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Forensic Entomology Maggots and Time of Death Estimation.

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1 Forensic Entomology Maggots and Time of Death Estimation


3 Entomology is the Study of Insects Images from: myento/files/ArmyEntomology.ppt

4 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.

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 werent 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 Image:

9 Time of Death can be broadly estimated up to about 36 hours Temperature Stiffness Time of death Warm Not stiff Not dead more than three hours Warm Not stiff Not dead more than three hours Warm Stiff Dead between 3 to 8 hours Warm Stiff Dead between 3 to 8 hours Cold Stiff Dead between 8 to 36 hours Cold Stiff Dead between 8 to 36 hours Cold Not stiff Dead in more than 36 hours Cold Not stiff Dead in more than 36 hours

10 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

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12 Calculating PMI from Accumulated Degree Hours (ADH) FromToTempHoursADH Cumulative ADH Egg1 st Instar70° F2323 x 70= 1610 ADH st Instar2 nd Instar70 ° F2727 x 70= 1890 ADH nd Instar3 rd Instar70 ° F2222 x 70= 1540 ADH rd InstarPupa70 ° F x 70= 9100 ADH PupaAdult Fly70 ° F x 70= ADH

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

14 Fresh Begins at death Flies begin to arrive within 10 mins Temperature falls to that of the ambient temperature. Blow flies –(Calliphoridae) Flesh flies –(Sarcophagidae)

15 Bloat Swells due to gases produced by bacteria Temperature rise of the corpse Flies still present – house flies join –(Muscidae)

16 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 its original mass.

17 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.

18 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.

19 Arrival First flies search our natural orifices –Mouth, nostrils, eyes, ears, genitals Trunk of body is invaded later This can determine foul play

20 Factors that Affect Rate The following things can affect the rate of growth: –Drugs present in the body –Temperature –Location of the body (urban/rural determines species)

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