December 9
Forensic
Entomology
2012
This term paper is going to discuss and examine the usefulness of forensic
entomology in death investigations. It will discuss the role of insects,
examine how the life cycle of these insects can assist in proposing an
accurate time of death and paper will examine the usage of forensic
entomology in court and the results that is has achieved.
Tabitha
Watkinson
Watkinson
Forensic entomology is the study of insects to determine the post-mortem interval (time
since death) of a decaying human corpse. The insects found in, around, and near the body are
collected and examined to generate a precise time of death. Forensic entomology can be useful in
situations where decomposition is too extreme for a medical examiner alone to determine time of
death1. Hundreds of different insects or bugs can be drawn to a decomposing corpse, but only a
few are useful in the study of forensics entomology2. The two species most instrumental to a
forensic entomologist investigation are blowflies and beetles. Both species have a
metamorphosis life cycle making apparent which cycle of life the insect is in. Using the current
stage of the insect, in comparison to how long it takes the insect to complete that cycle, presents
investigators with an accurate post-mortem interval3.
In China, during the thirteenth century, we see the first documentation of forensic
entomology recorded in a Medico-Legal journal. The case was reported by Chinese lawyer and
death investigator, SÒNG CÍ; the case consisted of a stabbing that had taken place in a rice field.
SÒNG CÍ investigated the murder the following day knowing traces of blood would still be on
the murder weapon. Upon confronting all the rice field workers, he had them lay out their sickles
on to the table in front of him blowflies were automatically attracted to the tool with the trace
amounts of blood on it. The owner of the tool automatically confessed to the crime once
questioned4.
A significant legal case, which helped establish forensic entomology as a recognized tool
for forensic investigation, was that of a murdered and mummified newborn.
1
(Gennard, 2007)
(Benecke, 2008)
3
(Gennard, 2007)
4
(Benecke, 2008)
2
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In the eighteen-fifties, during renovation work taking place in a boarding house, a baby’s
mummified corpse was discovered encased in the chimney. While performing the autopsy, Dr.
Marcel Bergeret discovered the larvae of flesh flies and the remnants of moths. With this
information Dr. Bergeret deduced the date in which the body had been sealed into the chimney
based on the arrival of the moths being a year after death. With the estimation of the time of
death, occupier of the boarding home prior to the current owners were accused of the murder5.
During the first seventy-two hours of death, depending on conditions and fall of body
temperature, a medical examiner can accurately report time of death. Once this seventy-two hour
window is closed there is less medical information apparent to report time of death so a different
method is needed. This is where forensic entomology comes in. Using the life cycle of a specific
species of insects a forensic entomologist can deduce a post-mortem interval over a period of
hours, weeks, and months. It has been established that the start of the post-mortem interval
generally coincides with when a fly first laid eggs on the body. Once the body is discovered
entomologist look to identify the ‘oldest colonizing’ species and its current stage. With this
information and taking into account the particular stage of decay a forensic entomologist gives
the best estimated time of death6.
Realistically speaking, stages of decomposition don’t truly exist. Most characteristics of a
stage can be mixed between more than one stage. However, stages of decomposition are
categorized between five general stages. The five stages of decomposition consist of: fresh,
bloated, active decay, advanced decay, and skeleton. Fresh decomposition stage usually shows
initial insect colonization. During this stage there are no signs of physical change to the body.
5
6
(Gennard, 2007)
(Gennard, 2007)
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Chemicals released during the first few minutes of death can attract blowflies and one to three
hours following their arrival eggs may be laid on the body. The bloat stage consists of
putrefaction and the release of fluids and gasses. During this stage maggots are active.
Active decay consists of an increase in the releasing of fluids, skin marbling and slippage,
and exposure of internal organs. During this stage maggot and insect activity is at its peak. By
advanced decay and skeleton stage the flesh is off of the body some hair may still remain. The
insects have, for the majority, migrated away from the body. Adult insects are no longer attracted
to the body during these stages7.
As previously stated the insects most important for examination by a forensic
entomologist are the blowfly and beetle. Many other species of flies, wasps, and months are also
associated with the decaying of a corps but are not as prominent as the blowfly and beetle.
Because these two particular species go through a complete metamorphosis from stage to stage
and look very different at each, it is easier to estimate how old the specimen is and then convert
the information into an estimated post-mortem interval.
Blowfly life cycles consist of egg, three larva stages, pre pupa, pupa, and adult. At a
certain temperature there is a set amount of time that is known for how long it takes each of these
stages to occur and the duration of each8.
On fresh corpses adult blow flies start to lay eggs in the mouth, nasal openings, ears, and
in wounds and bruises as early as fifteen minutes after death9.The eggs are approximate two
millimeters in length and typically stay the same for the first eight hours with more noticeable
7
(Carter)
(Hall, 2006)
9
(Bullington, 2008)
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changes in the following hours10. The stage typically lasts twenty-four hours and even if they
don’t seem that significant, the eggs can be both identified and aged during this time. The flies
then progress into their larval stage. There are three larval stages or ‘instars’ referred to as L1, L2
and L3.These instars take place over a period of one to five days. The specific larval stage can be
determined by the number of splits present in each posterior spiracle. There is also a difference
in larval size that can validate the larval stage L1 consisting of less than two millimeters in
length and L3 being capable to progress to twenty-two millimeters long. Larvae in the third stage
are the largest and stop feeding halfway through the stage and begin to migrate focusing on
finding a place for pupariation 11. We begin to see this migration into prepupa stage eight to
twelve days after eggs are laid. Eighteen to twenty-four days, after the prepupas gradually
become a pupa, one begins to see darkness with age. The pupa becomes nine millimeters in
length and begins the process of pushing out of operculum; therefore, the presence of empty
operculum is an indication the entomologist that the body has been dead for at least twenty
days12.
A beetles metamorphism is very similar to the blow fly consisting of: egg stage, three to
five larval stages and, pupal stage. The beetles holometabolous development can take anywhere
from seven to ten days, or a year to three years depending on the species of beetle. All species of
beetles have a similar resemblance in the egg stage, all seeming to appear oval or spheroid shape.
10
(Starkeby, 2008)
(Gennard, 2007)
12
(Starkeby, 2008)
11
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Unlike the blowfly, the beetle buries itself into the ground or body in order to pupate.
‘Less detailed information is available about beetle life cycles than is known about the
Diptera’13.
Insects are cold blooded, which forces them to use their environment as a heat source;
they need to utilize a particular amount of energy in order to achieve the life stages. Therefore,
insect growth is influenced by the temperature of their environment. After identifying the insects
found on the body, the information gathered from them would them would then need to be linked
to the temperature at the crime scene. From this information, you can determine the length of
time the flies took to grow from an egg to the developmental stage recovered from the body14.
Forensic entomology has had judicial acceptance as evidence in courts for more than a
century due to its fundamental scientific principles including insect development associated with
temperature and beetles ecological behavior patterns. Insect evidence is evaluated by state /
federal courts under the general rubric of scientific ‘expert testimony.’ For these reason the
entomological evidence collected and presented by the expert witness must be collected,
examine, and calculated precisely and properly. Samples of insects of all stages should be
collected from different areas of the body, clothing, and soil. Information such as vegetation, soil
type, weather and temperature time of collection, elevation and sunlight should all be recorded.
Notes will also have to be made about the extent and type of clothing, if the body was covered by
dirt or exposed, directionality of body, and stage of decomposition if available15.
13
(Gennard, 2007)
(Gennard, 2007)
15
(Anderson)
14
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A forensic entomologist’s job is to provide an unbiased, objective, scientific analysis of
the evidence in the court room or in their working daily endeavors. Some crimes would never
have the capacity to be solved without the information gathered from entomological evidence.
In early June, alongside a rural highway, the body of a young female was discovered.
Following an autopsy it was determined the cause of death was multiple stab wounds inflicted by
a ‘heavy-sharp object’ to the head and neck. The Jane Doe was reported missing by her brother
approximately four days prior, June first, to the body being discovered. The primary suspect, a
thirty- year- old army sergeant, was the last person to be seen with Ms. Jane Doe on the morning
of May thirty-first. Circumstantial evidence had supported the theory that the victim had been
murdered by the sergeant but an accurate estimation of time of death was crucial in establishing
what events had truly transpired. The times of death presented by the medical examiners were
more approximate then specific. The doctors came to their conclusions superficially. The
medical examiners based their approximated time of death on the stage of decomposition the
body was in but, this was not accurate enough to be used in court. This case had to be solved
based solely on the entomological evidence gathered from the crime scene. Numerous insects
were collected from the scene including those that were around the victims open head wound.
Some larvae were collected alive, as to be able to morph into adult stage, while others were
placed into liquid preservation so the developmental stage at time of collection could be
discovered. Weather data, including temperatures, rainfalls, cloud cover, wind direction/speed,
and humidity were gathered from the weather station located a short distance away from where
the body was discovered to indicate the environmental conditions it had been exposed to. Jane
Doe’s conditions when found and autopsy procedures were also looked over. All of these pieces
of evidence together determined a more precise time of death. An entomologist was able to
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analyzes the information and confirm that the first insect colonized on the body had arrived on
May thirty-first, the day the victim was last seen with the sergeant. When questioned and
presented with the evidence the suspect admitted to murdering the young girl by striking her with
a small hatchet six to eight times. The sergeant entered a plea of guilty to murder and received
life in prison without parole16.
Since World War Two, only a few scientists and crime scene investigators have
established progress in the field of forensic entomology. The challenges they faced consisted of
convincing authorities and fellow scientists of the benefits of using entomological evidence in
criminal investigations. Today, judges all over have come to the decision that forensic
entomology is suitable for usage in cases ranging from murders to wildlife violations17.
The field of forensic entomology is rapidly expanding into areas that may not have been
possible if it weren’t for the technology that is available today. With the advancement of new
technology, entomological research can become more accurate and detailed leading to a variety
of new possibilities for the field.
16
17
(Forensic Investigation Forensic Entomology, 2009)
(Forensic Entomology: The Next Step, 2001)
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Bibliography
Anderson, D. G. (n.d.). Forensic Entomology: The use of Insects in Death Investigation.
Retrieved from Simon Fraser University:
http://www.sfu.ca/~ganderso/forensicentomology.htm
Benecke, M. (2008). A Brief Survey of the History of Forensic Entomology. Köln, Germany:
International Forensic Research & Consulting.
Bullington, S. W. (2008, August 3). Blow Flies: Their Life Cycle and Where to Look For The
Various Stages. Retrieved from Forensic Entomology:
http://users.usachoice.net/~swb/forensics/index.htm
Carter, D. O. (n.d.). Human Decomposition Ecology. Retrieved from Forensic Osteology:
http://forost.org/seminar/Segundo_seminario/Human_Decomposition_Ecology.pdf
Forensic Entomology: The Next Step. (2001). Retrieved from Preventing Disease, Disability, and
Premature Death: http://www.phsource.us/PH/ME/nextstep.pdf
Forensic Investigation Forensic Entomology. (2009, March). Retrieved from The University of
Western Australia: Centre for Learning Technology:
http://www.clt.uwa.edu.au/__data/page/112507/fse09_case_studies.pdf
Gennard, D. E. (2007). Forensic Entomology. West Sussex: John Wiley & Sons Ltd.
Hall, A. B. (2006, July 26). Forensic Entomology. Retrieved September 9, 2012, from Science in
Schools: http://www.scienceinschool.org/2006/issue2/forensic
Starkeby, M. (2008). Forensic Entomology Overview. Retrieved from Forensic Science:
http://www.cienciaforense.com/pages/entomology/overview.htm#What
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