The ants pictured here are leaf-cutter ants (Atta colombica) and are native to South America from Guatemala to Columbia (which may be where the species name originates from). There are also populations found in parts of Costa Rica. Although these ants aren't native to Missouri or anywhere else in North America they are still very interesting and right now they are on display at Reiman Gardens in Ames, Iowa at the Iowa State University. They have created a very unique and fun exhibit to showcase these ants, and if you are in the area it will be worth a visit to see these ants, as well as the rest of the Reiman Gardens exhibits, which includes a large butterfly pavilion.
These ants are reddish in color with a matte sheen, there are no shiny spots on these ants. These ants forage for leaves to cut and bring back to the nest that is used in a fungus garden. The fungus that is created from the fermenting leaves is eaten by the ants and fed to the offspring. When leaves rot or become otherwise unusable the ants will carry these leaves out in the form of refuse to an outside dump that is located to the side of the main soil mounds. These refuse dumps are cone-shaped and distinctive in appearance.
Occasionally these ants go a little crazy in the leaf-cutting department and cut more than the colony can consume. These excess leaves are cached on nearby trails or near the entrance to the nest. When more leaves are needed they will collect from these caches first before cutting more leaves. Sort of a "want not, waste not" mentality.
These are very interesting ants, not to mention beautiful and fun to watch. Hope you all get the chance to visit Reiman Gardens to see these little ants hard at work.