The One That Digs With Its Teeth

10 Mar 2020

Dirk Heinrich 

After rainfall, when the land is wet, they start digging. The soil is loosened with the teeth and pushed backwards with the front legs. The hind legs shovel the damp earth still further to the back. This is the Damara mole-rat (Fukomys damarensis) at work. Mole-rats construct networks of tunnels which can reach a length of up to one kilometre. The incisors of the upper and lower jaw are very large in relation to their body’s total size of 15 to 18 cm, and also serve to defend themselves – should they encounter an enemy in the tunnels or should they venture to the surface, which happens very rarely. 

In contrast to moles, the Damara mole-rat and other mole-rat species are herbivorous and only feed on roots, tubers and other parts of plants. Moles on the other hand eat earthworms and insects. 

According to Professor Jennifer Jarvis of the University of Cape Town, there are three mole-rat species in Namibia. The Damara mole-rat is the most common and the most widely distributed, while Bocage’s mole-rat (Cryptomys bocagei) is rare, and little is known about it.  This species has been found at Ondjeva, Ongha and Ondongera in the central north. The Namaqua dune mole-rat (Bathyergus janetta) prefers sandy habitats on the fringe of the coastal dunes close to the Orange River in the far south. This mole-rat is a rather aggressive loner. Professor Jarvis points out that unlike the other two species in Namibia, the Namaqua dune mole-rat does not dig with its teeth but only with its front legs. 

Damara mole-rats live almost exclusively underground, in colonies of typically around a dozen animals. Colonies of up to 40 individuals have also been found, however. Males are usually somewhat larger and heavier than the females. The colour of both sexes varies from fawn or dark brown to brown-black, the fur is short and thick with a characteristic white spot of varying size on the head and neck. The incisors are ungrooved and never stop growing.  They extend far over the lips and are therefore always visible. Only one female and one or two males in a colony are able to reproduce. The remaining animals, mostly the offspring of different generations, do not mate but take care of tunnel construction and foraging for food. Mole-rats are considered eusocial, i.e. they have a high level of organisation similar to termites, ants and bees. The breeding female can give birth to an average of three pubs (1-6) up to three times a year. 

Very few people have seen a Damara mole-rat in the wild because these small mammals hardly ever come to the surface. Those that do, are usually animals that leave the burrow at night to look for a mate and start a new colony. The presence of Damara mole-rats is revealed by the mounds of soil pushed up a metre or more apart from the other. As mentioned earlier, mole-rats are particularly active in the rainy season when the soil is moist and softened. Research by Professor Jarvis and colleagues has shown that large colonies of Damara mole-rats are able to dig several kilometres of new tunnels during a rainy season. Small tubers are eaten on the spot. Larger tubers or bulbs are taken to a pantry close to the nest. Big tubers are partly eaten, then covered with sand again and left in their place to regenerate, says Professor Jarvis. 

Their predators below ground include snakes such as the mole snake and some cobra species, while above ground raptors pose a danger, particularly owls. Damara mole-rats are almost blind. Their eyes are very small and they have no external ears. But their hearing is very good and they are sensitive to vibrations.