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Maggots and Time of Death Estimation

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1 Maggots and Time of Death Estimation
Forensic Entomology Maggots and Time of Death Estimation

2 Entomology is the Study of Insects
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3 Insect Biology Insects are the most diverse and abundant forms of life on earth. There are over a million described species- more than 2/3 of all known organisms There is more total biomass of insects than of humans. of humans. Insects undergo either incomplete or complete metamorphosis (Egg to larva to pupa to insect) Larva have a soft tubular body and look like worms. Fly species larvae are “maggots”

4 What is Forensic Entomology?
Forensic Entomology is the use of the insects and other arthropods that feed on decaying remains to aid legal investigations.  Medicolegal (criminal) Urban (criminal and civil) “legal proceedings involving insects and related animals that affect manmade structures and other aspects of the human environment” Stored product pests (civil) 

5 Medicolegal Forensic Entomology
Often focuses on violent crimes Determination of the time (postmortem interval or PMI) or site of human death based on identification of arthropods collected from or near corpses. Cases involving possible sudden death Traffic accidents with no immediately obvious cause Possible criminal misuse of insects

6 Postmortem interval (PMI)
Forensic Entomology is used to determine time since death (the time between death and corpse discovery) This is called postmortem interval or PMI). Other uses include movement of the corpse manner and cause of death association of suspects with the death scene detection of toxins, drugs, or even the DNA of the victim through analysis of insect larvae.

7 Forensic Entomology is Applied Biology
If it weren’t for decomposition of all living things, our world would fill up with dead bodies. When an animal dies, female insects will be attracted to the body. They enter exposed orifices or wounds and lay eggs or larvae. A forensic entomologist: identifies the immature insects determines the size and development of the insects calculates the growth of the insects and passage through stages of the life cycle in laboratory compares the growth against weather conditions to estimate time of oviposition

8 Succession of Insects on the Corpse
Estimates of postmortem intervals based on insects present on the remains are based on: The time required for a given species to reach a particular stage of development. Comparisons of all insect species present on the remains at the time of examination. Ecological succession occurs as an unexploited habitat (like a corpse) is invaded by a series of different organisms. The first invasion is by insect species which will alter the habitat in some form by their activities. These changes make the habitat attractive to a second wave of organisms which, in turn, alter the habitat for use by yet another organisms.

9 Ecology of Decomposition
Necrophages - the first species feeding on corpse tissue. Includes rue flies (Diptera) and beetles (Coleoptera). Omnivores - species such as ants, wasps, and some beetles that feed on both the corpse and associated maggots. Large populations of ominvores may slow the rate of corpse’s decomposition by reducing populations of necrophagous species. Parasites and Predators - beetles, true flies and wasps that parasitize immature flies. Incidentals – pill bugs, spiders, mites, centipedes that use the corpse as an extension of their normal habitat

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11 Decay Rates Are Variable
Studies of decay rates of 150 human corpses at in the Anthropological Facility in Tennessee (The Body Farm) Most important environment factors in corpse decay: Temperature Access by insects Depth of burial Other Factors Chemical-- embalming agent, insecticides, lime, etc. Animals disrupting the corpse

12 Time of Death can be broadly estimated up to about 36 hours
Temperature Stiffness Time of death Warm Not stiff Dead less 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

13 Differentiate between PMI and Time of Death
These may not always equate. Post mortem interval is restricted to the time that the corpse or body has been exposed to an environment which would allow insect activity to begin. Closed windows Body in box or bag Cold temperatures Deeper burial

14 Insect species arrive at a corpse in waves like clockwork
Calculate the heat/thermal energy (accumulated degree hour) required for each stage of the Green Bottle Fly’s life cycle. Possibly the greatest potential source of error in using arthropod successional patterns lies in the collection of speciments. Must only be done correctly to accurately sample the insects.

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16 Calculating PMI from Accumulated Degree Hours (ADH)
To Temp Hours ADH Cumulative ADH Egg 1st Instar 70° F 23 23 x 70= 1610 ADH 1610 2nd Instar 70 ° F 27 27 x 70= 1890 ADH 1610+ 1890 3rd Instar 22 22 x 70= 1540 ADH 1540 Pupa 130 130 x 70= 9100 ADH Adult Fly 143 143 x 70= 10010 ADH +10010 24100 ADH

17 Calculating ADH from Climate Data

18 Using the Data 3928 ADH in these three days (952+1488+1488).
How many ADH of 70º are there in these 3 days? 3928/70=56.11 hours 72 hours at 70º would have the insects passing to the 3rd instar. But 72 hours at colder temperatures and insects will only be at 2nd instar stage.

19 Five Stages of Decomposition Fueled by Insect Activity.
Fresh Bloat Decay Post-decay Dry (skeletal)

20 Fresh Begins at death Flies begin to arrive
Temperature falls to that of the ambient temperature. Autolysis, the degradation of complex protein and carbohydrate molecules, occurs. Gasses produced by the metabolic activities of the anaerobic bacteria first cause a slight inflation of the abdomen. The carcass may later assume a fully inflated, balloon-like appearance. Adult and larval blowflies in large numbers attracted to fluids seeping from body, normal soil dwelling fauna depart soil because of seepage of fluids; some muscid flies and ants which can feed on larvae and retard maggot activity.

21 Bloat Swells due to gases produced by bacteria
Temperature rise of the corpse Flies still present

22 Decay Gases subside, decomposition fluids seep from body.
Bacteria and maggots break through the skin. Large maggot masses and extreme amounts of fluid. Unpleasant odor Larvae beginning to pupate. Corpse reduced to about 20% of it’s original mass. Decay Stage - Black Putrefaction (Days 5-11) -- Decay stage begins when the abdominal wall is broken, allowing gasses to escape and carcass deflates. This process is facilitated by feeding activities of larval flies present on the exposed remains. Adult flies start to leave body, mainly larval mass. Carcass begins to assume a blackened, wet appearance, and most of the flesh will be removed by the maggots. Toward end of this period, carcass will begin to dry and beetles feed on drier tissue. Flies start to pupate. Predatory beetles such as rove beetles and histerids come to feed on other insects.

23 Post-Decay Carcass reduced to hair, skin, and bones.
Fly population reduced and replaced by other arthropods. Hide beetles are dominant in dry environments. Mite and predatory beetle populations increase. Postdecay Stage - Butyric fermentation (Days 10-25) -- In dry habitats, remains consisted of dry skin, cartilage and bones. Site for dermestid beetles, histerids, fly pupae, immature and adult rove beetles. In wet habitats, a large quantity of wet, viscous material, termed byproducts of decomposition, was found in the soil under the remains. Site for immature and adult moth flies, sphaerocerid and muscid flies, rove beetles.

24 Dry (Skeletal) Does not always occur especially if corpse is in a wet region. Maggots will stay longer and hide beetles will not appear. In wet environments the hide beetles are replaced with nabid and reduviid insects. The corpse is reduced to at least ten percent of the original mass. In the last stage (Skeletal Stage), only bone and hair remain. Dry Stage (Days 25 +) -- This stage is reached when mainly bones and hair remain. Odor is primarily that of normal soil and litter. Some dermestid beetles, histerids, fly pupae, immature and adult rove beetles, normal soil fauna (mites) start to return. Can last several months to even years.

25 Accumulated Degree Hours
ADH may be calculated using temperature and hours. This works because there is direct correlation between temperature and maggot development. These calculations were somewhat approximate but relatively accurate.


27 Review Questions 1-9 What is Forensic Entomology?
Explain 5 applications/uses of insects in forensic science. Describe the stages of death: Algor Mortis; Livor Mortis; Rigor Mortis. Describe the stages of decompositions. What are the most important environmental factors in corpse decay? Identify the name and origin of chemical released during each stage of decomposition. Why is it important to know what chemicals are produced as the body proceeds through decomposition? What are the 2 insect orders most commonly found on a decaying corpse. Describe the life cycle of the Insects found on a decaying corpse. How does this life cycle help explain time of death.

28 Review Questions 10-15 What is postmortem interval (PMI)?
Time of death can be estimated up to about 36 hours using temperature and stiffness. Explain how temperature and stiffness is used to estimate time of death Explain the difference between (PMI) and time of death. What is Accumulated Degree Days (ADD) and Accumulated Degree Hour (ADH). How is the (PMI) used to calculate (ADH or ADD)? Provide an example? Explain the proper techniques, equipment and procedures required for collecting insects for use in forensic investigations.

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