Wood ants are predatory insects and feed on a variety of other insects including caterpillars, beetles, and other ant species.

Ninety percent of their diet however, comes from honeydew produced by aphids which feed on trees and shrubs. Aphids feed on tree sap which is high in sugars and as they feed they excrete any excess sugars as honeydew. Ants “milk” the aphids of their honeydew, and in return protect the aphids from predators and even move them to better feeding grounds. Wood ants are commonly seen moving up the trunks of pine trees, sometimes 30m tall, to collect honeydew from pine aphids living high in the tree canopy. With abdomens distended from honeydew, the ants return to the rest to regurgitate honeydew for the queen and other workers. The developing brood require protein for growth and rely much more on insect prey that the workers return to the nest.

The related species F. exsecta is believed to rely more on insect prey and possibly even root aphids for food as its nests are generally situated away from trees in order to obtain as much sunlight as possible.