Back in late September I came across these ants (Hymenoptera: Formicidae) foraging on a wreath goldenrod (Solidago caesia, Asteraceae) at Pinckney State Recreation Area here in southeast Michigan. Ants are a very large and diverse family, and their behavior can vary considerably between species. This is perhaps most evident in their feeding habits. Some ants are carnivorous, some are phytophagous, some farm fungi grown on harvested organic matter, and some ranch aphids like cattle in order to feed on their honeydew secretions. Many ants like the individuals shown here also feed on nectar and pollen from flowers.
All ants are eusocial and live in colonies where labor is divided between castes. Reproduction, defense, care of young, and foraging are performed by different yet equally important classes within each community. Foragers like those shown here not only find food, but also share it with others through trophallaxis. These ants regurgitate part of their meals, feeding it mouth-to-mouth to others (especially to non-foraging individuals).
Millions of years of ants feeding on nectar and pollen have lead to the evolution of extrafloral nectaries in some plants. These plants have structures outside of the flowers that exude large amounts of nectar. Ants feed at nectaries and consequently work hard to protect these stable food sources. When other insects attempt to feed on and damage the plants, the ants will attempt to fight them off. Since this arrangement benefits both the ants and the plants, it’s an example of a mutualism. The goldenrod shown here lacks extrafloral nectaries, but that could change in the course of another few million years of ant foraging.