1. Insects in the Forensic Sciences
Forensic Entomology
Insects in the Forensic Sciences

2. What is Forensic Entomology?
The application of insects and other arthropods to legal issues and court proceedings

3. What is it used for? Applications Estimation of time of death
Cases involving possible sudden death
Traffic accidents with no immediately obvious cause
Possible criminal use of insects

4. How does FE work?
Fact – insects feed on humans after death. Yup – not good news, but we are part of the cycle of life!
If insects are found on a corpse, the life stage of the insect can be used to determine time of death
This calculation is known as the POSTMORTEM INTERVAL (PMI)

5. PMI Conditions
PMI must take into consideration many environmental variables
Temperature
Time of day death occurred
Time of year death occurred
Whether the corpse is submerged in soil or water.

6. Divisions of Forensic Science
Urban – Relates insects to human structures and environments
Stored Products – Insect infestations of stored food and beverages
Mediocriminal – The only division that has a criminal aspect. Relates to insects feeding on human tissue in the postmortem period.

7. After Death
As the body decays, odors attract insects to the dead body. Levels of putricine (decomp. enzyme,) sulfur and methane compounds send up an “open for dinner” flare.
The flies (order Diptera) are the first to arrive. Blowflies (F. Calliphoridae) and flesh flies (F. Sarcophagidae) are flesh feeders and will be the first in line.
Flies can arrive within minutes or up to a couple hours after death.
In many cases flies arrive before the completion of a crime and are silent witnesses.

8. Phylum Athropoda
Not as large of a biomass as bacteria – but run a respectable second!
Unifying Characteristic – hard exoskeleton
Class Insecta includes bees and wasps (Order Hymenoptera,) flies (O. Diptera,) butterflies (O. Lepidoptera,) dragonflies (O. Odanata,) beetles (O. Coleoptera,) etc.
“True Bugs” are Order Hemiptora. No hemiptorans have any consequence for forensic science – so erase “bugs” from your vocabulary!

9. Fly Life Cycle
If no trauma is present on the body, female blowflies will lay eggs in exposed body openings (ears, nose, mouth, anus, genitalia.)
Flesh flies don’t lay eggs, they deposit larvae.
The colonization pattern is due to the mouth parts of adult flies.
Blowflies and flesh flies have spongy mouth parts. They lack piercing apparatus that can cut through unbroken human skin. The body openings provide a moist, warm environment for larvae development.

10. Blowflies Blowfly Classification Kingdom: Animalia Phylum: Arthropoda
Subphylum: Uniramia
Class: Insecta
Order: Diptera
Family: Calliphoridae

11. Blowfly Eggs
Small, 2-3 mm length, elongated shape, white to yellow color
Found in large clusters in and around body openings as well as injuries
Clearly visible to naked eye
Colder months may see fewer in numbers
Can be found in more hidden locations such as under eyelids or in nostrils
Eggs typically hatch within hours but may take up to 2-3 days depending on conditions

12. Blowfly Larvae
One fairly small and featureless larvae hatches from each egg
The body tapers from anterior to posterior – Mouth at the anterior, spiracles at the posterior
Posterior contains breathing apparatus called spiracles
Spiracles, along with body size and shape provide important info for identification

13. Blowfly larvae
Large numbers of blowfly typically hatch at a time and remain together while they feed on a corpse
These maggot masses generally form in the head region and move down the torso as they feed.
As they feed the larvae secrete digestive enzymes which allows them to consume nearly all the soft tissue on the corpse

14. Blowfly life cycle Blowfly larvae go through three instars (molts)
They are considered fully grown at the third instar
This can occur in several days or several weeks depending on species, environmental conditions and number of larvae present

15. Pupa Stage
After the 3rd instar larvae go through a drastic behavioral change
they crawl away from the corpse and burrow down into the soil to transform into the pupal stage and complete the life cycle

16. Pupa The pupa form when the outer larval skin hardens and shrinks
Inside this “case” the adult blowfly will form
Once the adult fly emerges, the pupal case does not decompose. It can remain under a corpse for hundreds of years
Pupal cases can provide valuable forensic info to investigators long after a crime has been committed.

17. Postmortem Interval (PMI)
Entomological evidence collection can be done in a variety of ways
For our purpose we will:
Identify the species
Document larvae length
Determine the instar
Determine postmortem interval estimation
Depending on species we will use extrapolation of instar length or the accumulated degree day theory

18. Post Mortem Intervals
PMI – The use of insect life cycles to estimate the time a corpse has been in the location where it was found
PMI does not DETERMINE the time of death
Time of death is established by the medical examiner
Forensic entomology can provide value information for the M.E.

19. Forensic Applications
Time of injury vs. death
Estimation of time of death
Whether or not a corpse has been moved
Instances of insects as weapons
Child and elderly abuse and neglect
Single vehicle car accidents (insect stings and path vehicles have traveled)
Aircraft crashes (instrument obstruction and engine and fuel line clogging)

20. F.E. Applications – Blood Evidence
“Roach Track” Confusion
Roaches are notorious for confusing blood spatter analysis
Blood trajectory is often critical to forensic investigations
Roaches, silverfish and other household insects often travel through bloodstained areas
“Roach tracks” frequently confuse forensic investigators that are untrained in how to identify them

21. Blood Spatter Confusion – Fleas and Flies
Flies also track through blood, but “fly specks” are a far greater problem for investigators
Flies ingest blood and can leave large undigested droplets behind in previously uncontaminated areas. These droplets can enlarge a crime scene unneccessarily.
Fleas also leave behind undigested blood in their feces (commonly known as “flea dirt.”)
Flea dirt in a heavily infested dwelling can falsely suggest blood “evidence”

22. Roaches, Flies, Fleas
It is becoming more clear that household insect infestations need to be included as a variable in forensic investigations
Proper identification of household pests can save valuable time and resources for technicians and investigators
Best for juries to hear about insect “confusion” from CSI’s rather than from attorneys for the defense!

23. Insects and Illegal Drugs
Shipments of illegal drugs often contain insect infestations, especially cannabis and heroine (derived from poppy plants.)
Analysis of insect “stowaways” can allow investigators to track country of origin, and in many cases the local area of cultivation.
PMI used to detect illegal drugs/poisons in fly larvae (consumed from corpses)

24. The moral of the story…
Insects are becoming invaluable in the investigation of crime
Forensic entomology is one of the fastest growing specialties in forensic science.
All Crime Scene Investigation Units MUST be prepared to include insect collection, identification and analysis in their investigations.