Today I was out with a group of naturalists.  One of them told us of a TV program she’d recently watched on the speed with which maggots consumed an entire small animal carcass.  As I recall she said the animal was completely gone in 26 hours.  

When we look at the real world, that’s what we witness,…..the rapid recycling from dead plants and animals back to rich, humic soil to fresh life and beauty.  Nowhere do we see billions and billions of life forms being laid down in pancake flat sedimentary layers, pressing and preserving every kind of plant and animal into stone layers, many of those layers being paper thin, yet capturing within those fine, flat layers, fish, fowl, flowers, and every kind of plant and animal living among us today.  People fiercely deny the overwhelming evidence of earth’s geology.  That geology, beyond any question states that the normal processes of death, decay and renewal were altered for a brief period in earth’s history.  

Something huge, catastrophic, global and water laden captured vibrant life and slammed it into a cementing matrix……..layer upon layer upon layer.  The oxygen got squeezed out, the decomposers, large and small could not get at those dead things.  They hardened into rocks.

The global flood of Noah’s day is real, as is the book that preserves that story of the judgment of an angry God against the sins of people who turned their backs on their creator.


Dr. Gail S. Anderson, Associate Professor
Diplomate, American Board of Forensic Entomology

School of Criminology, Simon Fraser University


Forensic (or medico-legal) entomology[1] is the study of the insects associated with a human corpse in an effort to determine elapsed time since death. Insect evidence may also show that the body has been moved to a second site after death, or that the body has been disturbed at some time, either by animals, or by the killer returning to the scene of the crime. However, the primary purpose of forensic entomology today is to determine elapsed time since death.

Forensic entomology was first reported to have been used in 13th Century China and was used sporadically in the 19th Century and the early part of the 20th Century, playing a part in some very major cases. However, in the last 20 years, forensic entomology has become more and more common in police investigations. In 1996, some of us developed the American Board of Forensic Entomology, a certification Board for Forensic Entomologists, similar to the Board certification available for forensic odontologists and forensic anthropologists.

Most cases that involve a forensic entomologist are 72 h or more old, as up until this time, other forensic methods are equally or more accurate than the insect evidence. However, after three days, insect evidence is often the most accurate and sometimes the only method of determining elapsed time since death. Recently, I have also analyzed and testified in cases in which elapsed time since death was only a few hours previous to discovery.

There are two main ways of using insects to determine elapsed time since death : –
I  – using successional waves of insects
II – using maggot age and development.

The method used is determined by the circumstances of each case. In general, the first method is used when the corpse has been dead for between a month up to a year or more, and the second method is used when death occurred less than a month prior to discovery.

The first method is based on the fact that a human body, or any kind of carrion, supports a very rapidly changing ecosystem going from the fresh state to dry bones in a matter of weeks or months depending on geographic region. During this decomposition, the remains go through rapid physical, biological and chemical changes, and different stages of the decomposition are attractive to different species of insects. Certain species of insects are often the first witnesses to a crime. They usually arrive within 24 h of death if the season is suitable i.e. spring, summer or fall in Canada and can arrive within minutes in the presence of blood or other body fluids. These first groups of insects are the Calliphoridae or blowflies and the Sarcophagidae (the fleshflies). Other species are not interested in the corpse when the body is fresh, but are only attracted to the corpse later such as the Piophilidae or cheese skippers which arrive later, during protein fermentation. Some insects are not attracted by the body directly, but arrive to feed on the other insects at the scene. Many species are involved at each decomposition stage and each group of insects overlaps the ones adjacent to it somewhat. Therefore, with a knowledge of the regional insect fauna and times of carrion colonization, the insect assemblage associated with the remains can be analyzed to determine a window of time in which death took place. This method is used when the decedent has been dead from a few weeks up to a year, or in some cases several years after death, with the estimated window of time broadening as time since death increases. It can also be used to indicate the season of death e.g. early summer. A knowledge of insect succession, together with regional, seasonal, habitat and meteorological variations, is required for this method to be successful.

The second method, that of using maggot age and development can give a date of death accurate to a day or less, or a range of days, and is used in the first few weeks after death. Maggots are larvae or immature stages of Diptera or two-winged flies. The insects used in this method are those that arrive first on the corpse, that is, the Calliphoridae or blowflies. These flies are attracted to a corpse very soon after death. They lay their eggs on the corpse, usually in a wound, if present, or if not, then in any of the natural orifices. Their development follows a set, predictable, cycle.

The insect egg is laid in batches on the corpse and hatches, after a set period of time, into a first instar (or stage) larva. The larva feeds on the corpse and moults into a second instar larva. The larva continues to feed and develop into a third instar larva. The stage can be determined by size and the number of spiracles (breathing holes). When in the third instar, the larva continues to feed for a while then it stops feeding and wanders away from the corpse, either into the clothes or the soil, to find a safe place to pupate. This non-feeding wandering stage is called a prepupa. The larva then loosens itself from its outer skin, but remains inside. This outer shell hardens, or tans, into a hard protective outer shell, or pupal case, which shields the insect as it metamorphoses into an adult. Freshly formed pupae are pale in colour, but darken to a deep brown in a few hours. After a number of days, an adult fly will emerge from the pupa and the cycle will begin again. When the adult has emerged, the empty pupal case is left behind as evidence that a fly developed and emerged.

Each of these developmental stages takes a set, known time. This time period is based on the availability of food and the temperature. In the case of a human corpse, food availability is not usually a limiting factor.

Insects are ‘cold blooded’, so their development is extremely temperature dependent. Their metabolic rate is increased with increased temperature, which results in a faster rate of development, so that the duration of development decreases in a linear manner with increased temperature, and vice-versa.

An analysis of the oldest stage of insect on the corpse and the temperature of the region in which the body was discovered leads to a day or range of days in which the first insects oviposited or laid eggs on the corpse. This, in turn, leads to a day, or range of days, during which death occurred. For example, if the oldest insects are 7 days old, then the decedent has been dead for at least 7 days. This method can be used until the first adults begin to emerge, after which it is not possible to determine which generation is present. Therefore, after a single blowfly generation has been completed, the time of death is determined using the first method, that of insect succession.


From Australian Museum:


Many kinds of organisms live by feeding on dead bodies.

Intestinal Bacteria

Intestinal Bacteria
Photographer: D. Colgan © Australian Museum

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.

Parasitic wasps

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.

Last Updated: 26 October 2015