Dung beetle
Dung beetles refer to those beetles which feed partly or exclusively on feces. Most of these species belong to the subfamilies Scarabaeinae and Aphodiinae of the family Scarabaeidae. As most species of Scarabaeinae feed exclusively on feces, that subfamily is often dubbed true dung beetles. There are dung-feeding beetles which belong to other families, such as the Geotrupidae (the earth-boring dung beetle). The Scarabaeinae alone comprises more than 5,050 species.
Many dung beetles, known as rollers, are noted for rolling dung into spherical balls, which are used as a food source or brooding chambers. Other dung beetles, known as tunnellers, bury the dung wherever they find it. A third group, the dwellers, neither roll nor burrow: they simply live in manure.
Appearance
The size of a dung beetle varies from species to species. The "dwellers" are usually small and elongate. Dung beetles are basically black or brown in colour; some are of metallic lustre, especially the tropical species. Most dung beetles have a flattened, but stout body. The male of some species has horns at the head or thorax. Some dung beetles, other than the "dwellers", have strong, often "toothed" legs specialised for rolling dung and burrowing. The tarsi at the forelegs of an old dung beetle are usually damaged or lost owing to the labor of burrowing - some species do not have tarsi at the forelegs at all. The desert species also have hair on the legs which facilitates their movement on sand. Dung beetles have soft mouthparts suited to their diet.
Ecology and behavior
Dung beetles live in many different habitats, including desert, farmland, forest, and grasslands. They do not like extremely cold or dry weather. They occur on all continents except Antarctica.
Dung beetles eat dung excreted by herbivores and omnivores, and prefer that produced by the former. Many of them also feed on mushrooms and decaying leaves and fruits. They do not need to eat anything else because the dung provides all the necessary nutrients. Nor do they even need to drink water. The larvae feeds on the undigested plant fiber in the dung, while the adults do not eat solid food at all. Instead they use their mouthparts to squeeze and suck the juice from the manure, a liquid full of micro-organisms and other nutrients (as well as the body fluids from some unlucky animals such as dung-feeding maggots that sometimes get trapped between their mandibles).
Most dung beetles search for dung with the aid of their strong sense of smell. Some of the smaller species, however, simply attach themselves to the dung-providers to wait for their reward.
Researchers at the University of Lund have found that one species of dung beetles navigate by using polarization patterns in moonlight.[1] Quite often dung beetles will try to steal the dung ball of another beetle, so the dung beetles have to move rapidly away from a dung pile once they have rolled their ball to prevent it from being stolen. The optimal path is a straight line, and they use the polarization of moonlight to chart this path.
The species studied by the researchers, S. zambesianus, normally rolls small balls with a diameter of 2 cm, except when a male is looking for a mate; then they will roll a 5 cm diameter "special" ball. A female will ride on the ball as it is being rolled sometimes, and then the ball will be used as food for offspring after mating.[2][3][1]
The dung beetle goes through a complete metamorphosis. The larvae live in brood balls made with dung prepared by their parents. During the larval stage the beetle feeds on the dung surrounding it.
The "rollers" roll and bury a dung ball either for food storage or for making a brooding ball. In the latter case, two beetles, one male and one female, will be seen around the dung ball during the rolling process. Usually it is the male that rolls the ball, with the female hitch-hiking or simply following behind. In some cases the male and the female roll together. The beetles are intent upon rolling in a straight line, despite all obstacles. During the rolling process, other dung beetles may attempt to steal the ball. The attacker is usually a male. An ensuing fight is not uncommon. After the combat, the separated couple joins and continues their labor. When a spot with soft soil is found, they stop and bury the dung ball. They will then mate underground. After the mating, both or one of them will prepare the brooding ball. When the ball is finished, the female lays eggs inside it. Some species do not leave after this stage, but remain to safeguard their offspring.
The behaviour of the beetles was much misunderstood, until the pioneering studies of Jean Henri Fabre. For example, Fabre corrected the myth that a dung beetle would seek aid from other dung beetles when confronted by obstacles. By painstaking observations and experiments, he found that the seeming helpers were in fact robbers awaiting an opportunity to steal the roller's treasure:
Vainement, je me demande quel est le Proudhon qui a fait passer dans les moeurs du Scarabée l'audacieux paradoxe : «La propriété, c'est le vol» ; quel est le diplomate qui a mis en honneur chez les bousiers la sauvage proposition : «La force prime le droit.» ...[4]
Benefits and uses
Dung beetles play a remarkable role in agriculture. By burying and consuming dung, they improve nutrient cycling and soil structure. They also protect livestock, such as cattle, by removing the dung which, if left, could provide habitat for pests such as flies. Therefore, many countries have introduced the creature for the benefit of animal husbandry. In developing countries, the beetle is especially important as an adjunct for improving standards of hygiene.
The American Institute of Biological Sciences reports that dung beetles save the United States cattle industry an estimated $380 million annually through burying above-ground livestock feces.[5]
Like many other insects, the (dried) dung beetle, called qianglang (蜣蜋) in Chinese, is used in Chinese medicine.
Scarab in Ancient Egypt
Several species of the dung beetle, most notably the species Scarabaeus sacer (often referred to as the sacred scarab), enjoyed a sacred status among the ancient Egyptians.
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| ḫpr in hieroglyphs | ||
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The hieroglyphic image of the beetle represents a trilateral phonetic that Egyptologists transliterate as xpr or ḫpr and translate as "to come into being", "to become" or "to transform". The derivative term xprw or ḫpr(w) is variously translated as "form", "transformation", "happening", "mode of being" or "what has come into being", depending on the context. It may have existential, fictional, or ontologic significance.
The scarab was linked to Khepri ("he who has come into being"), the god of the rising sun. The ancients believed that the dung beetle was only male in gender, and reproduced by depositing semen into a dung ball. The supposed self-creation of the beetle resembles that of Khepri, who creates himself out of nothing. Moreover, the dung ball rolled by a dung beetle resembles the sun. Plutarch wrote: "The race of beetles has no female, but all the males eject their sperm into a round pellet of material which they roll up by pushing it from the opposite side, just as the sun seems to turn the heavens in the direction opposite to its own course, which is from west to east."[6]
The ancient Egyptians believed that Khepri renewed the sun every day before rolling it above the horizon, then carried it through the other world after sunset, only to renew it, again, the next day. Some New Kingdom royal tombs exhibit a threefold image of the sun god, with the beetle as symbol of the morning sun. The astronomical ceiling in the tomb of Ramses VI portrays the nightly "death" and "rebirth" of the sun as being swallowed by Nut, goddess of the sky, and re-emerging from her womb as Khepri.
The image of the scarab, conveying ideas of transformation, renewal, and resurrection, is ubiquitous in ancient Egyptian religious and funerary art.
Excavations of ancient Egyptian sites have yielded images of the scarab in bone, ivory, stone, Egyptian faience, and precious metals, dating from the Sixth Dynasty and up to the period of Roman rule. They are generally small, bored to allow stringing on a necklace, and the base bears a brief inscription or cartouche. Some have been used as seals. Pharaohs sometimes commissioned the manufacture of larger images with lengthy inscriptions, such as the commemorative scarab of Queen Tiye. Massive sculptures of scarabs can be seen at Luxor Temple, at the Serapeum in Alexandria (see Serapis) and elsewhere in Egypt.
The scarab was of prime significance in the funerary cult of ancient Egypt. Scarabs, generally, though not always, were cut from green stone, and placed on the chest of the deceased. Perhaps the most famous example of such "heart scarabs" is the yellow-green pectoral scarab found among the entombed provisions of Tutankhamen. It was carved from a large piece of Libyan desert glass. The purpose of the "heart scarab" was to ensure that the heart would not bear witness against the deceased at judgement in the Afterlife. Other possibilities are suggested by the "transformation spells" of the Coffin Texts, which affirm that the soul of the deceased may transform (xpr) into a human being, a god, or a bird and reappear in the world of the living.
One scholar comments on other traits of the scarab connected with the theme of death and rebirth: "It may not have gone unnoticed that the pupa, whose wings and legs are encased at this stage of development, is very mummy-like. It has even been pointed out that the egg-bearing ball of dung is created in an underground chamber which is reached by a vertical shaft and horizontal passage curiously reminiscent of Old Kingdom mastaba tombs."[7]
In contrast to funerary contexts, some of ancient Egypt's neighbors adopted the scarab motif for seals. The best-known of these being Judean LMLK seals (8 of 21 designs contained scarab beetles), which were used exclusively to stamp impressions on storage jars during the reign of Hezekiah.
The scarab remains an item of popular interest thanks to modern fascination with the art and beliefs of ancient Egypt. Scarab beads in semiprecious stones or glazed ceramics can be purchased at most bead shops, while at Luxor Temple a massive ancient scarab has been roped off to discourage visitors from rubbing the base of the statue "for luck".
In literature
In Aesop's fable "The Dung Beetle and the Eagle", the eagle kills a hare despite the beetle's appeals. The beetle takes revenge by twice destroying the eagle's eggs. The eagle, in despair, flies up to Olympus and places her latest eggs in Zeus's lap, beseeching the god to protect them. When the beetle finds out what the eagle has done, it stuffs itself with dung, goes straight up to Zeus and flies right into his face. Zeus is startled at the sight of the unpleasant creature and jumps to his feet. The eggs are broken. Zeus then learns of the beetle's plea which the eagle had ignored. He scolds the eagle and urges the beetle to stay away from the bird. But his efforts to persuade the beetle fail; so he changes the breeding season of the eagles to take place at a time when the beetles are not above ground.
Aristophanes alluded to Aesop's fable several times in his plays. In Peace, the hero rides up to Olympus to free the goddess Peace from her prison. His steed is an enormous dung beetle which has been fed so much dung that it has grown to monstrous size.
In Franz Kafka's The Metamorphosis, the transformed character of Gregor Samsa is called an "old dung beetle" (alten Mistkäfer) by the charwoman.
Notes
- ^ a b Dacke, M. and E.J. Warrant. 2003. "Insect orientation to polarized moonlight". Nature. 424 (July 3): 33.
- ^ "Moonlighting: Beetles navigate by lunar polarity", Susan Milius, Science News, Week of July 5, 2003; Vol. 164, No. 1 , p. 4
- ^ "Dung Beetles Navigate by the Moon, Study Says", John Roach, National Geographic News, July 2, 2003
- ^ "Le Scarabée sacré", dans Souvenirs entomologiques, Série I, Chapitre 1
- ^ BioScience, April 2006, Vol. 56 No. 4, p. 312
- ^ In the essay "Isis and Osiris", collected in his Moralia.
- ^ Andrews, Amulets of Ancient Egypt, p. 51.
References
- Carol Andrews. Amulets of Ancient Egypt. University of Texas Press, 1994. ISBN 0-292-70464-X.
- Hannes Buchberger. Transformation und Transformat. Sargtextstudien I, Wiesbaden, Harrassowitz Verlag, 1993. ISBN 3-447-03078-X.
- Jean-Henri Fabre. Souvenirs entomologiques: étude sur l'instinct et les moeurs des insectes, Tome 1 et 2. Robert Laffont: Bouquins, 2000. ISBN 2-221-05462-8, ISBN 2-221-05463-6.
- Raymond O. Faulkner. A Concise Dictionary of Middle Egyptian. Oxford: Griffith Institute, 2002. ISBN 0-900416-32-7.
- Gonzalo Halffter and Eric G. Matthews. The natural history of dung beetles: Of the subfamily Scarabaeinae. Folia Entomologica Mexicana, 1966.
- Ilkka Hanski, Yves Cambefort. Dung Beetle Ecology. Princeton University Press, 1991. ISBN 0-691-08739-3.
- John H. Taylor. Mummy: The inside story. The British Museum Press, 2004. ISBN 0-7141-1962-8.
- Richard H. Wilkinson. Symbol & Magic in Egyptian Art. London: Thames and Hudson Ltd., 1994. ISBN 0-500-23663-1.