1. Forensic Entomology

2. Taxonomy Classification of Living Things in an Orderly Way
We are interested in the phylum Arthropoda; class Insecta; orders:
Diptera (flies)
Coleoptera (beetles)

3. Forensic Entomology Entomology is the study of insects.
Forensic entomology involves the use of insects and other
arthropods to aid in legal investigations (Flies, Beetles, Ants, Wasps)
There are three areas of application:
Insect damage to structures
Infestation of foodstuffs
Insects that inhabit human remains
The latter category is the subject of this chapter.

4. Post Mortem Interval (PMI)
is the interval between death and time of postmortem examination
This term is more accurate than referring to 'Time of Death' since the exact time of death is difficult to impossible to predict.
A longer PMI usually results in a wider range

5. Routine Methods used to Determine PMI
Algor mortis (cooling of body)
Livor mortis (settling of blood)
Rigor mortis (stiffening of muscles)
Changes in fluid of eye
Stomach & bowel contents
Decomposition changes
Insect colonization
Circumstantial evidence

6. The Process of Death Algor Mortis: Body cooling rate
98.4°F – internal body temperature
1.5
Hours since death =
Livor Mortis: skin discoloration caused by pooling of blood
Rigor Mortis: rigidity of skeletal muscles
Temperature of body
Stiffness of body
Time since death
Warm
Not stiff
Not dead more than 3 hours
Stiff
Dead between 3 and 8 hours
Cold
Dead between 8 and 36 hours
Dead for more than 36 hours
A pathologist estimates time of death from these factors.

7. The Process of Death, continued
Stage
Description
Initial or fresh decay (autolysis)
The cadaver appears fresh externally but is decomposing internally due to the activities of bacteria present before death (0–4 days).
Putrefaction or bloating
The cadaver is swollen by gas produced internally, accompanied by the odor of decaying flesh (4–10 days).
Black putrefaction
Flesh of creamy consistency, with exposed body parts black. Body collapses as gases escape. Fluids drain from body. Odor of decay very strong (10–20 days).
Butyric fermentation
Cadaver drying out. Some flesh remains
at first; cheesy odor from butyric acid
(20–50 days).
Dry decay (diagenesis)
Cadaver almost dry; slow rate of decay. May mummify (50–365 days).

8. Factors Affecting Rate of Decomposition
Temperature
Access by insects
Burial, and depth of burial
Access by carnivores or rodents
Humidity, or dryness
Rainfall
Body size and weight
Prior embalming
Clothing
The surface the body rests on
Trauma, including wounds and crushing blows

9. Insect Evidence can be used to determine PMI
can indicate the season of death.
can indicate whether the death occurred in an urban or rural setting.
can be used to determine whether a buried body was on the surface for some time after death and then buried.
also indicates whether a body has been previously buried
aquatic insects can indicate the season and conditions under which the body came to be in the water

10. Forensic Entomology Relies Strongly on the Following Ecological Concepts
Different species of insects go through developmental stages in predictable fashions
Developmental time is temperature dependant.
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. 10

11. Life Cycle of Insects Metamorphosis egg larva (maggot) pupa
winged adult
The life cycle of Musca domestica

12. Time of Death
Insects arrive at a decomposing body in a particular order (succession) and then complete their life cycle based on the surrounding temperature. By collecting and studying the types of insects found on a body and their metamorphic stage, a forensic entomologist can estimate the time of death.

13. Diptera Insects of Death First to arrive Then
Blowflies
Flesh flies
Houseflies
Flies can arrive within minutes. They lay eggs that hatch to maggots. Maggots feed on soft, mushy body parts. More insects arrive to feed on the body and each other.

14. Coleoptera Insects of Death, continued
In rough order of appearance, from within hours to dry decay:
Rove beetle
Sexton beetle
Clown beetle
Dermestid beetle
Hide beetle
Some beetles feed on the corpse, some on maggots, some on other beetles.

15. Insects begin to arrive at a corpse in a little as ten minutes after death
5 Stages of Decomposition and Colonization
The Fresh Stage –insects arrive as flies & lay eggs
The Bloated Stage- the production of gases causes bacterial break down of the tissue. The eggs of the flies will have hatched by this stage.
The Decay Stage- the skin ruptures and body fluids permeate the surrounding area. Maggots stop feeding and move off of the body
The Post-Decay stage- beetles are the most prominent order found on a body
The Skeletal Stage - only soil dwelling insects remain

16. Temperature–Dependent Development
Insects are cold blooded.
Rate of development is more or less dependent on ambient temperature
Each species there has a threshold temperature below which no development occurs
As temperature rises above this threshold, a certain amount of time is required for the insect to pass through each life stage.
Because this heat is accumulated as "thermal units," it can be calibrated and described as "degree-days" or "degree-hours"

17. Temperature Variables Affecting Metamorphosis
The higher the temperature (within limits), the faster the growth.

19. Eggs Laid around body openings & injuries Can vary in: Size Shape
Color
Quantity

20. Habitat Variables Affecting Metamorphosis, continued
Fly species can vary geographically according to climate, season, and habitat.
Phormia regina
Lucilia illustris
For example, the fly pictured on the left prefers shade; the one on the right, sunlit areas.

21. Larval Stages Stages of growth called INSTARS
# of instars can vary by species
Molt between instars

22. Larval Growth Secrete digestive enzymes to break down tissue
Rate of growth determined by:
Species
Environmental Conditions
# of larva present

23. Larva Anatomy # of spiracular slits often correlates to instars'

24. Pupa Larva crawls away from corpse and burrow
Will want to collect soil sample
Outer skin hardens, providing protective shell
Resilient to environmental changes
Complete physical metamorphisis
Hard to identify to species---will want to collect and “grow” to adult form

25. Adult Fly Adults difficult to collect
Can use larvae to produce adults in laboratory

26. Case Study Establish PMI:
Body found – all larvae collected are Lucilia sericata (green bottle fly)
The biggest and oldest are mid 3rd in-star larvae
Weather reports from the crime scene indicate the average temp was 21 C°
This species does not colonize bodies for 48 hours after death
Development rate of Lucilia sericata (in hours) at three different temperatures 26

27. Solution
Use 21 C°
It takes 21 hours to hatch from the egg, plus 31 hours for 1st instar, plus 26 hours for 2nd instar, plus roughly 25 hours for mid-3rd instar
Add 48 hours colonization time
Total: = 151 hours
151 hours/24 hours per day = 6.29 days pmi
RANGE: 126176 hours 27