On their own, termites—such as the eastern subterranean termites (Reticulitermes flavipes), shown here—are not able to derive energy and nutrients from wood. But, some bacterial groups, such Enterobacteria, can degrade cellulose and live within the gut of termites. Thus, wood-degrading bacteria and termites co-exist in a type of symbiosis that represents mutual benefit for both, a relationship called mutualism. (Photo by Joseph Berger, Bugwood.org)