Entomology Flashcards
(15 cards)
Define forensic entomology
The interpretation of insect evidence in civil and criminal investigations.
Define postmortem interval
(PMI)
The time difference between the time of death and the discovery of the body.
The longer the PMI, the larger the time of death window will become, and the harder it will be to determine an accurate time of death.
What are the four principal stages of metamorphosis of blowflies?
Egg,
Larva
(instar 1, instar 2, instar 3), Pupa
Adult
What are they important to forensic entomology?
Blowflies are usually the first to inhabit a dead body. Within 24 hours,
blowflies will infest the body and lay eggs that will hatch into fly larvae.
Forensic entomologists can approximate how long a body has been left
exposed by examining the stage of development and estimate
Postmortem interval (PMI)
What are they important to forensic entomology?
Blowflies are usually the first to inhabit a dead body. Within 24 hours,
blowflies will infest the body and lay eggs that will hatch into fly larvae.
Forensic entomologists can approximate how long a body has been left
exposed by examining the stage of development and estimate
Postmortem interval (PMI)
What are the five stages of decomposition ? Describe each stage
5 stages of decomposition serve as a food source for different of insects, Each stage provide changing habitats.
1. Fresh (0-4 days) a warm, hewly dead body.
2. Bloated (4-10 days) a corpse emitting odors
of decaying flesh
3. Decay(10-20 days) emitting gases of decay
with strong odors; signs of
darkened tissues
4. Active decay(20-50 days)dry out; most flesh
is gone
5. Dry, or skeletal, decay (50-365 days) bones
remain
Why do blowflies usually the first to arrive on the dead body while
ant and bees will be later?
Decomposing bodies undergo 5 stages of decomposition that serve as a
food source for different types of insects. Insects that suck up liquids
may get nourishment from moister/softer parts of the body at earlier
stages of decomposition, while insects with sharp mouthparts may get
nourishment from a dry decaying body in a later stage of
decomposition.
Can we determine whether the person was exposed to toxins or drugs by analyzing the insects on that decomposing body of the person?
Yes, as food is ingested, it passes into the maggot’s crop. Because no digestion occurs in the crop, ingested body tissue containing DNA can be removed and analyzed. If the person was exposed to toxins or drugs, their presence can then be detected by analyzing the contents of the crops by forensic chemists.
Why are blowflies so important in forensic entomology?
Arrive usually within minutes of death
E.g., if only blowfly eggs are present, and no blowfly larvae are present
PMI is estimated to be less than 24 hours
Configuration of spiracles allows investigators to know the developmental stage of the instar.
An empty pupal case signals that a body has been in an area long enough for the blowfly to complete its full lifecycle.
Any limitations in forensic entomology?
Limitation: Insect data is less helpful in estimating PMI if the body is moved after death
E.g. Insects found on the body in the woods can estimate how long the body was in the woods, but not how long since the person was killed.
What information can be obtained by forensic entomologists by collecting and identifying insect evidence?
Insect evidence can help to
1) Estimate PMI
2) Reveal a body or remains
3) Determine if the body was moved
4) Identify a geographic range of the crime
5) Link a suspect to a crime by the presence of insect evidence or similar bites on both suspects and victim
For example, a murder suspect had chigger bites like those investigators got at the crime scene. The chiggers were found to be localized to that one area, yet the suspect denied he had ever been there.
6) Indicate where a suspect had been traveling based on vehicle/belonging
What is the role of forensic entomology in the criminal justice system?
The interpretation of insect evidence in civil and criminal investigations.
Suggest and discuss TWO factors affecting insect development to estimate PMI.
- Local temperatures
- Warmer the
temperature,
faster the
development
- If the temp is
below 10 °C,
growth and
development
stops - Environmental conditions
- Fly species can vary
geographically
- The fly pictured on the
top prefers shade; the
one on the bottom
prefers sunlight
- Egg laying will not occur
at night or in the rain
What are the procedures for documenting and collecting insect evidence from
a crime scene. List ALL the steps from observing, recording and collecting.
* Death-scene observations
* Collection of meteorological data
* Two collections: collect live insects; collect and preserve other insects
from the body at the crime scene
* After body removal: collect insects from the surrounding soil
- Death-Scene observations
- Location of crime scene, description of general habitat, weather conditions, locations of any open windows or doors near
body, whether body is inside or outside
- Location of body in reference to vegetation, sun, shade
- Body condition: locations of wounds/injuries,
decomposition stage - Collection of Meteorological Data
- Ambient temperature at scene taken at chest level
- Ground surface temperature
- Interface between body and ground
- Maximum and minimum daily
temperatures - Two collections: collect live insects; collect and preserve other insects from
the body at the crime scene.
i. Collect adults first
-Trap adults with a net and place in a killing jar with 75-80% ethanol
- Label the jars with geographical location,
date and hour of collection, case
number, location on body where insect
was collected, and name of collector
ii. Collect larvae and egg
- Collect about 50 maggots per mass, collecting the most-developed larvae (=oldest; provide the most accurate
estimate of PMI)
- Place in killing jars with 75-80% ethanol
- Living specimens should be placed in containers with tight-fitting lids; add air holes, moist paper towels and a meat source. - After Body Removal: collect insects from the surrounding soil.
- Collect insects from the area where the corpse was located and in the immediate surrounding. Keep some as live samples and preserve some insects. Label all specimen jars.
- Collect and label soil and leaf samples from the area under the body and the immediate locations of the body (to a depth of 2 inches).
Why is it so important to know which stage the corpse is being decomposed in forensic entomology?
- Insects arrive at a decomposing body in a particular order (succession) and then complete their life cycle based on the surrounding temperature
- Determine PMI (time since death) by identifying species present and/or where they are in their life cycle (since we know how long for each species to reach their
different stages of development)
