The Forensic Entomology
American Board of Forensic Entomology
M o r e · A b o u t · t h e · S c i e n c e
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.
S c o p e · o f · M e d i c o c r i m i n a l · E n t o m o l o g y. . .
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.
T h e · H i s t o r y · o f · F o r e n s i c · E n t o m o l o g yIn 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.
P r o f e s s i o n a l · S t a t u s · o f · F o r e n s i c · E n t o m o l o g i s t s
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.