HISTORY

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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.

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