A number of plant species have come to depend on ants to disperse their seeds.  To entice the ants, the seeds have a tasty, lipid-rich structure called an elaiosome at one end, and the ants carry the seed along when then take the elaiosome back to their nest. Here, Formica exsectoides mound ants have found the seeds of leafy spurge, an invasive pest plant whose spread might be facilitated by the ants.  Wisconsin, USA