Decomposition - Corpse Fauna
Many kinds of organisms live by feeding on dead bodies. In the process, their activities result in the decomposition of the body and the recycling of nutrients.
The dominant groups of organisms involved in decomposition are:
Other animals, feed on the animals that feed on the corpse. These are mainly:
A dead body is therefore an ecosystem of its own, in which different fauna arrive and depart from the corpse at different times. The arrival time and growth rates of insects inhabiting corpses are used by forensic scientists to determine the circumstances surrounding suspicious deaths.
There are many forms of bacteria, which gain their energy in a variety of ways.
Some bacteria are autotrophic, making their own food in a similar way to plants by splitting carbon dioxide using energy from the sun, or through the oxidation of elements such as nitrogen and sulphur.
Bacteria involved in the decomposition of animal bodies are heterotrophic, breaking down complex molecules into their constituent elements through respiration or fermentation (depending on whether they are aerobic or anaerobic bacteria). Bacteria are largely responsible for the recycling of carbon, nitrogen and sulphur into forms where they can be taken up by plants.
For example, heterotrophic bacteria like Bacillus decompose proteins, releasing ammonia, which is oxidised by other bacteria into nitrogen dioxide, and eventually into nitrate. Nitrate can be assimilated by plants as a source of nitrogen.
The larvae of flies (maggots) are the most obvious and abundant fauna present on corpses in the early stages of decomposition.
House flies Muscidae and blowflies Calliphoridae are the first to arrive (pioneer flies). Flies in both these families lay eggs (although some blowflies 'lay' larvae). The recently hatched larvae, as well as their parents, initially feed on the fluids that exude from the body. Later they enter the body through natural openings or wounds, and eventually feed over the whole body as the tissues decay.
Different species of housefly and blowfly arrive at different times after death, and there can be considerable competition among flies for access to a corpse. Early arrivals, and flies which hatch faster, can gain a competitive advantage, although the flesh is easier to consume after it has undergone some decomposition. Flesh flies Sarcophagidae arrive slightly later than the other families, but they compensate for their late arrival by giving birth to larvae (maggots) rather than eggs. The succession of fauna that inhabit the corpse change its condition, making it suitable for succeeding fauna.
Juicy maggots provide an abundant food source for other animals, including other species of fly. The Blowfly, Chrysomya rufifacies, feeds on maggots of other flies as well as consuming decaying flesh. The larvae of Chrysomya are covered with protrusions called papillae, which serve as protection against the predatory attacks of other maggots.
When the corpse has dried out, two other groups of flies, the cheese flies Family Piophilidae and the coffin flies Family Phoridae join the beetles and mites in cleaning up the skeleton.
The first beetles arrive at a corpse soon after the body begins to putrefy. In contrast to the flies, beetles have chewing mouthparts and can manage tougher foods than the semi-liquid material that fly larvae are so efficient at exploiting.
Three types of beetle make their living out of corpses. The early arrivals tend to be predatory adults that feed on fly larvae. Some of these species lay their eggs in the corpse, and the emerging larvae, which share their parents' powerful jaws, also feed on fly larvae. These species include the rove beetles (Staphylinidae), and hister beetles (Histeridae).
Late-arriving species tend to be specialist scavengers which feed on tougher parts like skin and tendons as the body dries out. The dominant late stage scavengers include the larvae of hide beetles (Dermestidae), and ham beetles (Cleridae).
Species such as the carrion beetles (Silphidae) are more variable in their diets. The adults are predatory, although they will eat some carrion, but their larvae are restricted to carrion on moist corpses.
Other families of beetles also eat carrion, for example, the carcass beetles (Trogidae), but they are minor players in the decomposition of corpses. In Australia, several dung beetles (Scarabaeini) are attracted to large carcasses, especially to the intestine of herbivorous mammals. These beetles have specialised, fluid-feeding mouthparts.
Beetles have a life cycle similar to the fly life cycle with egg, larval, pupal and adult stages. However, the number of instars (stage of development between moulting) in the larval stage varies between species from 2 up to 16, and the stages differ more from each other than the instars of fly larvae.
Mites belong to the group Arachnida which includes spiders, ticks, mites, scorpions and harvestmen (i.e. they are not insects).
Many thousands of mites feed on a corpse over the full term of its exposure to the elements. Gamasid mites like Macrocheles are common in the early stages of decomposition, while tyroglyphid mites feed on dry skin in the later stages of decomposition.
Some mites and carrion beetles have developed lifestyles that benefit each other. For example beetles from the genus Necrophorus find the ammonia excretions of blowfly maggots toxic, making it impossible for them to inhabit a carcass dominated by maggots. However these beetles carry on their bodies a type of mite from the genus Poecilochirus which feeds on fly eggs. If the beetle and its cargo of mites arrive at the corpse before any fly eggs hatch into maggots, the mites keep the maggot population in check by eating the eggs allowing the beetles to safely occupy the corpse.
Some of the familiar clothes moths (Family Tineidae) feed on mammalian hair during their larval stages. Adult moths lay their eggs on a carcass after all the fly larvae have finished with it. On hatching, their larvae forage on any hair that remains. Tineid moths are therefore the final animals contributing to the decomposition of a carcass.
A number of families of wasp lay their eggs inside the larvae or pupae of flies, and are known as parasitoids. The wasp eggs hatch inside the maggot or fly pupa. The wasp larvae then feeds on the maggot or pupa, eventually killing it. The wasp larvae then pupate inside the maggot or fly pupa and emerge as adult wasps.
Wasps from the family Pteromalidae parasitise a variety of species but prefer the pupae of the predatory blowfly Chrysomya rufifacies. This is probably because this species pupates on the surface of the ground and is more accessible than the pupae of species that bury their pupae in the ground. One pupa is host to an average of 12 wasps.
Brachymeria calliphorae (Family Chalcidae) parasitises maggots rather than pupae, and only one wasp emerges from each maggot.
Only one wasp emerges from pupae parasitised by Hemilexomyia abrupta (Family Diapriidae) but this species appears to lay its eggs only in the pupae of the blowfly Calliphora stygia.