As in mammals, insect health is strongly influenced by the composition and activities of resident microorganisms. However, the microbiota of insects is generally less diverse than that of mammals, allowing microbial function in insects to be coupled to individual, identified microbial species. This trait of insect symbioses facilitates our understanding of the mechanisms that promote insect-microbial coexistence and the processes by which the microbiota affect insect well-being. As a result, insects are potentially ideal models to study various aspects of interactions between the host and its resident microorganisms that would be impractical or unfeasible in mammals and to generate hypotheses for subsequent testing in mammalian models.