Nest populations or colonies of the harvester termite, Trinervitermes trinervoides (Sjöstedt) (Termitidae: Nasutitermitinae), which commonly occurs in the semi-arid grasslands of southern Africa, were assessed. The entire contents of nests, mounds and subterranean sections were excavated following fumigation. Termites were extracted by flotation from volumetric sub-samples of the nest material and counted. Nest populations were found to be considerably larger than those of other members of the genus. Sterile adult populations varied from 9000 in small mounds (height = 12 cm) to 889 000 in large mounds (height = 59 cm). Workers, major and minor soldiers make up 75%, 9% and 16%, respectively, of the total adult sterile population. The proportion of soldiers decreased with increasing colony size, constituting 51% of populations of the smallest nest and only 16% of a large nest. This decrease in total soldier proportions in larger nests reflected a decrease in the proportion of minor soldiers. Ratios of workers to soldiers varied from 1:1 in the smallest colonies to 5:1 in larger nests. Undifferentiated larvae comprised 51% of the total larval composition on average and were particularly low (20–29% ) in winter when low temperatures restricted foraging and scarce resources were directed towards the development and growth of the alates. Small larvae, from which both minor and major soldier lines develop, constituted 12% on average. The proportion of large larvae from which workers are derived, varied between 26–45%. No clear pattern of changing proportions of soldier or worker larvae emerged that could be linked to seasonal fluctuations in activities such as foraging. The first nymphs appeared in the nest in March and a number of different nymphal instars were present in the nest simultaneously. By October all nymphs had reached the adult stage and were ready to fly.