1. Forensic Entomology
Critters on Cadavers

4. What do Forensic Entomologists Do?
Forensic Entomologists apply their knowledge of entomology to provide information for criminal investigations.
A forensic entomologist’s job may include:
Identification of insects at various stages of their life cycle, such as eggs, larva, and adults.
Collection and preservation of insects as evidence.
Determining an estimate for the postmortem interval or PMI (the time between death and the discovery of the body) using factors such as insect evidence, weather conditions, location and condition of the body, etc.
Testifying in court to explain insect-related evidence found at a crime scene.
Cool Jobs: Forensic Entomology
Discovery Video
Did you know? Maggots can be used to test a corpse for the presence of poisons or drugs. Some drugs can speed up or slow down the insect’s development

5. Insects as Evidence
Most insects used in investigations are in two major orders:
1 – Flies (Diptera) and
2 – Beetles (Coleoptera)
Species succession may also provide clues for investigators. Some species may to feed on a fresh corpse, while another species may prefer to feed on one that has been dead for two weeks. Investigators will also find other insect species that prey on the insects feeding on the corpse.

6. Five Stages of Decomposition Fueled by Insect Activity.
Fresh
Bloat
Decay
Post-decay
Dry (skeletal)

7. Fresh Begins at death Flies begin to arrive
Temperature falls to that of the ambient temperature.
Autolysis, the degradation of complex protein and carbohydrate molecules, occurs.
Gasses produced by the metabolic activities of the anaerobic bacteria first cause a slight inflation of the abdomen. The carcass may later assume a fully inflated, balloon-like appearance. Adult and larval blowflies in large numbers attracted to fluids seeping from body, normal soil dwelling fauna depart soil because of seepage of fluids; some muscid flies and ants which can feed on larvae and retard maggot activity.

8. Bloat Swells due to gases produced by bacteria
Temperature rise of the corpse
Flies still present

9. Decay Gases subside, decomposition fluids seep from body.
Bacteria and maggots break through the skin.
Large maggot masses and extreme amounts of fluid.
Unpleasant odor
Larvae beginning to pupate.
Corpse reduced to about 20% of it’s original mass.
Decay Stage - Black Putrefaction (Days 5-11) -- Decay stage begins when the abdominal wall is broken, allowing gasses to escape and carcass deflates. This process is facilitated by feeding activities of larval flies present on the exposed remains. Adult flies start to leave body, mainly larval mass. Carcass begins to assume a blackened, wet appearance, and most of the flesh will be removed by the maggots. Toward end of this period, carcass will begin to dry and beetles feed on drier tissue. Flies start to pupate. Predatory beetles such as rove beetles and histerids come to feed on other insects.

10. Post-Decay 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.
Postdecay Stage - Butyric fermentation (Days 10-25) -- In dry habitats, remains consisted of dry skin, cartilage and bones. Site for dermestid beetles, histerids, fly pupae, immature and adult rove beetles. In wet habitats, a large quantity of wet, viscous material, termed byproducts of decomposition, was found in the soil under the remains. Site for immature and adult moth flies, sphaerocerid and muscid flies, rove beetles.

12. Dry (Skeletal)
Does not always occur especially if corpse is in a wet region. Maggots will stay longer and hide beetles will not appear.
The corpse is reduced to at least ten percent of the original mass.
In the last stage (Skeletal Stage), only bone and hair remain.
Dry Stage (Days 25 +) -- This stage is reached when mainly bones and hair remain. Odor is primarily that of normal soil and litter. Some dermestid beetles, histerids, fly pupae, immature and adult rove beetles, normal soil fauna (mites) start to return. Can last several months to even years.

13. Insects as Evidence
Weather data is also an important tool in analyzing insect evidence from a corpse. Investigators will make note of the temperature of the air, ground surface, the interface area between the body and the ground, and the soil under the body as well as the temperature inside any maggot masses. They will also collect weather data related to daily temperature (highs/lows) and precipitation for a period of time before the body was discovered to the time the insect evidence was collected.
Other factors that might affect their PMI estimates:
Was the body enclosed in an area or wrapped in a material that would have prevented flies from finding the corpse and laying eggs?
Were other insect species present that may have affected the development of the collected species?
Were there drugs or other poisons in or on the body that might have
affected the larvae’s development?
Did you know…
The “Body Farm” in Knoxville, Tennessee is a university research facility
to investigate human decomposition under various conditions in order to understand the factors which affect its rate.
Click the image to view a video about the Body Farm!

14. Decay Rates Are Variable
Studies of decay rates of 150 human corpses at in the Anthropological Facility in Tennessee (The Body Farm)
Most important environment factors in corpse decay:
Temperature
Access by insects
Depth of burial
Other Factors
Chemical-- embalming agent, insecticides, lime, etc.
Animals disrupting the corpse

15. Time of Death can be broadly estimated up to about 36 hours
Temperature Stiffness Time of death
Warm Not stiff Dead less
than three hours
Warm Stiff Dead between 3
to 8 hours
Cold Stiff Dead between 8
to 36 hours
Cold Not stiff Dead in more
than 36 hours

16. Medicolegal Forensic Entomology
Often focuses on violent crimes
Determination of the time (postmortem interval or PMI) or site of human death based on identification of arthropods collected from or near corpses.
Cases involving possible sudden death
Traffic accidents with no immediately obvious cause
Possible criminal misuse of insects

17. Phylum Arthropoda
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!

18. Postmortem interval (PMI)
Forensic Entomology is used to determine time since death (the time between death and corpse discovery)
This is called postmortem interval or PMI).
Other uses include
movement of the corpse
manner and cause of death
association of suspects with the death scene
detection of toxins, drugs, or even the DNA of the victim through analysis of insect larvae.

19. 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.

20. 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 a silent witnesses.

21. 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.

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

23. Blowfly Eggs Small, 2-3 mm length, elongate, whitish to yellowish
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

24. 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

25. 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

26. 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

27. 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

28. 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.

30. Blow Fly Metamorphosis
1st – Adult flies lay eggs on the carcass especially at wound areas or around the openings in the body such as the nose, eyes, ears, anus, etc.
2nd – Eggs hatch into larva (maggots) in hours.
3rd– Larvae continue to grow and molt (shed their exoskeletons) as they pass through the various instar stages.
1st Instar - 5 mm long after 1.8 days
2nd Instar - 10 mm long after 2.5 days
3rd Instar – mm long after 4-5 days
4th – The larvae (17 mm) develop into pupa after burrowing in surrounding soil.
5th – Adult flies emerge from pupa cases after 6-8 days.
Adult
pupa
eggs
1st instar
larva
3rd instar larva
2nd instar larva
It takes approximately days from egg to adult depending on the temperatures and humidity levels at the location of the body.

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

32. 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.

33. Differentiate between PMI and Time of Death
These may not always equate.
Post mortem interval is restricted to the time that the corpse or body has been exposed to an environment which would allow insect activity to begin.
Closed windows
Body in box or bag
Cold temperatures
Deeper burial

34. Examples of Diptera (Flies)
Early Stage Decomposition
Blow & Greenbottle Flies(Calliphoridae)
Metallic thorax and abdomen
Life Cycle of a Calliphoridae Fly
Late Stage Decomposition
Flesh Fly
(Sarcophagidae) Striped thorax
House Fly
(Muscidae)
Cheese Skipper
(Piophilidae)

35. F.E. 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)

36. 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)

37. The morale 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.