The main objective of this study was to assess the damage to grazed pastures in the Mokwa area of the Southern Guinea savanna zone of Nigeria by Trinervitermes geminatus (Wasmann) (Isoptera, Termitidae, Nasutitermitinae) and to determine its role as a competitor with grazing livestock. In Nigeria, T. geminatus is the only species which cuts down standing grass and at the same time is sufficiently abundant to be considered a potential threat. T. geminatus builds domed-shaped mounds which are highly aggregated and serve as breeding and storage sites. Some of these mounds are subsequently abandoned and are either eroded away or are reoccupied by the nonmound building species of the same genus or other termites notably Cubitermes sp., Promirotermes sp. and Microtermes spp. During the rainy season, new mounds are constructed and old mounds are enlarged. Population density of T. geminatus was estimated in grazed and ungrazed areas of a secondary woodland, as well as in a primary savanna woodland. Populations were low (203/m ; 232 mounds/ha) in the areas of study and seasonal fluctuations in them were indicated. Decrease in population during the dry season, coincided with the period of active foraging and intense predation, and they increased during the rains. Following the flight of alates in July/August, populations again declined. The foraging habits of T. geminatus and the quantity of grass removed were investigated. Foraging in the Mokwa area was in early morning or late afternoon and lasted about 2-3 hours. It was greatly influenced by environmental factors such as rain, soil surface temperatures and relative humidity. Grass production was estimated at approximately 3000 kg/ha/annum, and of this quantity cattle consumed approximately half the annual production 48%). A method was developed for quantifying the amount of grass harvested by T. geminatus, and following this method, the quantity of grass removed by this species was estimated as representing 3.5% of the total annual grass production. Therefore, the quantity of grass removed and hence made unavailable for cattle consumption was insignificant in this locality. Although, field and laboratory investigations on the choice of grass indicated a strong preference by T. geminatus for Andropogon gayanus, a grass species equally preferred by cattle, they hardly competed for it in the Mokwa area. It is however suggested that the impact of grass harvesting by T. geminatus would be relatively greater in areas with high populations of termites and in overgrazed pastures especially during periods of drought when grass production is lowered by poor management or low rainfall