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Trinervitermes trinervoides (Sjostedt) (Termitidae: Nasutitermitinae) is principally a grass litter-feeding species common to the semi-arid and arid grasslands of southernAfrica. Abundance of sterile adult termites (workers and soldiers) at eight sites within an area of semi-arid grassland, northwest of Bloemfontein in the Free State Province, varied between 34 and 4871/m(2) (mean = 2261/m(2)) with a live biomass of 0.2 to 27.8 g/m(2) (mean = 12.9 g/m(2)). The numbers of live mounds in an area do not necessarily reflect termite abundance. At two sites at Bultfontein fewer termites and lower biomass were present on the site with 137 mounds/ha than that with 97 mounds/ha. Experimental studies on grass consumption of artificially fed field colonies of different sizes were used to estimate consumption by termites at the different sites. Consumption at the various experimental sites varied between 2.7 and 451.2 kg/ha/year (mean: 203.4 +/- 175.1 kg/ha/year) and a marked seasonal periodicity in consumption was demonstrated. The impact of T. trinervoides within well-managed grassland ecosystems where the litter-feeding species form an important link in the food chain, is chiefly beneficial and far outweigh its harmful effects which tend to be associated with degraded, overgrazed grassland and drought.