The typical death scene investigator learns quickly that maggots and corpses go together. For many years, the "worms" crawling in the eyes, nose, and other orfices and wounds on dead bodies were considered just another disgusting element of decay -- something to be rinsed away as soon as the corpse was placed on the table for autopsy. While ballistics, firearm examination, bitemarks, gunpowder residue chemistry, blood spatter analysis, and other elements of scientific criminology were studied and refined, the insects associated with death scenes were largely ignored.
Through the years, however, a few scientists have
researched forensic entomology, which has become a fascinating, and at
the same time a more arcane, field of biological study. However, the
scope of the field is broad. The potential for
contributions of entomology to legal investigations has been known for at
least 700 years, but only within the last decade or so has entomology
been defined as a discrete field of forensic science.
Forensic entomology is the name given to any aspect of the study
of insects and their arthropod counterparts that interacts with legal
matters. Lord and Stevenson (1986) divided it into three components:
urban entomology (legal proceedings involving insects and related animals
that affect manmade structures and other aspects of the human
environment), stored products entomology (proceedings involving insects
infesting stored commodities such as cereals and other kitchen products),
and medicolegal entomology. The latter field, sometimes termed "forensic
medical entomology," and in reality "medicocriminal entomology" (because
of its focus on violent crime), relates primarily to 1) determination of
the time (postmortem interval or PMI) or site of human death, 2) cases
involving possible sudden death, 3) traffic accidents with no immediately
obvious cause, and 4) possible criminal misuse of insects
(Leclercq 1969). Forensic entomology is inextricably linked with the
broader scientific fields of medical entomology, taxonomy, and forensic
pathology.
Scope of Medicocriminal Entomology....
As presently practiced, medicocriminal entomology deals mainly
with inferences made after examination and identification of arthropods
collected from or near corpses. Forensically significant conclusions
often can be drawn by noting the state of successive colonization of a
corpse by local arthropod fauna, or by identifying the developmental
stage of necrophilous (deadflesh eating) insects collected in, on, or
near the body. A professional entomologist is skilled in obtaining an
adequate sample of appropriate arthropod specimens, properly preserved
for study, from a death scene. In most cases, additional specimens need
to be reared to the adult stage, and a professional entomologist knows
how to accomplish this successfully. Knowledge of arthropod (especially
blow fly) biology and geographic distribution can allow the determination
of accurate estimates relative to the interval of time that a body has
been exposed to arthropod activity, and an indication of whether the
fauna collected is indigenous or foreign to the site where the body was
found. Often this can prove useful in determining the actual location of
death. For example, certain species of blow flies tend to be found
primarily within large urban centers. Identification of such species in
association with a corpse found along a rural roadside suggests that the
victim was killed in town and subsequently dumped in the remote rural
environment.
Identifying arthropods accurately is the principal
role played by medicocriminal entomologists. This more than any other
factor provides the solid foundation for all subsequent inferences
relative to that fauna. Although specimens may be collected by crime
scene technicians, medical examiners, or forensic pathologists, skill in
identification will rest with a fully qualified entomologist.
Case histories have documented the utility of medicocriminal
entomology and point out the unique contributions of this field of
science. Nuorteva et al. (1967, 1974) presented a series of cases from
Finland in which blow flies were used as indicators for indoor as well as
outdoor death scenes, and where the immature (larval) or adult stages
were used for identification. Leclercq (1969) provided a
typical case scenario and outlined how insect data were used to
corroborate information obtained from other sources. Greenberg (1985)
outlined several cases, including a description of how laboratory
fly rearing data were used to calculate the number of accumulated
degree hours (ADH) required for certain blow fly species to develop, and
how such data were applied to the solution of a murder case in Illinois.
In another recent case, Greenberg (pers. comm.) described how the absence
of insects, in a seemingly straightforward death scene, led to a killer's
confession. A window next to the victim was open when the body was found,
thus giving the impression that the murderer had forced entry into the
room the night before. However, the air conditioned room was cool even
though it was very hot outdoors. In reality, the killer was known to the
victim, had a key, and had returned to "set the stage" by opening the
window just prior to feigning discovery of the corpse. The insects thus
had insufficient time to colonize the body because the window had been
closed prior to the return of the killer. When confronted by this
biological reality as pointed out by medicocriminal entomology, the
killer confessed.
The History of Forensic Entomology
In an experiment famous as much for its demonstration of scientific method
as for its contribution to entomology, Francesco L. Redi (1668) studied
rotting meat that was either exposed to or protected from flies. From his
analysis of subsequent blow fly infestation, he refuted the hypothesis of
the "spontaneous generation" of life. Up to that time, it was generally
believed that under the right conditions maggots came from rotten meat.
Later, Bergeret (1855), near Paris, France, was the first westerner to use
insects as forensic indicators. The body of a baby was found behind the
plaster mantle in a house, and an investigation was begun. Bergeret
determined that the assemblage of insects associated with the corpse
pointed to a state of decay that dated back several years; consequently,
the question of guilt was thrown upon the earlier occupants of the house,
and not upon the current ones.
Bergeret's methods and materials were quite similar to one of the main
medicocriminal entomological techniques still in use today; that is, the
successive colonization of a corpse by a predictable succession of
arthropod species. Between 1883 and 1898, J. P. Megnin in France published
a series of articles dealing with medicocriminal entomology. The most
famous of these, La Faune des Cadares, served in large part to make the
medical and legal professions aware that entomological data could prove
useful in forensic investigations.
Although entomologists are most familiar with the references cited above,
medicocriminal matters in the Far East predate these considerably. In 1235
A.D., Sung Tz'u, a Chinese "death investigator," wrote a book entitled The
Washing Away of Wrongs (as translated by McKnight 1981) in which forensic
science as known at that time was detailed. In this text, what was probably
the first actual medicocriminal entomology case was recounted. A murder by
slashing occurred in a Chinese village, and the local death investigator
was deputized to solve the crime. After some fruitless questioning, the
investigator had all villagers bring their sickles to one spot and lay them
out before the crowd.
Flies were attracted to one of the sickles, probably because of invisible
remnants of tissue still adhering to it, and the owner subsequently broke
down and confessed to the crime. In other portions of the text, Sung Tz'u
demonstrated knowledge of blow fly activity on bodies relative to those
orifices infested, the time of such infestation, and the effect of trauma
on attractiveness of tissue to such insects.
Any analytical system is as reliable as is the data upon which it is
founded, and forensic entomology is no exception. Because accurate
identification of necrophilous arthropods is of paramount importance, few
repeatable results could be obtained before adequate taxonomic work had
been accomplished on the invertebrates (the insects and related animals) in
question. Taxonomy and systematics comprise the science describing,
classifying, and proposing evolutionary relationships of the various forms
of life.
Although many synanthropic (strongly associated with human activity) flies
(such as Drosophila, Musca, Muscina, Ophyra, Stomoxys, and others)
are not encountered frequently in typical forensic investigations, other
species assume great importance (Greenberg 1985). Carrion (dead tissue)
feeding blow flies (Calliphoridae) and flesh flies (Sarcophagidae) are
those most useful in death investigations. Aldrich's (1916) monograph on
the Sarcophagidae made use of distinctive male genitalia, thereby enabling
entomologists to identify adult male specimens from this important
family.
This concept involved the so called "lock-and-key" arrangement in many
insects that facilitates reproductive isolation between species. The male
copulatory organs of each kind (species) of higher flies are composed of
unique, complex structures that are used as key characters to enable
specific determination. This adaptation has been applied with equal success
to the forensically important blow flies.
Twenty years later, Knipling (1936) published descriptions and keys to many
common early (first instar) maggots of flesh flies. Although considerable
work had been done on the blow fly fauna of North America (for instance,
Knipling 1939), Hall's 1948 monograph, The Blowflies of North America, made
possible the accurate identification of adults and mature larvae of most
species of this family as well.
Although very few new (that is, previously unrecognized) North American
calliphorid species have been described recently, efforts have been devoted
to accumulate improved distributional information (Hall and Townsend 1977,
Hall 1979, Goddard and Lago 1983). More research is needed on accurate
identification of the critical larval and pupal stages (those most
frequently collected in death investigations). At present, first instar
blow fly larvae (the stage that hatches directly from the egg) generally
are not identifiable to species, and second instars (the next maggot stage)
can be identified accurately only on occasion.
The situation is somewhat better with respect to third instar or prepupal
larvae (the largest maggot stage, and that most commonly observed), but
only if such specimens are preserved properly. Even so, a significant
number of indigenous blow flies cannot be identified at present as
immatures. This is currently an area of active research, and to this end
the relatively new technique of scanning electron microscopy is being
applied (Liu and Greenberg 1989).
Because of the medicocriminal requirement for reliable data on rates of
larval development, considerable effort has been expended to measure such
intervals. Anecdotal information on blow flies contained in earlier works
was largely supplanted by Hall's (1948) rearing data, and the latter has
been refined for some forensically important species to degree hour status
(Greenberg 1985). Because insects are coldblooded animals, their rate of
development is more or less dependent on ambient temperature. Research has
shown that for each species there generally is a threshold temperature
below which no development takes place.
As temperature rises above this threshold, a certain amount of time is
required for the insect to attain defined stages of development (for
instance, from the newlylaid egg through the second instar maggot). Because
this heat is accumulated as "thermal units," it can be calibrated and
described as "degreedays" or "degreehours," depending on the accuracy of
temperature readings and time period involved.
However, most laboratory rearings (upon which the degreehour data are
developed) have been done at constant temperature, so additional research
will be necessary to establish correlations between these data, typical
fluctuating field temperatures (warmer during the day and cooler at night),
and the average daily measurements frequently reported from weather
stations. Retrospective weather records from the nearest weather recording
station (such as an airport) are those most often used in medicocriminal
evaluations.
Access to the scientific literature pertaining directly to medicocriminal
entomology has been facilitated by two recent bibliographies. An initial
guide to entomological involvement in forensic pathology, plus a selected
bibliography, was provided by Meek et al. (1983). A bibliography of all
publications dealing wholly or in large part with medicocriminal entomology
worldwide was compiled by Vincent et al. (1985). The latter paper contained
329 references and was current through 1983; therefore, the actual body of
literature pertaining to this subdiscipline of forensic entomology is not
large when compared to many other biological or legal subjects. The first
textbook devoted to forensic entomology was published in 1986: A Manual of
Forensic Entomology (Smith 1986). This is an excellent reference for the
entomologist, and it brings together in one place all the salient
information contained in the literature on this subject.
A procedural guide, Entomology and Death, was published in 1990 and
is intended for crime scene investigators and other forensic specialists.
Professional Status of Forensic Entomologists
The most current worldwide directory of forensic entomologists listed
a total of 62 scientists involved in this field of study. Of these, 33 (53
percent) were linked solely with the "medicolegal" subdiscipline, and an
additional five (eight percent listed "medicolegal" entomology as one of
their forensic specialties). Most (44 percent of the total) were affiliated
with colleges or universities, taught entomology or biology and performed
research or worked with the Cooperative Extension Service.
A few conducted research primarily on medicocriminal entomological
subjects. A significant number (35 percent) functioned as consultants
working for private industry, being self employed, or having retired from
previous employment in entomology. U.S. medicocriminal entomologists who
were members of the Entomological Society of America (the scientific
"society" of entomologists in the U.S.) were generally affiliated with
Section D (Medical and Veterinary Entomology) of that organization.
Only about 39 percent of such U.S. workers were members of the American
Registry of Professional Entomologists (ARPE), the formal organization
comprised of professional entomologists (now known as Board Certified
Entomologists), and still fewer are members of the American Academy of
Forensic Sciences. Following the lead of physicians (who draw their
professional identity from the American Medical Association), attorneys
(who have the American Bar Association), and other professionals, it will
become increasingly necessary for medicocriminal entomologists to affiliate
through a professional organization with strict educational, ethical and
maintenance standards. Facilitation of qualification as expert witnesses is
one reason for encouraging such a connection.
The American Board of Forensic Entomology (ABFE) constitutes the first step
toward such professionalism. Exhibiting strigency commensurate with the
medical and legal arenas, achieving status as Diplomate, ABFE, requires the
applicant to possess an earned Ph.D. and appropriate experience,
credentials far in excess of those demanded by other certification efforts
in entomology.
Most (82 percent) current medicocriminal entomologists hold an earned Ph.D.
degree or its equivalent (Lord and Stevenson 1986). The remainder possess
M.S. or M.D. degrees. Given the requirement for demonstrating "expertness'
as part of the medicocriminal procedure, it is likely that an earned Ph.D.
with emphasis in cogent areas of medical entomology, taxonomy and allied
disciplines will remain essential. The possibility of combining graduate
entomological education in the medicocriminal field with ancillary
professional medical or legal degrees remains largely unexploited. One
compelling reason for this may be that, at present, few entomologists
worldwide are employed fulltime as medicocriminal experts. In at least one
instance, an individual with prior training in criminology entered a
graduate program with emphasis on medicocriminal entomology, and one medicocriminal entomologist developed credentials as an attorney.
Although the situation may be changing slowly, medicocriminal entomologists
are seldom included on routine crime scene investigation teams. Whether
this has occurred because such specialists are rare, because their presence
is inconvenient or impractical, or because their area of expertise is not
appreciated fully for either its uniqueness or potential contribution to
forensic pathology is immaterial. A major result has been that an important
responsibility of medicocriminal entomologists consists of training crime
scene technicians and allied personnel to recognize, obtain, and properly
preserve entomological evidence. The entomologist then reviews such
evidence and often provides expert assistance if entomological data appear
crucial to the case. Important to the latter function are eventual
qualification as an expert witness, the increased professional status of
entomologists toward that end, a facility with courtroom protocol, and a
fee structure related to this effort.
Most up-to-date investigative units acknowledge in their standard operating
procedures (SOP's) the potential for acquisition of entomological evidence.
The purpose of the Procedural Guide is to facilitate that objective.
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