Academic Reading — Test 59

Reading passage

Across the open grasslands of Africa, vast herds of grazing animals such as buffalo, antelope and elephants produce enormous quantities of waste each day. If this material were simply left to accumulate, it would smother the grasses on which the herds depend and provide a breeding ground for parasites and disease. That this does not happen is largely due to a group of insects whose work is rarely noticed: the dung beetles. Despite their modest size, these creatures perform an ecological task of remarkable importance, quietly returning to the soil the nutrients locked inside animal waste and keeping the savannah healthy and productive. Dung beetles are usually divided into three broad groups according to how they handle the material they collect. The first, known as rollers, shape a portion of dung into a ball, roll it some distance away from the original pile and then bury it underground. The second group, the tunnellers, dig directly beneath a pile and drag the dung down into chambers in the soil. The third group, the dwellers, neither roll nor tunnel but simply live and breed within the dung pile itself. Each strategy moves the waste in a different way, yet all three contribute to the same outcome: organic matter is broken apart and incorporated into the earth far more quickly than it would be through weathering alone. The benefits of this activity extend well beyond the mere removal of waste. When dung is buried, the nitrogen, phosphorus and other elements it contains are released gradually into the surrounding soil, where plant roots can absorb them. In effect, the beetles act as a natural fertilising system, recycling nutrients that would otherwise be lost to the air through evaporation. Their tunnelling also loosens compacted ground, allowing rainwater and oxygen to penetrate more deeply. Studies on managed grasslands have found that soils enriched by beetle activity tend to support more vigorous plant growth, which in turn sustains the very herds whose waste began the cycle. The relationship is therefore circular, with the health of the grasses and the abundance of the grazers bound tightly together. Dung beetles also provide a valuable service in controlling pests. Many flies and intestinal worms rely on undisturbed dung in order to complete their life cycles, laying eggs in the moist surface where their larvae can develop. By burying or dispersing a pile within hours, beetles deprive these organisms of the stable environment they require. In regions where cattle are farmed, this can significantly reduce the population of biting flies that trouble livestock, lowering the need for chemical treatments. The economic value of such natural pest control, though difficult to calculate precisely, is thought to be considerable, particularly for farmers who cannot afford expensive veterinary products. The reproductive behaviour of these insects is closely tied to the resource they exploit. A female typically lays her eggs inside a buried ball or chamber of dung, which then serves as a ready supply of food for the developing larvae. Some species show a degree of parental care that is unusual among insects: the parents may remain near the buried dung, tending it and protecting the brood until the young are able to fend for themselves. This investment improves the chances that the next generation will survive, but it also means that each pair processes a relatively small amount of waste, so the overall impact depends on the presence of large numbers of beetles working together. Remarkably, some dung beetles are guided across the landscape using cues in the sky. Researchers have demonstrated that certain species orient themselves by the pattern of polarised light produced by the sun, and that a few can even navigate by the faint band of the Milky Way at night. This ability allows a beetle rolling its ball to travel in a straight line away from the competition gathered at a dung pile, reducing the risk that its prize will be stolen by rivals. Such sophisticated behaviour, in an animal often dismissed as lowly, has attracted growing scientific interest. Today the populations of many dung beetle species are under pressure. The conversion of savannah into farmland removes the wild herbivores on which the beetles depend, while certain drugs given to domestic cattle pass through the animals and remain active in their dung, poisoning the insects that feed on it. Conservationists warn that a decline in dung beetles could weaken the entire grassland system, allowing waste to build up, soils to lose fertility and pest numbers to rise. Protecting these unobtrusive engineers, they argue, is essential not only for the savannah itself but also for the people and animals that ultimately rely upon it.