Forensic Entomology

January 13, 2018 | Author: Anonymous | Category: Science, Biology, Zoology, Entomology
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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 servicetwo dishes, but to one table. That’s the end.” ….Hamlet (Act 4: Scene 3) 1


China 200 BC- Sung Tz’u o



The death of Sung Tz’u, a poor farmer in China, represents the first time insects were used in a death investigation. The investigator asked all neighboring farmers to bring their sickles (70-80) Flies gathered at one sickle due to the presence of blood and tissue remains. The man was determined to be guilty of the murder.


Forensic Entomology 

Forensic Entomology has been used in all of the following:  Determine the time of death of a rotting corpse  Provide evidence in abuse cases: (Open wounds in elderly)  Analyze “Spatter” evidence from insects walking through blood.  Check for drugs, poisons (toxins will build up in the insects feeding on a corpse)  Determine the identity of insects hidden in shipments of products from other countries  Determine the types of insects that can cause crop damage  Determine the types of insects that can be used as biological controls in place of pesticides.


Flies: Order Diptera o o


Flies are usually the first insects attracted to a dead body. Their life cycle can provide important clues: particularly for time of death. Life cycle of flies: Egg Larvae : 1st, 2nd, 3rd instars Pupa Adult


Finding a Carcass o


Flies can detect smell of decomposition (as little as a few parts per million) by using special hairs called sensilla trichoidea that are equipped with chemical receptors. Flies must find carcass early, before it turns to mush


Egg Laying o o

o o

Flies must lay eggs in a moist area. Clothing that sops up blood and other fluids.. becomes a nursery for the eggs. Females cannot pierce skin. Lay eggs in mucous membranes of nose, mouth, eyes, open wound, scratches.


Egg Laying A

female fly has chemoreceptors on soles of her 6 feet to locate the proper location to lay her eggs.  Eggs are released through the ovipositor on the tip of her abdomen.  A single female can lay up to 400 eggs in 6 minutes


Maggots: Larva o

Eggs will hatch within10-24 hrs.


Maggots will nurse on liquid protein before their mouth hooks grow large enough to tear through flesh.


Maggots o

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


Mouth Parts of Maggots

As seen with an electron microscope


Maggots  Maggots

breath through anal spiracles (butt breathers)  These can be used to help determine the larval stage:  

1st instar = 1 anal spiracle 2nd instar = 2 anal spiracles 3rd instar = 3 anal spiracles


The Feeding Mass o

o o o o o

Maggots use collagen splitting enzymes to break through connective tissue Larvae bury heads in flesh The feeding mass generates a lot of metabolic heat The mass will periodically move to the surface to cool. Some insects will remove most maggots by eating them. This delays the decomposition of the carcass


 As

maggots grow, they put on their 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


Pre-pupa Flies  Maggots

will stop feeding once they reach the 3rd instar stage (about 1/2 inch long)  They will then drop to ground, and seek darkness; moving their light sensitive heads right and left as they move.


Determining the Species 

Determining the species of maggot is difficult and requires the third instar. Often, forensic entomologists will collect half and grow the others in lab to determine the species after pupation. If maggots not well preserved: rely on simple length of maggots: compare to day to day growth


Pupa 

 

When ready to pupate, maggots will bury themselves in soil, or move under leaves or carpets They will contract into short, thick plugs and wait for larval skin to harden They will then metamorphosize into adults New flies emerge within 1 week to 6 months later (depending on environmental conditions)

Pupa stages of the house fly


Emergence of Adult Flies A

fleshy sac pops out of slit above the eyes  The sac fills with fluid and presses against the top of the pupal case  The case pops open along a fracture line  The adult fly will fully emerge within thirty minutes Blow fly emerging (as seen with an electron microscope)


Typical infestation: o



First to arrive are usually blow flies: aka bottle flies They will appear within a few minutes They have shiny, metallic colors


Flesh flies o


Flesh flies will be attracted to the site within a day or two. They are recognized by their large red eyes.


Rove beetles and Soldier Flies o


Rove beetles and soldier flies will appear once the fly eggs have hatched and maggots are present. They will feed on the developing maggots

Rove Beetles

Soldier Fly


Cheese Skippers and Scuttle Flies  Cheese

Skippers and Scuttle Flies will appear towards the end of the infestation to feed on the fermented protein of the later stages of decomposition

Cheese Skipper

Scuttle Fly


Mites, Moths and Spider Beetles o o

Mites show up very late in the infestation. They prefer a dry cadaver Clothes moths and spider beetles will be the last to clean up the completely desiccated remains

Moth Mites

Spider Beetle


Other Insects Commonly Scene Include:

Carcass beetle

Hide beetle

Carrion Beetle


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

Third instar of Maggot



Converted to hours: 8-14 hours 8-14 hours 48-72 hrs 168-192 hrs

Totals to: 232 – 292 hrs (this represents the total time needed to reach 3rd instar)  In days: 9.6-12.2 days 


PMI estimates o PMI

estimates are affected by:  Temperature  Time of day  Time of year  Exposure


Rate of development of immature blow flies vs temperature 

Cooler weatherchoose later range of 12 days; insects develop slower

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


Jobs at the scene The following information should be documented or collected at the scene: 1. Observations and notes 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


Observations  What

is the setting: rural, urban, aquatic  Estimate # and kind of flying and crawling insects visible and already present  Which types appear to be the cause of the major infestations of the body


Observations  What

is the compass direction that the body is facing?  Is the body in sunlight or shade?  What is the position of body?  Take photos


Climatological data  The

following temperatures should be documented at the scene:      

Ambient temp Ground temp Body surface temp Under body temp Maggot mass temp Soil temp after body removed


Climatological data o

Once an approximate time frame is established, it should be adjusted by gathering additional weather data from local weather stations 

Maximum and minimum temperatures during the presumed time period and amount of precipitation should be traced back to the time when the victim was last seen


Taking field samples o


½ of the sample is generally collected and preserved in alcohol (70-80% solution of ethyl alcohol) The other ½ is kept alive and raised to adulthood in the lab to help with identification and confirm timing.


Things you collect  Eggs,

larvae, pupae, pupal cases, cast larval skins, feces, feeding marks  Insect predators including: beetles, ants, wasps, or insect parasites


Insects Provide Other Clues  Insects

are also used to show movement of:  Victim  Suspect  Cars  Goods


“The Body Farm”

Dr. William Bass: University of Tennessee


Pig decomposition- 0 to 3 days


Pig 4- 10 days after death


Pig 10 to 20 days after death


Pig 20- 50- days after death


Dry decay 50- 365 days

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