Forensic entomological decomposition

Medicolegal entomology is a branch of forensic entomology that applies the study of insects to criminal investigations, and is commonly used in death investigations for estimating the post-mortem interval (PMI). One method of obtaining this estimate uses the time and pattern of arthropod colonization. This method will provide an estimation of the period of insect activity, which may or may not correlate exactly with the time of death. While insect successional data may not provide as accurate an estimate during the early stages of decomposition as developmental data, it is applicable for later decompositional stages and can be accurate for periods up to a few years.

Decomposition is a continuous process that is commonly divided into stages for convenience of discussion. When studying decomposition from an entomological point of view and for the purpose of applying data to human death investigations, the domestic pig Sus scrofa (Linnaeus) is considered to be the preferred human analogs. In entomological studies, five stages of decomposition are commonly described: (1) Fresh, (2) Bloat, (3) Active Decay, (4) Advanced or Post-Decay, and (5) Dry Remains. While the pattern of arthropod colonization follows a reasonably predictable sequence, the limits of each stage of decomposition will not necessarily coincide with a major change in the faunal community. Therefore, the stages of decomposition are defined by the observable physical changes to the state of the carcass. A pattern of insect succession results as different carrion insects are attracted to the varying biological, chemical and physical changes a carcass undergoes throughout the process of decay.

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

The fresh stage of decomposition is generally described as the period between the moment of death and when the first signs of bloat are apparent. There are no outward signs of physical change, though internal bacteria have begun to digest organ tissues. No odor is associated with the carcass. Early post-mortem changes, used by pathologists as medical markers for early post-mortem interval estimations, have been described by Goff and include livor mortis, rigor mortis and algor mortis.

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