1. Insects used to determine TOD
Forensic Entomology
Insects used to determine TOD

2. Insect Biology
Insects are the most diverse and abundant life forms on earth
Existed for over 250 million years
How long have humans existed?
There are over a million described species
More than 2/3 of all known organisms
There is more total biomass of insects than humans
Insects under either incomplete or complete metamorphosis
Humans 300,000 years

4. Metamorphosis Complete has four distinct life cycle stages
Egg
Larva - Can be worm-like; can see six legs; eat constantly and grow rapidly
Pupa - Hard protective case
Adult
Incomplete only has three life cycles
Egg
Nymph - Looks like a smaller, wingless version of the adult
Adult

7. Forensic Entomology
Use of insects and other arthropods that feed on decaying remains to aid in legal investigations
Used to determine PMI or time since death

8. Arthoropoda Invertebrate/exoskeleton/segmented body/joint appendages
Insects
Chitinous exoskeleton, a three-part body, three pairs of jointed legs, compound eyes and one pair of antennae
Arachnids
Eight (4 pair) legs, 2 additional with adaptation (feeding, sensory); no wings, body is cephalothroax and abdomen
Myriapods
Many, many legs
Crustaceans
Appendages split in two; mostly aquatic

10. Medicolegal Forensic Entomologist
Focus on violent crimes
Determination of PMI or site of death based on identification of arthropods collected near corpse

11. Post Mortem Interval (PMI)
Forensic Entomology is used to determine time since death
Also used to determine
Movement of corpse
Manner and cause of death
Association of suspects with death scene
Detection of toxins, drugs, or DNA of victim through insect larvae analysis

12. Forensic Entomology - Applied
Forensic Entomologists…
Identification immature insects at various stages of life cycles
Determine size and development of insects
Calculations growth of insects and passage through life cycles in the lab
Compares growth to weather conditions to estimate time of oviposition

14. Succession of Insects on a Corpse
PMI estimates based on insects present
Time required for a given species to reach a particular stage in life cycle
Comparison of all insect species on the corpse at the time of examination
Ecological succession
The first invasion by insect species will alter the habitat by their activities
These changes make the habitat more attractive to a second wave of organisms who in turn the habitat for yet another organism

15. Ecology of Decomposition
Necrophages
First species feeding on corpse tissue
Diptera (rue flies)
Coleopter Carrion (beetles)

16. Ecology of Decomposition
Omnivores
Species such as ants, wasps, and some beetles that feed on the corpse and associated maggots
Large populations of omnivores can slow the rate of corpse decomposition by reducing populations of necrophage species

17. Ecology of Decomposition
Parasites and Predators
Beetles and true flies and wasps that parasitize immature flies
Incidentals
Pillbugs, spiders, mites, and centipedes use corpse as an of their natural habitat

18. Life Cycle of a Fly

19. Decay Rates are Variable
Decay rates of 150 human corpses studied at the Body Farm in Tennessee
Most important environmental factors
Temperature
Access by insects
Depth of burial
Other factors
Chemicals
Embalming agent, insecticides, lime, etc…
Animals disrupting the corpse

21. Five Stages of Decomposition
Fresh
Bloat
Decay
Post-decay
Dry (skeletal)

22. Five Stages of Decomposition Fresh
Days 1-2
Begins at death
Flies begin to arrive
Temperature falls to that of ambient temperature
Autolysis occurs

23. Five Stages of Decomposition Bloat
Days 2-6
Swells due to gases produced by bacteria
Temperature of corpse rises
Flies still present

24. Five Stages of Decomposition Decay
Days 5-11
Gasses subside, decomposition fluids seep from body
Bacteria and maggots break through skin
Unpleasant odor
Larvae begin to pupate
Corpse reduced to 20% of original mass

25. Five Stages of Decomposition Post-Decay
Days 10-25
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

26. Five Stages of Decomposition Dry
Days 25+
May not occur if corpse in wet region
Maggots stay longer and hide beetles will not appear
In wet regions hide beetles replaced by nabid and reduviid insects
Corpse reduced to at least 10% of original mass
Only bone and hair remain