Determination of the time of death is an integral part of any investigation. It is a difficult and complex process, and quite often impossible. There is one more problem: the bigger the interval between the death time and the body found, the more inaccurate will be the estimation. One of the factors used in estimating the time of death is environmental markers, particularly insect activity. A study that investigates insects and uses them to provide more information about crimes is called forensic entomology. Insect activity may give a clue of how long an individual has been dead. Entomologists may identify an approximate time of death by determining “what insects have preyed on the body and at what stage in their development they are at in their progress from egg to adult” (DiMaio & Dana, 2006, p. 27). One of such insects is a blowfly.
A blowfly is a carrion-breeding species of medical and forensic importance (Alvarez Garcia, RĂ©rez-HĂ©razo, & Amat, 2017). In a forensic sense, blowflies can colonize decomposing bodies, and their larvae have been found in human corpses. The typical life cycle consists of 4 stages: egg, larva, pupa, and adult (Rutty, 2013). Dead animals attract adults, and female flies deliver their eggs on the carcass. Blowflies sometimes mistake the necrotic wound of a corpse for a food source and lay their eggs there. It is called wound myiasis (Rutty, 2013). At room temperature in less than a day, the eggs hatch, and the newly appeared wormlike larvae, called maggots, secrete digestive enzymes into the surrounding environment and start to absorb liquefied necrotic tissue (Rutty, 2013). During this stage they pass through various instar stages:
1st Instar – 5 mm long after 1.8 days;
2nd Instar – 10 mm long after 2.5 days;
3rd Instar – 14-16 mm after 4-5 days.
They feed for 2–5 days, and then they leave the host and try to find a concealed, secured spot to pupate. Within puparium in less than 3 weeks, they turn into adult flies, leaving an empty pupal case behind as evidence (Rutty, 2013). The common blowfly life cycle in warm weather lasts for 2.5-3 weeks.
Bansode, More, and Zambare (2016) conducted research to find out how temperature and humidity affect the blowfly life cycle. It turned out that low temperatures and low moisture conditions increase the duration to complete the life cycle, while high temperatures and high humidity conditions decrease the time needed for it and insects grow faster (Bansode et al., 2016). Thus, to provide a more accurate estimation of time since death, entomologists should take into account the history of surrounding temperature and moisture in the location where the body was found.
When the time of death is in question, forensic entomologists undertake several actions to collect samples. First of all, proper equipment is crucial for the accurate collection of data. Preconfigured Forensic Entomology Kits are usually used for such purposes. Nevertheless, several police departments cannot buy ready-made collection kits due to the lack of budget. Entomological collection equipment contains about 20 names of necessary instruments and materials. They include, for instance, aerial insect nets, vials, forceps, collection containers, aluminum foil, thermometers, small hand trowels, gloves, and cameras (“Entomological collection equipment,” 2014).
According to Dr. Anderson (n. d.), there are two methods of using insects to determine the time since death: the first is using successional waves of insects; the second is using maggot age and development. The method of successional waves of insects is used if the individual has been dead for a month or longer, while maggot development is applied when the death occurred less than a month before the body was found. Blowflies are the most common insects associated with a dead body. They can arrive within 24 hours of death.
Forensic investigators rely on evidence and material found at the crime scene. The evidence must be recorded and carefully collected. Samples of insects should be collected from different areas of a body, from the clothing and the soil. Flies can be found in the form of eggs, larvae or maggots, pupae or empty pupal cases, and adults. Insects collected from different parts of the body or different species of insects should be all kept separate. Other samples like, for instance, soil and leaf litter, are also useful. Besides this information, entomologists should pay attention to the surrounding area and conditions: the habitat, the site, the soil type, the weather, the temperature, and humidity (Anderson, n.d.). The best procedure that follows sampling is preservation. One of the processes in the laboratory is to put the insect material into hot water and then into 70-90% ethyl alcohol. At the laboratory, entomologists examine and measure immature specimens. They are constantly checked, and when they pupate, investigators remove them. The date of pupation and emergence of a new adult is noted for every insect. This process is very important since adult flies are much easier to identify species than maggots (Rutty, 2013). Moreover, entomologists use the times of pupation and emergence to calculate the age at the time of collection, and as a result to identify the time of death.
Decomposition is a perpetual process, which varies in its characteristics and rate. This process can be divided into several stages: fresh, bloat, decay, dry, and skeletal stages. The infestation of the blowfly affects the rate of decomposition. In the earlier stages of decomposition, insect colonization may highlight the sites of wounds and accelerate this process since the blowflies are feeding on the dead body (Sukchit, Deowanish, & Butcher, 2015). At the same time, insect succession helps to define the stage of decomposition since different carrion insects are attracted to the different biological, physical, and chemical changes the body undergoes through this process.
Though blowflies are the most studied flies, which are relevant to forensic entomology, other types of insects can also be met at the crime scene. Flesh flies are one of them; they arrive at the scene within minutes like blowflies. Despite the fact that they are prevalent at the crime scene, they are hard to identify in many of their life stages. House flies also are typical insects, which arrive at the bloated stage of decomposition. The cheese fly is one more type, but they do not tend to colonize a body until 3-6 months after death. Beetles may also be found. Many species of beetles prefer a corpse at the late stages in the decomposition process (“Forensic entomology,” n.d.).
To sum up, examining insects during the investigation is a useful technique. In the earlier hours of death, entomology techniques may be more reliable in establishing the death time. However, after a few days, the use of insect evidence may be the only reliable way of identifying the amount of time passed since the victim died.
References
Alvarez Garcia, D. M., RĂ©rez-HĂ©razo, A., & Amat, E. (2017). Life history of Cochliomyia macellaria (Fabricius, 1775) (Diptera, Calliphoridae), a blowfly of medical and forensic importance. Web.
Anderson, G. S. (n.d.). Forensic entomology: The use of insects in death investigations. Web.
Bansode, S. A., More, V. R., & Zambare, S. P. (2016). Effect of different constant temperature on the life cycle of a fly of forensic importance Lucilia cuprina. Entomology, Ornithology & Herpetology: Current Research, 5(3), 1-6.
DiMaio, V., & Dana, S. (2006). Handbook of forensic pathology (2nd ed.). Boca Raton, FL: CRC Press.
Entomological collection equipment. (2014). Web.
Forensic entomology. (n.d.). Web.
Rutty, G. N. (2013). Essentials of autopsy practice: Advances, updates and emerging technologies. Heidelberg, Germany: Springer Science & Business Media.
Sukchit, M., Deowanish, S., & Butcher, B. A. (2015). Decomposition stages and carrion insect succession on dressed hanging pig carcasses in Nan Province, Northern Thailand. Tropical Natural History, 15(2), 137-153.