1. How do insects determine PMI?
Forensic Entomology Forensic entomology is the application of the study of insects and other arthropods to legal issues, especially in a court of law.
How do insects determine PMI?

2. Do Now: Diatom Detective
1. What important information do microscopic organisms reveal about a crime?
2. How did the forensic scientist prove that the husband had been in the water of that stretch of the river?

3. History of Forensic Entomology: The Earliest Case
Sung Tz'u (1235 AD) – Chinese “death investigator”
Wrote The Washing Away of Wrongs
First forensic entomology case recorded
A murder by slashing occurred in a village, and the local death investigator was ordered to solve the crime. The investigator had all villagers bring their sickles to one spot and lay them out before the crowd. Flies were attracted to one of the sickles, probably because of invisible remnants of tissue still remaining on it, and the owner subsequently broke down and confessed to the crime.
History of Forensic Entomology: The Earliest Case

4. Developmental time is temperature dependant at the microhabitat level.
Ecological succession – A corpse will be invaded by a series of different species or insect groups over time. Each species or group changes the microenvironment through its activities which makes it attractive to new waves of organisms and so on.
What other important information do the insects provide?
Forensic Entomology Relies Strongly on the Following Ecological Concepts

5. The Most Common Application Relates to Death Investigations
Determining PMI – postmortem interval.
Movement of the corpse.
Manner and cause of death
Association of suspects with the death scene
Detection of toxins or drugs through analysis of insect larvae.

6. Estimates of PMI Using Insects May Be Based On:
Period of time for a given species to reach a particular stage of development
Comparisons of assemblages of insect fauna on corpse at time of examination
A combination of both above
Estimates of PMI Using Insects May Be Based On:

7. Blow Fly Life Cycle

8. How do Entomologists use Corpse Fauna to Estimate Time of Death?
Do: Now: From Eggs to Maggots
What are some factors that affect the “fly clock”?
Based on feeding habits, what types of insects do you think would constitute corpse fauna?

9. Ecological Roles of Insects in Decompositon
Necrophages – species feeding on corpse tissue; mostly true flies and beetles; age determination (larval instar) important for PMI
Omnivores – insects that feed both on the corpse and associated fauna; ants, wasps and some beetles; may alter rate of decomposition.
Parasites and Predators – many beetles, true flies and wasps that attack immature flies
Incidentals – use the corpse as a resource extension; springtails, spiders, centipedes, some mites.
Ecological Roles of Insects in Decompositon

10. Five Stages of Human Decomposition Have Been Recognized
Stage One - Fresh Stage (Days 1-2)
Livor, Rigor, Algor mortis
First sign of bloating due to putrefaction by anaerobic bacteria
Autolysis- cellular breakdown
Some blistering at the skin surface
Flesh flies, blow flies, ants eating fly eggs and predatory wasps
Five Stages of Human Decomposition Have Been Recognized

11. Flesh Flies – 2 Species

12. Two Blowfly Species

13. Blowfly Larvae

14. House Flies on Dead Host

15. The abscess on the hind leg of the pig is getting some attention from blowflies looking to deposit eggs on the swollen mass (left). Blowflies are present on the carcass, but maggots are mostly active on the face (right)

16. Five Stages … Stage two - Bloated stage (Days 2-6)
putrefaction begins; gases such as hydrogen sulfide, carbon dioxide, and methane produced by anaerobic bacteria resulting in considerable bloating
seepage of fluids from orifices, such as mouth, nose, and anus
Tissue may become frothy
adult and larval blowflies attracted in large numbers to seepage
Maggots have hatched and begun to feed on the tissue
Purging of gases and fluids results in strong decay odors
soil fauna moves away due to wetness of earth; ants and other species of flies prey on maggots
Five Stages …

17. Bloated unidentified animal on Long Island Shore

18. Blowfly activity on the carcass; skin is sloughing off the bloated pig

19. Most egg masses are on the head and neck and appear as thick white clumps on the carcass. Close up of a large egg mass on the cheek with adult blow fly; maggots feeding in mouth and nose.

20. Five Stages … Stage three - Decay Stage (Days 5-11)
Period of greatest mass loss resulting from the voracious feeding maggots and the purging of fluids
The purged fluids accumulate around the body and create a cadaver decomposition island (CDI)
Abdominal wall is broken and carcass deflates; adult flies begin to leave the body to pupate, but great masses of maggots remain and feed
carcass will begin to dry and beetles begin feeding on drier tissue;
predatory beetles such as rove and hister beetles are attracted
Strong decay odor persists
Five Stages …

21. Pig Carcass Infested With Blowfly Maggots

22. Cadaver Decomposition Island (CDI)

23. Hister Beetles Prey on Blowfly Larvae

24. Rove Beetles – 2 Species

25. Carrion Beetles decomposing the carcass of a dead animal

26. Five Stages … Stage 4 Stage Four - Post decay Stage (Days 10-25)
in dry habitats - remains consist of dry skin, cartilage and bones; site for dermestid beetles, histerids, fly pupae, immature and adult rove beetles
in wet habitats – large quantities of wet, viscous material (byproducts of decomposition) found in soil under the remains; site for adult and immature moth flies, rove beetles
Five Stages … Stage 4

27. Pig carcass in advanced stage of decomposition

28. Dermestid Beetles – Adult and Larvae

29. Stage Five - Dry Stage (Days 25+) – Mainly bone and hair is all that remains; odor is primarily that of soil and litter; some dermestids, fly pupae, immature and adult rove beetles, normal soil fauna consisting of mites, etc. start to return; this stage could last for several months to years.
Resurgence of plant growth around the CDI due to increased nutrients such as phosphorus, K, Ca, Mg, and C.
Five Stages …

30. Carrion Beetles – 2 Species

31. Rat will be completely buried and eggs laid upon it.
Female Carrion Beetle and Kangaroo Rat
Rat will be completely buried and eggs laid upon it.

32. Skeletonized pig carcass showing the production of a cadaver decomposition island surrounding the remains as a result of leaching of decomposition fluids into the surrounding environment.

33. Barriers to Decomposition and Irregular Decomposition
Physical – soil, water, caskets, antermortem and postmotem injuries
Chemical – embalming agent, insecticides, lime, etc.
Climatic – heat, cold, wind, rainfall
Animals – bird, mice, rodents, canids, cats, etc.
Barriers to Decomposition and Irregular Decomposition

34. Watch the short Nature video “Pig in a blanket”
How did the forensic entomologist determine PMI from the files?

35. Interactive Insect Activity

36. Forensic Entomologist Video
Question: What are some other applications of forensic entomology in addition to PMI?

37. Catching Killers with Insects