Eduardo Galante and Mª Angeles Marcos-Garcia Centro Iberoamericano de la Biodiversidad Alicante, Spain
In any natural or semi-natural that the decomposers operate at all the habitat, three types of organisms exist: levels. Thus, all energy not used by the producers, consumers and consumers and producers, as well as decomposers. Good functioning of the that accumulated in excretory products, ecosystem will depend on their suitable is used by the decomposers and action and interaction. Organisms recycled into the ecosystem. This capable of catching energy and process constitutes the energy cycle , synthesizing organic matter from and good functioning and subsistence of inorganic compounds constitute the the ecosystems depends on effective producers. Though chemosynthetic energy cycling. bacteria exist, most producers are In a terrestrial ecosystem, more plants. Green plants use solar energy than 90% of the organic matter and fix CO2, producing organic synthesized by the green plants remains compounds rich in energy. Most of this unconsumed, and it passes to the level accumulated energy will get used in the of decomposers as plant material ecosystem by respiratory processes and decaying on soil, together with the other vital functions, whereas some remains of animal corpses, and the organisms of the community such as the excretory products of all levels. consumers and decomposers will use The process of decomposition is the energy accumulated by other one of the most important events in the organisms. functioning of ecosystems. The consumers are heterotrophic Decomposition can be defined as the organisms that obtain food from process by means of which a dead producers or from other consumers, with organism or its remains are broken the possibility of several levels of down into the parts or elements that complexity inside an ecosystem. comprise it, and at the end of the Primary consumers feed directly on the process the animal or plant remains will producers. Secondary consumers feed have gradually disintegrated until their on primary consumers, etc. Finally, we structures cannot be recognized, and have the decomposers, saprophytic their complex organic molecules will organisms feeding on dead matter or have fragmented. This involves a decaying remains derived from complex process in which biotic and producers and consumers. Thus, the abiotic agents interact within the organic matter synthesized by ecosystem. To sum up, the producers goes on to other levels of decomposition processes cause the organisms across the trophic chains, liberation of energy and mineralization though much of the energy will be used of chemical nutrients, turning the in respiratory processes at all levels. organic matter into inorganic elements. In these trophic processes, an In the process of decomposition, important element to take into account is there are two phases, sometimes difficult to distinguish, that we could call centipedes (Diplopoda), woodlice ‘destruction’ and ‘degradation’ of the (Isopoda), etc. All these groups are organic matter. The process of responsible for the fragmentation of destruction refers to the initial phase of plant or animal remains, contributing to the decomposition cycle and is the destruction phase. They contribute characterized by breaking down the both to the redistribution of the organic organic remains by mechanical means remains and formation of soil elements. so that at the end of this process small- These groups of arthropod sized particles are obtained. During this decomposers are present in nearly all initial phase both abiotic (rain, wind, terrestrial habitats, and generally in very temperature, etc.) and biotic elements high numbers. In some cases, millions (decomposer fauna) play an important of individuals belonging to hundreds of role. In the second phase, degradation species have been identified in just one of the organic matter occurs, resulting in square meter. Especially in temperate the disintegration of the small particles areas, arthropods are the major into molecules, producing CO2, H2O and decomposers, playing a very important mineral salts as final products. role in degradation of waste. Thanks to The destruction phase also the action of the arthropods during the results in dispersion of the organic initial phase of fragmentation, organic matter, because the small resulting remains can be degraded, and particles can be taken by means of eliminated from the soil surface. diverse mechanisms out of the initial When a suitable community of source (dragging by wind and water, or decomposers exists, it prevents the direct action of animals such as burial, appearance of potential bottlenecks in ingestion, movement, etc.). It is the recycling of basic elements in the important to note that nutrients released ecosystem. Thus, when entomofauna by decomposers constitute a food capable of acting effectively on plant source for numerous animal species, and animal remains does not exist in a extending the cycle by means of terrestrial ecosystem, serious alterations incorporation of the nutrients into in the ecosystem arise, with a reduction tissues, and eventually constituting new in energy flow and great loss of corpses and excrements. biodiversity. The groups of arthropods involved in the processes of Decomposers of plant remains decomposition of animals and plants Arthropods play an important role remains belong to many taxa (Fig. 1). in degradation processes of plant They are considered to be mesofauna remains. Nevertheless, most lack the when their size ranges between 100 and ability to develop enzymatic processes 200 mm (such as mites (Acari), for degrading the fundamental springtails (Collembola) and small components of any plant: lignin and insects), or macrofauna when they are cellulose. Degradation of cellulose larger, such as some beetles (e.g., requires the presence of the enzyme Scarabaeidae, Geotrupidae or cellulase, which most arthropods lack. Silphidae), Diptera larvae (e.g., Many insects have solved this problem Muscidae, Sarcophagidae, by means of mutualistic relations with Scatophagidae or Calliphoridae), micro-organisms, having bacteria or symbiotic protozoa in the intestinal tract. (bacteria, fungi and protozoa) and plant Others take advantage the cellulase remains is very close, and therefore, in produced by external microflora. Among most cases it is inevitable that the the well-known insect decomposers are arthropods consume both resources termites (Isoptera) and cockroaches simultaneously. In some cases, the (Blattodea). The termites possess ingested biomass of micro-organisms is symbiotic bacteria and protozoa, and in more important nutritionally than the their absence wood cannot be ingested plant remains. assimilated by these insects. In many ecosystems millipedes The entomofauna of excrement and (Diplopoda) have special importance as corpses decomposers. These arthropods, which The studies of ecosystems have specialize in leaf litter consumption, generally paid preferential attention to sometimes are abundant, concentrated the decomposition processes of in relatively small areas, and active vegetative remains, due to the during a great part of the year. importance that litter has in the Another important group in the composition of the soil and the degradation of plant remains is woodlice contribution of its nutrients. The process (Isopoda), which also possess symbiotic of decomposition of carrion and dung, microorganisms in their intestine that though sometimes not well known and allows them to degrade cellulose. little studied in many ecosystems, is Not all arthropods assimilate also important. cellulose by means of symbiotic To understand the processes of bacteria, but they make use of woody degradation of corpses and excrements, materials that are pre-digested by and the attractiveness of this decaying extraintestinal microorganisms. Included matter to arthropods, we must consider in this group are some species of that they are very rich resources of springtails such as Tomocerus organic components that have very (Collembola), ambrosia beetles special microclimatic conditions. Dung (Coleoptera: Scolitydae), ants of the and carrion represent not only a rich genera Atta (Hymenoptera: Formicidae) source of energy, but also a very and termites (Isoptera) that cultivate specialized habitat that is exploited, in fungi. most cases, by very specific All plant remains do not always entomological fauna. This fauna obtains present the same difficulty of digestion food either directly, such as in the case for arthropods. Fruits are extensively of the coprophages and carrion-eating exploited by arthropods, thanks to the arthropods, or indirectly, such as in the existence of yeasts that enhance fruit case of the predators that feed on the decomposition, allowing many decomposers. arthropods such as flies (Drosophila is It is generally difficult to establish probably the best known example) and the limits of an arthropod community, wasps (Hymenoptera: Vespidae) to feed but when we study carrion or dung we into the product resulting from the meet a perfectly defined ecological unit, fermentation. Nevertheless, a fact that limited in both space and time. Carrion must be remembered is that the (Fig. 2) and dung present many special relationship between micro-organisms characteristics that influence the composition and dynamics of the set of taxonomic categories of carrion or dung species using them. These resources specialists are similar worldwide. constitute isolated microhabitats inside Sometimes it is difficult to discern an ecosystem in which they are whether the arthropod fauna involved in deposed, forming a patchy system. decomposition processes contributes These microhabitats are relatively small directly to the recycling of organic matter in size (except for corpses of large or, as in leaf debris systems, they make vertebrates), rich in nutrients, and with a the substrate more available to the short existence (generally not more than microorganisms (bacteria and fungi) one insect generation). Carrion and considered by some authors to be the dung are special microhabitats true decomposers. The action of the characterized fundamentally by their larvae of flies and other insects, for rapid ecological successions, being example, produces liquefaction of extremely ephemeral micro-ecosystems corpse tissues, preparing the that are rapidly destroyed by the action substratum for the intervention of of the arthropods that colonize them. microbial decomposers. On the other Arthropod species are sometimes very hand, the mechanical action associated abundant in these resources, and with removal of excrement by beetles, thousands of individuals belonging to a and in making tunnels by both beetles set of arthropod decomposers may be and fly larvae, enhances microbial attracted to an isolated unit. For activity. The existing studies show that example, more than 100 species of the action of decomposer species of arthropods belonging to 16 orders and arthropods and microorganisms is 48 families have been found in just one complementary, but not purely additive. rabbit corpse, or 16,000 dung beetles Vertebrates are often considered found in elephant dung. to be important scavengers, and many The arthropods involved in species feed on carrion. Vertebrates succession vary according to may not distinguish between freshly geographical areas, even in places with killed prey and a freshly dead animal, similar climates. Also, the number of and many predators eat both of them. It individuals and the species colonizing is not easy to know how much organic these microhabitats vary enormously matter is recycled in this manner, but from one patch to another, and also depending on the period of the year, through time. Typically, these species many of the small animal corpses can are more or less aggregated in these be totally destroyed by scavengers. limited resources, with interspecific However, during summer and autumn in differences in foraging and breeding temperate regions, and in the rainy behavior. The aggregated spatial period in tropical areas, corpses are distribution and resource partitioning rapidly colonized by arthropods. As a allow a great number of decomposer result, rapid decay is observed, with the species to coexist in an ecosystem, but vast majority of carrion being consumed great differences in numbers of by various arthropod species, principally individuals and species composition are fly larvae. generally found among similar amounts The process of decomposition of carrion or dung. However, the broad among excrement and corpse systems varies as a result of the particular composition of the remains, which the arthropods involved in this attracts its own specialist community of processes, and the intensity of the arthropod decomposers. Likewise, action of these animals, vary according differences between the entomological the spatial location of the corpse, type of fauna of excrement are found, soil and depth of burial. The number of especially between the excrement of insects living in carrion diminishes with carnivores and those of herbivores. This depth of burial. occurs because the composition of The arthropods colonizing nutrients is totally different between corpses form a sequential succession of carnivore and herbivore excrement. groups and species that depends on the While the excrement of herbivores size of the carrion, and on the climatic contains a great number of vegetative and edaphic conditions of the area components that are little changed from where they live. Very few species are the plants ingested (80-75% of the widespread throughout the world, and ingested weight), the digestive system each geographical area and ecosystem of carnivores is much more efficient and has its specialist species feeding on the excrements contain less organic carrion. matter suitable for exploitation by The colonization of a corpse is a arthropod species. The fauna feeding on sequence of arthropods arriving as the carnivore excrement is generally successive waves at the carrion. The depauperate, and decay often results form, nature and timing of the exclusively from the actions of succession depend on the geographic microorganisms. area, the surrounding non-biological environment, and the size of the carrion. Decomposers of corpses The first waves involve blow flies Arthropod species attracted to (Diptera: Calliphoridae) and house flies corpses change according to the (Diptera: Muscidae) arriving for a few ecosystem and environmental hours to oviposit or drop live larvae. conditions. The importance of Later, there is a second wave of necrophagous arthropods is not only the sarcophagid flies (Diptera: ingestion of carrion, but also in making Sarcophagidae) that together with the carrion available to microorganisms. species of calliphorid and muscid flies, Many insects, principally fly larvae, deposit their eggs or live larvae on the secret enzymes directly into the carrion, corpse. The larvae of these flies are, in producing liquefaction of the tissues. turn, consumed by larvae and adults of Likewise, adult and larval beetles, and predatory beetles living in corpses. fly larvae, make tunnels through the Staphylinids (Coleoptera: carrion, increasing aeration and Staphylinidae), histerids (Coleoptera: microbial activity. The dominant groups, Histeridae) and silphids (Coleoptera: both in number of individuals and Silphidae), all are predators of flies, diversity, are dipterous and though they also feed on carrion. When coleopterous species. Also, in the viscera decompose and the fat of geographic areas where ants are the corpse turns rancid, a third wave of abundant, the corpses are removed insects starts, with some species of rapidly by these insects, specially the phorids (Diptera: Phoridae), drosophilids corpses of invertebrates. Nevertheless, (Diptera: Drosophilidae) and hover flies of the subfamily Eristalinae (Diptera: year) and pupation takes place away Syrphidae) arriving. The fourth wave from the corpse, in the soil surrounding consists of cheese skipper species it. Sometimes the mature larvae may (Diptera: Piophilidae) and related migrate more than one meter from the families of flies. Finally, a fifth wave carrion. Ten to 30 days after pupation, occurs, the larvae and adults from some the new adults emerge and fly off to groups of beetles such as dermestids search for new corpses, starting a new (Coleoptera: Dermestidae), trogids life cycle. (Coleoptera: Scarabaeoidea: Trogidae) Among Coleoptera, a principal and clerids (Coleoptera: Cleridae) and group in many temperate ecosystems is tineid caterpillars (Lepidoptera: Silphidae (e.g., Nicrophorus, Silpha). It Tineidae) that eat keratin and feed on is a group specifically adapted to living the remaining hair and feathers. in carrion and its action is comparable to Diptera are among the most that of the Diptera. The adults of important decomposers, especially Nicrophorus species show a very some of the Calliphoridae (e.g., Lucilia, special biology. When a species of this Calliphora, Chrysomyia, etc.), followed genus arrives at the fresh corpse, the by some Muscidae (e.g., Fannia), and male and female bury the carrion Sarcophagidae (e.g., Sarcophaga). underground (Fig. 3), thereby reducing Though the adults feed on the fluids of the risk of colonization by other insects. the corpse, the larvae are the true Once the carrion is safe in the burial decomposer organisms, secreting chamber, and the beetles have enzymes directly into the carrion and copulated, they make the corpse into a helping with the liquefaction of the ball. The eggs are deposited into a short corpse tissues while assisting the chamber above the carrion ball. The increase of microbial activity. These female makes a conical depression on families of Diptera are more abundant the top of the ball, and defecates and from early summer to mid autumn in regurgitates droplets of partially temperate regions, and also in the rainy digested food, and stridulates, attracting season in tropical areas. the larvae to the depression in the The biology of all the Diptera carrion. The female, and sometimes the species is similar. Females of blow flies male, give parental care and provide and house flies lay eggs or drop live food by regurgitating into this larvae on to the surface of the fresh depression. Thus, they ensure the corpses, generally at the base of the survival of the offspring and avoid hairs or near to the natural holes. Such predation and competition. natural openings facilitate the In tropical forests, many species penetration of larvae into the inner of Scarabaeinae are attracted to both regions of the corpse. The ovoviparous carrion and dung. Availability of females of sarcophagids are less fecund resources for dung beetles in most than blow flies and house flies, and do Neotropical forests is low because of the not deposit all their larvae in the same low density of large mammals and the carrion, rather distributing them evenly low availability of any particular type of among several corpses. Development of dung. This absence can probably be fly larvae is normally very fast (3 to 6 attributed to the absence of suitable days during the favorable periods of the numbers of large herbivores in the forests of Central and South America, into account that each succession will and the few natural pastures of this consist of different species in different region (except where cattle have been geographical regions. This is true even introduced). In African forests, where in sites with similar climatic conditions, large herbivores are present in relatively because few species are widespread in large numbers, many dung beetles distribution, and each area may have its specialized in the use of excrement may own carrion-feeding species. be found. Nevertheless, the broad taxonomic levels of decomposers of carrion are Forensic entomology constant worldwide. Also, some Knowledge of the succession of differences may be found as a result of species taking place in a corpse variation in ambient temperatures that following death has been used in may speed the process (sunlight and studies of forensic entomology. This high temperatures) or retard it (shelter rather consistent succession has been and cold conditions), variation in used for medical legal analyses to exposure of the carrion, possible burial estimate the time elapsed since death of of the corpse, cause of death, etc. an animal. The study of arthropod Some carrion-feeding flies can species from a cadaver gives us cause myiasis, an infestation of live information about the location, time, and vertebrates by larvae of Diptera, conditions to which the corpse was particularly blow flies of the genera exposed before being found. The Lucilia, Chrysomyia, Cochlyomyia, etc., generalized sequence of fly colonization that feed on live or dead tissues of the is most frequently used. The first host. This infestation causes problems colonizing species are the bigger flies in some farming areas, and may be of belonging to the blow fly family considerable economic importance. (Calliphoridae) followed by Probably one of the best known sarcophagids (Sarcophagidae) and examples of myiasis is with Cochliomyia house flies (Muscidae). The adults of hominivorax (Diptera: Calliphoridae), a the lesser-sized families such as species living in neotropical regions. Psychodidae, Scatopsidae, Sciaridae, Larvae of C. hominivorax develop on Phoridae, Sepsidae and wounded animals and humans, and can Sphaeroceridae come to the corpse in provoke the death of the host. the last phase of decomposition, after the corpse has been abandoned by the Decomposers of excrement larvae of the first colonizing flies. Their The excrement of vertebrates larvae leave the corpse to pupate away generally is a rich source of nutrients, from the larval site, normally in the and insects play an important role in the ground or substrate below carrion. The rapid recycling processes of feces. development of larvae is temperature However, carnivorous excrement dependent, and knowledge of the larval contains little material useable by cycle and its relationships at different insects because of their efficient temperatures, can be used to estimate digestive process. In contrast, the of age a cadaver. Forensic entomology digestive system of herbivores is less is an important instrument in criminal efficient, and the dung produced is quite investigation; however, we must take similar to the original leaf material. More than half the food consumed by probably Scatophaga stercoraria, a herbivorous animals is returned to the species frequently found visiting dung ground in the form of unassimilated anywhere in the Northern Hemisphere, material, i.e., dung. Because it is and also in northern and southern abundant in organic matter and moist, Africa. Scatophaga stercoraria has herbivore dung is an ideal medium for coprophagous larvae, but adults are establishment of a specific, rich primarily predators or nectar feeding, entomofauna involved in the process of only occasionally feeding on liquefied decomposition and elimination of feces. dung. Quantitatively, large herbivore dung pats Females of flies may lay eggs in are the most important resource for batches of about 150, which hatch in dung beetles in most regions, and this from 8 to10 hours, to three days, fauna is especially abundant in historic depending on the environmental grazing areas. conditions and the species involved. Excrement is a very special Muscid larvae may complete their habitat for coprophagous species, and development within two days in the spatial distribution of dung increases favorable environmental periods, or the tendency of these insects to delay several weeks in the colder concentrate in a limited space. The temperatures. process of colonization of excrement Among beetles that use dung typically consists of three waves of resources, the dung beetles belonging insects. The first wave of colonizers to the Scarabaeidae (Scarabaeinae, involves certain flies arriving within Geotrupinae and Aphodiinae) are the hours to lay eggs or larviposit on the most important and numerous. Not all dung before a crust is formed on the scarab larvae are strictly coprophagous, pat. The second wave is several families and some ingest soil organic matter or of beetles. Lastly, mites become feed on roots of plants. However, many abundant. are coprophages, and often exceedingly The main groups of flies are abundant. Thousands of individuals Muscidae and Scatophagidae, followed from many species may be found by Fanniidae and Calliphoridae. Most colonizing single dung pats in temperate adults and larvae of flies are and tropical grazing ecosystems. Most coprophagous, but feeding also on the Aphodiinae are saprophagous and micro-organisms present in the dung. within the Geotrupinae coprophagy is Others are facultative or obligate the rule for the Geotrupini. Only predator species. Many species are Scarabaeinae has coprophagy as a attracted to any decaying matter, but characteristic of most of its species. In others only feed and breed in dung. this case, most of the nutrients eaten by Throughout the world, muscid the adults are derived from eating coprophages such as Musca domestica, microbes or colloids suspended in dung. Musca vetustissima and Haematobia The larvae feed on the dung supplied by irritans are pests of cattle. But some their parents in a nest chamber. muscids are facultative predators (e.g., Various other groups of beetles Muscina spp.) and obligate predatory visit dung but they are primarily larvae (e.g., Mydaeae spp.). The best- predators. Coleoptera of the families known species of Scatophagidae is Hydrophilidae, Staphylinidae, and Histeridae are associated with carrion and Geotrupini is their nesting behavior. as predators of larvae of flies and dung- Geotrupini nests are the most primitive beetles. However, the two former and consist of simple burrows filled with families also include coprophagous ‘sausages’ of dung, usually containing species. In the temperate region, the one egg each. hydrophilids Cercyon and Sphaeridium The reproductive biology of (Coleoptera Hydrophilidae) are Scarabaeinae has several distinct coprophagous, arriving within the early patterns, which have been reviewed and hours after deposition of dung. compiled in comprehensive and The behavior of dung beetles wonderful books by Halffter and (Coleoptera: Scarabaeidae) is Matthews (1966) and Halffter and specialized and diversified in response Edmonds (1982). The process of to exploitation of excrement by adults nesting involves the creation of a place and larvae (Fig. 4). The Scarabaeidae in the soil where a supply of dung is consist of approximately 7,000 species accumulated for development of larvae. (5,000 Scarabaeinae, 1,900 Aphodiinae Scarabaeinae nesting frequently and 150 Geotrupinae). Many species of involves bisexual cooperation of a pair Scarabaeinae and Geotrupinae have of beetles, for either short or long developed special feeding and breeding periods of time, and parental care strategies that allow them to remove sometimes exists. The adults make dung rapidly the soil surfaces by digging brood balls in the protected nest, each burrows below the dung pad to store of which contains the amount of food fragments of dung in tunnels. The also required for larvae to enable them to may form dung into balls and roll them complete larval development. Nesting away from the pad for burial far from the behavior is considered as an adaptation food source. The importance of these to isolate immature larvae from each habits is the protection of food for adult other and from adults, increasing the or larvae, avoiding competitors, survival of offspring. Obviously this is a predators and unfavorable climatic process that requires the investment of conditions. Only Aphodiidae do not considerable time and energy on the make a nest. Aphodiidae eat directly part of the parents. Nesting derives from into the dung and many species deposit feeding behavior and basically theirs eggs directly in dung pads without corresponds to food relocation: nest chamber or in the surrounding soil. tunneling and ball rolling. Geotrupinae and many tribes of The tunneling scarabs take food Scarabaeinae are tunnelers. These from the dung pat and bring it into a species dig a tunnel below the dung pat previously excavated gallery. Various and accumulate dung in the bottom of types of nesting have been described the burrow; this food can be used either for tunnelers, and it is sometimes for adult or for larval feeding. Finally, difficult to ascribe a particular type of some species of Scarabaeinae are nesting to a species. rollers, making a ball of dung that is The most primitive and simplest rolled away from the pat for a variable nest behavior is observed in some distance before burying. genera of Dichotomini, Oniticellini, One of the most important Onitini, and also Onthophagini. A female aspects of the biology of Scarabaeinae digs a simple burrow, fills it with food, forms a brood mass and provides a the ball can be up to more than fifty single egg. In this case, there is no times the weight of the beetle. The bisexual cooperation or maternal care, process is initiated by one partner and and the species involved show relatively the ball acts as a sexual display to the high fecundity. other sex. The brood ball also may be Other groups of dung beetles rolled by two partners, but sometimes make nests containing several or many the female is transported on the ball. brood masses such as those observed Combat is common between members in some species of Dichotomini, Onitini, of the same species when rolling balls. Onthophagini and Oniticellini. The brood Generally, sexual cooperation finishes masses are constructed in series, in the when copulation takes place in the same tunnel or separated in individual burrow, after which the male leaves the side branches. In this type of nesting, female. Females prepare 4 to 5 pyriform bisexual cooperation may exist, but the brood balls and lay eggs in a narrow role of the male is restricted to cavity at the upper end of each pair. The introducing food into the tunnel. These female may abandon the nest after species have relatively high fecundity, oviposition, such as in Scarabaeini, and there is no maternal care. Canthonini, Gymnopleurini and Coprini and several Dichotomini, Sisyphini, or they can remain in the nest Onitini and Oniticellini species construct until the offspring emerge, as has been nests that contain several spherical described for the African genus Kheper. brood masses arranged in a single or Finally, there are some species of branched tunnel with or without dung beetles that demonstrate special separation. feeding and nesting biology. They are Some scarabs produce a nest species using part of the food resources containing only a few brood balls in a accumulated by other dung beetle chamber, and physically separated from species in burrows or a breeding other chambers. This nesting behavior chamber. These species are called is present in species with low fecundity: kleptoparasites, and examples are Phanaeni (without maternal care), found in Aphodiidae and Scarabaeidae. several Dichotomini (with or without These species live as parasites in the maternal care), and several Coprini nest prepared by either roller or tunneler (with maternal care). dung beetles. Finally, the species of Oniticellus (Oniticellini) show endocoprid nesting Beneficial actions of decomposer behavior: digging burrows and making insects in ecosystems brood chambers in the dung pat, where The viability of every ecosystem nesting takes place. The species of this is based on the normal functioning of its genus present moderate to extensive nutrient cycle. This is a very complex maternal care. ecological process with a great number The roller habit of food relocation of components, including decomposer is only present in some tribes of organisms. The activity of decomposers Scarabaeinae: Scarabaeini, Chantonini, benefits humus formation in the soil, and Gymnopleurini and Sisyphini. Species of the availability of nutrients for plants. these groups make a brood ball that is This feature is especially evident in rolled away from the pat. The weight of pasture ecosystems, where an indispensable condition for correct agents in the control of flies breeding in functioning is that the cattle dung is dung. The scarabs compete with fly rapidly used and transformed. If this larvae for food, reducing the amount of does not occur, dung deposited on the breeding by depriving the flies of food. soil may eventually cause serious Some authors have calculated damage because it deteriorates the the economic value of the role pastureland by preventing plant growth. recovered by dung beetles in pastures. When pats are not removed, they Fincher (1981) estimated that the cover the pasture, inhibiting the growth agricultural sector in the U.S.A. would of grass. The effect is a loss of available have potential benefits of more than surface for cattle. Several authors have 2000 million dollars a year if suitable reported several estimates of the loss of fauna were present for rapid burial of pasture. In the U.S.A., for example, cattle dung. The value of dung beetles Fincher (1981) reported that cattle in pasture ecosystems was first continuously covered more than 300 observed in Australia, where dung hectares of pasture with dung each beetles were introduced to help solve year. the problems of loss of pasture surface Dung pats remaining on pasture and increase of flies breeding in dung. have a noxious effect because cattle do The Australian pasture was profoundly not graze on the rank growth around disturbed by domestic animals brought these cowpats. Refusal by cattle to by the first European settlers who graze on pasture grass growing near arrived 200 years ago. The native dung dung is a response to the offensive beetles were adapted to the dung properties of the dung itself. pellets of kangaroos and other Furthermore, most of the valuable marsupials, not to the large grazing and nutrients of the unburied pats are lost. browsing herbivores. The large, For example, 80% of the nitrogen voluminous accumulated dung of content in a pat may be lost, but when horses, cattle, and sheep generated a adequate numbers of dung beetles are pollution problem as a result of its present and efficient burial by dung unattractiveness for the native beetle beetles exist, the nitrogen loss is fauna. In Australia, a program of dung reduced by 15%, with the nitrogen held beetle species introduction was by soil colloids. Another potential benefit proposed by Bornemissza about 1960 of dung beetle activity is the increase in and several species of scarabs from pasture by the incorporation of organic South Africa, France and Spain, matter into the soil and increases in soil adapted to use the dung of domestic aeration and water content. cattle in open pastures, were Several authors have mentioned established successfully. These beetles the possible role of dung beetles in were introduced to help solve the reducing infestation of livestock by worm problems of pasture degeneration and parasites. Feces remaining on the soil increase of populations of fly pests could be an incubator for parasite worm breeding in dung. larvae. If dung beetles bury these feces See also, FORENSIC before parasites reach the infectious ENTOMOLOGY. stage, the parasitism of cattle can be minimized. Dung beetles are also useful
References Bornemissza, G.F. 1979. The Australian Dung Beetle Research Unit of Pretoria. South African Journal of Sciences 75: 257-260. Byrd, J.H., and J.L. Castner. 2001. Forensic entomology. The utility of arthropods in legal investigations. CRC Press, New York, New York. Fincher, G.T. 1981. The potential value of dung beetles in pasture ecosystems. Journal of the Georgia Entomological Society 16 ( suppl.): 316-333. Halffter, G., and W.D. Edmonds. 1982. The nesting behaviour of dung beetles (Coleoptera: Scarabaeidae). An ecological and evolutive approach. Publication of the Institute of Ecology, Mexico. Halffter, G., and E.G. Matthews. 1966. The natural history of dung beetles of the subfamily Scarabaeinae. Folia Entomologica Mexicana. México 12-14. Reprint for Medical Books di C. Cafaro (1999). Palermo. Italy. Hanski, I., and Y. Cambefort (eds.). 1991. Dung beetle ecology. Princeton University Press, Princeton, New Jersey. Putman, R.J. 1983. Carrion and dung. The decomposition of animal wastes. Edward Arnold, London, United Kingdom.
Figure 1. The arthropods involved in the process of decomposition of animal and plant remains belong to such taxa as Diplopoda (1 and 2), Isopoda (3), Collembola (4), Diptera larvae (5), Coleoptera (6), Acari (7).
Figure 2. Adult and larva of a blow fly (Diptera: Calliphoridae) on a lizard cadaver. Blow flies constitute the first wave of insects colonizing corpses.
Figure 3. Male and female Nicrophorus (Coleoptera: Silphidae) burying a mouse corpse underground. These insects are specifically adapted for living in carrion.
Figure 4. Behavior of dung beetles (Coleoptera: Scarabaeidae) is both specialized and diversified to allow exploitation of excrement. Aphodiinae do not make nests, and dwell within the dung (1). Geotrupinae and many tribes of Scarabaeinae are tunnelers (2). Some tribes of Scarabaeinae are rollers (3), making a ball of dung that they roll away from the dung pat.