Forensic Entomology A Tool In Death Investigations Biology Essay


When a body is found it is assumed that whoever found it was the first there. But long before any person discovered the remains insects and their arthropod relatives occupied it. These bugs have been found useful in the aid of determining time of death and even in other important legal elements surrounding the case (Arnold, 2002).

This field of study falls upon a Forensic Entomologist, who uses their knowledge of insects and their arthropod relatives to assist the legal system and help find the who, what, where and how (Arnold, 2002). The expansive field of forensic entomology is commonly broken down into three general areas: medico-legal, urban, and stored product pests. 

The medico-legal section focuses on the criminal element of the legal system and deals with the necrophagous (or carrion) feeding insects that characteristically swarm human remains (Catts, 1990). The urban aspect deals with the insects that affect man and his direct environment (Catts, 1990). This area has both criminal and civil workings as urban pests may feed on both the living and the dead (Catts, 1990). The damage caused by their mandibles as they feed can create markings and wounds on the skin that may be misinterpreted as preceding abuse (Catts, 1990). All this information can then be used to support or oppose witness and the accused statements, and can also help lead investigators to the actual scene of the crime (Catts, 1990).

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Whereas the use of forensic entomology in investigations has proven to be greatly worthwhile, especially in determining time of death, it also has definite limitations. The study of insects and their life cycles as they relate to forensic issues is being relied upon more and more as it time and again demonstrates itself to be valuable to death investigations.

Determination of the postmortem interval (PMI) is a vital and essential step in any death scene investigation when a death is not witnessed by an individual. The estimation of the time of death is defined as the length of time between death and when the corpse is discovered by someone (Hamilton, 2008).

At the arrival of death, the medical parameters to establish the origin, mode, and time since death begin to deteriorate. With the development of time and soft tissue decomposition, a PMI determination by a pathologist or coroner becomes more complicated and less precise (Bass 2003).

In death investigations, the finding of a corpse are often belated (i.e., days, weeks, months or years) because of the suspect trying to conceal what they have done or a death taking place in a remote area such as wooded or even near major bodies of water.

In such cases, the role of the entomological evidence associated with the corpse becomes critical for PMI determination (Hamilton, 2008). In death investigations when foul play is alleged or the body found is of unknown identity (i.e. missing person), a PMI determination is essential for narrowing the fields of suspects and for giving the corpse a name to the face (Hamilton, 2008).

Many diverse tests can be preformed to establish postmortem interval, including the use of body temperature ("Trio of Stopwatches"), forensic entomology, and forensic botany (the use of plant life) (Carnaby, 1974).

After an individual has expired, their body will slowly cool to the surrounding temperature, whether the ground or room their body is discovered in (Camaby, 1974). Before the body reaches the corresponding surrounding area, it is possible to calculate the postmortem interval by extrapolating back from the original average body temperature, which is 98.6 degrees Fahrenheit (Carnaby, 1974).

The "Trio of Stopwatches" or "Death's First Known Clocks" are broken into three categories and is the standard for determining time of death used today. The first is Livor mortis; a pooling of blood in capillaries that is gravitationally dependent and can be observed in the first 1-2 hours after the death has occurred. After which the body will become fixed between 8-12 hours. The second stage is known as Algor mortis. This is a cooling of the body from a normal temperature, which then decreases 1.5 degrees Fahrenheit per hour. So depending on when the body is discovered the coroner, or medical examiner will conduct a liver temperature by placing a probe inside the chest above the liver. The last stage is known as Rigor mortis. This is where the muscles stiffen, due to chemical changes such as lactic acid build up. Eventually the muscle fibers break up and the rigor dissipates (Walker, 2005).

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There are those times when normal practices for determining postmortem interval are not accurate or cannot be used. That is when a Forensic Entomologist is called into determine the postmortem interval or "time since death" in the homicide investigation (Hamilton, 2008).  More specifically, forensic entomologists can give an approximation of the postmortem interval based on the age of the insects present at the crime scene and in the body itself (Hamilton, 2008). 

This entomological based evaluation is commonly called the "Time Since Colonization" or the time since the first insect populated the corpse (Arnold, 2002). 

With these known facts about Forensic Entomology and the older practices still used today, this is why Forensic Entomology should become the new standard for determining Post Mortem Interval (PMI) in criminal cases because the use insect science to determine time of death is easier and more accurate.

A Forensic Entomologist can employ a number of diverse techniques in the determination of postmortem interval including: species succession (the succession of insects to the body after death has occurred), larval insect weight, larval insect length, and a more technical method known as the accumulated degree hour method which can be precise if the necessary data is available (Gennard, 2007).

When a person dies, insects begin to take over the body, but in a predictable sequence, also known as insect succession, this is how a Forensic Entomologist figures postmortem interval out, as well as other important factors surrounding the identity of the individual and cause of death (Bass, 2003). Blow flies can invade a corpse within minutes of death, and flesh flies follow close behind them, this is due in part of both sets of flies' ability to smell death, even from miles away.

Once the flies have had their fill and the body begins to deteriorate through decomposition, beetles of all types will flock to the corpse. Taxidermists use specific beetle, called a dermestid beetle, to strip bone of all flesh and muscle, these beetles do just that when they take up residency in the body (Greenberg, 2005). Over time more flies will gather, including the everyday normal house fly. Eventually, as the corpse dries from decomposition and exposure to the environment, hide beetles and clothes moths find the remains and begin their part in the decomposition (Greenberg, 2005).

Forensic entomologists gather samples of all the insects present at the time the body is discovered. They need to make sure they take as many types of every species at their latest stage of development in order to accurately predict postmortem interval (Haglund, 2002). Because arthropod development is linked directly to temperature, a good Forensic Entomologist will collect the weather data from a local source to help with factoring PMI (Haglund, 2002).

In the lab, a Forensic Entomologist must properly identify each insect to their species, as well as figure out at what stage of development they are at when collected from the corpse (Haglund, 2002). Since identification of maggots can be difficult, the entomologist usually raises some of the maggots to adulthood to confirm their species (Kunich, 2002).

Blow flies and flesh flies are the most useful crime scene insects for determining the postmortem interval, or time of death. Through laboratory studies, scientists have established the developmental rates of necrophagous species, based on constant temperatures in a laboratory environment (Kunich, 2002). These databases relate a species' life stage to its age when developing at a constant temperature, and provide the entomologist with a measurement called accumulated degree days, or ADD, which represents physiological time (Kunich, 2002).

Using the known ADD, one can then calculate the likely age of a specimen from the corpse, adjusting for the temperatures and other environmental conditions at the crime scene (Kunich, 2002). Working backwards through physiological time, the forensic entomologist can provide investigators with a specific time period when the body was first colonized by necrophagous insects (Haglund, 2002). Since these insects almost always find the corpse within minutes or hours of the person's death, this calculation reveals the postmortem interval with good accuracy (Kunich, 2002).

Studies of insects have provided evidence that an insect requires a given amount of thermal energy (heat) to develop from one stage to the next in its life cycle (Kunich, 2002). The total thermal energy (ambient temperature multiplied by hour or day) is called the accumulated degree hour (ADH) (Kunich, 2002). Forensic entomologists calculate ADH in order to count back and estimate the age of the insect or the time when the eggs were first deposited (Kunich, 2002).

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Understanding the stages of decomposition, the colonization of insects, and factors that may affect decomposition and colonization are key in determining forensically important information about the body (McAlpine, 1989).

Different insects colonize the body throughout the stages of decomposition. These stages are categorized into fresh, putrefaction, black putrefaction, butyric fermentation, and dry decay. Identifying which insect present can be useful in determining what stage of decay the body is in, and therefore determine time of death (Arnold, 2002).

Some insects are only found in certain regions and this information can help determine if a body has been moved by the type of maggots feeding on the body. The environment surrounding the body is also very important to consider when using insect evidence. Insects, such as the coffin fly Megaselia scalaris, are nearly always found on bodies that have been buried. Using evidence that is very species specific can reveal a great deal of information about a body (Arnold, 2002).

The fresh stage is the first phase of decomposition that begins approximately four minutes after death and lasts around three days until putrefaction. Autolysis initiates decay as digestive enzymes in the body begin to break down nearby cell membranes and digest the internal organs. The acidity in the body also increases due to lack of oxygen in tissues. The liver, which has high enzyme content, releases nutrient-rich fluids into the body. At this time, the body has little to no odor. Insects will feed between the muscles during rigor mortis because of the lactic acid produced from the breakdown of the muscle (Arnold, 2002).

The first necrophages observed on the body after death is the Calliphorid flies. The female green bottle fly (Lucilia cuprina in the United States) is generally the first to colonize the body; the second is the Hairy Maggot Blowfly, Chrysomya rufifacies. Other fly families generally present during this stage are Sarcophagidae, Piophilidae, and Muscidae (Arnold, 2002).

Predators of both immature and adult flies are prevalent at the beginning stages of decomposition. These are important factors to consider when determining the insect colonization time. Chrysomya rufifacies, the second fly to colonize, facultatively predates on fly larvae in its second and third larval instar. Saprinus pennsylvanicus, is a predaceous beetle in the United States that feeds on the early fly larvae (Arnold, 2002). Parasitic wasps, fire ants, and other insects also predate on fly larvae. The parasitic wasps (such as the Chalcidae) use the flies' pupae as a nest for their eggs; upon hatching, the wasp larvae feed on the host maggots or pupae (Arnold, 2002). Once the wasp larvae have killed the host, they use the fly remains to pupate into mature wasps (Arnold, 2002).

Following initial decay, approximately 4 to 10 days after death, the body begins the second stage of decay called putrefaction. During putrefaction, bacteria and other microorganisms continue to anaerobically metabolize the soft tissues of the body (Arnold, 2002). This breakdown of tissue releases gases into the body and causes an increased internal pressure, which results in a bloated corpse. As a result of the gas accumulation and the progression of decay, the corpse begins to emit a smell. This smell is a putrid odor that tends to attract an increasing number and various species of flies, beetles, and other arthropods (Arnold, 2002).

During putrefaction, maggot habitation begins as flies continue to arrive and oviposit in the orifices and natural openings of the corpse (Arnold, 2002). Moreover, the first blowflies that arrived on the corpse during initial decay have produced larva that are in their first and second instars. Clown beetles from the family Histeridae such as Hister quadrinotatus and Hister seqkovi in the United States are also attracted during the bloat stage and can be found underneath the decaying body (Arnold, 2002).

Black putrefaction, also known as active decay, happens about 10 to 25 days after death. A good indicator of black putrefaction is a strong odor and black coloration of the corpse (Arnold, 2002).

The bloating begins to subside as the skin starts to peel back and break from the large amount of gas and fluids produced. This makes the body appear flat. The breaking of the skin allows insects and other consumers better access to the inside of the body (Arnold, 2002).

At this stage, the maggot mass starts to decrease as most of the maggots have reached their third molt and will start to leave the body in order to pupate in the soil. These maggots may live along side the larvae and adults of carrion beetles (family Silphidae) and the skin beetles (family Dermestidae) (Arnold, 2002).

Beetles usually make up the most of the population of insects on the body during black putrefaction (Bass, 2003). This beetle mass can vary in the types of families, making it hard to designate a certain beetle family to this stage of decay (bass, 2003). Parasitic wasps continue to prey on these maggots and many generations of mites feed on the fluids let out by the body (Bass, 2003).

Butyric fermentation is the name of the fourth stage of decomposition. This fermentation process usually starts around 20-25 days after death. The body has finished flattening out from the previous putrefaction stage and the flesh and fluids on the body are slowly drying up. Butyric acid produces a distinct smell which is a component in breaking down the fluids in the body. This progression attracts different species of fauna to the carrion (Arnold, 2002).

Maggots and other insects that feed on soft flesh are unable to feed due to the drying out of the body; beetles and other insects with similar chewing mouth appendages are able to crush and chew the tougher segments of the dead body (Bass, 2003).

At this time, most of the beetles are in the larval stage. Other insects such as cheese skippers and some parasitic wasps are also present. Hide Beetles from the family Trogidae and Carcass Beetles from the family Dermestidae are among the last beetles and generally the most common beetles seen during this fermentation period (Bass, 2003). The Hide Beetles as well as the Carcass Beetles are not predacious and are found on the tougher portions of the body such as bone and ligaments (Bass, 2003). Also, they are the only beetles that are capable of using an enzyme to break down proteins such as keratin. The cheese fly from the family Piophilidae, is attracted to the smell produced by butyric acid (Arnold, 2002).

The final stage in animal decomposition is dry decay. Dry decay begins between 25 and 50 days after death and can last up to a year. The only remnants of the body are dry skin, hair, and bones. Mummification occurs when dehydrated tissues lack the nutritional value to be broken down by other means (Bass, 2003). This is observed in dry heat or low humidity environments and can last for decades. The bones go through a process termed diagenesis that changes the organic to inorganic constituent ratio within the bones. Any odor exuding from the body at this point is merely the natural flora and fauna associated with the area (Bass, 2003).

The fauna seen at this stage is limited. Bacteria feed on the hair and skin of the body, attracting many mites (Arnold, 2002). Certain tineid moths also feed on the remaining hair (Arnold, 2002). Silphidae, a family of carrion beetles, may still be present during this stage (Hamilton, 2008). They typically arrive early in decomposition and stay until dry decay feeding on the larvae of other insects. Beetles of the family Nitidulidae can also be seen inhabiting the body (Hamilton, 2008). The normal soil fauna of the environment will begin to return during this stage (Hamilton, 2008).

Currently, it is now possible to use DNA technology not only to help determine insect species, but to recover and identify the blood meals taken by blood feeding insects (Walker, 2005).  The DNA of human blood can be recovered from the digestive tract of an insect that has fed on an individual (Walker, 2005).  The presence of their DNA within the insect can place suspects at a known location within a definable period of time and recovery of the victims' blood can also create a link between perpetrator and suspect (Walker, 2005).

The insects recovered from decomposing human remains can be a valuable tool for toxicological analysis.  The voracious appetite of the insects on corpses can quickly skeletonize the remains (Walker, 2005).  In a short period of time the fluids (blood and urine) and soft tissues needed for toxicological analysis disappear (Walker, 2005).  However, it is possible to recover the insect larvae and run standard toxicological analyses on them as you would human tissue (Walker, 2005).  Toxicological analysis can be successful on insect larvae because their tissues assimilate drugs and toxins that accumulated in human tissue prior to death (Walker, 2005).

Some insects have evolved a gradual or "paurometabolous" development in which there is an egg that hatches into an immature or "nymph", which resembles the adult form, but is smaller and lacks wings (Hamilton, 2008).  In the forensically important insects, this is best represented by the cockroaches (Hamilton, 2008). 

However, most forensically important insects undergo a complete or "holometabolous" development (Gennard, 2007). There is an egg stage (except for a few insects such as the flesh flies that deposit living larvae) which hatches into a larval form and undergoes a stepwise or incremental growth (Gennard, 2007). This pattern is caused by the successive molts (shedding of the outer skin that has become too small) that the larva must undergo before it finally enters the inactive pupal stage. The pupa is simply the hardened outer skin of the last larval stage and the adult will develop inside of this protective skin (Gennard, 2007).

In the insects that undergo complete development, the larval stages appear quite different from the adult form.  The larvae of flies (order Diptera) that are commonly recovered from decomposing human remains lack functional legs, and the body of many species appears cream colored, soft-bodied, and quite "maggot-like" (Gennard, 2007). 

Once the larva or "maggot" is through feeding it will migrate away from the corpse in order to find a suitable site to form the pupal stage and develop (Gennard, 2007).  The pupae of blow flies are often overlooked, as they closely resemble rat droppings or the egg case of cockroaches (Gennard, 2007). The pupal stage is an extremely important stage to the forensic entomologist and a thorough search should be made for the presence of pupae at any death scene (Gennard, 2007). 

If the adult insect has not emerged, the pupa will appear featureless and rounded on both ends. If the adult insect has emerged, one end will appear as if it has been cut off, and the hollow interior will be revealed. Most adult blow flies appear a metallic green or blue and are easily recognizable (Gennard, 2007). 

The beetles (order Coleoptera) are one of the largest groups of animals and they also undergo complete development (Hamilton, 2008). Because of their development the larvae appear very different from the adult form. Although the larvae or "maggots" of a large number of blow fly species may look almost identical; the larvae of beetles may look very different from one species to the next (Hamilton, 2008).

Beetle larvae recovered from corpses can be easily differentiated from maggots as they have 3 pairs of legs and the maggots found on decomposing remains will not have any legs (Hamilton, 2008). Once a larva has been identified as that of a beetle, further field identification can be accomplished because of the wide diversity of larval forms. The bodies of beetle larvae may range from almost white, robust, and hairless to dark brown, slender, and quite hairy. Others may appear almost black and have armored plates on their back (Hamilton, 2008).

Forensic Entomology PMI is a better choice than the "Trio of Stopwatches" technique still used today because when it comes to determining time of death insects are more of an exact science.

The classical method of estimating time of death is the rate method, or "Trio of Stopwatches," which measures postmortem (after death) stages and the types of transformation a body undergoes such as cooling rates (Algor mortis), stiffening (rigor mortis), initiation and duration, postmortem lividity (discoloration stains), degree of putrefaction, adipocere (body fat saponification), and maceration (tissue softening due to the presence of liquid) (Bass, 2003).

Not all these stages take place in a single cadaver. Adipocere, for instance, is not common in most male adult corpses. It occurs most often in women or obese adult individuals and children, requiring enough humidity or the presence of water to take place. The process of maceration occurs at known rates in fetuses that died in the womb. Stomach contents can reveal the stage of digestion of the last meal at the time of death (Bass, 2003).

The time of onset and rates of each postmortem transformative event are also subjected to variations originated by existing chronic diseases, types of medication, and individual metabolic characteristics (Bass, 2003). These variables are known as endogenous factors. For example, if the deceased individual was taking antibiotics at the time of death, the internal process of bacterial-mediated putrefaction may be delayed beyond the normal observed rates, thus masking the real PMI (Bass, 2003). This makes the old techniques for PMI determination difficult. But by using Forensic Entomology PMI can be determined even in the most difficult of decomposing cadavers.

Even when the cadaver states something different than what insects are present, it can be figured out. Because some flies prefer specific habitats such as a distinct preference for laying their eggs in an outdoor or indoor environment. Flies can also exhibit preferences for carcasses in shade or sunlit conditions of the outdoor environment.

Therefore, a corpse that is recovered indoors with the eggs or larvae of flies that typically inhabit sunny outdoor locations would indicate that someone returned to the scene of the crime to move and attempt to conceal the body (Bass, 2003).

Similarly, freezing or wrapping of the body may be indicated by an altered species succession of insects on the body.  Anything that may have prevented the insects from laying eggs in their normal time frame will alter both the sequence of species and their typical colonization time.  This alteration of the normal insect succession and fauna should be noticeable to the forensic entomologists if they are familiar with what would normally be recovered from a body in a particular environmental habitat or geographical location (Bass, 2003). The complete absence of insects would suggest clues as to the sequence of postmortem events as the body was probably frozen, sealed in a tightly closed container, or buried very deeply (Bass, 2003).

Determining time of death can be an exact science. Current methods for evaluating the time of death - such as looking at rigor mortis, loss of body heat, and pooling of blood inside the body - are useful only for the first two or three days after death. With the help of science and knowing what insects are present when on a cadaver, especially knowing their life cycles, can give an investigation the evidence it needs to solve the crime faster and more accurately. Forensic Entomology is the future in Postmortem Interval (PMI) determination, and with shows like "CSI," and "Bones" showcasing the scientific facts to this field of Forensics, it will not be a dying art form and will become the standard.

In order to illustrate that Forensic Entomology is more accurate and efficient than the older practices of determining PMI an experiment can be conducted. By using pigs, which have been found to be a model corpse due to their similarities to our internal anatomy, have fat distributed similar to ours, their internal cavity is similar in size to ours and they lack fur but do have hair close to our own body hair (Catts, 1990). Another reason a domestic pig would be ideal for this experiment is because they also share an omnivorous diet close to our own which indicates that they may have a similar gut bacteria, much like our own (Bass 2003). In order to have good testing subjects the pigs must be free of disease, and have died of accidental or natural causes. Pigs that have been euthanatized may cause slight changes in the experiment itself, and therefore should not be used (Catts, 1990).

The University of Tennessee's Body Farm is always conducting experiments on pig and human cadavers. They do these experiments not only to determine postmortem interval but other forensically important factors, such as experiments to determine the outcome of different burns caused by accelerants used to dispose of a body (Catts, 1990). Searching through their experimental data, I was able to gain a direction into proving my thesis statement. I acknowledge them for helping with guidance in this experiment as well as the budget to conduct it.

During transport, the pig carcasses, four total, should be handled using heavy leather, latex, or polyethylene gloves and double bagged or covered in other ways to prevent insect colonization happening (Catts, 1990). Also delivering the cadavers and placing them into the experimental area after sunset ensures that blowflies do not begin to populate the cadavers before the experiment can begin. Blowflies do not fly at night (Catts, 1990).

To reduce the effects of two- and four-legged scavengers, the carcass is placed inside two welded-wire cages of a double-nested design (both with 1 in Ã- 1 in mesh), such that the smaller cage (60 Ã- 60 Ã- 90 cm) fits inside the larger (90 Ã- 90 Ã- 120 cm)

Cages are held together using hog rings and ringer pliers. The outer cage slides up and down on four reinforcement bars or "rebar" hammered into the ground at each corner at a depth of 30 cm. Rubber tie downs and S-hooks, with one end looped around each rebar and the other end to a tent stake, secure the outer cage to the ground at each corner.

Inside the "alley" between the four cages are four pitfall traps that are buried along the four cardinal directions (N, S, E, and W) to collect surface-active arthropods. Each pitfall trap is constructed from a 20-cm section of 10-cm diameter PVC pipe, a 1-pint wide-mouth canning jar, and a 10-cm maximum diameter plastic funnel with its stem removed.

Each PVC pipe is buried vertically with its top edge just below ground level. On each sampling day, each jar is filled 3-cm deep with alcohol, placed into the PVC pipe, then covered with the funnel.

A day marker with changeable 38-mm high, reflective metal digits, constructed from plastic wood and a mailbox address frame is attached to a stake and hammered into the ground just left of the carcass.

A weather station, in the form of a "4 by 4" by 2-m long vertical post, is installed 1 m from the cages and secures a rain gauge and max/min thermometer.

Signboards on the post identify the project's director, purpose, significance, and contact information. A tripod and weighing balance to record daily weight loss of the carcass is also available.

Before starting this activity, I will alert campus security and administrators in writing of the project's starting date. I will also contact the proper authorities in concerns for the pig cadaver. Sorting, counting, and identification of arthropod specimens are the most time consuming component of this project. But proper identification of the insects collected, especially naming their Phyla, Class and other biological and entomological information is crucial for this experiment's design and outcome. Day-to-day records of arthropod counts, weather, and physicochemical changes in one or more carcasses constitute a "baseline study" for a particular region, season, and set of ecological circumstances.

In a death investigation, insects sampled from the human corpse are then matched against those from the baseline carcasses whose succession timetables are known (Bass, 2003). Some entomologists have also used species determinations from previously verified death cases to supplement and validate their baseline records (Bass, 2003).

Comparison of the baseline and corpse faunas yields an upper and lower estimate of the PMI, whose limits may converge on the same day or may be several days long (Bass, 2003). Consequently, the ability of the forensic entomologist to perform succession-based estimates of the PMl critically depends on the quality of field data from baseline studies (Bass, 2003).