The development of forensic entomology as the science dates back till the 18th century. At the current time, criminologists and researchers use insects to determine the postmortem interval in criminology. In particular, such approaches as the development of Diptera and the successional colonization of carrion insects are actively utilized. During the application of the first methodology, much attention is paid to the instar of blowflies, their size, and the stages of life cycles of insects as they serve as predeterminants of the time of death. Moreover, such factor as the time of the day, season, and temperature are taken into the consideration. The above methodology is more effective during the first 18 days after the death. During the longer periods, the study of the successional colonization of carrion insects is usually performed because it provides more accurate results.
Nowadays, the development of accurate and effective techniques for crime investigation receives much attention. In this process, thorough consideration is devoted to identification of the time of death, since this information is rather relevant for determination and searching of criminals and their further conviction. The current work provides the description of some technique utilized to identify the time of death and that is based on studying the insects which develop, live, and feed in the dead body. It is based on the two different approaches: examination of the development of Diptera and the succession of the colonization. Both methods complement each other. Nevertheless, the information about them enables to determine their distinct characteristic thus providing the possibility to choose the most effective one for the particular cases.
The History of Forensic Entomology
The history of the methodology under consideration dates back to the 13th century records of the use of insects for a criminal investigation in China, namely the case of revealing the farmer’s murderer by attracting blow flies to the blood on his sickles, which is depicted in the book The Washing Away of the Wings (Joseph et al., 2011). As the scientific field, forensic entomology was established in the 18th century by Yovanovich and Megnin (Joseph et al., 2011). Since that time, scientists from various countries has made significant contribution to rapid development of the field in order to determine the earliest and the latest time of death, also known as postmortem interval (Sharma & Singh, 2015).
The Methods of Estimating the Time of Death
The Development of Diptera
One of the main methods of estimation of the time of death is the analysis of the development of Diptera the benefits of which include precise determination of postmortem interval. According to James, James, & Bell (2014, p.174), the above is achieved by identifying the “passage of time from when the first egg is laid on the remains until the first adult flies emerged”, and this time may vary from several hours to a few weeks.
The method is based on the fact that Diptera use dead animal material and humans for survival. These metallic-looking green or sometimes blue flies are attracted by dead bodies because of the two major reasons: obtaining proteins for the development of their genetalia and for laying their eggs there (James, James, & Bell, 2014). Small maggots feed from dead animals and consequently grow. Fresh bodies are more suitable for the survival of maggot Dipteras. Thus, the old females try to find the freshest bodies with the help of various cues that become evident immediately after the death. The additional emphasis should be made on the season, temperatures, and the time of the day. Dipteras are inactive during the periods of time with low temperatures, like winters in the North America, or at night (James, James, and Bell, 2014). They are more active in the daytime. Therefore, if death occurs during the night, or in the winter, no eggs will be lied. Consequently, the specialist of the forensic entomology should take into consideration these factors and make a little margin during the estimation of the time of death.
In the course of the current term paper, it should be noted that Dipteras are attracted not by the dead body itself, but even by the small unrecognized wound which can usually be found on the bodies of the victims of the homicide. However, the first place of the colonization is the human orifices, which are moist and soft, and thus are more suitable for growing of maggots (James, James, and Bell, 2014). The development of their eggs of maggots be divided into several stages.
The Stages of the Development of Maggot
As per studies performed by Tullies and Goffman, decomposition of the human body is connected with the development of maggots, and can be presented in the form of the below stages (Joseph et al., 2011):
- -The fresh stage begins from the moment of death until bloating of carcass (Joseph et al., 2011). The insects are attracted by the chemical release from the dead body, but they usually do not lay eggs.
- -The bloated stage lasts from the 2nd till the 7th day after death (Joseph et al., 2011). It is characterized by putrefaction caused by the work of anaerobic bacteria which is reflected in the inflation of abdomen and balloon-like form of carcass and the raise of the internal temperature. The discovery of the first and the second instar flies usually signifies that the human has been dead for about four days (Joseph et al., 2011). While the first instars tend to migrate inside the body and are from 2 to 5 mm long, the second instars move around the maggot mass and reach the size of about 10 mm long (Australian Museum, 2015). Hatching from the first moult of both instars lasts about one day (Australian Museum, 2015). However, the morphological traits of the life stage can be determined more accurately on the third instar stage: these insects are moving at mass and have the size of between 15 to 20 mm long (Tomberlin & Eric, 2015; Sharma & Singh, 2015).
- -The decay stage lasts from the 5th till 13th day (Joseph et al., 2011). It is characterized by the deflation of carcass, raising and falling of the temperature, and decaying of odors. The researcher can observe the departure of larvae from the carcass for pupation (Joseph et al., 2011).
- -The post-decay stage can be observed from the 10th till the 23th day (Joseph et al., 2011). Almost all the larvae have left the body; those insects which have remained in the dead body are usually pupate, they complete their life cycle and fly away, “leaving behind the hard, dark puparial case” that can also serve as the factor enabling to determine the time of death (James, James, and Bell, 2014, p. 177).
- -The remains stage begins after the 18th day (Joseph et al., 2011). On this stage, the researcher can observe the lowering of the Diptera population.
The Factors which Influence the Diptera’s Life Cycle
The life cycle of Diptera is influenced by numerous factors which should be taken into the consideration during the identification of the time of death. These factors are shortly described below.
- -The latest stage of Diptera is associated with the dead body, i.e. the stage of the progression of the insect’s life cycle (James, James, and Bell, 2014). The flies which arrived first have the highest stage.
- -The species of the fly, namely the examination of their DNA, predetermine the development cycle (James, James, & Bell, 2014).
- -The temperature of the body influences internal processes.
- -Developmental data helps to identify the age of the insects. It can be obtained from special literature that describes the development of the insects at different temperatures of the outer environment.
The Deficiencies of The Method Under Consideration
The described method has several deficiencies which may affect the accuracy of the determination of the death time. As it was mentioned above, the daytime period influences the time of laying the eggs. The colonization may be delayed due to the unfavorable weather conditions, like extreme cold at winter.
The Colonization as the Consequence of Carrion
Another method for determination of the time of death is used on the basis of the information concerning the predictable successional colonization of the dead human body as the consequence of carrion insections (James, James, and Bell, 2014). This method can be applied for identification of the time of death starting from several weeks and till the remaining of bones. This implies that the discussed methods may complement each other, because they can be utilized during different periods of time.
This particular method bases on the understanding that the dead human body serves as the resource of components for nutrition of different organisms and ecosystems. As it was mentioned above, after the death, the human body extracts various chemicals that attract different insects. They feed from the body and change its carcass as well as cause various biological and chemical changes by making it more attractive to other insects. It should also be noted that the insects can eat almost all the components of the human body. The scientists use this knowledge together with other observed and identified changes in the body and the consideration of the sequence of insects for determination of the time of death. When applying this method, they usually pay attention to the season, location and local habitation, temperature, microclimate etc. (James, James, and Bell, 2014). First of all, the researchers identify all the found species in the body and determine which of the insects come to or leave the body. This enables to identify the time frames of the death (i.e. the minimum and the maximum possible time) (James, James, & Bell, 2014).
To summarize, the current paper provides the short overview of the history of the usage of insects for the purposes of criminology. The modern forensic entomology dates back to the 18th century. Various methods of the determination of postmortem interval were developed since that time, but several methods are still actively applied in the field of forensic entomology, including the development of Diptera and the successional colonization. The first technique is more effective at the time period before the 18th day of death, while the second one gives more precise information in regard to the longer periods of time. During their application, it is essential to pay much attention to the spices of the insects, season, temperature, and many other factors, as they can have the significant effect on the accuracy of the investigation.