Forensic Entomology

There is more total _______ of insects than of humans

biomass

There are over a million described species; more than ____ of all known organism

2/3

Insects are the most ________ and ________ forms of life on earth

diverse, abundant

Forensic Entomology

the study of insects associated with a deceased body

How many hours after death is when entomological evidence is the most accurate, as well as the only method available to determine elapsed time since death?

72 hours

What can insects be used to determine?

1. Whether a body has been moved after death

2. Whether a body has been disturbed

3. The presence or position of wound sites

4. Whether the victim used drugs or was poisoned

5. Length of time of neglect or abuse in living victims

Where do you collect insect examples

At the crime scene (preferred) and during autopsy

How should entomological evidence be collected?

• Remains and environment should be observed and photographed before collection of insect stages begins

• Thermometer placed on top of maggot masses to measure temperature—aids with calculating the minimum post-mortem interval

• *For each maggot mass…

  • Keep ½ of the maggots alive

    • Why? → the species of maggots cannot be identified until they are adults

Once evidence is received, the first step is to _________________

identify the species of samples

Why is species identification important?

• Different species grow at different rates

  • ex. 7mm maggot may be anywhere from 3 days old to 10 days old, depending on the species

What are the two methods for estimated post-mortem interval (PMI)?

1. Development of larval Diptera (primarily blow flies)

2. Seasonal, successional colonization of body by carrion insects

Carrion insects

specialized invertebrates, primarily beetles (Coleoptera) and flies (Calliphoridae, Sacrophagidae), that feed on and breed in decaying carcasses

Larval diptera

also known as fly larvae, are legless, often worm-like immature insects that undergo complete metamorphosis; commonly known as maggots

What can be used to determine elapsed time since death in diptera larva development?

• Flies are attracted to the body immediately after death

• Blow flies (Calliphoridae) are among the first

• Males and females require a protein meal (the body) before sexual development

• Females primarily are looking for a place to deposit eggs (oviposition)

Oviposition

the process where adult female flies (commonly blowflies) lay eggs or larvae on a decomposing body, typically within minutes to hours of death; this acts as the starting point for estimating the minimum post-mortem interval, as the age of the oldest larvae is determined by when this egg-laying occurred

Calliphoridae

blow flies

Sacrophagidae

flesh flies

What are the four stages of diptera larvae development?

1. Egg

2. Larvae

3. Pupae

4. Adult

How many life cycles does the blowfly have (diptera/maggots)? What is the order?

6; the egg, three larval stages, the pupa, and adult

What are the hour increments for each stage?

1. Flies will lay their eggs, soon after the individual is deceased

2. Within 23 hours, you will have the 1st instar stage

3. 27 hours after that, you will have the 2nd instar stage

4. 22 hours after that, you will have the 3rd instar stage

5. 130 hours after that, you will have the pupa stage

6. 6. Finally, 143 hours after that, you will have your fly

**This is known lifecycle for this type of fly, and occurred in 70F

1st instar stage

very delicate, prone to desiccation, must be near mucoidal or moist area, such as wounds and/or orifices

2nd instar stage

can penetrate skin by rasping mouth and enzymes; important to be laid in wounds and orifices so they can eat

3rd instar stage

voracious feeder and aggregates in large masses—maggots; during this time, the crop (a food storage organ in the forgut) can be seen as a dark oval through the translucent tissue of the maggot

Crop

a food storage organ in the forgut; can be seen as a dark oval through the translucent tissue of the maggot

What is the foam in the crop created by?

metabolism and the movement of the insects

Instar can be determined by looking at _______

spiracles

How can you tell which instar stage a maggot is in?

you count the number of “mini-footballs” on the spiracles; can only be seen under the microscope

3 “footballs”

3rd instar

2 “footballs”

2nd instar

Glob

1st instar

What happens after the 3rd instar stage of development?

the larvae leaves the corpse and finds a suitable pupation site to develop into a pupa; usually close, but away from the body, and will burrow into mud or dirt

Pupal case

the leftover case by the pupa once the fly emerges

How long does it take for the fly to dry so it can fly?

24 hours

Phototrophic

obtains energy from the sunlight; the fly

Development of insects is __________ dependent, and also affected by species, humidity and nutrition available

temperature

How is blowfly pupa evidence collected?

it will be collected and placed in a vial with paper towel to cushion them; do not preserve

How deep and far away are pupae generally found in the dirt?

several centimeters deep and scattered several meters away from the body

Should empty pupal cases be collected?

yes

Adult blowflies have little forensic value, unless they are…

still wet and emerging from pupae

While blowflies are the predominant insects used to determine death in the first few weeks after death, what other insects should be collected and preserved in alcohol?

flies and beetles

How should beetles be stored?

individually, as they will eat other smaller beetles and flies

When do beetles arrive in the decomposition process?

early or late; species dependent

In blowfly development in corpses, the researcher must know…

1. Oldest stage of blowfly associated with body

2. The species of insect

3. Temperature data

4. Developmental data—locally and from published works

When all information is available, the question asked is, “how long does it take this species to reach this stage?”

What other information is rquired with entomological evidence?

1. A soil sample from close to but not under torso should be collected

2. Weather conditions recorded

3. Description of scene and body should be provided

Collection at morgue—collect insects at morgue in same manner as when in field when unable to do so at the scene

How should the evidence be collected?

½ should be alive, ½ should be dead

Successional colonization of body

• The corpse provides an attractive environment for insects to feed, mate, and deposit eggs

• The corpse passes through relatively predictable stages of decomposition

• Within minutes, insects arrive, blowflies being among the first

• Different species of insects will be attracted to the corpse at different times

Sequence of insects colonizing body is impacted by…

1. Nutritional changes of body

2. Geographic region

3. Habitat

4. Season

5. Meteorological conditions

6. Microclimate

Sequence is normally predictable

Lack of a specific pupae or insect, such as blowfly, could reflect _________________

death occurring at a different time of year

Other conditions that affect colonization include…

1. Altitude, geographic region, sun exposure

2. Temperature; hotter = faster

3. Inside or outside a house

4. Buried or above ground

5. Hanged, burned, wrapped or in a vehicle

Since eggs are rarely deposited on a corpse before death…

the age of immature insect specimens is the absolute minimum amount fo time a person has been dead; ex. a three-day-old maggot on a corpse would indicate the body has been dead for at least three days

What is the metamorphosis for flies and beetles?

1. Egg (0-24 hours)

2. Maggot (4-7 days)

3. Pupa (10-20 days)

4. Adult

How do you determine whether a body has been moved?

• Specific types of insects inhabit specific geographical areas

• Killer may not move body initially, then move it, leaving behind possible pupa or other clues

Body disturbance

• Killers may return to the scene of a crime and disturb remains

• Evidence of time of death and disturbance of body corroborate other evidence

• Blowfly development in different parts of body may suggest the body has been moved due to exposure of the body, etc.

Presence and position of wounds

• Blowflies are attracted to wounds—moist location

• Female flies are genetically programmed to find wounds to lay eggs at that site

• Irregular insect colonization may indicate a wound

• Inferences to colonization of genital areas does not always mean a r*** has occurred—moist area with mucosal layer

What are the five stages of decomposition fueled by insect activity?

1. Fresh

2. Bloat

3. Decay

4. Post-Decay

5. Dry (Skeletal)

Fresh Stage of Decomposition

• Begins at death

• Flies begin to arrive

• Temperature begins to fall to that of the ambient temperature

• Autolysis, the degradation of complex protein and carbohydrate molecules, occurs

• Gases will be produced by the metabolic activities—will cause slight inflammation of the abdomen

Autolysis

the degradation of complex protein and carbohydrate molecules

Bloat Stage of Decomposition

• Swells due to gases produced by bacteria

• Temperature will rise in the corpse

• Flies are still present

Decay Stage

• Gases subsite; 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 its original mass

  • The abdominal wall is broken; the gases are escaping and the carcass is deflating

  • Facilitated by feeding activity of larvae flies; will be present on exposed remains

  • Adult flies will start to leave the body—mainly the larval mass

• Carcass begins to have blackened wet appearance and most of the flesh will be removed by the maggots

• Towards the end of this period, the carcass will begin to dry, and the beetles will feed on the dryer tissue

• Flies will being to pupate and the predatory beetles will come to feed on other insects

Post-Decay Stage of Decomposition

• Carcass reduced to hair, skin and bones (and cartilage)

• Fly population reduced and replaced by other arthropods

• Hide beetles are dominant in dry environments

• Mite and predatory beetle populations increase

• Immature and adult moth flies, musket flies, and rove beetles

Dry (Skeletal) Stage of Decomposition

• 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 10% of the original mass

• In the last stage (skeletal stage), only bone and hair remain

• Odor is primarily of normal soil and litter

• Some insects will return, and this can last for several months to years

  • Historides, fly pupae, immature and adult rove beetles, normal soil mites