1. Analyzing Entomological Evidence to Solve Crimes
What the Blow Fly Saw
Analyzing Entomological Evidence to Solve Crimes

2. There are five questions posed during a death scene investigation
Who is the deceased?
How did the death occur?
Where did the death occur?
When did the death occur?
Is the death natural, accidental, or criminal?
A forensic entomologist is primarily involved with the when and the where…

3. Why Use Insect Evidence?
Insects are generally the first to discover a corpse. In outdoor cases, blow flies arrive and lay eggs on the body within minutes of death.
Insects arrive in a somewhat predictable order.
The absence of insects when they should be present can provide evidence about the nature of the crime.

4. Do You Remember Your Classification System from Biology?
Kingdom
Phylum
Class
Order
Family
Genus
species

5. Where do Insects Fit In? Animal Kingdom Arthropod Phylum Insect Class
Order
Odonata
Orthoptera
Mantidae
Diptera
Coleoptera
Hemiptera
Hymenoptera
Lepidoptera

6. Odonata – The Dragonflies

7. Orthoptera – The Grasshoppers and Crickets

8. Mantidae – The Praying Mantis

9. Diptera – The Flies (and don’t forget baby flies as well)

10. Coleoptera – The Beetles

11. Hemiptera – The Bugs PLANT BUG STINK BUG CICADA

12. Hymenoptera – The Stingers

13. Lepidoptera – The Butterflies and Moths

14. Two Orders of Insects that are Especially Useful to Forensic Entomologists:
Diptera (the flies) – Larva, the maggots, like to live in a semi-liquid medium. These insects are generally the first to move in on a corpse. They are responsible for most of the tissue loss.
Coleoptera (the beetles) – They like slightly dried out corpses and will come in later.

15. To Classify a Fly Kingdom – Animal Phylum – Arthropod Class – Insect
Order – Diptera
Family – Calliphoridae
Genus - Calliphora
Species - vomitoria

16. Calliphora vomitoria The blue bottle fly

17. Blow Flies – hard at work reducing tissue mass

18. Dermestid Beetles – hard at work cleaning bones for the Smithsonian

19. Clues from Insects as to Where
Certain insects and mites live in sub corpse communities. If those animals are not present, it suggests that the corpse has been moved.
Insects like specific niches. If you find an insect on a body that doesn’t belong in the surrounding environment, the body may have been moved.

20. In the Northern U.S. This black blow fly prefers shade.
This green bottle fly frequents corpses in open, brightly lit areas.
This black blow fly prefers shade.

21. In the Northern U.S.
The blue bottle fly dominates during cooler months
The green bottle fly dominates during warmer months

22. Clues from Insects as to How
If you find locations of concentrated insect activity on a corpse, that may suggest ante mortem (before death) injury.
For example, blow fly maggots concentrated on the neck of a victim are most likely there because a wound provided fresh blood.

23. Clues from Insects as to When
The Concept of PMI PMI stands for Post Mortem Interval. This is the time period between when the person died and when the body was discovered. PMI is important because it narrows the field of suspects and may help with the identification of the deceased if you look at a list of missing persons and when they went missing.

24. Video Clip - Forensic Entomology

25. Clues from Insects as to When
Video Clip: Decay of a Fox Case Studies

26. Let’s Learn More about Determining PMI
Since insects are cold blooded, their rate of development is proportional to temperature. Cooler temperatures slow development. Warmer temperatures stimulate development.

27. Practice Question
Suppose an insect species develops twice as fast at 20 ⁰C than at 10 ⁰C. Complete development takes 10 days at 20⁰C. Would it take more or less time at 10 ⁰C? How long would it take at 10 ⁰C? It would take 20 days, twice as long.

28. The Concept of ADH – Accumulated Degree Hours
Because insect development is so closely tied to temperature, entomologists have developed a system to help determine time of death by taking into account average daily temperatures and what is known about rearing insects in the lab.
The accumulated degree hour is calculated by multiplying the temperature times the hours it takes to go through a certain stage.
ADH = temp x hours it takes to get to a stage

29. Blow Fly Life Cycle
The clock starts at oviposition – the time the egg was laid.
Stage
Calculation
ADH
Egg to 1st Instar
70 x 23
1610
1st Instar to
2nd Instar
70 x 27
1890
2nd Instar to
3rd Instar
70 x 22
1540
3rd Instar to Pupa
70 x 130
9100
Pupa to Adult
70 x 143
10010
Total from
Egg to Adult
70 x 345
24150

30. So what’s an instar?
An instar is a larval stage of development of a maggot named for its number of spiracle slits. A first instar has one set of spiracle slits. A second instar has two sets of spiracle slits, and so on.
The spiracles are what the maggot breathes through.

31. What Does This Mean?
You won’t find lab conditions in the field. But, you can use knowledge of how many ADH’s it takes for an insect to develop and then count backwards to see when a body was left.
For example, suppose a body was found at 1 pm on August 14th. The average temperature each day for the last 15 days was 85 F. You collect maggots in the 2nd instar stage. You note the absence of pupa. How long has the body been there?
Stage
Calculation
ADH
Egg to 1st Instar
70 x 23
1610
1st Instar to
2nd Instar
70 x 27
1890
2nd Instar to
3rd Instar
70 x 22
1540
3rd Instar to Pupa
70 x 130
9100
Pupa to Adult
70 x 143
10010
Total from
Egg to Adult
70 x 345
24150

32. Step One
Figure out how many degree hours it takes to get the second instar.
= 3500ADH
The insect must accumulate 3500 ADH to get to the 2nd instar stage.
Stage
Calculation
ADH
Egg to 1st Instar
70 x 23
1610
1st Instar to
2nd Instar
70 x 27
1890
2nd Instar to
3rd Instar
70 x 22
1540
3rd Instar to Pupa
70 x 130
9100
Pupa to Adult
70 x 143
10010
Total from
Egg to Adult
70 x 345
24150

33. Step Two
Figure out how long it would take to earn that many ADH’s with the given temperature.
ADH = Temp x Time
3500 = 85 x Time
Time = 3500/85 = hours
= 1 day and 17 hours
If the body was found at 1pm on August 14th, it was dumped on August 12th at 8pm.

34. Try this one!
A woman walking her dog in the woods on October 9th found a body. A forensic entomologist obtained larval samples at 3pm. He noted 2nd and 3rd Instar larva. Assuming the average temperature was 74 F, what is the PMI?
Stage
Calculation
ADH
Egg to 1st Instar
70 x 23
1610
1st Instar to
2nd Instar
70 x 27
1890
2nd Instar to
3rd Instar
70 x 22
1540
3rd Instar to Pupa
70 x 130
9100
Pupa to Adult
70 x 143
10010
Total from
Egg to Adult
70 x 345
24150

35. Solution It takes 5040 ADH to get to 3rd Instar larva.
At a temperature of 74F, you can accumulate 5040 ADH in 68 hours, or two days and 20 hours.
This body was dumped at 7pm on October 6th.
Total ADH = = 5040 ADH = Temp x Time 5040 = 74 x Time Time = 5040/74 = 68 hours Count backwards October 9th 3pm, take away 68 hours, and you get 7pm on October 6th.

36. Other Factors Can Complicate Calculating the PMI
Weather plays a role (flies can’t fly in a storm).
Time of day plays a role (some flies only lay eggs in daylight).
A wrapped or otherwise inaccessible body will take longer for flies to get to.
A mass of maggots generates heat as they feed.
Presence of other species can speed development.
Drugs in the body can affect larva development times – some speed it up, some slow it down.

37. How a wrapped body throws off the time estimate
Pig in a Blanket
How a wrapped body throws off the time estimate