Microorganisms subsist in the guts of some insects and help with the breakdown of cellulose and lignin and with nitrogen fixation. These particular insects and microorganisms developed a need for each other somewhere along evolutionary lineages, and now they actually benefit from each other in symbiotic relationships. Termites are one example of insects with protists, fungi, and bacteria living in their hindgut. Because termites diverged from cockroaches about 250 million years ago, exploring the similarities and differences of these two insects helps shed light on the evolution of microbial communities in their hindguts and the state of symbiosis in which they exist.
First, it is necessary to understand the digestion of these insects. Termites and cockroaches contribute to the degradation of wood because they have the ability to digest cellulose, a complex carbohydrate that makes up the cell walls of plants and is therefore the major component of wood. The diet of termites is usually high in cellulose because their food is mainly woody material. Cellulose is the most abundant form of carbon on Earth, excluding fossils (Martin, Jones, and Bernays 1991). Termites digest cellulose more efficiently than any other animal, and most animals are not able to digest this bountiful resource. Martin, Jones, and Bernays propose four ways that cellulose is digested in termites.