Symbioses, the interactions between two different species, make the world go ‘round. Everything from our agricultural systems to our own gut depends on groups of interacting organisms doing their thing. Our guest today, Dr. Alison Hansen, studies how a common aphid gets its nutrition. It turns out that its entire diet is dependent on a bacterium living inside each and every aphid. But how did it get there? What does it do for the aphid? Let’s dive into the big world inside small insects.