This individual had been dead for approximately four days. His body was found in the backyard by neighbors. During this period of time, temperatures had reached into the 90s. Note the fly larvae (maggots) in his eyes, nose, and mouth.
Insects are invariably the first witnesses to a crime, arriving within minutes or even seconds after death. There are two ways to use insects to determine time since death. The first method involves using dipteran larval development, and the second involves using insect succession over time. The first method is used in the first hours, days, or weeks after death and can determine the time of death accurate to a day or less, or a range of days. The insects used in this method are those that arrive first on the corpse, that is, the calliphoridae or blow flies (diptera). These flies are attracted to a corpse very soon after death. They lay their eggs on the corpse, usually in a wound, if present, or in any of the natural orifices. Their development follows a set, predictable cycle, and each of these developmental stages takes a set, known time. This time period is based on the availability of food and the temperature. In the case of a human corpse, food availability is not usually a limiting factor.
Fig.1 Fly larvae in the mouth and eyes.
Insects are “cold blooded,” so their development is extremely temperature-dependent. Their metabolic rate increases with increased temperature, which results in a faster rate of development, so that the duration of development decreases in a linear manner with increased temperature, and vice versa. An analysis of the oldest stage of insect on the corpse and the temperature of the region in which the body was discovered allows an entomologist to determine the day or range of days in which the first insects oviposited or laid eggs on the corpse. This, in turn, leads to a day or range of days during which death occurred.
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