Dr Frank Krell of the Natural History Museum in London thinks he may have discovered one crucial piece of the puzzle that ensures that the savannah remains the same Garden of Eden that gave birth to our own species. It all revolves, Krell believes, around one small, shiny beetle, its appallingly bad diet and an unexpected symbiosis with people.
The insect in question is the dung beetle and Krell and his entomologist colleagues have been studying its deplorable habits in stomach-churning detail. His latest results, presented at a lecture in the museum, suggest the savannah and many of its plants and animals may owe their very continued existence to the complex life of these beetles.
"There are more dung beetles than dung on the savannah," explains Krell, who estimates that the mass of dung beetles is sometimes around twice that of the dung that they survive on, "and so many competing species, each with different strategies, that they take it in turn at dung piles." In the dung beetle world, it seems, survival involves a rota where competing beetles, which use dung in similar ways, each take their turn at the smelly feeding trough.
It is how the beetles make use of dung that is so important to the ecosystem of the grasslands. Some species of dung beetle make their homes in the dung pile itself; however, it is those that have their dung "to go" that contribute most to the savannah since they spread nature's own fertiliser far and wide.
"Rollers," Krell says, "can transport a ball of dung 40 times their body weight for as much as 70 metres, distributing the nutrients over a large area surrounding a dung pile and thus increase the fertility of soil in the savannah." The extent of the beetle's manure spreading abilities is complicated since rollers prefer open areas.
Rollers store their dung under a shady tussock or in shallow holes. Specialised tunnellers, however, bury their dung in the hard soil. Large species can reach depths of 30 to 40 cm and even a mole-like 1.5 m below the ground surface is not unknown. The amount of dung they bury depends on its purpose. Dung buried as a nutrient-rich nursery for the dung beetles' larvae can be of mammoth quantity since in some species it has to sustain the youngsters for more than a year.
Dung is more than just waste, explains Krell; it is often full of seeds and burial by dung beetles may be crucial in the germination success of several plant species found on the savannah. Tunnelling and rolling species together not only distribute nutrients over the surface of the savannah but also dig it in for good measure, providing fertiliser at all levels of the soil profile to ensure a lush growth of vegetation during the rains. Around one tonne of nutrient-rich dung is deposited per hectare of the savannah each year, so there is more than enough to go round, especially once dug in by the enterprising insects.
Piecing together the complex life of dung beetles on the savannah is not a particularly pleasant business. The rota of species at the dung pile poses a problem in collecting them. Krell and his colleagues have to resort to using fresh beetle-free dung to trap beetles. Buffalo dung is the dung of choice for the scientists and they make use of the buffalo's sheep-like habit of staying on a road once they've stumbled on to it. "Drive far enough and you'll find all the fresh dung you could ever want," says Krell. When kerb-crawling fails to provide, however, Krell admits that human dung will do at a pinch.
Krell's latest results on the biodiversity of dung beetles have revealed a surprising symbiosis between man and beetle. Collecting dung beetles in savannah used for cattle grazing on the Ivory Coast of West Africa, Krell and his team have been investigating the effects of human agriculture on dung beetle diversity. The savannah in the region, unlike that of East Africa, is not natural but maintained by seasonal fires set by the farmers to clear the grasslands for their herds, and the dung beetle appears to play an important role in ensuring their livelihood.
After burning, Krell has discovered that, once the rain comes, the population of rolling and tunnelling beetles explodes since these require the open landscape for their activities. Cattle, unlike buffalo, defecate in set areas and so the beetles are crucial in distributing the nutrients present in their dung across the savannah, ensuring its fertility.
Krell's results provide an important environmental lesson. The human and beetle populations are dependent on each other. The people burn the savannah allowing the beetles to distribute the nutrients required to sustain the vegetation and cattle. In West Africa nature has adapted to human activity and preserves the biodiversity of the savannah, all because of one particularly enterprising, if toilet-obsessed, beetle.