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The Dung beetle

17 November 2014

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Ground-living beetles are a major functional asset in ecological systems and have been present on the land surface of the Earth for many millions of years although their fossils are elusive. Many types of beetle burrow into the soil to lay eggs, pupate, feed and hibernate. Dung beetles are beetles that have developed a specialized life-style after the appearance of large herbivores. They are part of the subfamily Scarabaeinae which includes the so-called flesh-eating scarab beetle, one of the myths of ancient Egypt where it was regarded as being sacred. There are more than 5000 species of dung beetle in the world. The sacred scarab beetle Scarabaeus sacer was linked to Khepri the god of the rising sun and was a dung-rolling dung beetle. In ancient Egypt dung beetles were believed all to be males who reproduced by depositing semen in a ball of dung. They were therefore linked with Khepri who could create himself out of nothing. To them the ball of dung was also similar to the rising sun. In ancient Egypt, images of dung beetles were carved in bone, ivory and stone, some of the latter being massive sculptures, one of which appears on a plinth in the temple of Karnak. Carved scarab beetles were often placed on the chest of a deceased person of high status during burial. The most famous of these was the yellow-green scarab beetle sculpture that was placed with Pharaoh Tutankhamen in his sarcophagus.

Dung beetles range from as small as 6 mm to as large as 50 mm and occur worldwide. They are usually black or brown with occasional species being blue, green or purplish-black. In South Africa, dung beetles are numerous and diverse and the majority of them feed on dung although a few species have adapted to feed on carrion, fungi, nectar or plant litter. They are so adaptable that they occur from true deserts to tropical forests but different types are active at different times of the day.

Dung beetles that feed on dung utilize this resource in different ways. These differences are used to classify them ecologically. The most simple behaviour involves direct feeding on fresh dung pads where they have dropped and the most complex behaviour involves the cooperation of both sexes to create balls of dung which they bury in excavated tunnels and chambers in the soil. The females lay their eggs in the buried dung and the larvae can at times take two years to become mature.

Some dung beetles breed in dung balls that remain inside dung pads without burying the dung. The dung rollers knead the dung into a ball and then roll the ball with their hind legs for long distances before burying them in underground tunnels and chambers. These balls can have a diameter of as much as 50 mm. Some of the dung is eaten by the dung beetles while some of it is used in which to lay eggs and to feed the larvae. The dung of mammalian herbivores are favoured by a number of types of dung beetle. Those that do not roll dung balls will drag individual dung pellets, which they hold between the hind legs, to a suitable chamber.

The ancient Egyptian myth of scarab beetles that attack living organisms probably originated from those dung beetles that eat carrion. If the carrion is still malleable, the meat will also be tamped into balls before being rolled away to underground chambers. Some of these necrophagous (eating dead meat) beetles have even specialized to only eating dead millipedes. Other dung beetles in turn collect and bury dead plant material underground and eat the mushrooms which develop on it.

At Shayamanzi it can be expected to find at least the following beetles that are associated with dung: the white-spotted fruit chafer Mausoleopsis amabilis which is a small and shiny black beetle whose larvae develop in dung; the brown-and-yellow chafer Pachnoda sinuata, a beetle of medium size with variable colour patterns and whose larvae develop in manure; the emerald fruit chafer Rhabdotis aulica, a small, emerald-green beetle whose larvae develop in manure, the woolly chafer Sparrmannia flava, a large, fawn-coloured dung beetle that lives in burrows and around dung pads and feeds on dung; the green dung beetle Garreta nitens, a metallic green or copper-coloured dung beetle of medium size that cuts dung from a fresh pad and rolls it into a ball which is buried underground; the grooved dung beetle Heteronitis castelnaui, a large and shiny black dung beetle with an oblong head that packs dung into the blind ends of tunnels, the bronze dung beetle Onitis alexis, a bronze-bodied dung beetle of medium size with a metallic green head which packs dung into tunnel ends; spider dung beetles of the genus Sisyphys, small to medium-sized beetles that vary from dull black to dark grey or brown and forms balls of dung that are buried underground; the nursing dung beetle Copris mesacanthus, a dull-coloured dung beetle of medium size with shallow grooves or punctures on the carapace that buries dung balls underground and where the female remains underground until the larvae are mature; the three-horned dung beetle Catharsius tricornatus a large, black dung beetle with a horn on the head and two horns on the front part of the pronotum (the part just behind the head) that burrows below or beside a fresh dung pad and packs dung in expanded tunnels; the plum dung beetle Anachalcos convexus, a large, black dung beetle with a coppery sheen that rolls dung balls into shallow underground chambers; the bi-coloured dung beetle Proagoderus tersidorsis, a dung beetle of medium size with a metallic green head and pronotum, a coppery body and a long, backward curving horn on the head that packs dung into the blind ends of tunnels; the flattened giant dung beetle Pachylomerus femoralis, a massive, broadly flattened, dull black dung beetle with raised polished areas that excavates burrows beside fresh dung pads, fills tunnels with dung for feeding and seals them with soil; and the fork-nosed dung beetle Coptorhina klugi, a black dung beetle of medium size with the top of the head being forked with two upturned prongs which mainly feeds on mushrooms.

Dung beetles play an extremely beneficial role in promoting topsoil health. In one study in Oklahoma in the USA each dung beetle buried 2 tonnes of wet manure per ha per year. Their tunnels increased the water infiltration rate from rainfall by 129 per cent. Each additional 25 mm of rainfall that was absorbed added 254 530 litres of water to the topsoil per ha per year. In Canada it is estimated that dung beetles provide benefits to the land which is worth 2000 million Canadian dollars per year. In Australia there are an estimated 27 million cattle, or more. Each animal produces 18 kg of wet dung per day. Its 300 or so native species of dung beetle cannot cope with this amount of dung and some dung beetle species are now being imported into Australia. The main enemy of dung beetles is the blanket and indiscriminate use of pesticides. Few if any animal producers ever factor the benefits of dung beetles into their financial calculations.

 

References:

Picker, M, C Griffiths and A Weaving 2002. Field guide to insects of South Africa. Cape Town: Struik, pp 198 - 213.

Richardson, P O and R H Richardson 2000. Dung beetles and their effect on soil. Ecological Restoration 18: 116 - 117.

Scholtz, C H and E Holm 1985. Insects of southern Africa. Durban: Butterworth, p. 220.

Wikipedia 2012. Dung beetle. http://wikipedia.org/wiki/Dung_beetle

 

article by Prof J du P Bothma

 

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