When Ze Frank took several years off from his True Facts series, he was apparently stockpiling scripts for his return. This is his third video in the past month! And it's quite interesting, even past the snarky comedy. Leafcutter ants are farmers. They use plants to grow fungus to feed animals. This benefits both the ants and the fungus (but maybe not the tree so much) in an example of mutualism. Other ants use various insects in other mutualism schemes, some of which can be pretty gross.