Episode 2, The Enemy of My Enemy (Human Footprint, Season 2)

Humans have transformed Earth for millennia, making enemies and allies with species along the way. In The Enemy of My Enemy, Shane Campbell-Staton visits three continents to explore "biocontrol"--and meets experts using one species to control another. But the allies we recruit don't always behave as expected, sometimes causing catastrophe. Can we harness biocontrol without creating new foes?