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Termite assemblages, particularly those dominated by fungus-growing termites of the subfamily Macrotermitinae, play a major role in plant litter decomposition in and and semiarid regions, but the ecological similarities or differences among these species remain poorly understood. Determining whether termite species differ in their diets has been difficult, and thus it remains unclear if the diets and, by extrapolation, the ecological roles of these species in decomposition processes differ. Grasses in arid regions use the C4 photosynthetic pathway, which produces a stable carbon isotopic ratio (delta(13)C) distinct from that of the C3 photosynthetic pathway of woody plants. Because the isotopic signature of animals is similar to that of their diets, in dry regions stable isotope analysis can estimate relative proportions of grass and woody litter consumed by termites. I used this approach to study a termite assemblage in northern Botswana that is known to significantly influence rates of woody litter decomposition. I found that the diets of all four influential termite species (Macrotermes michaelseni, Odontotermes sp.,Allodontermes sp., and Microtermes sp.) were relatively broad, with VC values ranging from those of C4 grasses in grass-dominated areas to values close to woody vegetation in woody species-dominated sites. I also found that diets of the fungus-growing species that are active year-round (M. michaelseni and Odontotermes sp.) did not differ significantly and exhibited little seasonal variation. These findings suggest that this assemblage consumes grass and is therefore likely to be influencing grass litter decomposition as demonstrated for wood litter decomposition. Furthermore, the existence of functional redundancy, in terms of dietary breadth, among the fungus-growing species suggests that the absence or scarcity of some members in some habitats is unlikely to substantially alter the relative decomposition rates of plant litter types.