**1. Introduction**

Forensic entomology is the intersection between the study of arthropods and the justice system [1–4]. The study of arthropods, particularly insects and their close relatives, is entomology. The word comes from the Greek words "entomo," meaning insect, and "logus," meaning research. The area includes a variety of biological disciplines and areas of study, including forensics [5]. Such disciplines' common denominator is that they all include insects as the study subject.

A scene's analysis of entomological evidence has the potential to provide invaluable information about the scene and circumstances surrounding the situation. Interpretation of entomological evidence as the ability to inform an investigator about many different aspects of the case, including: colonization period and, by extension, death time; colonization season; colonization location; potential movement or storage of the remains after death; evidence of neglect; sites of trauma on the remains; and the presence of chemicals in the remains [3, 4, 6, 7]. Such data can then notify the investigation in several stages.

Insects reveal a lot to a knowledgeable researcher about a scene. First, the information most sought after is the time of colonization (TOC) estimate, which is often associated with the postmortem interval or time of death [1–4]. Most essential insects in forensics belong to the ecological class of decomposers—the ones that use the nutrients bound in dead matter [8]. Decomposers locate and exploit dead matter efficiently, and those who respond to ephemeral resources such as animal carcasses excel in the location of resources [8, 9]. Insects may arrive at a newly dead animal within minutes after death [7, 10] and either feed upon the carcass directly or colonize the carcass through egg oviposition [4, 8]. According to the resource

position output, it can be concluded that an insect with unfettered access to a carcass arrived and colonized it within minutes of animal death. The calculation of the age of the insects colonizing the animal body (TOC estimate) can therefore be used as a measure of how long this carcass was available for insect colonization and, by logical extension, how long it was dead (postmortem interval or PMI) [4, 11].

rapidly or slowly they develop [12, 16, 19]. The warmer the temperature in the area, the faster they go through their instars and pupal stage. The higher the ambient temperature, the faster their instars and pupal stage are going through. This estate allows forensic entomologists to use information on insect growth to assess the time of colonization estimate of animal remains. This also makes temperature the most

Temperature has a profound effect on the metabolic of dipteran and the speed of development [16]. Warmer temperatures generally result in faster development, within certain temperature ranges. But, this is not accurate at extreme temperatures. Insects have both upper and lower thermal limits, below and above which the insect either dies or no longer develops. These are known as threshold temperatures [16, 19, 20]. In different species, these thermal levels are naturally different. Organisms that have evolved in tropical and warmer areas will have higher limits than those that have developed in temperate or colder areas [21]. Therefore, when it comes to temperature scales, there is a huge variation between species. The lower limits are better known than the upper limits and are significant when measuring a colonization estimate period mathematically [17, 20]. Developmental thresholds for forensically important flies are usually between 6 and 10°C and are experimentally determined. If a specific fly species developmental threshold is not available, a general rule of thumb is to use 6°C for winter species or flies in cold areas and 10°C for warm

Each stage of insect growth requires a certain amount of heat above the minimum temperature and below the maximum temperature, from egg to an adult [12, 25]. This growth rate can be represented with a linear model that represents the amount of heat necessary for a given fly to go through each of its developmental stages. These linear models are called degree day or degree hour models, because development is recorded as the temperature above the minimum developmental

This model allows us to calculate the time a fly takes to develop using ambient

(average ambient temperature minimum threshold) unit of time

This formula takes the average ambient temperature over a given time period, subtracts the minimum threshold for the insect species, and multiplies the result by unit of time. The result is called a "degree day" (if the unit of time used was a day) or a "degree hour" (if the unit of time used was an hour). These are the two most common units of time seen in this type of model, simply because weather stations

The formula may be used to calculate how many degree days or degree hours are necessary for an insect to get through various stages in its life cycle, as well as how many degree days have been accumulated over time. The DD/DH necessary for an insect to get through its lifecycle is determined by experiment. The data are recorded as hours needed for a species to develop at a given

temperature, and these data may be converted into DD or DH simply by using the

**Table 1** shows several forensically important insects and the time it takes each insect to develop at various temperatures. Take, for example, the hours necessary for the black blow fly, *Phormia regina* (Meigen)*,* to develop at 27°C. According to research, it takes *P. regina* eggs 16 h to go from freshly laid to hatching, 18 h to go through the first larval instar, 11 h to go through the second larval instar, and 36 h to go through the third larval instar. To turn this information into degree hours,

important density-independent factor for insects [4, 19].

*Diptera Development: A Forensic Science Perspective DOI: http://dx.doi.org/10.5772/intechopen.90859*

weather species or flies in warmer areas [7, 22–24].

temperature, and this formula is

simply plug the data into the equation

formula.

**163**

threshold multiplied by time (days or hours) [13, 14, 26, 27].

often record ambient temperature at daily or hourly intervals.
