They swim and dive with ease. The diet consists mainly of grass and cane and also includes bark, nuts, fallen fruits, and cultivated crops. Rocks, bones, and ivory are sometimes gnawed, apparently to hone the incisors rather than as a source of nutrients. T. swinderianus seems to live in groups of mixed ages and sexes, but in the dry season there is reportedly a division into solitary males and groups of females. T. gregorianus lives in small family groups, each of which may have a territory of 3,000-4,000 sq meters.
Captive males live peacefully with females and young but fight other adult males.
In South Africa the young are born from June to August. In that country, females probably have two litters annually. The gestation period was calculated to vary from 137 to 172 days and to average 155 days. Embryo counts ranged from one to eight, and mean litter size was four young. Thryonomys makes a special natal nest, usually scooping out a hollow depression in a sheltered area and lining it with grass and leaves.