Forensic entomological decomposition

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. This process best describes the relationship between insect colonization and the availability of different food sources throughout decay. Seconds after death, insects are attracted to carrion for food and to oviposit eggs in natural openings and orifices of the body. 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 post mortem interval of a body, as well as the cause and location of death.

According to M. Grassberger and C. Frank in the Journal of Medical Entomology, a decaying carcass provides “a temporarily, rapidly changing resource which supports a large, dynamic arthropod community.”

Factors of Decomposition

There are several factors that affect how fast a body decomposes. Some of the major and more common factors include:

o Temperature
o Access to the body
o How deep the body is buried
o Reduction of corpse by scavengers and carnivores
o Age at time of death
o Percent body fat of corpse
o Cause of death

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.

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 walls 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. At this time, the body has little to no odor, and may begin to show signs of Liver mortis in less than 12 hours. 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.

The first necrophages observed on the body after death is the Calliphorid flies. The female Bronze Bottle Fly, Lucilia cuprina is generally the first to colonize the body; the second is the Hairy Maggot Blowfly, Chrysomya rufifacies. Other flies generally present during this stage are Phormia regina and adults of the fly families Sarcophigidae, Piophilidae, and Muscidae. Predators of both immature and adult flies are prevalent at the beginning stages of decomposition. 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 from the family Histeridea that feeds on the early fly larvae.Parasitic wasps from the family Vespidae, fire ants, and other insects also predate on fly larvae. These are important factors to consider when determining post mortem interval.

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 in 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 putrescine. 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 many orifices of the corpse. Moreover, the first blowflies that arrived on the corpse during initial decay, Lucilia cuprinaand Chrysomya rufifacies, have produced larva that are in their first and second instars. Clown beetles such as Hister quadrinotatus and Hister seqkovi are also attracted during the bloat stage and can be found underneath the decaying body.

Black Putrefaction

Black putrefaction, also known as active decay, happens about 10 to 25 days after death. A good indicator of black putrefaction is a strong odor and black coloration of the corpse. The bloating begins to escape as the skin starts to peel back and break from the large amount of gas and fluids produced. This makes the body appear flat. Mostly skin and bone remain as viscera and other soft tissue are decaying at an increased speed. Any remaining flesh still on the body has a soft creamy consistency.3 The nails on the fingers or toes of the body will readily fall off. However, there are processes that can slow down the rate of decay and lengthen the putrefaction process for years.

Dry Decay

The final stage in animal decomposition is dry decay. Dry decay begins between 25 and 50 days; and lasts up to a year after death. The only remnants of the body are dry skin, hair and bones. Mummification is a possibility in a dry heat or low humidity environment. This process is the dehydration of tissues that lack the nutritional value to be broken down by other processes. The bones go through a process termed diagenesis, which changes the organic to inorganic constituent ratio within the bones. Any odor exuding from the body at this point is merely the natural flora and fauna associated with the area(1).

The fauna seen at this point is limited. Bacteria feed on the hair and skin; they also attract mites which consume them. Certain tineid moths also eat the hair. Silphidae, a family of beetles, may still be present. They typically arrive early in decomposition and feed on larvae of other insects. Beetles of the family Nitidulidae are sometimes seen. The normal soil fauna will begin to return during this stage (1).

Butyric Fermentation

Butyric Fermentation is the name of the fifth 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 the process of the breaking down of fluids in the body. This progression attracts different species to the carrion. 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. In this particular stage, most of the beetles are in the larval stage. Other insects such as cheese skippers and some parasitic wasps are also present.

Hide Beetles (Family Deremestidae) and Carcass Beetles (Family Trogidae) 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 found on the tougher portions of the body such as bone and ligaments. Also, they are the only beetles that are capable of using an enzyme to break down proteins such as keratin. Cheese skippers, also known as cheese flies,(Family Piophilidae) are attracted to the smell produced by butyric acid. The cheese skipper larvae can “skip” up to 15cm in the air. The parasitic wasps (such as the Brachymeria calliphorae) use the flies’ pupae as a nest for their eggs. Upon hatching, the wasp larvae feed on the host maggots or pupae and once they have killed the host they use the maggot or pupa to pupate into mature wasps.