Forensic Entomology Notes
Terms in this set (37)
What do forensic entomologists do?
Apply their knowledge of entomology (insects) to provide information for criminal investigations
This job includes 3 aspects:
of insects at various stages of their cycles; such as eggs, larva, and adults
and preservation of insects as evidence
an estimate for the postmortem interval (PMI) using different factors
The time between death and the discovery of the body
Factors used in determining PMI:
- Insect evidence
- Weather conditions
- Location and condition of the body
in court to explain insect-related evidence found at a crime scene
Most insects on a body are from two major orders:
1. Flies (Diptera)
2. Beetles (Coleoptera)
Different species arrive after different amounts of time has elapsed after death
When do some species of arrive?
- Some arrive right away, while others prefer to feed on an older corpse
- Certain species will also arrive that prey on the insects already feeding on the corpse
Temperatures taken at the scene:
-ground surface next to body
-interface area (between the body and the ground)
-soil under the body
-inside any maggot masses
Weather data needed:
-Daily temperature (highs/lows)
-Data needed from before the body was discovered to the time the insect evidence was collected
Factors that might affect 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 on it?
-Were other insect species present that may have affected the development of the collected species?
-Were there other drugs or poisons in/on the body that might have affected the larvae's development?
-Microbes might make a difference
First step in a blow fly life cycle:
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.
Second step in a blow fly life cycle:
Eggs hatch into larvae (maggots) in 12-24 hours
Third step in a blow fly life cycle:
Larvae continue to grow and molt (shed their exoskeleton) as they pass through the various instar stages
1st instar larva:
5mm long after 1.8 days
2nd instar larva:
10mm long after 2.5 days
3rd instar larva:
14-16mm long after 4-5 days
Fourth step in a blow fly life cycle:
The larvae (17mm) develop into pupae after burrowing in surrounding soil
Fifth step in a blow fly life cycle:
Adult flies emerge from pupa cases after 6-8 days
Blow fly life cycle picture:
-1st Instar Larva
-2nd Instar Larva
-3rd Instar Larva
Approximately how long does it take for eggs to turn into adults?
14-16 days, depending on the temperatures and humidity levels at the location of the body
Early stage decomposition flies:
1. Blow and Greenbottle flies (metallic thorax and abdomen)
2. Flesh Fly (striped thorax)
Late stage decomposition flies:
1. House Fly
2. Cheese Skipper (long body, segmented)
Early stage decomposition beetle:
1. Carrion Beetles (adults and larvae feed on fly larvae)
Early to late stage decomposition beetles:
1. Rove Beetles (predator of fly eggs)
2. Clown Beetles (predator of fly eggs)
Late stage decomposition beetles:
1. Ham and Checkered Beetles (predator of flies and beetles; also feed on dead tissue)
2. Skin Beetles (feed on dried skin and tissues)
3. Hide Beetles (usually the last to arrive)
What is ADH?
A number that entomologists calculate
What does ADH stand for?
Accumulated Degree Hour
What does ADH represent?
The amount of heat that it takes for an insect to change from one larval stage to another
How to calculate ADH:
Time between stages x (multiplied by) Temperature
Example of ADH:
If a stage takes 12 hours at 70 degrees, the the ADH (12x70) = 840 degree-hour
Does ADH change or is it constant?
It is constant (does not change) for each species and life cycle stage
What can you do if you know the average temperature at the scene?
You can use ADH to figure out how long it has been since the eggs were laid on the body by dividing the ADH by the average temperature
Since we know how long after death each species arrives at a body, what can we use ADH to estimate?
Time of Death