Crime and Clues

The Role Of Entomology In Forensic Investigations

Prologue

This paper is intended for use by police and other emergency personnel who have occasion to be in contact to the recently and not so recently deceased. When first introduced I will mention the scientific name of the various species of insects which colonize bodies after death. After the first mention I will use the common name which is easier to both remember and pronounce.

All too often insect evidence is accidentally destroyed be emergency personnel who fail to realize the importance of this evidence. This author has personally witnessed well meaning emergency personnel shooing away insects and maggots at a scene. I have even observed emergency personnel stomping on maggots as they attempt to flee from the activity around the body. Education in the proper collection and preservation procedures is essential.

Personnel should be aware of the behavior of maggots. They should be able to recognize the types of insects normally associated with a body. They should be able to recognize evidence of insect activity such as beetle frass (Bryd, 2001), and pupal casings (Erzinclioglu, 2000).

Introduction

Insects (Arthropods) are everywhere. There are so many of them that each species has developed a unique niche in which to breed and feed. This is what the Forensic Entomologist hopes to take advantage of. Each species comes with a unique and predictable set of environmental conditions under which they can and will grow and thrive. To know the conditions in which a particular species will live is to know the history of the corpse they are living on or near.

Insects and the Time of Death Question

When used in conjunction with other standard methods insect evidence can be used to estimate the Post Mortem Interval(PMI). This term is more accurate than referring to 'Time of Death' since the exact time of death is difficult to impossible to predict(Erzinclioglu 2000).

The most commonly used and widely known method of determining the PMI is use of temperature readings. Temperature is used to calculate how many degrees from normal body temperature the body has dropped. There are several problems with this method. The temperature of a body is affected by many variables such as the circumstances of death, the environmental conditions, whether the deceased took drugs or whether the deceased struggled.(Baden and Hennesse, 1989) Bodies also cool at various rate according to weight and fitness (Knight, 19??).

The following quote is from Dr. Ian West's Casebook: The Chilling Investigations of Britain's Leading Forensic Pathologist.

"Temperature is not as useful an indicator as some people think. It is fine for a body found indoors, assuming the temperature in the house remains constant but for the outdoor scene temperture is notoriously unreliable." (West and Stern, 1996, p. 231)

Another problem with Temperature, other than the range of variables to be considered, is that each investigator seems to use different standards to estimate the cooling rate per hour. Dr. Micheal Baden, the former chief medical examiner of New York, NY. uses a one degree per hour cooling rate (Baden and Hennesse, 1989). Dr. Ian West uses a formula of 1.5 - 2 degrees Celsius per hour for the first two hours and then .75 degrees after that until the body reaches environmental temperature. Dr. West points out that environmental factors such as rain can greatly affect the cooling rates( West & Stern, 1996). The Encycleopedia of Forensic Science uses a standard of 1.5 degrees Celsius per hour (Lane, 1992).

Once the body reaches environmental temperature the only thing this can tell an investigator is a rough estimate of the minimum time since death. However, anyone who has experienced -40 degrees Celsius knows there are conditions in which cooling would occur more rapidly. The Nanogram developed by Henssage and Madea(n.d.) takes into consideration weight but does not compensate for environmental conditions or the effects of drugs (Knight, 19?? ).

The predictable progression of Rigor Mortis is also used as in indicator of the PMI. Rigor mortis is the gradual stiffening of the muscle due to a build up of Lactic Acid in the muscles(Knight 19??). Rigor starts in the small muscles of the face and progresses to the neck , upper extremities, trunk and lower extremities(Lane, 1992). Rigor alone is also unreliable in that is affected by exertion prior to death (Knight, 19??), body fat(Thomas 1989) , drug use (Baden and Hennesse, 1989) and other environmental conditions. A body may pass through rigor much more quickly than the standard 36 hours according to body fat and other variables (Thomas 1989). There are some medical conditions which cause stiffening of the muscles with no relation to Rigor Mortis (Lane, 1992).

Hypostasis is also used to predict the PMI. Hypostasis is the settling or pooling of the blood due to gravity. Once the heart stops pumping blood will pool in the area of the body closest to the ground. Hypostasis begins to appear 6-10 hours after death and is fixed after 24 hours (Lane, 1992). These rates are highly variable and provide a very short window in which any estimates of the PMI can be made. Hypostasis may not be fixed if the body is moved within the first 12 hours after death (Baden & Hennesse, 1989). Color of the hypostasis may provide some indication of cause of death but in general is also unreliable as a form of estimating P.M.I,(Lane, 1992).

A relatively new method is sampling of the Vitreous Humor of the eye. As red blood cells in the retinal vessels break down Potassium is released as a by product. This potassium accumulates in the Vitreous Humor at a predictable rate (Lane, 1992). This method is considered relatively accurate however the eyes must be intact for this procedure. As well, an advanced stage of decomposition may make this procedure impossible. Finally, in bodies drained off blood or where the body is not intact the rate of break down of red blood cells may be affected.

Insect evidence can be used to confirm the PMI established through body temperature, hypostasis and or rigor. Conversely the insect evidence recovered from a scene may contradict the standard temperature, hypostasis and rigor indications bringing into question the findings. This in turn can lead to the development of new and more accurate hypothesis regarding the circumstances of death and the PMI (Baden & Hennesse, 1989).

As well as the PMI, insect evidence can indicate the season of death. Insect evidence can indicate whether the death occurred in an urban or rural setting. Insect evidence can be used to determine whether a buried body was on the surface for some time after death and then buried. Insect evidence also indicates whether a body has been previously buried.( Anderson 2001)(Goff 2000)(Erzinclioglu, 2000) Aquatic insects can indicate the season and conditions under which the body came to be in the water(Thomas, 1985)Aquatic insects on a body found on land indicate death in a wetter season or movement of the body.

Insects begin to arrive at a corpse in a little as ten minutes after death (Goff, 2000)(Lane, 1992). In buried bodies colonization can be found as much as ten years after death (Erzinclioglu, 2000). Insect colonization can be found on bodies sealed in plastic bags, rugs and cars (Anderson, 2001). Insect colonization occurs on bodies indoors (Anderson, 2001) and those which have been buried (Erzinclioglu, 2000). This means that insect evidence can be used in wide variety of circumstances and over much longer periods of time as opposed to other widely used methods for estimating the PMI.

Stages of Decomposition and Colonization

In A Fly for the Prosecution , M. Goff identifies five distinct stages of decomposition. The stages of decomposition are; "fresh, bloated, decay, post decay and skeletal."(Goff, 2000, p.43). Each of these stages are accompanied by distinct insect activity. Goff also notes that , "regardless of where the decomposition studies are conducted, I have observed that certain patterns are common to most if not all of them.".

The Fresh Stage

In the fresh stage the first insects to arrive are the flies (Order Diptera).This is where the literature becomes somewhat confusing. Some researchers refer to the entire colonization as Blowflies (Saferstein, 2004). Others refer to Blowflies and Fleshflies as seperate entities (Erzinclioglu, 2000)(Goff, 2000). Still others refer to Blowflies as being Sarcophigae(Lane 1992) which is incorrect. The most accurate discription is the actual classification. In the family Calliphoridae are the Blowflies also known as Green bottles, Blue bottles and House flies. The fleshflies are in the family Sarcophagidae. Here is a way of distinguishing the classes. Blowflies are metallic in color and may be green, blue or black. Fleshflies are dull in color and may be striped with a red protuberance at the posterior of the abdomen ( Bryd and Castner, 2001). Blowflies lay eggs into any wounds or openings such as eyes, nose, penis, or vagina. Fleshflies deposit live larva onto the body (Erzinclioglu, 2000)(Goff, 2000).

The insects to arrive in the fresh stage are the Green bottle and Blue bottle blowflies. They may arrive anywhere from minutes to several hours after death depending on the environmental conditions. Females lay eggs in any opening of the body. The first ovipostion of eggs may not be immediately noticable because the eggs are deposited very deeply inside the orifices of the body(Goff, 2000). The eggs of the blowfly are approximately 2mm in length and are white or yellow. Flesh flies may arrive at the same time or several hours after the blowflies (Goff, 2000). As already noted Fleshflies deposit live maggots on the corpse.

In the Fresh stage their may be wasps which prey on the adult flies. Ants may also appear and take eggs and maggots (Erzinclioglu, 2000).

During the fresh stage there are several methods used to estimate the PMI. The investigator may collect the eggs, when that is all that is found, and rear them in the laboratory. In the laboratory the investigator must reproduce the environmental conditions in which the body was found. M. Goff suggests including a sample of the flesh from the body to replicate the food source (Goff, 2000) However, this practices raises moral and ethical issues. Also, this practice could potentially disturb evidence and create false wound patterns. Other researchers suggest beef liver as a good source of food for laboratory rearing of maggots (M.Stoerkay, 2000) (Bryd, 2001)

The eggs are allowed to hatch and proceed through the five stages of development ending in the emergence of adult flies. Some adult flies are collected for identification at this point. Working backwards from the time of collection using the known life cycle of a particular species the investigator can estimate the PMI.

Some literature suggests allowing a second cycle to occur. This enables the investigator to record the exact time in hours of each stage and the total hours for a complete cycle(Bryd, 2001) The Table below shows some development times for some common species of flies.

Some development data on different species of blowflies (Calliphoridae) and fleshflies (Sarcophagidae) Life histories of 11 species of blowflies and fleshflies reared at 27 degrees Celsius, and 50 percent relative humidity.

The life cycle of flies come in five stages. The first is the eggs. Second, are three instar stages, each resulting in a larger maggot. The fourth is the pre-pupal stage in which the maggot leaves the body and seeks an area to encase itself where it will pupate and become an adult fly. The pupation stage is the fifth and final stage. In the third instar stage the maggot does not completely shed the skin. It retains this skin around the body. This skin is what will become the pupal case (Stoerkay, 2000)(Goff, 2000)(Saferstein, 2004).

The three instar stages are identifiable by the morphology of the mouth parts and posterior spiracles. (Bryd and Castner 2001)

When live maggots are found the investigator may collect sample an compare the measurements with known growth rates (Stoerkay 2000). However, growth rates are affected by both environmental conditions and the species of fly. This method should be used in conjunction with laboratory rearing.

The Bloated Stage

The bloated stage is distingushed by the production of gases caused by bacterial break down of the tissue. The eggs of the flies will have hatched by this stage. The maggots will be actively feeding which also contributes to decomposition. The feeding activities of fly maggots speed the breakdown of tissue. Feeding activity also raises the temperature of the body. The higher the temperature of the body the more bacterial activity occurs. Maggots predigest their food. They use saliva to digest flesh and then suck up the liquid just as adult flies do (Goff, 2000). As a mass they are more effective than alone and tend to move in masses. The action of both bacteria and maggots can raise the temperature of the body as high as "127 degrees Fehrenheit."(Goff,2000, p. 45).

This raising of the body temperature has a signifigant result for those reseachers working in temperate to cold climates. If the body has reached this stage before the frost maggots may survive in temperatures lower than usually associated with maggot activity. The maggots will retreat to the inside of the body consuming it from the inside. By doing this they protect themselves from freezing temperatures. Maggots may continue to develop past where low temperatures would normally arrest development. Thus, a body found in the spring with a shell of skin but no internal structures was probably in the bloated stage in the late fall(Erzinclioglu, 2000).

Other species found on a body at this stage are Histor beetles (Histerade), Rove beetles (Staphylinidae) and burying beetles(Silphidae). As well, predatory wasps and ants may be present(Goff, 2000).

The Decay Stage

In the decay stage the skin has ruptured and body fluids permeate the surrounding area. Maggots stop feeding and move off of the body. The maggots are in the third instar stage during this phase. The maggots will move off of the body as a mass or individually according to species (Bryd, 2001)(Goff, 2000). Some will move as far away as 20 feet away from a body (Goff, 2000). The surrounding area around any remains in this stage should be searched for maggot masses under carpets and ground cover. Beetles become the most common insect at the end of this stage(Goff, 2000).

The Post-Decay stage

In the Post-Decay stage beetles are the most prominent order found on a body. The species will vary according to the conditions. Some beetles will not feed in wet conditions while others require wet conditions (Goff, 2000).

The Skeletal Stage

Evidence Collection

The following is a short description of the proper methods for collection of insect evidence.

The first step in any investigation is to secure the scene. Once this is done the scene should be documented with sketches, notes and photograghs(Byrd, 2001)(Saferstein, 2004). The initial investigation for insect evidence should be done by stand still and observing the insect activity around the body. Notes, as to the type and location of insects in the area should be made(Haskell, Lord and Byrd, 2001). By approaching the scene carefully the investigator can avoid scaring away those species which will flee from human disturbance around the body.

Before the body is disturbed the investigtor should perform 5-6 sweeps of the area around and above the body using a large insect net(Haskell,Lord and Bryd, 2001). The insects collected can be killed onsite and preserved for later identification(Bryd, 2001).

Once the insects around the scene have been noted and sampled the temperatures in and around the body should be recorded. Typically the ambient temperature, the temperature at the surface,the temperature under the body and an internal temperature are taken. The temperature of and maggot masses present should also be taken(Haskell,Lord and Byrd, 2001).

Once the body is removed the soil temperature under it should be taken(Haskell,Lord and Bryd, 2001).

Finally, meteorological data should be obtained for the area. Soil Samples should be taken under and up to three feet from the body. Peak high and low temperatures should be sampled over several days in the exact location of the body(Haskell,Lord and Byrd 2001).

Once the tempeatures have been record the insects on the body can be examined and samples taken. Samples of eggs and larvae from flies can be collected put into 75% ethyl acetate and then fixed an 80% ethyal alcohol(Haskell,Lord and Bryd, 2001)

Live sample of larvae at various stages can be collected and stored for transport in sandwich bags or aluminum foil pouches filled with sand or vermiculite(Haskell, Lord and Bryd 2001). Care should be taken not to use commercially available potting soil or playsand both of which contain insecticides.

Live samples can be raised in a small aquarium with a temperature control of some sort. The maggots themselves can be kept in a low sided dish with beef liver as a food source. Cotton balls soaked in water can be provided as a source of water. The aquaruim should have a base of sandy material for the maggots to burrow in during the pre-pupal stage(Haskell,Lord and Byrd 2001).

What Insect Evidence Tells an Investigator

The most commonly understood use of insects evidence is the use of fly larvae to determine the P.M.I. However, by identifiying the species of insects and the stage of developmental so much more can be determined.

Urban species in a rural environment or vice versa can indicate that the body has been moved from one setting so another. Similarily the identification of the species can indicate an indoor rather than outdoor death (Anderson, 2000). This does not mean that Blowflies and Fleshflies do not colonize bodies indoors. Some species rarely enter indoor settings and may be abscent from the samples obtained. Death indoors, in a vehicle or in water does not stop colonization but does effect the order, family and species of insects which may be recovered (Anderson, 2001)(Erzinclioglu, 2000)(Goff, 2000).

Each type of insect colonizes a body in accordance with its own preference for shade or sunlight, wet or dry conditions, urban or rural and many other environmental conditions. In retrieving these insects an investigator can read the story of where the body has been and for how long.

Skuttle flies colonize buried bodies and may pass through several life cycles underground(Erzinclioglu, 2000). The presence of Skuttle fly larva on a body found on the surface may indicate a previous burial. Likewise blowfly larvae on a buried body may indicate burial after some time on the surface.

Lack of insect activity can indicate storage at freezing temperatures or enclosure in an air tight container. Sealing a body in a plastic garbage bag, a vehicle, a rug and/or burning it does not deter colonization (Anderson, 2001).

Insects in the soil around a body can be very usefull in determining whether the body has decomposed in that location. Over time the normal types of bacteria and insects will be replaced by those associated with decomposition(Goff,2000). By sampling the soil an investigator can determine whether this is a primary or secondary site of death.

Finally, insects not normally associated with bodies may be found in the soil above a buried body. For example, Sphinx moth larvae found in and area central Alberta typically drop from the vegetation on which they feed and burrow into the soil in August and September. If pupa or pupal casings are found in the soil above a buried body then the investigator could conclude that the body was buried before August(from research done by the author fall 2003). Sphinx moth larvae seek out disturbed soil in which to burrow and would be expected to be found in areas of burials for this reason.

Conclusion

There are infinate possibilities for the use of insects in forensic investigations. Every insect tells a story about the conditions the body has passed through and the places it's been. It is essential that personnel recognize the importance of this evidence. Preservation of evidence can only occur when it is recognized as evidence. Once lost the only witnesses to the processes of death are gone and silent forever.

References

1. Anderson G. S. (2001). Insect Succession on Carrion and its Relationship to Determining Time of Death. In Byrd J.H. & Castner J.L. (ed.), Forensic Entomology: The Utility of Arthropods in Legal Investigations (pp.143-175) . Boca Raton , Florida : CRC Press .
2. Baden M.M. & Hennesse J. (1989). Unnatural Death: Confessions of a Medical Examiner. Toronto: Random House of Canada.
3. Baden M. & Roach M. (2001). Dead Reckoning : The New Science of Catching Killers. New York, N.Y.: Simon & Schuster.
4. Bryd J.H. (2001). Laboratory Rearing of Forensic Insects . In Bryd J.H. & Castner J.L. (ed.), Forensic Entomology: The Utility of Arthropods in Legal Investigations (pp. 121-140).: Boca Raton, Florida. CRC Press.
5. Erzinclioglu Z.Y. (2000). Maggots, Murder and Men . New York, N.Y.: St. Martin's Press.
6. Goff M.L. (2000). A Fly for the Prosecution. Cambridge, Mass.: Harvard University Press.
7. Haskell N.H., Lord W.D. and Bryd J.H. (2001). Collection of Entomological Evidence during Death Investigations. In Byrd J.H. and Castner J.L (ed.) Forensic Entomology: the utility of Athropods in Legal Investigations. (pp. 81 - 120). Boca Raton, Florida : CRC Press.
8. Knight B. (19??). Simpson's Forensic Medicine. (11th ed.): Oxford Uiversity Press.
9. Lane B. (1992). The Encylopedia of Forensic Science. London, England: Headline Book Publishing PLC
10. Saferstein R. (2004). Criminalistics: An Introduction to Forensic Science. ( 8th ed.). Upper Saddle River, N.J. : Pearson Education Inc..
11. Stoerkay M. (2000) Introduction to Forensic Entomology. Retrieved December 1, 2003 from http://folk.uio.no/mstarke/forens_ent/tables_development.html
12. Thomas P. (1995). Talking Bones: The Science of Forensic Anthroplogy. New York, N.Y. : Facts on File.
13. West I. & Stern C. (1996). Dr. Ian West's Casebook: the Chilling Investigations of Britain's Leading Forensic Pathologist. Boston, Mass.: Little & Brown Co.

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