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Death & Decomposition

Decomposition

Decomposition is the process by which dead tissues of an organism break down into simpler forms of matter.

The process is essential for new growth and development of living organisms as it recycles the finite matter that occupies physical space in the biome.

Bodies of living organisms begin to decompose shortly after death. It is a cascade of processes that go through distinct phases.

Human Decomposition

Flesh

Bloat

Active Decay

Advanced Decay

Dry/Remains

“Fresh”The fresh stage begins immediately after cessation of the heart.

Blood is no longer being pumped through the body and so drains to the lower parts of the body, under gravity, creating a discoloration of the body, termed livor mortis.

Shortly after death, the muscular tissue becomes rigid and incapable of contraction, known as rigor mortis.

Finally, the body begins losing heat to the surrounding environment, resulting in an overall cooling, called algor mortis.

Blowflies and flesh flies will be the first carrion insects to arrive, and will seek a suitable oviposition site

Livor Mortis

Postmortem lividity or hypostasis

a settling of the blood in the lower portion of the body, causing a purplish, red discoloration of the skin: when the heart is no longer agitating the blood, heavy red blood cells sink through the serum by action of gravity. This discoloration does not occur in the areas of the body that are in contact with the ground or another objects, as the capillaries are compressed.

Livor Mortis

Livor mortis starts twenty minutes to three hours after death and is congealed in the capillaries in four to five hours.

Maximum lividity occurs within 6-12 hours. The blood pools into the interstitial tissues of the body.

Rigor MortisCausing the limbs of the corpse to become stiff and difficult to move or manipulate.

In humans it commences after about 3 hours, reaches maximum stiffness after 12 hours, and gradually dissipates until approximately 72 hours (3 days) after death.

Heat sources can speed up the process of rigor mortis such as fire.

Algor Mortis

Is the reduction in body temperature following death. This is generally a steady decline until matching ambient temperature, although external factors can have a significant influence.

Although the heat conduction which leads to body cooling follows an exponential decay curve, it can be approximated as a linear process: 2° Celsius during the first hour and 1° Celsius per hour until the body nears ambient temperature.

As decomposition occurs the internal body temperature tends to rise again.

“Bloat”The bloat stage provides the first clear visual sign that microbial proliferation is underway. During this stage, anaerobic metabolism takes place, leading to the accumulation of gases, such as hydrogen sulphide, carbon dioxide, and methane.

The accumulation of gases within the bodily cavity causes the distention of the abdomen and gives a cadaver its overall bloated appearance.

The gases produced also cause natural liquids and liquefying tissues to become frothy.

As the pressure of the gases within the body increases, fluids are forced to escape from natural orifices, such as the nose, mouth, and anus, and enter the surrounding environment. The build up of pressure may also cause rupturing of the skin.

“Bloated” Hairless Sloth

“Bloat” – Maggot Activity

Maggots will have hatched and begun to feed on the body’s tissues.

Maggot activity, typically confined to natural orifices and masses under the skin, will cause the skin to slip and hair to detach from the skin.

Maggot feeding, and the accumulation of gases within the body, will eventually lead to post-mortem skin ruptures which will further allow purging of gases and fluids into the surrounding environment.

Ruptures in the skin will allow oxygen to re-enter the body and provide more surface area for the development of fly larvae and the activity of aerobic microorganisms.

The purging of gases and fluids results in the strong distinctive odors associated with decay.

Active Decay

Begins when bloating finishes.

Active decay is characterized by the period of greatest mass loss, resulting from the voracious feeding of maggots, as well as from the purging of decomposition fluids into the surrounding environment.

The purged fluids accumulate around the body and create a cadaver decomposition island. Liquefaction of tissues and disintegration become apparent during this time and strong odors persist.

The end of active decay is signaled by the migration of maggots away from the body to pupate.

Active Decay

Advanced DecayDecomposition is largely inhibited during advanced decay due to the loss of readily available cadaveric material.

Insect activity is also reduced during this stage. When the carcass is located on soil, the area surrounding it will show evidence of dead vegetation.

The CDI surrounding the carcass will display an increase in soil carbon and nutrients, such as phosphorus, potassium, calcium, and magnesium; changes in pH; and a significant increase in soil nitrogen.

Dry/RemainsDuring the dry/remains stage, the resurgence of plant growth around the CDI may occur and is a sign that the nutrients present in the surrounding soil have not yet returned to their normal levels.

All that remains of the cadaver at this stage is dry skin, cartilage, and bones, which will become dry and bleached if exposed to the elements.

If all soft tissue is removed from the cadaver, it will be referred to as completely skeletonized, but if only portions of the bones are exposed, it will be referred to as partially skeletonized.

Stages of Decomposition

This is gross!!!

Factors Affecting Decomposition

Temperature and Climate

Access

Reduction and cause of death

Clothing and pesticides

Percent body fat of corpse

Drugs

Temperature and Climate

Low temps – slow down activity of blow flies and their colonization of a body.

High temps – favor large maggot masses

Dry/windy – dehydrate a corpse, leading to mummificaiton

Dryness – causes cessation in bacterial growth since there are no nutrients present to feed on

Access

Access can limit which insects can get to the body in order to feed and lay eggs.

Brightly lit areas – generally inhabited by Lucilia illustris

Shaded areas – inhabited by Phormia regina

Darkness, cold, & rain – limit those that normally colonize bodies

Submerged corpses – colonized by very few terrestrial insects

Buried bodies – harder to get to (The Coffin fly 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 & 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.

ClothingWraps, 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

Pesticides

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.

% Body Fat

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.

Forensic Entomology

Forensic entomology is the application and study of insect and other arthropod biology to criminal matters.

Forensic entomology is primarily associated with death investigations; however, it may also be used to detect drugs and poisons, determine the location of an incident, and find the presence and time of the infliction of wounds.

Forensic entomology can be divided into three subfields: urban, stored-product, and medico-legal/medico-criminal entomology.

Medico-legal Forensic Entomology

Medicolegal forensic entomology covers evidence that may be gathered through arthropod studies at events such as murder, suicide, rape, physical abuse and contraband trafficking.

In murder investigations it deals with which insect eggs when and where, and in what order they appear in dead bodies. This can be helpful in determining a post mortem interval (PMI) and location of death in question.

Since many insects exhibit a degree of endemism (occurring only in certain places), or have a well-defined phenology (active only at a certain season, or time of day), their presence in association with other evidence can demonstrate potential links to times and locations where other events may have occurred. Another area covered by medicolegal forensic entomology is the relatively new field of entomotoxicology. This particular branch involves the utilization of entomological specimens found at a scene in order to test for different drugs that may have possibly played a role in the death of the victim.

Medico-legal Forensic Entomology

Another area covered by medicolegal forensic entomology is the relatively new field of entomotoxicology. This particular branch involves the utilization of entomological specimens found at a scene in order to test for different drugs that may have possibly played a role in the death of the victim.