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Re: The Ultimate Guide to Forensic Entomology
Introduction to forensic entomology
So, you wonder what Forensic Entomology is?
I will tell you:
Forensic entomology can be said to be the application of the study of insects and other arthropods to legal issues. It can be divided in three subfields: urban, stored-product and medicolegal. It is the medicolegal aspect that I will discuss in this document.
Medicolegal forensic entomology includes arthropod involvement in events such as murder, suicide and rape, but also includes physical abuse and contraband trafficking.
Since the earth is a predominantly arthropod world, it is not uncommon that we mere humans comes in contact with these creatures. They make the world go round, as they pollinate, eat other arthropods, eat living plants and trees, dead plants and trees, living vertebrates, dead vertebrates and vertebrate dung and urine and a lot of other things.
The feature with arthropods that are most important in medicolegal forensic entomology is that they are important carrion feeders, that is they eat dead vertebrate bodies, including man. Thus they perform a valuable recycling of organic matter in our ecosystem.
One of the first groups of insects that arrive on a dead vertebrate is usually blowflies (Diptera: Calliphoridae). Usually the female oviposits within two days after death of the vertebrate. Then the blowfly goes trough the following stadiums: egg, 1. instar larvae, 2. instar larvae, 3. instar larvae, prepupae, pupae within puparium, imago.
If we know how long it takes to reach the different stadiums in an insects life, we can calculate the time since the egg was laid. This calculation of the age of the insects can be considered as an estimate of the time of death. But even if the estimate of the insect age is correct, the death of the victim (usually) occurred before the eggs were laid. This period is quite variable and depends on temperature, time of day the death occurred, time in year the death occurred, whether the corpse is exposed or immersed in soil or water. As a general rule insects will lay eggs on a corpse within two days after the corpse is available for insects.
Insects can also be of help in establishing whether the corpse has been moved after death, by comparing the local fauna around the body, and the fauna on the body.
In some instances, movement of suspects, goods, victims or suspect vehicles can be traced with the help of insects. Insects parts, or whole insects can for example be captured in different car parts, such as in radiators or tyre treads. By identifying the insects found, and plotting the distribution of each insect, as well as the biology of each species one can find the greatest degree of overlap, and describe the areas where the suspect has been. Many arthropods lives in close relation to carrion.
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Feb/23/2005, 10:50 pm
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SatinNLace
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Re: The Ultimate Guide to Forensic Entomology
What happens after death?
Everybody will die, that is one thing that we are absolutely certain of. What exactly is death, and what happens in the time after death? From a biological point of view, death is a process, not an event. This is because the different tissues and organs in a living body dies at different rates. We can divide death into somatic death and cellular death. Somatic death is when the individual is not longer a unit of society, because he is irreversibly unconscious, and unaware of himself and the world.
Cellular death is when the cells quits respiration and metabolism. When all cells are dead, the body is dead. But all cells do not die simultaneously, except perhaps in a nuclear explosion. Even in a victim of a car bomb, where the body becomes fragmented, individual cells will continue to live for a few minutes or longer. Different celltypes can live for different times after cardiac arrest. Nervous cells in the brain are particulary vulnerable to oxygen deprivation and will die within 3-7 minutes after complete oxygen deprivation.
In many countries brain stem death is considered legal death, even if the body is kept alive with artificial means. This opens up for organ transplants of heart, liver and lungs, where the donor has to be dead.
What we will discuss in this text, is what happens after cardiac arrest in a body wich is lying dead outdoors (or indoors).
One of the first things that happens after death is that the temperature in the body starts to drop. Before the temperature in the body core drops, a temperature gradient must be established from the outside to the core. After this gradient has become established the body temperature will drop with a theoretically predictably rate. This fact can be used to estimate time of death. Even if one succeeds in predicting when the temperature of the body core was 37 degrees Celsius, one has to remember that the time it takes to form the temperature gradient will vary from individual to individual, and will vary from almost no time, to over two hours.
After the onset of putrefaction (about two days after death) the body temperature will increase again, due to the metabolic activity of the bacteria and other decomposing organisms.
Rigor mortis
Rigor mortis is a well known phenomenon, and is due to a complex chemical reaction in the body. In the living body muscles can function both aerobic and anaerobic. In the dead body muscle cells can only function anaerobically. When muscle cells work anaerobically the end product is lactic acid. In the living body, lactic acid can be converted back, by means of excessive oxygen uptake after an anaerobic exercise. In the dead body this can not happen, and the breakdown of glycogen in the muscles leads irreversebly to high levels of lactic acid in the muscles. This leads to a complex reaction where actin and myosin fuses to form a gel. This gel is responsible for the stiffness felt in the body. This stiffness will not be over before decomposition begins.
As rigor mortis is due to a chemical reaction, the reaction time is due to temperature and the initial concentrations of lactic acid. High metabolic activity in the time just before death, for example when running, leads to higher levels of lactic acid, and shorter time for the rigor mortis to develop. Higher environmental temperature also leads to a shorter reaction time.
In temperate regions the following rules of thumb can be used in estimating death, but must be used with caution:
Warm - Not stiff - Not dead more than three hours
Warm - Stiff - Dead between 3 to 8 hours
Cold - Stiff - Dead between 8 to 36 hours
Cold - Not stiff - Dead in more than 36 hours
Rigor mortis should never be the only basis for estimating time of death.
After death, a lot of internal organisms in the intestine will become very active. Escherishia coli and others will start multiplying, and the decomposition begins. First the intestine and the blood will be attacked, and when gas formation and other things leads to rupture of the intestine other organs will be attacked.
Organs starts decomposing at different times after death, and may also be used in estimating time of death.
The decomposition of a body can be divided into several stages, even if the duration of each stage will vary a lot:
1) Initial Decay
The cadaver appears fresh externally but is decomposing internally due to the activities of bacteria, protozoa and nematodes present in the animal before death
2) Putrefaction
The cadaver is swollen by gas produces internally, accompanied by odour of decaying flesh
3) Black putrefaction
Flesh of creamy consistence with exposed parts black. Body collapses as gases escapes. Odour of decay very strong
4) Butyric fermentation
Cadaver drying out. Some flesh remains at first, and cheesy odour develops. Ventral surface mouldy from fermentation
5) Dry decay
Cadaver almost dry; slow rate of decay
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Feb/23/2005, 11:00 pm
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SatinNLace
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Re: The Ultimate Guide to Forensic Entomology
Estimating time of death with Forensic Entomology
After the initial decay, and the body begins to smell, different types of insects are attracted to the dead body. The insects that usually arrives first is the Diptera, in particular the blow flies or Calliphoridae and the flesh flies or Sarcophagidae.
The females will lay their eggs on the body, especially around the natural orifices such as the nose, eyes(2), ears(2), anus, penis and vagina. If the body has wounds the eggs are also laid in such. Flesh flies do not lay eggs, but deposits larvae instead.
After some short time, depending on species, the egg hatches into a small larvae. This larvae lives on the dead tissue and grows fast. After a little time the larva molts, and reaches the second larval instar. Then it eats very much, and it molts to its third instar. When the larvae is fully grown it becomes restless and begins to wander. It is now in its prepupal stage. The prepupae then molts into a pupae, but keeps the third larval instars skin, which becomes the so-called puparium. Typically it takes between one week and two weeks from the egg to the pupae stage. The exact time depends on the species and the temperature in the surroundings. A table of life histories to some species of blow flies and flesh flies are available here, and an illustration of the blowfly life cycle is available here.
The theory behind estimating time of death, or rather the post mortem interval (PMI for short) with the help of insects are very simple: since insects arrive on the body soon after death, estimating the age of the insects will also lead to an estimation of the time of death.
How to estimate age of blowfly eggs, larvae, pupae and adults
Eggs:
When blow flies oviposit, their eggs has come very short in their embryonic development. The eggs are approximate 2 mm in length. During the first eight hours or so there is little signs of development. This changes after that, and one can see the larvae through the chorion of the egg at the end of the egg stage. The egg stage typically lasts a day or so.
Larvae:
The blowfly has three instars of larvae. The first instar is approximately 5 mm long after 1.8 days, the second instar is approximately 10 mm long after 2.5 days, the third instar is approximately 17 mm long after 4-5 days. Identifying the right instar is the easiest part, and is done relatively easy based on size of larvae, the size of the larva's mouth parts and morphology of the posterior spiracles. The time it takes to reach the different instars depends very much on microclimate, i.e. temperature and humidity.
Prepupae:
At the end of the third instar the larva becomes restless and starts to move away from the body. The crop will gradually be emptied for blood, and the fat body will gradually obscure the internal features of the larvae. We say that the larva has become a prepupa. The prepupa is about 12 mm long, and is seen 8-12 days after oviposition.
Pupa:
The prepupa gradually becomes a pupa, which darkens with age. The pupa which are about 9 mm in length are seen 18-24 days after oviposition. The presence of empty puparia should therefore tell the forensic entomologist that the person in question has been dead in more than approximately 20 days. Identification can be done based on the remaining mouth parts of the third instar larvae.
A more precise way to determine age of larvae and eggs is the use of rearing. For example: the body is found with masses of eggs on it, none have hatched. How long time is it since the eggs was oviposited? Note the time of the discovery, note the time when the first 1. instar larvae occur. Subtract the first occurrence time with the discovery time, call this time A. Rear the blow flies to adults, let them mate, let them lay eggs on raw beef liver under conditions similar to the crime scene, take the time from oviposition to the first occurrence of 1. instar larvae. Call this time B. By subtracting B-A, one gets C, which is an estimate of the time since oviposition to discovery. Similar calculations can be done for other instars as well. If one has good base-line data from before under different temperatures and for different species, one only needs to rear the flies to a stage where they can be identified, and that is the third stage or the adult stage.
One important biological phenomenon that occurs on cadavers are a succession of organisms that thrive on the different parts. E.g. beetles that specialize on bone, will have to wait until bone is exposed. Predatory rove beetles or parasites that feed on maggots will have to wait until the blow flies arrive and lay their eggs.
The succession on cadavers happens in a fairly predictable sequence and can be used in estimating time of death if the body has been lying around for some time. Here is a table over a succession experiment on guinea pigs performed by Bornemizza in 1957.
There are several things to note about this table:
The first groups to arrive is blow flies, followed shortly by staphylinids. As putrefaction develops, more groups arrive at the scene, with most groups present just before the body is drying out due to seepage of liquids. After the body is drying out, dermestids, tineids and certain mites will be the dominant animal groups on the body, and blow flies will gradually vanish. Note also how the fauna changes in the soil. This can also be used to estimate time since death.
Succession data can be incorporated in a database, and when the forensic entomologist investigates a case, he can use the taxa found on the body as input, and get an estimate of the time of death as output.
Day number
Taxa 1 2 3 4 5 6 7 8 9 10
A 1 1 1 0 0 0 0 0 0 0
B 0 0 1 1 1 1 0 0 0 0
C 0 0 0 0 1 1 1 1 1 1
D 0 0 0 0 0 0 1 1 1 0
E 0 0 0 0 0 0 0 0 1 1
The hypothetical table above shows the presence (1) and absence(0) of five different taxa (A, B, C, D and E) over ten days. The tabulated data is usually obtained from decay studies done on pigs or other animals.
Let's say the investigator finds taxa C, D and E on the remains. From the table above, we can see that taxa C occurs on the cadaver from day 5 to day 10, and taxa D from day 7 to day 9, and taxa E from day 9 to day 10. By studying the overlap, the entomologist estimate the PMI to be about 9 days.
Several insects are specialized in living in very decayed dead bodies. One example is the cheese skipper, Piophila casei, where the larvae usually occurs 3-6 months after death. The cheese skipper is a well known pest of cheese and bacon worldwide, and has a cosmopolitan distribution. Adult cheese skippers may occur early after death, but larvae occurs later. The earliest observation on human remains are when the body is two months, and this was under excellent summer conditions. In 1898, Potter examined 150 graves, and found remains of P. casei in ten of them. These graves were from three to ten years old and three to six feet deep.
In temperate regions dead bodies often appear in spring, after the snow is gone. The forensic entomologist and the forensic pathologist must then try to determine whether the death occurred during the winter or before the snow set in. If the death occurred before November, it is possible to find dead insects in and on the body. By analyzing the dead insect fauna, and estimating when the insects probably died (this can be found by looking at meteorological records). Another hint is when the different adults stop flying before the winter. For example: here in Norway, we have had some cases where the bodies have been found in the spring. In one case we found dead third stage blow fly larvae in the back of the mouth. The blow fly larva was of an species that is flying from May to October. It was from this concluded that the eggs probably was laid during October, and since it was relatively few larvae, probably late in October. In another case, we found several live insects on a dead body, and also many dead third stage larvae. The dead larvae was found on the stomach, the arms, the shoulders, and inside the head. We concluded that the live insects had colonized the dead body in the spring, and that the dead larvae had died during the winter. Based on the widespread occurrence of the larvae, we had to say it was likely that the body was colonized before October, probably in September.
If the death occurred in the winter things become difficult in outdoor settings, as very few insects are active in the winter. It is reported that larvae of the winter gnat, Trichocera sp. can develop on carrion in the winter. By estimating the age of these larvae, if present, it could be possible to estimate the PMI.
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Feb/23/2005, 11:09 pm
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SatinNLace
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Re: The Ultimate Guide to Forensic Entomology
Finding the cause of death using forensic entomology
In a crime investigation, there is not only of great interest to find out when a victim died, but also of interest to find out how the victim died, as this can be used to find the killer.
In some instances the insects themselves are the killers, in other instances the insects occuring on the carrion can shed a light on what happened when the victim died.
Wasps and bees, for example, can inject venom through a sting. Some people are sensitive and allergic to these venoms, and can die if not treated in time. One other important aspect of wasps and bees are their effect on drivers. Many car accidents are probably caused by some wasp, bee or bumble-bee coming through the window, causing hysteria, or a distraction from the road leading to a collision or other accidents. In some cases wasps and bees has been used as murder weapons, as in case where some parents had shut their infant in a room full of wasps, in order to get rid of it.
Poison can be traced in blood, urine, stomach contents, hair and nails. One other important source is maggots occuring on a corpse. After a while it will be impossible to sample stomach contents, urine and blood from the dead body, but it will still be possible to sample from maggots, empty puparia or larval skin cast. The following list of chemicals has to my knowledge been traced in maggots:
* Triazolam
* Oxazepam
* Alimemazine
* Chloripriamine
* Phenobarbitol
* Malathion
* Mercury
* Amitriptyline
* Nortriptyline
* Cocaine
* Phenycyclidine
* Heroin
Many of these chemicals will also influence the life-cycle of the maggot. For example will high dosages of cocain accelerate the development of some sarcophagids. Malathion, an insecticide, is commonly used in suicide, and is usually taken orally. Presence of malathion in the mouth may lead to a delay in the colonisation of the mouth. Presence of amitriptyline, an antidepressant, can prolong the developmental time with up to 77 hours, at least in one species of Sarcophagidae. Knowledge of drug use in the victim is therefore important not only in finding the death cause, but also in estimating the time of death.
The sites of blowfly infestation on the corpse may be important in determining the cause of death, or at least in reconstruction of events prior to death. For example: if there have been trauma or mutilation of the body prior to death, this may lead to heavy infestation of other body parts than the usual sites when the victim is not mutilated. Under a knife attack, it is usual to guard oneself with arms in front of thorax and head. This may lead to injury on the lower part of the arm. After death, blowfly may oviposit in these wounds.
The usual sites of oviposition on dead humans are natural openings. Even here there is preference. Blowflies will most often lay their eggs in the facial region, and more seldom in the genitoanal region. If there is a sexual assault prior to death, leading to bleeding in the genitoanal region, blowflies will be more likely to oviposit in these regions. Therefore, if there is observed blowfly activity in the genitoanal region, one can start to suspect a sexual crime. This must of course be corroborated with other evidence as well. The interpretation of maggots in the anogenital region becomes very fuzzy after a few (4-5) days, as eggs will be oviposited in this region during the course of decay in the natural course of decomposition.
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Feb/23/2005, 11:11 pm
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SatinNLace
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Re: The Ultimate Guide to Forensic Entomology
Has the body been moved after death?
After death, a succession of fungi, bacteria and animals will colonize the dead body. The substrate on which the body is lying will also change over time. Leakage of fluids from the dead body will lead to the disappearance of certain insects, and other insects will increase as the time goes. A forensic entomologist can then look for how long the body has been there by looking at the fauna at the body, and also estimate the time the body has been lying there by sampling soil insects underneath the dead body. If there is a difference in the estimates, and the analysis of the soil suggests a short PMI, and the analysis of the body fauna suggests a longer PMI, one can suspect that the body has been moved. One can also see that a body has been lying at a particular place long time after the body has been removed, both by botanical means, and by analysis of the soil fauna.
Some times dead bodies are found in concealed environments, where blowflies have no access. If there is blowflies, it means that the body has been moved there. An example of this is given in case history no. 20. Some Calliphorids are heliophilic, that is, they prefer to lay their eggs on warm surfaces, which means that they usually occur where the bodies lies in sunny places. Other blowflies prefer shade. For example, Lucilia species prefer sunlight, and Calliphora prefer more shady conditions. Some species are synanthropic and occurs in urban areas, other species are not synanthropic and occurs in rural areas. Calliphora vicina is a synantropic fly, very common in cities, and Calliphora vomitoria is a more rural species.
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Feb/23/2005, 11:12 pm
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SatinNLace
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Re: The Ultimate Guide to Forensic Entomology
Common arthropods occurring on dead bodies
Acari
The Acari, or mites as they also are called, are small organisms, usually less than a mm in length. Mites occur under the dead body in the soil, during the later stages of decay. Many mites are transported to the body via other insects, such as flies or beetles. Other mites are soil dwelling forms which can be predators, fungus feeders or detritus feeders. Most species will be found in soil samples from the seepage area under the body.
Aranea
The Aranea or spiders are predators on insects occurring on bodies. No species is specific to the carrion fauna, and will have limited or no value in estimation of the PMI.
Diptera
The order diptera contains insects with one pair of wings, the second ones modified to halteres. About 100,000 species are known to science, many more awaits discovery. Among the flies we find many members of the carrion fauna. The larvae of flies lives in very different habitats, also aquatic.
NEMATOCERA
Trichoceridae
Trichocera sp.
or winter-gnats as they also are called because the common species Trichocera regelationis, T. saltator, T. maculipennis, etc, fly abundantly in the winter months, although they occur at lower frequencies throughout the year. The adults resemble small crane-flies. The larvae are saprophagous and feed on decaying material. Trichocerid larvae constitutes an important part of the carrion fauna during the winter months, when the blowfly fauna are missing.
BRACHYCERA
Stratiomyidae
Larvae of Hermetia illucens is recorded eating on human excrement and human remains. Usually this species occur late in the decomposing process.
CYCLORRHAPHA-ASCHIZA
Phoridae
A large family of flies, containing about 3000 species. They are minute to medium-sized (0.75-8.00 mm), dull black, brown or yellowish flies of hump-backed appearance. They are generally bristly and with a very characteristic wing venation. They run about in an active erratic manner which has earned them the popular name of scuttle-flies. They breed in a wide variety of decaying organic material, in addition some develop in fungi and others are parasites. In the larval stage some species are predators. Several genera is regularly found in vertebrate carrion e.g. Anevrina, Conicera, Diplonevra, Dohrniphora, Meopina, Triphleba and some Megaselia species.
Conicera tibialis also known as the coffin-fly because of its association with coffined bodies that have been underground for about a year. Adult C. tibialis is able to bury to a depth of 50 cm in about four days. At normal grave depths (1-2 m) temperature variation is slight, about 5 degrees Celsius, so development from egg to adult will take considerable time. Development can take place independent of season, since the body is buried at frost free depth.
Syrphidae
These are the familiar hover flies, often camouflaged as wasps or bumble bees. Among the larvae of syrphids we find the famous rat-tailed maggots. These occur in filthy water, and may occur in dead bodies.
ACALYPTRATAE
Dryomyzidae
A small group of relatively rare flies. Most species are found in moist woods. Their larvae occur in decaying organic matter.
Coelopidae
These flies are small to medium-sized, usually dark-brown or black in color, and have the dorsum of the thorax flattened. The body and legs are very bristly. They occur along the seashore and are very abundant where seaweeds have washed up. Occasionally larvae may develop in other organic matter, such as a dead body which has been lying along the seashore.
Heleomyzidae
Fairly large group of small to medium-sized often brownish flies. Adults are often found in moist places, larvae in decaying plant or animal matter, or in fungi.
Sepsidae
Very characteristic flies when alive, the adults occur in large numbers around excrements and decaying materials, where the larvae develops. The adults have a peculiar habit of wing-waving. This family have been recorded feeding on dead human bodies in the time of caseic fermentation and before ammoniacal fermentation. Eggs of Sepsidae have a very long respiratory horn, often longer than the egg itself.
Sphaeroceridae
Minute or small dark flies that breed in dung.
Piohilidae
Dark, shining flies. The larvae are scavengers and are often found on dead bodies that have been lying for a while. Piophila casei is also called the Cheese-skipper, because the larvae jumps for a considerable height, when disturbed. This behaviour is probably a defencive tactic against predators. These flies also infests stored bacon and cheese, which, to the flies, are almost the same as dried corpses.
Ephydridae
Large group with several common species. They are small to very-small. Adults are found in moist places: marches, the shores of ponds and streams, and the seashore. The larvae are aquatic, and many species occur in brackish or even strongly saline or alkaline water.
Drosophilidae
These are the well-known fruitflies that every biologist have heard about, and probably most other people too. Minute and small flies, brown, yellow or grey with brightly colored eyes. The larvae feeds on decaying vegetable matter, but some also feed on fungi. Some species may occasionally occur on dead humans, and these are probably feeding on fungi.
Milichiidae
Minute, dark flies. Adults and larvae are scavengers.
CALYPTRATAE
Sarchophagidae
Among the Sarcophagids we find the large flesh-flies with red eyes and a grey-checkered abdomen. These flies does not deposit eggs, but larvae on the corpse. They are, together with the Calliphorids, among the first insects to arrive at the corpse. The larvae are predators on blowfly larvae, as well as carrion feeders. Many Sarcophagids are feeding on snails and earthworms.
Calliphoridae
These are the famous green-bottles and blue-bottles. There is many species of blowflies, and each species has their own biology. Some prefers to oviposit in shade, others in light. Some are mainly urban in their distribution, others mainly rural.
Fanniidae
Here we find the lesser house-fly, Fannia canicularis among others. These flies are mainly breeding in faeces, but can also develop in cadavers, especially if there are patches with semiliquid tissue. The larvae have fleshy processes all over the body, which assist in floating.
Muscidae
Among this large family we find the common house-fly, Musca domestica. These flies occur in houses, and are one of the most widely distributed species on this planet. In warm weather they can complete development in 14 days. Eggs are laid in decaying material, including, but not limited to, dead bodies.
COLEOPTERA
Several beetles occur on carrion. There exists necrophagous beetles and predators. The various groups occur in different stages of decomposition.
Staphylinidae
Staphylinids - or rove-beetles may arrive a few hours after death, and remain active throughout the decomposition process. The adult and larvae feeds on eggs and larvae of other species. They have a characteristic short elytra.
Dermestidae
Dermestids are common beetles in the later stages of decomposition. Larvae of dermestids does not occur before the body is dry. The larvae and adults feeds on dry skin and hairs and other dry dead organic animal matter. Dermestids is a common stored product pest in homes, and a pest in insect collections and furs at museums and other places.
Histeridae
Members of this family has short elytra, but not as short as the Staphylinids. This family occurs wherever there is decay and putrefaction. They have been found during the bloated, decay and early parts of the dry stage. Both larvae and adults feed on maggots and puparia. They are usually concealed under the corpse during daylight, but becomes active in the night. Saprinus and Dendrophilus occur on dead animals and on air-dried and smoked foods. They prey on larvae of Dermestes.
Silphidae
In this family we find the Nicrophorus species, well known for their habit of undertaking small carcasses. Some of the species of Nicrophorus lives mainly on larger carcasses, and does not bury them. The adults prefer feeding on maggots, but also feeds on the carrion. The adults feed their larvae until pupariation. Easton reports that 13 specimens of Necrodes littoralis was found on the body of a man which had been lying on the North Downs for 17 days in October 1969.
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Feb/23/2005, 11:14 pm
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SatinNLace
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Re: The Ultimate Guide to Forensic Entomology
Analyzing the crime scene for entomological evidence
To make the most use of entomological evidence at a crime scene, an experienced and well trained forensic entomologist should do the collecting at the scene.
The exact procedure at the crime scene varies with the type of habitat, but in general we can divide the work of the forensic entomologist in five parts.
1. Visual observation and notations at the scene.
2. Initiation of climatological data collection at the scene.
3. Collection of specimens from the body before body removal.
4. Collection of specimens from the surrounding area (up to 6 m from the body) before removal of the remains.
5. Collection of specimens from directly under and in close proximity to the remains (1 m or less) after the body has been removed.
Observation on insect activities at the crime scene may be useful, because the entomologist is trained in a different science than the crime scene investigators. An entomologist will probably observe elements that the investigators will ignore (and vice versa).
What should be looked for at the crime scene?
The type of habitat the crime scene is located in? Is it rural, urban/suburban or aquatic? Is it a forest, a roadside, a closed building, an open building, a pond, a lake, a river, or another habitat type. The type of habitat dictates what types of insects that could be found on the body. Finding of insects typical of other habitats than the crime scene may suggest that the body has been dumped.
* Estimate the number and kinds of flying and crawling insects.
* Note locations of major infestations associated with the body and surrounding area. These infestations may be egg, larval, pupal or adult stages, alone or in any combinations of the above.
* Note immature stages of particular adult insects observed. These stages can include eggs, larvae, pupae, empty pupal cases, cast larval skins, fecal material, and exit holes or feeding marks on the remains.
* Note any insect predation such as beetles, ants and wasps or insect parasites.
* Note the exact position of the body: compass direction of the main axis, position of the extremities, position of head and face, noting of which body parts are in contact with substrate, noting where it would be sunlight and shade during a normal daylight cycle.
* Note insect activity within 3-6 m of the body. Observe flying, resting or crawling insect adults or larvae or pupae within this proximity to the body.
* Note any unusual naturally occurring, man-made, or scavenger-caused phenomenon which could alter the environmental effects on the body (trauma or mutilation of the body, burning, covering, burial, movement, or dismemberment)
Photographs should be taken of all this, with closeup photos of the different stages of insect found before collecting.
Collecting of climatological data at the scene
When estimating the PMI, climatological data about the crime scene is absolutely critical. The length of the insect life cycle is determined mostly by temperature and relative humidity in the environment development takes place.
The following climatological data should be collected at the scene:
1. Ambient temperature can be evaluated by taking readings at 0.3 to 1.3 m heights in close proximity to the body.
2. Ground temperature can be obtained by placing the thermometer on the ground, immediately above any surface ground cover.
3. Body surface temperatures should be obtained by placing the thermometer on the skin surface.
4. Under-body interface temperature can be obtained by sliding the thermometer between the body and the ground surface.
5. Maggot mass temperatures can be obtained by inserting the thermometer into the center of the maggot mass.
6. Soil temperatures should be taken immediately after body removal at a ground point which was under the body before removal. Also take soil temperatures at a second point 1-2 m away from the body. These temperatures should be taken at 3 levels: Directly under any ground cover (grass, leaves, etc.), at 4 cm soil depth and at 20 cm soil depth.
Weather data for the scene should be collected from the nearest meteorological station. Minimum requirements should be maximum and minimum temperature and amount of precipitation. Any other information is also welcome, and may aid in the reconstruction of the events. The climatological data should extend back to the time the victim was last seen.
Collecting specimens before body removal
A passive technique for collecting adult insects at the crime scene is by using sticky traps with a slow drying adhesive substance. These traps are made from waxed cardboards with a pup tent configuration set at a approximately 60 degree angle with sticky material on both exposed sides. This trap will collect many insects in a few minutes. An insect net can be used to collect flying insects. Eggs, larvae, pupae and adults of insects on the surface of the human remains should be collected and preserved to show the state of the entomological data at the time of discovery. Insects within the body should not be collected before the autopsy. If there is enough insects, samples of egg, larvae and pupae should be collected alive and placed on a rearing medium such as raw beef liver. Rearing to the adult stage makes identification easier, and may give vital clues to the PMI estimation. It is important that the temperature in the rearing container is as constant as possible, in the range of 20-27 degrees Celsius. It is absolutely necessary that the temperature is recorded in the rearing container.
In the laboratory
All samples, both live and dead specimens should now be processed as fast as possible. Live specimens are placed in incubators with known temperature and humidity levels. Several times each day these containers should be watched, and changes such as hatching of eggs or larvae, pupariation or eclosion of adult insect should be noted. The exact time should be noted. Pictures could be taken to illustrate to a jury or others. Each kind of larvae and adult should be determined to genus and species if possible. This may require the assistance of an expert of the taxon in question. It may be necessary to do experiments outdoors near the crime scene to recreate the environmental conditions for the larvae to estimate PMI.
Analyzing the data
When all the data is processed it is time to make some conclusions:
Determine whether or not the remains have been disturbed or disarticulated during the PMI. Ask if there is presence of any antemortem administered drugs such as alcohol, cocaine or heroine.
Estimate the age of as many specimens as possible, based on presence of drugs, temperature and humidity conditions. Consider whether or not insect activity was delayed after death.
There are several other things to take into account, but these points can be read in the excellent book "Entomology and Death: A procedural guide" edited by Catts and Haskell.
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Feb/23/2005, 11:20 pm
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