Forensic entomological decomposition

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One aspect of forensic entomology is the use of insect science in investigations of human deaths. A detailed background on the stages of decomposition and associated fauna is key to interpreting information such as postmortem interval. Forensic entomologists use the time of insect colonization in order to give the shortest estimate for the postmortem interval. This estimate is determined by using degree days to find when the first eggs were layed on the body. However, the time of death and time of insect colonization may not occur simultaneously. Colonization can be delayed by many factors, which is why exploring the external factors that affect decomposition and the colonization of fauna is vital when using entomological evidence in an investigation.

Contents 1 Decomposition 1.1 Fresh 1.2 Putrefaction 1.3 Black putrefaction 1.4 Butyric fermentation 1.5 Dry decay 2 Factors affecting decomposition 3 Current research 4 Conclusion 5 References 6 External links

[edit] Decomposition

Decomposition is the process whereby bodily tissues are broken down into smaller molecules after death. The physical and chemical properties observed during decay are categorized into five stages: (1) fresh, (2) putrefaction, (3) black putrefaction, (4) butyric fermentation, and (5) dry decay.^[1] Seconds after death, insects are attracted to a body for food and to lay eggs in natural openings and orifices of the body. This process of decomposition best describes the relationship between insect colonization and the availability of different food sources throughout decay. The presence or absence of a particular insect, location on the body, and food source, can help determine forensically pertinent information about the body. Insects can provide significant insight to the manner of death, movement of the corpse from one sight to another, and length of the postmortem interval.^[2]

A decaying carcass provides “a temporarily, rapidly changing resource which supports a large, dynamic arthropod community.” --M. Grassberger and C. Frank

[edit] Fresh

The fresh stage is the first phase of decomposition that begins approximately four minutes after death and lasts around three days until putrefaction. Autolysis initiates decay as digestive enzymes in the body begin to break down nearby cell membranes and digest the internal organs. The acidity in the body also increases due to lack of oxygen in tissues. The liver which has high enzyme content releases nutrient-rich fluids into the body.^[3] At this time, the body has little to no odor, the skin is quickly turning pale (pallor mortis) and showing signs of livor mortis. The body loses heat until it reaches ambient temperature, known as algor mortis. After several hours, fibers in the muscles of the body begin to bind together and stiffen. This is known as rigor mortis and is first seen in the smaller muscles of the body like the face.^[4] Insects will feed between the muscle during rigor mortis because of the lactic acid produced from the break down of the muscle.^[5]

The first necrophages observed on the body after death is the Calliphorid flies. The female green bottle fly (Lucilia cuprina in the United States) is generally the first to colonize the body; the second is the Hairy Maggot Blowfly, Chrysomya rufifacies.^[6] Other fly families generally present during this stage are Sarcophagidae, Piophilidae, and Muscidae.^[7]

Predators of both immature and adult flies are prevalent at the beginning stages of decomposition. These are important factors to consider when determining the insect colonization time.^[7] Chrysomya rufifacies, the second fly to colonize, facultatively predates on fly larvae in its second and third larval instar. Saprinus pennsylvanicus, is a predaceous beetle in the United States that feeds on the early fly larvae.^[8] Parasitic wasps, fire ants, and other insects also predate on fly larvae. The parasitic wasp (such as the Chalcidae) uses the flies’ pupae as a nest for their eggs; upon hatching, the wasp larvae feed on the host maggots or pupae. Once the wasp larvae have killed the host, they use the fly remains to pupate into mature wasps.^[1]

[edit] Putrefaction

Following initial decay, approximately 4 to 10 days after death, the body begins the second stage of decay called putrefaction. During putrefaction, bacteria and other microorganisms continue to anaerobically metabolize the soft tissues of the body. This breakdown of tissue releases gases into the body and causes an increased internal pressure, which results in a bloated corpse. These gases commonly consist of hydrogen sulfide, carbon dioxide, methane, cadaverine, ammonia, sulfur dioxide, hydrogen, and putricine.^[3] According to Arpad Vass, a greenish discoloration of skin due to the formation of sulfhaemoglobin in settled blood often signals the onset of the putrefaction stage. As a result of the gas accumulation and the progression of decay, the corpse begins to emit a smell. This smell is a putrid odor that tends to attract an increasing number and various species of flies, beetles, and other arthropods.

During putrefaction, maggot habitation begins as flies continue to arrive and oviposit in the orifices and natural openings of the corpse. Moreover, the first blowflies that arrived on the corpse during initial decay, have produced larva that are in their first and second instars.^[6] Clown beetles from the family Histeridae such as Hister quadrinotatus and Hister seqkovi in the United States are also attracted during the bloat stage and can be found underneath the decaying body.^[8]

[edit] Black putrefaction

Black putrefaction, also known as active decay, happens about 10 to 25 days after death.^[7] A good indicator of black putrefaction is a strong odor and black coloration of the corpse. The bloating begins to subside as the skin starts to peel back and break from the large amount of gas and fluids produced. This makes the body appear flat. The breaking of the skin allows insects and other consumers better access to the inside of the body. This open access to the inside of the body cavity aids in increasing the rate at which viscera and other soft tissue decay. ^[9] Any remaining flesh still on the body has a soft creamy consistency.^[3] The nails on the fingers and toes of the body will readily disconnect.

Saponification is a processes that can slow down the rate of decay and lengthen the putrefaction process for years. This process has also been called adipocere or grave wax. In humid, warm conditions, saponification may be seen on the body in the form of an oily, waxy yellowish–white substance. This process occurs in the fats of animals and humans when ester bonds, such as those in triglycerides, are exposed to a chemical base. In this case, water from moisture in the environment acts as the chemical base and breaks the ester bonds of triglycerides of fat deposits. ^[10] When these bonds break, fatty acids are released, which can form new bonds. What these free fatty acids bond to can influence the rate of decay and the characteristics of the waxy substance formed. ^[3] This is aided by putrefactive bacteria, such as Clostridium perfringens, to help make fat turn into a soapy substance. ^[11]

At this stage, the maggot mass starts to decrease as most of the maggots have reached their third molt and will start to leave the body in order to pupate in the soil.^[4] These maggots may live along side the larvae and adults of carrion beetles (family Silphidae) and the skin beetles (family Dermestidae).^[1] In the United States, types of carrion beetles seen on the body may include Thanatophilus lapponicous, Necrophila americana, Oiceoptoma rugulosum and the burying beetle Nicrophorus tomentosus.^[8] Beetles usually make up the most of the population of insects on the body during black putrefaction. This beetle mass can vary in the types of families, making it hard to designate a certain beetle family to this stage of decay.^[12] Parasitic wasps continue to prey on these maggots and many generations of mites feed on the fluids let out by the body.^[1]

[edit] Butyric fermentation

Butyric Fermentation is the name of the fourth stage of decomposition. This fermentation process usually starts around 20-25 days after death. The body has finished flattening out from the previous putrefaction stage and the flesh and fluids on the body are slowly drying up. Butyric acid produces a distinct smell which is a component in breaking down the fluids in the body. This progression attracts different species of fauna to the carrion.^[1]

Maggots and other insects that feed on soft flesh are unable to feed due to the drying out of the body; beetles and other insects with similar chewing mouth appendages are able to crush and chew the tougher segments of the dead body. At this time, most of the beetles are in the larval stage. Other insects such as cheese skippers and some parasitic wasps are also present.^[1] Hide Beetles from the family Trogidae and Carcass Beetles from the family Dermestidae are among the last beetles and generally the most common beetles seen during this fermentation period. The Hide Beetles as well as the Carcass Beetles are not predacious and are found on the tougher portions of the body such as bone and ligaments.^[8] Also, they are the only beetles that are capable of using an enzyme to break down proteins such as keratin. The cheese fly from the family Piophilidae, is attracted to the smell produced by butyric acid.^[1]

[edit] Dry decay

The final stage in animal decomposition is dry decay. Dry decay begins between 25 and 50 days after death and can last up to a year. The only remnants of the body are dry skin, hair, and bones. Mummification occurs when dehydrated tissues lack the nutritional value to be broken down by other means. This is observed in dry heat or low humidity environments and can last for decades.^[3] The bones go through a process termed diagenesis that changes the organic to inorganic constituent ratio within the bones.^[7] Any odor exuding from the body at this point is merely the natural flora and fauna associated with the area.^[13]

The fauna seen at this stage is limited. Bacteria feed on the hair and skin of the body, attracting many mites. Certain tineid moths also feed on the remaining hair.^[3] Silphidae, a family of carrion beetles, may still be present during this stage. They typically arrive early in decomposition and stay until dry decay feeding on the larvae of other insects. Beetles of the family Nitidulidae can also be seen inhabiting the body.^[8] The normal soil fauna of the environment will begin to return during this stage.^[14]

[edit] Factors affecting decomposition

Main article: Environmental effects on forensic entomology

Understanding how a corpse decomposes and the factors that may alter the rate of decay is extremely important for evidence in death investigations. Campobasso, Vella, and Introna consider the factors that may inhibit or favor the colonization of insects to be vitally important when determining the time of insect colonization.^[13]

Temperature and climate

Low temperatures generally slow down the activity of blow-flies and their colonization of a body. Higher temperatures in the summer favor large maggot masses on the carrion. Dry and windy environments can dehydrate a corpse, leading to mummification. Dryness causes cessation in bacterial growth since there are no nutrients present to feed on.

Access

Access to the body can limit which insects can get to the body in order to feed and lay eggs. In the United States, corpses found in brightly lit areas are generally inhabited by Lucilia illustris. This is in contrast to Phormia regina, which prefers more shaded areas. Darkness, cold, and rain limit the amount of insects that would otherwise colonize the body. A submerged corpse can vary in temperature and is colonized by very few terrestrial insects. Fish, crustaceans, aquatic insects and bacteria would be the likely fauna in this case. Bodies that have been buried are harder to get to than freely available bodies which limits the availability of certain insects to colonize. The Coffin fly Megaselia scalaris is one of the few fly species seen on buried bodies because it has the ability to dig up to six feet underground to reach a body and oviposit.

Reduction and cause of death

Scavengers and carnivores such as wolves, dogs, cats, beetles, and other insects feeding on the remains of a carcass can make determining the time of insect colonization much harder. This is because the decomposition process has been interrupted by factors that may speed up decomposition. Corpses with open wounds, whether pre or post mortem, tend to decompose faster due to easier insect access. The cause of death likewise can leave openings in the body that allow insects and bacteria access to the inside body cavities in earlier stages of decay. Flies oviposit eggs inside natural openings and wounds that may become exaggerated when the eggs hatch and the larvae begin feeding.

Clothing and pesticides

Wraps, garments, and clothing have shown to effect the rate of decomposition because the corpse is covered by some type of barrier. Wraps, such as tight fighting tarps can advance the stages of decay during warm weather when the body is outside. However, loose fitting coverings that are open on the ends may aid colonization of certain insect species and keep the insects protected from the outside environment. This boost in colonization can lead to faster decomposition. Clothing also provides a protective barrier between the body and insects that can delay stages of decomposition. For instance, if a corpse is wearing a heavy jacket, this can slow down decomposition in that particular area and insects will colonize elsewhere. Bodies that are covered in pesticides or in an area surrounded in pesticides may be slow to have insect colonization. The absence of insects feeding on the body would slow down the rate of decomposition.

Percent body fat of corpse

More fat on the body allows for faster decomposition. This is due to the composition of fat, which is high in water content. Larger corpses with higher percent body fat also tend to retain heat much longer than corpses with less body fat. Higher temperatures favor the reproduction of bacteria inside high nutrient areas of the liver and other organs.

Drugs

On occasion, drugs that are present in the body at death can also affect how fast insects break down the corpse. Development of these insects can be sped up by cocaine and slowed down by drugs containing arsenic.^[13][9]

[edit] Current research

New research in the related field entomotoxicology is currently studying the effects of drugs on the development of insects who have fed on the decomposing tissue of a drug user. The effects of drugs and toxins on insect development are proving to be an important factor when determining the insect colonization time. It has been shown that cocaine use can accelerate the development of maggots. In one case, Lucilia sericata larvae that fed in the nasal cavity of a cocaine abuser, grew over 8 mm longer than larvae of the same generation found elsewhere on the body.^[15] Other researchers in entomotoxicology are developing techniques to detect and measure drug levels in older fly pupae. This research is useful for determining cause of death on bodies that are found during later stages of decay. To this date, bromazepam, levomepromazine, malathion, phenobarbital, trazolam, oxazepam, alimemazine, clomipramine, morphine, mercury, and copper have been recovered from maggots.^[2]

[edit] Conclusion

Understanding the stages of decomposition, the colonization of insects, and factors that may affect decomposition and colonization are key in determining forensically important information about the body. Different insects colonize the body throughout the stages of decomposition. These stages are categorized into fresh, putrefaction, black putrefaction, butyric fermentation, and dry decay. Identifying which insect is present can be useful in determining what stage of decay the body is in. Some insects are only found in certain regions and this information can help determine if a body has been moved by the type of maggots feeding on the body. The environment surrounding the body is also very important to consider when using insect evidence. Insects, such as the coffin fly Megaselia scalaris, are nearly always found on bodies that have been buried. Using evidence that is very species specific can reveal a great deal of information about a body.

[edit] References

[edit] External links

• American Board of Forensic Entomology
• The North American Forensic Entomology Association
• Offwell Woodland and Wildlife Trust - Decomposition
• Decomposing Pig Video