1

Forensic Entomology

“ We fat all creatures else to fat us, and we fat ourselves for maggots. Your fat

king and your lean beggar is but variable service- two dishes, but to one

table. That’s the end.”

-HAMLET (ACT 4 SCENE 3)

2

Forensic Entomology

• Application of the study of insects to legal issues– Determination of time (PMI) or site of human death– Cases involving possible sudden death– Traffic accidents with no immediately obvious cause– Possible criminal misuse of insects

• Subfields:1. Urban (ex. Termites)

2. Stored Product (food, beverages, kitchen)

3. Medicolegal (focus of this lecture)

3

China 200 BC- Sung Tzu

• Farmer in neighborhood killed

• Death investigator- all bring their sickles (70-80)

• Flies gathered at one sickle

4

Forensic Entomology

• Time of death estimates• Abuse cases: Open wounds in elderly• “Spatter” or insects walking ??• Check for drugs, poisons in insects• Beer, soda industry• Insects hidden in shipments • Crops affected• Pesticides and biological controls

5

Flies = Diptera

Life cycle of flies:

• Egg

• Larvae : 1st, 2nd, 3rd instars (stages)

• Pupa

• Adult

6

7

Egg Laying in Moist Area

• Females cannot pierce skin. Lay eggs in mucous membranes of nose, mouth, eyes, open wound, scratches.

• 1st instar larvae: must nurse on liquid protein before their mouth hooks grow large enough to tear through flesh.

• Clothing that sops up blood and other fluids.. becomes a nursery for the eggs

8

Egg Laying

• Female has chemoreceptors on soles of her 6 feet and the ovipositor on the tip of the abdomen.

• Can lay up to 400 eggs in 6 minutes

9

• Flies must find carcass early, before it turns to mush

• Flies can detect smell of decomposition -- as little as a few parts per million

• special hair on flies that have chemical receptors (sensilla trichoidea)

10

Flies

• First flies lay down pheromones.. cause an oviposition frenzy

• Eggs hatch 10-24 hrs later

• Larvae tear at exposed flesh with a pair of tiny mouth hooks

11

Maggots (larvae)

• Breath through anal spiracles• Metabolic heat send mass to surface to

cool periodically• As maggots grow, put own layer of fat that

eventually hides all internal organs except for the crop (feeding tube) – seen as dark red line extending back from mouth

12

• Maggots grow- flattened rump, pointed mouth, ridges around the body

• Use collagen splitting enzymes to break through connective tissue

• Larvae bury heads in flesh

• Some insects will remove most maggots and delay decomposition

13

Anal spiracles

first instar: 1 anal spiracle

second instar: 2 spiracles

third instar: 3 spiracles

Need third instar to distinguish species

14

15

• Stop feeding after 3rd instar (1/2 inch long)

• Maggots then drop to ground, seek darkness, moving light sensitive heads right and left as they move.

16

Need third instar to distinguish species

• Internal mouthparts

• “Teeth”- simple hooks or compound barbs?

• Short and claw like or long like a saber?

• If maggots not well preserved: rely on simple length of maggots: compare to day to day growth rates.

17

Pupa

• Bury in soil, move under leaves, carpets

• Contract into short, thick plugs and wait for larval skin to harden

• Metamorphosis into adults

• New fly emerges from 1 week to 6 months later

18

Emergence of Adult Flies

• Emergence—fleshy sac pops out of slit above the eyes

• Sac fills with fluid, presses against top of pupal case, pops it open along a fracture line

• Fly within thirty minutes

19

Typical infestation:

a) Blow flies (bottles) -- few minutes

b) Flesh flies- within a day or two

c) Rove beetles, soldier flies – feed on developing maggots

20

Typical infestation

d) Cheese skippers, scuttle flies- feed on fermented protein of the later stages of decomposition

e) Mites- like dry cadaver

f) Clothes moths and spider beetles—completely desiccated remains

21

Example of post-mortem interval (PMI)

• 8-14 hrs for eggs to hatch

• 8-14 hrs to finish 1st instar

• 2-3 days 2nd instar

• 7-8 days- third instar

22

PMI

• 8-14 hours

• 8-14 hours

• 48-72 hrs

• 168-192 hrs

• 232 – 292 hrs (total time needed to reach 3rd instar)

• 9.6-12.2 days

23

PMI estimate affected by:– Temperature– Time of day– Time of year– Exposure?

24

• Cooler weather- choose later range of 12 days; insects develop slower

• Warmer weather – pick early part of range, 9 days; insects will develop faster

25

Typical Flies

• Green bottle Phaenicia sericata: urban settings, open, sunlit

• Black blow fly : Phormia regina rural areas

• Green bottle: Phaenicia eximia : southern states

• Holarctic blow fly: Protophormia terraenovae : north

26

Blow flies

• 1st to arrive• Family Calliphoridae• Lays eggs (oviposits) within minutes and up to

two days after death• Egg 3 instars prepupae pupae adult• Calculate the age of the insects using the life

stages• PMI= postmortem interval

27

• Insects are also used to show movement of:– Victim– Suspect– Cars– goods

28

Case study #1

• One puparium in barrel of gun

• Many of the same puparia under floor mat of burned out car

• Gun and car found 50 ft apart

• Boyfriend claimed – crime of passion- only 2nd degree murder- left car after it wrecked

29

• Prosecution- said he came back to burn car

• Entomologist: gun was inside the car when larvae finished feeding and crawled away to find dark place to metamorphose into an adult.

• 50 ft too far for maggot to crawl

30

Case Study # 2

• 1980’s female body found, maggots collected• Some preserved, some raised to adulthood• Found sheep blow flies and shiny bluebottles

which lay eggs the first day of death• Found one very large maggot ¾ inch• Would have meant the woman died three weeks

earlier but she had been seen alive 2 weeks before

31

• No other carcass nearby that may have been the source of the maggot

• Mystery solved--- woman was a cocaine user

32

Taking field samples

½ in alcohol – 70-80% solution of ethyl alcohol

½ kept alive- raise to adulthood in the lab

33

Jobs at the scene

1. Observations and notes at the scene

2. Climatological data

3. Specimens from the body

4. Specimens from near the body

5. Specimens under and near the body after the body is removed

34

Climatological data

• Ambient temp

• Ground temp

• Body surface temp

• Under body temp

• Maggot mass temp

• Soil temp after body removed

35

Climatological data

Weather data from station Max temp Min temp Amt precipitation Go back in time to when the victim was

last seen

36

Observations

• Rural, urban, aquatic ?

• Estimate # and kind of flying and crawling insects

• Major infestations of the body

• Eggs, larvae, pupae, pupal cases, cast larval skins, feces, feeding marks

• Insect predation by beetles, ants, wasps, or insect parasites

37

Observations

• Compass direction

• Sunlight vs. shade

• Position of body

• Photos

38

Weather station readings

• Find your local weather station and collect information

• Adjust data to compensate for: – Sun vs. shade– Windy hill or protected cove?– Maggot mass? (can be much warmer than air)– Ambient and ground temp at corpse may vary

from weather station