There are 129 different ant species that call Illinois home, about 1/3 of which live in the prairie. Today they are continuing their work as being one of the main bioturbators (animals that move soil) in the prairie, a job that was partially outsourced recently to an exotic invader: the earthworm.
Ants are still transporting and burying native seeds, allowing plants to move around a preserve. They are concentrating soil nutrients in and around their nests, which other animals and plants take advantage of. The ants are also taking care of some native plants and other insects, much like they are tending to a garden.
These are just a few of the tasks that ants take on that allows a prairie to function normally. Read more here, here and here.