Xylanase and β-xylosidase activities were assayed for each gut region of field-collected Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae) workers, as well as those kept on eight diets. Five diets were formulated, consisting of varying ratios of cellulose and xylan. The remaining three diets, red oak (Quercus spp.), pine (Pinus spp.), and filter paper, were intended to represent probable food sources in the field. Xylanase and β-xylosidase activities were primarily located in the hindgut (>92% total xylanase activity, ≈50–75% total β-xylosidase activity), providing strong evidence that xylan digestion is mainly carried out by hindgut symbionts in R. flavipes workers. Among the formulated diets, both xylanase and β-xylosidase activities were significantly higher in termites kept on 20 and 40% xylan than in termites kept on 0 and 5% xylan. Among the field diets, both xylanase and β-xylosidase total activities were highest on the oak diet, the diet with the highest xylan content, and lowest on the paper diet, a diet without xylan. Both activities were evident in termites fed on the 100% cellulose diet and the paper diet, in spite of the lack of xylan in these diets. The presence of xylanolytic activity on xylan-free diets indicates the presence of xylanolytic symbionts that can survive on a diet of pure cellulose. Xylanolytic activities in the R. flavipes colony changed to accommodate the xylan content of their diet, most likely by changes in the hindgut symbiont communities. This flexibility allows a termite colony to efficiently use a variety of wood species and wood-derived materials.