Forensic Entomological Decomposition - Factors Affecting Decomposition

Factors Affecting Decomposition

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.

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.