.
  
  Some ants use plants for creating nests. Weaver ants don't eat the leaves of the plants that they choose, but they do puncture the edges and use the silk produced by larvae to sew those edges together, giving the ant species its name. The nests of sewn leaves contain chambers for the queen and her eggs, chambers for nurseries for the growing larvae and storage chambers for the actual food of the ants -- other insects. Many of the ants that use plants to construct their homes actually eat other insects or the secretions of these insects, doing little damage to the actual plants that they choose.
Plant Root Damage
- Some ants are known for doing damage to the roots of plants, but their process of chewing through these roots isn't to consume them. Aphids will commonly be found feeding on the roots of a plant, and these small pests are a valuable food source for the ants. Ants will chew through plant roots to reach the aphids, which they will then often collect into a herd to feed and raise by harvesting other parts of the plant.