Entomology is the study of insects, that have an exoskeleton, six legs, three body segments, one pair of antennae, and one pair of compound eyes. The field of forensic entomology is broadly defined as the application of the scientific study of insects and arthropods in legal matters. Forensic entomologists also deal with non-insect arthropods such as spiders, mites, and ticks. Therefore, the basic definition of "forensic entomology" extends beyond "entomology."
Within the forensic sciences, forensic entomologists can help to establish the postmortem interval (PMI) (which is determined by the period of insect activity, or time since colonization), assist in establishing the geographic location of death in cases of body transport, helps to associate the victim and suspect to each other and to the scene, and help the pathologist identify sites of injury on the corpse. Additionally, entomologic evidence can be utilized as alternate toxicology samples as their gut contents can be a source of human DNA viable for forensic testing.
Other forensic uses of entomology include identifying deaths resulting from anaphylactic shock due to insect bites or stings, resolving traffic accidents resulting from panic due to stinging insects in an automobile, and to be used in consultation in criminal cases involving the misuse of insects that are induced to bite or feed upon the victim.
The major area of research and application of entomology in forensic science is the use of species identification, known growth rates, and insect succession data to determine both the location and approximate time of the victim's death. Due to the relatively recent widespread acceptance of entomology within forensic science, many police agencies, medical examiners, coroners, and federal agencies throughout the United States request assistance from entomologists knowledgeable in the behaviour and biology of carrion insects to help answer critical questions pertaining to human death investigations.
The hairy maggot blowfly (Chrysomya rufifacies) is a species that arrives very early in the process of decomposition. In some instances, it has been known to arrive within minutes after death. Chrysomya rufifacies is a species belonging to the blow fly family, Calliphoridae, and is most significant in the field of forensic entomology due to its use in establishing or altering post mortem intervals. The common name for the species is the hairy maggot blow fly, and it belongs to the genus Chrysomya, which is commonly referred to as the Old World screwworms. This genus includes other species such as Chrysomya putoria and Chrysomya bezziana, which are agents of myiasis. C. rufifacies prefers very warm weather and has a relatively short lifecycle. It is widely distributed geographically and prefers to colonize large carcasses over small ones. The species commonly has a greenish metallic appearance and is important medically, economically, and forensically.
Figure 1 - Hairy Maggot Blowfly
The first documented case involving the use of an insect in a death investigation can be dated to the 15th century.
A local farmer had been murdered in a rice field. The body exhibited a sharp force injury. Sung, who was investigating this case had a suspicion about the village people so he called all villagers together with their sickle which was used as a murder weapon. After examination of the tools, there was no potential evidence to link any of the suspects to the murder. However, after a time period, Liam (Another officer concerned in the case) noted a significant amount of insect activity on and around a scythe. Sung correctly deduced that the flies were attracted to trace amounts of blood and tissue remaining on the blade. It was also mentioned in 1668, By Francesco L. Redi in his experimental study of decaying meat
Trends in Forensic Entomology
Through the proper analysis of entomologic evidence, the modern forensic entomologist can assist police, medical examiners, coroners, and medicolegal death investigators in the determination of postmortem interval (PMI). Most frequently, the entomologic-based time frame is the minimum portion of the postmortem interval, and it is determined by a minimum time since insect colonization. This time period is calculated by using known developmental rates for insect species that are attracted to decomposing tissues, both human and animal. Therefore, the minimum postmortem time interval can be estimated through the knowledge of insect activity and development throughout the decomposition process.
The most useful and important group of insects associated with the early decompositional stages of a human corpse are the blowflies (Diptera and Calliphoridae).
Figure 2 - Freshly deposited blowfly eggs and newly hatched first instar larvae.
The eggs are the first stage in the life cycle of a blowfly.
Eggs such as these can hatch in 8-14 hours and are often overlooked by forensic investigators due to their small length size of 1-2 mm.
Entomology is not limited to identifying the postmortem interval. The entomologist's knowledge of the geographic distribution of various insect species can help investigators determine the location of death and possibly associate the suspect with a victim. This is possible because in some instances insect species are restricted to a particular geographic location.
The most general of these methods uses knowledge of insect succession by establishing the postmortem interval from the simple presence (or absence) of insects on human remains. This method is most accurate for cases in which the postmortem interval is several weeks to months. One advantage to this methodology is the ability to utilize seasonality, which can estimate the time since colonization over several seasons or years.
Figure 3 - Bronze Bottle Blowfly
The bronze bottle blowfly (Lucilia cuprina [formerly Phaenicia cuprina]) is most predominate in the spring and fall months throughout most of the United States. This species can arrive hours or days after death, and they usually do not arrive after the second week.
Insect temperature-dependent development
A more widely used approach to time since colonization determination is to utilize the rate of insect development in the decomposing tissues of the body. A principle advancement in the field of forensic entomology is the ability to apply the knowledge of insect temperature-dependent development to the time since colonization estimation. The difference in terminology implies a false sense of precision, which can be misinterpreted by law enforcement officials, attorneys, judges, and juries.
Death Scene: Entomological Evidence Collection
It is important for the death investigator to note that the collection of entomologic evidence at the death scene will often result in an unavoidable disturbance portion of the remains and/or associated objects.
Figure 4 - Colour changes in the Pupal Stage
The colour changes in the pupal stage as it ages and progresses toward adult emergence. It is important for the investigator to recognize and document the presence of the pupal stage. This is the intermediate stage between the larva and adult, and the photographic documentation of the pupal colour enhances the estimation of the period of insect activity or time since colonization.
Collection of insects from the body at the scene
The following insect types should be collected from the body at the scene:
- Adult flies and beetles
- Fly larvae (maggots)
- Beetle larvae (grubs)
- Fly pupae
Figure 5 - Pupae and Pupal Casings
Pupae and pupal casings may be found away from the body as well as on the body and in the clothing and items surrounding the remains. This life stage is later in succession than the larval stages and can be used to provide better estimations on the maximum range of the time of colonization estimation provided by the forensic entomologist.
Collection of specimens from under the body
Once the body has been removed from the scene, soil samples should be collected. This can be accomplished through the use of a hand trowel or spade. A core sample (about 3" wide and 6" deep) should be collected from the ground directly beneath the major body areas (one sample each from the head, torso, and upper legs).
Collection of specimens during the autopsy
Another insect collection should be made immediately before (and during) the autopsy. At this time, insect species may be present that were hidden at the scene or were feeding deeply within the body and thus not previously recovered.
The autopsy also provides the opportunity to closely inspect the body for additional entomologic evidence. The clothing of the victim should be thoroughly inspected for fly or beetle larvae that may pupated within the clothing. There may be a different species than those which has been collected from the body and are therefore essential to recovery. Such species have a tendency to pupate between the inner lining of the clothing and the skin. Collars, cuffs, and waistbands are common pupation sites. Pockets should also be inspected for larvae and pupae.
Pitfalls and Future Trends
It is clear to most scientists that forensic entomologists do not determine the exact postmortem interval. Instead, they determine the age of the insect larvae and use the behaviour of the adult insects and the growth and development of the insect larvae to calculate a time interval in which death could have occurred.
Therefore, entomologists do not directly estimate the postmortem interval but instead can reliably predict the period of insect activity (PIA) or, more accurately, the range in time for which colonization could have occurred.
Entomologists must always work within a reasonable time range for the age estimations of insects. This is because entomologists deal with organisms in natural systems and, therefore, accounting for the biological variation that occurs in these systems, exact estimations that pinpoint the time of death may never be possible.
With continued research in the field of forensic entomology, scientists can develop a better understanding of such variation and can allow for better predictions of the period of insect activity and, potentially, the amount of time that can elapse from the death of the organism to insect colonization. In the end, such an understanding of this variation could lead forensic entomologists closer to providing estimates of the true postmortem interval.
The following websites are additional resources on forensic entomology:
- European Association for Forensic Entomology: http://www.eafe.org/
- North American Forensic Entomology Association: https://www.nafea.net/
- Forensic Entomology by Dr. JH Byrd: http://www.forensic-entomology.com/
The following books are additional resources on forensic entomology:
- Byrd, JH, Castner JL, eds. Forensic Entomology: The Utility of Arthropods in Legal Investigations. Boca Raton, Fla: CRC Press; 2001. (ISBN: 0-8493-8120-7)
- Catts EP, Haskell NH, eds. Entomology & Death: A Procedural Guide. Clemson, SC: Joyce's Print Shop, Inc; 1990. (ISBN 0-9628696-0-0)
- Goff ML. A Fly for the Prosecution: How Insect Evidence Helps Solve Crimes. Cambridge, Mass: Harvard University Press; 2000. (ISBN 0-674-00220-2)
- Greenberg B, Kunich JC. Entomology and the Law: Flies as Forensic Indicators. Cambridge, UK: Cambridge University Press; 2002. (ISBN 0-521-80915-0)
- Smith KGV. A Manual of Forensic Entomology. Ithaca, NY: Cornell University Press; 1986. (ISBN: 0-8014-1927-1)
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