insects could determine human’s time of death
Insects are usually the ﬁrst organisms to arrive on a body after death, and they colonize in a predictable sequence. A corpse, whether human or animal, is a large food resource for a great many creatures and supports a large and rapidly changing fauna as it decomposes. The body progresses through a recognized sequence of decompositional stages, from fresh to skeletal, over time. During this decomposition, it goes through dramatic physical, biological and chemical changes (Coe and Curran, 1980; Henssge et al., 1995; Van den Oever, 1976). Each of these stages of decomposition is attractive to a different group of sarcosaprophagous arthropods, primarily insects. Some are attracted directly by the corpse, which is used as food or an oviposition medium, whereas other species are attracted by the large aggregation of other insects they use as a food resource.
When the sequence of insects colonizing carrion is known for a given area and set of circumstances, an analysis of the arthropod fauna on a carcass can be used to determine the time of death. This procedure can provide accurate and precise methods for estimating elapsed time since death and is used in many homicide investigations worldwide. When remains are found weeks, months, or more after death, insect evidence is often the only method available to determine reliably the time of death. Insects colonize in a predictable sequence, with some species being attracted to the remains very shortly after death; others are attracted during the active decay stage, and still others being attracted to the dry skin and bones. Insects continue to colonize a body until it is no longer attractive.
When the insects migrate from the remains, they invariably leave evidence of their presence behind, such as cast larval skins, empty pupal cases, and even peritrophic membrane. Meanwhile, the remains themselves have changed and entered a stage of decomposition that is attractive to other, later colonizers. Therefore, when remains are found, the forensic entomologist will study not only the insects that are present on the remains at the time of discovery, but the evidence left behind by earlier colonizers. They also will note the species that are absent, but normally expected to be present, in the colonization sequence. From this information an accurate time of death can be established. However, insect succession on a corpse is impacted by many factors, including geographical region, exposure, season, habitat, etc.
Anderson, 2001, plus several redaction edit