Entomology is the study of insects. For the purpose of this paper, only the life cycle of an insect, flies and beetles in particular, will be discussed. An insect's life cycle consists of four distinct stages. In the case of blowflies, the first stage is that of an egg. The eggs then hatch into larvae, or maggots, during the second stage. The anterior end has a pair of sharp digging hooks used for both locomotion and feeding while the posterior end is the respiratory apparatus so that the maggots can receive oxygen as they burrow through the material (Miller et al. 1307). Once the maggots reach their full size, they stop feeding and begin to migrate into a drier area, usually into the soil. In this third stage, the maggot develops into pupae, where the outer skin hardens to form a protective casing. Within a week, the pupae undergo metamorphosis and emerge from the shell as an adult fly, the final stage of the life cycle. 

     Surprisingly, forensic entomology, the use of insects to solve crime, is not a novel idea. Its origins date back to 13th century China. A rice field worker had been murdered with a sickle. No one knew who had killed him so the local magistrate ordered all the workers to lay their sickles in the sunlight. Although the killer's blade looked clean to the human eye, the magistrate knew that flies were attracted to the scent of blood. Faced with the evidence the killer confessed. (Goff, A Feast of Clues 31; Anderson; Kinney)
Forensic entomology is still being used today, though not as commonly, to solve crime. According to author Kinney Anderson and other forensic entomologists, there are two main ways of using insects to determine the amount of time that has passed since the death, also known as the postmortem interval or PMI. The maggot age and development, as well as the use of successive waves of insects, help to determine the length of the interval. 

     Once a body is dead, the first organisms to visit the corpse are the blowflies and the fleshflies. The scent of blood or bodily gases attracts the flies about ten minutes after death. They deposit their eggs in the natural orifices- the eyes, nose, mouth, ears or in the wounds and blood of the body. Once the eggs hatch into larvae they devour all the soft tissue of the body. Then the maggots migrate to the soil or to the clothes to develop into pupae and eventually into adults. This usually takes from several days to weeks depending upon the species of fly.

     The first step the forensic entomologist must take after collecting the maggots or pupae is to determine its species by examining the distinguishing features. Since each of the developmental stages of the fly takes a set, known amount of time, forensic entomologists can see which stage of development the larvae were at when collected at the crime scene and then calculate the PMI. This is the first method of using maggot age and development.

     The second method involves all the other insects that come to inhabit the body. After the invasion of the blowflies, other types of flies such as houseflies, flesh flies, skipper flies, fruit flies, and coffin flies come to devour the decomposing tissue. Beetles such as the carrion, rove, clown, sap, checkered, scarab, and dermestid come to feed on the maggots and on the drier tissues such as the remaining skin and cartilage (Miller et al 1307). When the body is eventually found there are hundreds and hundreds of species of insects crawling upon the body. By following this diverse ecosystem, and having adequate knowledge about which species inhabit the body at the different stages of decomposition, one can then calculate the PMI.

     As for drug related deaths, gas chromatography and mass spectrometry can be performed on the fly larvae to test for the presence of phencyclidine, cocaine, heroin, amitriptyline, and methamphetamine (Goff et al 126). With the development of hair extraction techniques, drugs such as amitriptyline and nortriptyline can also be detected by extracting material from the fly and beetle pupae casings, and beetle droppings using acids or bases (Miller et al 1308).

     As with all fields of science, forensic entomology has its advantages and its disadvantages. One of the advantages of using insects to determine time of death is that sometimes it may actually be more precise than the conventional method of looking at the different stages of decomposition, because that method is largely contingent upon body heat (Graves A12).
One of the disadvantages of using forensic entomology is that the growth rate of the maggots can be affected by changes in the temperature, geographic location or habitat, humidity, and rain (Goff 34; Hogan). Temperature is an extremely crucial factor for the utilization of this method because flies won't be able to lay eggs below 40 degrees, nor do they seek the body after sundown (Hogan). Entomologists will have to take each of these variables into consideration in order to give a more accurate estimate of PMI.

     Another complicating factor is the presence of foreign substances in the decomposing body such as drugs and toxins. They can affect the growth rate of feeding maggots, information that can be crucial in estimating the PMI (Goff 34). However, as mentioned above, having drugs in the body can actually be advantageous because traces of the drugs will also be present in the feeding maggots.

     From the research of Lord, Goff, Adkins, and Haskell on the "Black Soldier Fly as a Potential Measure of Human PMI," it was found that this species tends to lay eggs twenty to thirty days postmortem, thus dominating the body in the dry/post decay stage of decomposition (216). Because of their domination, they can be potentially useful in calculating PMI during the more advanced stages of decomposition.

     When the insects are brought to the lab, the most troublesome area for scientists is in the identification of the different species. Without identifying the species, scientists are unable to know the timing of a life cycle for that particular species and thus are unable to know when the victim died. With the use of DNA as a means of identification, scientists can now more easily, and accurately identify the species of flies (Why Flies, NSF).

     Although forensic entomology has been around for centuries, it is still not very widely used. Only about one percent of all homicide cases involves the use of forensic entomology (Williams, E1). Yet as can be seen, forensic entomology can be very useful in the broader area of forensic science (although not mentioned, it can also be used to determine if the body has been moved posthumously) and certainly has a lot of potential for further development.

     But with less than 20 forensic entomologists in the country, most as professors in the general field of entomology, forward movement in this field becomes difficult (Graves A12; Goff34). The next possible step is to train forensic scientists in entomological techniques, and to include these techniques more frequently in the forensic investigation of crime scenes. More workshops and presentations of forensic entomology can also help to generate more interest. There is definitely hope that someday in the near future, forensic entomology will be a more respectable field with a wider acceptance as evidence in court.