African swamp rats are characterized by having at least one conspicuous groove on all four incisor teeth. The upper incisors are strongly curved backward into the mouth. The head of Otomys is rounded and rather volelike, and the ears are relatively small. Dasymys closely resembles Otomys in external appearance, but that genus lacks the grooved incisors and has a longer tail. Otomys has a stocky body form.
Females have four mammae.
Both groups comprise grass and herb eaters that live mainly in moist, grassy areas and make runways under dense cover. The general habitats of Otomys include swamps, grasslands, savannahs, brush country, and alpine meadows. Most species usually shelter above ground, where they construct a nest of shredded plant material and twigs, often at the base of a small shrub or clump of grass. Others build a nest of fine grass at the bottom of a simple burrow, and still others appear not to make a nest at all. A conspicuous system of runways or tunnels is made through the grass to favorite feeding areas.