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Environmental Forensics > Forensic Entomology > Flashcards

Forensic Entomology Flashcards

1
Q

What is entomology?

A

Entomology is the study of insects.

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2
Q

What is forensic entomology?

A

Forensic entomology is the study of the insects associated with a dead body.

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3
Q

When would a forensic entomologist be called to a crime scene?

A

Forensic entomologists are called into homicide investigations when the time of death is unknown and their evidence is usually presented in court as expert testimony.

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4
Q

Why do we utilise forensic evidence?

A

Because rigor, algor, and livor mortis are useless after 72 hours.

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5
Q

What are Insects are also used to:

A

▪Determine whether the body has been moved after death
▪Determine whether it has been disturbed
▪Determine the presence or position of wound sites
▪Determine whether the victim used drugs or was poisoned
▪Determine the length of time of neglect or abuse in living victims

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6
Q

Why is determining time of death impprtant?

A
  • Understanding how, when, and why a person has died can help to give closure to family and friends and allow them to move on with their lives
  • ▪Insurance policies (Whether death occurred before or
    after insurance coverage began)
  • May indicate length of time that a fraud has occurred (Receiving monies for family members while family members are deceased)
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7
Q

When was entomology first used?

A

First recorded use was in the 13th century China.

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8
Q

When did the modern use of entomology in criminal investigation begin?

A

Modern use of entomology in criminal investigations began in France in the mid 1800s.

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9
Q

What training is important for forensic entomologists?

A

Must have extensive training in entomology:
▪ Bachelor’s degree in biology, zoology, or entomology
▪Masters in entomology
▪PhD in forensic entomology, insect ecology, and taxonomy
▪Board certification requires 5 years of experience after a PhD

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10
Q

What do entomologists do?

A

A forensic entomologist’s job may include:
* Identification of insects at various stages of their life cycle, such as eggs, larva, and adults.
* Collection and preservation of insects as evidence.
* Determining an estimate for the postmortem interval or PMI (the time between death and the discovery of the body) using factors such as insect evidence, weather conditions, location and condition of the body, etc.
* Testifying in court to explain insect-related evidence found at a crime scene.

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11
Q

What are blowflies?

A
  • Blow flies belong to the family Calliphoridae, in the order Diptera or “true flies”.
  • They are large, metallic flies seen near food or garbage cans in summer
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12
Q

How do blow flies assist in forensic entomology?

A

Blow flies are the first flies to be attracted to a body

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13
Q

Why is a protein meal important to blow flies?

A
  • Male and female blowflies require a protein meal to develop their reproductive organs and start producing eggs or sperm.
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14
Q

Why do female blowflies tend to be attracted to dead bodies?

A

Adult feeding often occurs at dead bodies, and the majority of flies attracted to remains are females seeking suitable sites to lay eggs

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15
Q

What are the stages in which the blowflies go through before becoming adults?

A

Blow flies develop from eggs through the first, second, and third instar stages, and then the pupal stage before becoming adults.

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16
Q

What factors can influence the developmental stages of blowflies?

A

Stages influenced by species of blowflies and temperature of surroundings.

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17
Q

How does temperature affect the development of insects?

A

Insects are cold-blooded, meaning their development is temperature-dependent. As temperature increases, they develop more rapidly, while as temperature decreases, they develop more slowly.

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18
Q

How can analysis of the oldest insect stage of blowflies assist in time of death?

A

By analyzing the oldest insect stage found on a body and considering the meteorological conditions at the scene, it is possible to estimate how long insects have been feeding on the body. This information can then be used to determine the approximate time of death of the victim.

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19
Q

What occurs in first instar larvae?

A

Blowfly eggs have been laid, they will hatch into first instar larvae.

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20
Q

How do blowfly larvae typically obtain their meals, and where do female blowflies usually lay their eggs?

A

Larvae rely on protein for their meals
▪ Females lay eggs on open wounds of dead individuals or around orifices of a living individual
▪Face is colonized before other areas because the skin is easier to penetrate
▪Except in the case of rape cases, flies attracted to genitalia

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21
Q

What occurs second instar stage?

A

First-instar larvae shed larval cuticles and mouthparts when entering the second instar stage.

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22
Q

How does the second instar stage of blowfly larvae penetrate the skin, and how does it differ from the first instar stage?

A

The second stage is more capable of penetrating the skin than the first instar larvae with the use of proteolytic enzymes.

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23
Q

What occurs in the third instar stage?

A

The third instar stage of blow fly larvae begins with the second instar larvae shedding its cuticle, and the larvae are commonly referred to as maggots.

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24
Q

What are the behaviours of third instar stage blowfly larvae, also known as maggots?

A
  • Maggots aggregate together in large masses and can remove a large amount of tissue in a very short amount of time.
  • After feeding, the maggots move on to a suitable site where they can pupate.
  • During the pupal stage, the maggots remove their outer cuticle, allowing them to emerge as a fly.
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25
Q

The life cycle of a fly includes?

A
  1. The Larva - First Instar
  2. The Larva - Second Instar
  3. The Larva - Third Instar
  4. Pre Pupa
  5. Pupa
  6. Adult Fly
  7. Eggs

The cycle begins again.

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26
Q

How can you identify the instar of a blow fly larvae, and how many instars do blow flies typically have?

A

Blow flies typically have three instars of larvae, which take between 1.8 to 5 days to complete. The identification of the right instar is relatively easy based on the size of the larvae, the larva’s mouth parts, and the shape of the posterior spiracles.

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27
Q

What happens to blow fly larvae at the end of the third instar, and what is a prepupa?

A
  • At the end of the third instar the larva becomes restless and starts to move away from the body. The fat body will gradually obscure the internal features of the larvae.
  • The larva has become a prepupa (8-12 days after oviposition).
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28
Q

What is a pupa, and how can the presence of empty puparia be used to estimate the time since death?

A
  • The prepupa gradually becomes a pupa, which darkens with age (18-24 days after oviposition).
  • The presence of empty puparia should therefore tell the forensic entomologist that the person in question has been dead in more than approximately 20 days.
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29
Q

How is insect growth measured?

A

Linear approach

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30
Q

Two different ways to use collected data in PMI determination

A

▪ The isomegalen diagram
▪ Controlled rearing

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31
Q

Explain the process of using controlled rearing to estimate the time since death of an insect sample collected at a crime scene.

A
  1. Collect sample from crime scene
  2. Rear until adults are close under constant conditions in the lab.
  3. Determine the ADD (accum. Degree days or ADH) required to complete development after collection
  4. Subtract this value from the total required for the species to determine unknown amount accumulated since oviposition
  5. Count back the days (or hours) prior to collection necessary for the maggot to reach the stage at which it was sampled
32
Q

How many eggs can a female blowfly lay in her lifetime?

A

Female lays 2,000 eggs in her lifetime.

33
Q

How long does it take for a fly to emerge from its pupal case, and what is the time frame for egg hatching in blow flies?

A
  • Once eggs are laid, they hatch between 12 and 48 hours
  • It takes 14 days for the fly to emerge from the pupal case
34
Q

What are the major groups of insects that are associated with cadavers in forensic entomology?

A

Flies
▪ Blowflies
▪ Flesh Flies
▪ House Flies
▪ Cheese Skippers

Beetles
▪ Carrion Beetles
▪ Dermestids

35
Q

What are the two factors that cause decomposition, and what are their respective roles?

A
  1. Autolysis
    ▪The breaking down of tissues by the body’s own internal chemicals and enzymes
  2. Putrefaction
    ▪The breakdown of tissues by bacteria
36
Q

What is the chief source of the characteristic odor of dead bodies, and how is it produced?

A

Autolysis and petrification processes release gases that are the chief source of the characteristic odor of dead bodies. These gases swell the body.

37
Q

What is the role of scavengers in the process of decomposition?

A

Insects and other animals are typically the next agent of decomposition, if the body is accessible to them.

38
Q

What are the most important insects typically involved in the process of decomposition, and why?

A

The most important insects that are typically involved in the
process include the fleshflies (Sarcophagidae) and
blowflies (Calliphoridae)
▪ The green-bottle fly seen in the summer is a blowfly

39
Q

What are some larger scavengers that may eat a body if it is accessible to them, and what may they do with the bones?

A

Larger scavengers, including coyotes, dogs, wolves, foxes, rats, and mice may eat a body if it is accessible to them
▪ Some of these animals also remove and scatter bones.

40
Q

What is the first method used to determine the elapsed time since death based on? How long is the evidence valuable for?

A

First method based on the predictable development of larval Diptera, known as the blow fly whose evidence valuable from a few hours to several weeks after death.

41
Q

Which insect is used in the first method to determine the elapsed time since death? When is it used?

A

Larval Diptera, known as the blow fly and it is used from the first time the first egg is laid on the remains until the first adult flies emerge from the pupal cases and leave the body

42
Q

What is the second method used to determine the elapsed time since death based on? When can it be used?

A
  • Second method is based on the predictable, successional colonization of
    the body by a sequence of carrion insects
  • Can be used from a few weeks after death until nothing but dry bones remain
43
Q

What is the difference in the time frame for evidence collection between the first and second methods used to determine the elapsed time since death?

A

The first method can only be valuable a few hours to week after (wet stage) whereas the second method can be used a few weeks after death why dry bones can be seen (dry stage).

44
Q

What are the stages of decomposition?

A

Fresh Stage (Days 1-2)
Bloated Stage (Day 2-6)
Decay Stage (Days 5-11)
Post-decay Stage (Days 10-25)
Dry Stage (Days 25+)Fresh Stage (Days 1-2)
Bloated Stage (Day 2-6)
Decay Stage (Days 5-11)
Post-decay Stage (Days 10-25)
Dry Stage (Days 25+)

45
Q

Describe the main characteristics of the Fresh Stage of decomposition and how long it lasts.

A

Commences at death, ends when bloating is first evident. Breakdown of protein and carbohydrates into simpler compounds.

46
Q

What happens during the Bloated Stage of decomposition and how long does it last?

A
  • The Bloated Stage last for Day 2-6.
  • Putrefaction begins. Gasses produced by anaerobic bacteria inflate the abdomen.
47
Q

Explain the process of decay that occurs during the Decay Stage of decomposition and how long does it typically last?

A

Decay Stage (Days 5-11)
▪ Abdominal wall breaks - gasses escape - carcass deflates.

48
Q

In what ways do remains differ between wet and dry habitats during the Post-decay Stage of decomposition?

A
  • In dry habitats, remains are skin, cartilage, and bones.
  • In wet habitats, wet, viscous material in the soil under the remains.
49
Q

What is the main component of remains during the Dry Stage of decomposition, and how does the odor differ from other stages?

A
  • Mainly bones and hair remain.
  • Odor is primarily that of normal soil and litter. Can last several months to years.
50
Q

What happens during the Fresh Stage of decomposition, and how do blowflies contribute to the process?

A
  • Blowflies have detected the cadaver.
  • Eggs are being laid, often around the eye, nostrils, mouth, followed by anus or genital openings
51
Q

Which insects are typically present during the bloated stage of decomposition, and what is their role in the process?

A

In the Bloated Stage:

  • Cadaver begins to swell and putrefy
  • Blowflies are still ovipositing
  • Flesh flies appear
  • Small maggots are feeding
52
Q

What happens in the post decay stage of decomposition ?

A

Cadaver is drying out. Large maggots are leaving or have left.

53
Q

What is left in the drying stage of decomposition?

A

Skin and bones.

54
Q

Which type of insects are capable of digesting keratin, a protein found in skin and hair, during the dry stage of decomposition and contributing to the breakdown of remains?

A

Clothes moths and Dermestid beetles

55
Q

What is the post mortem interval?

A

Elapsed time from a death to the discovery of a cadaver.

56
Q

What insects are helpful in determining the PMI?

A

Flies (especially calliphorids and sarcophagids) can be vital in determining the PMI.

57
Q

What are some of the premises for using insects to determine the post-mortem interval (PMI)?

A
  • Flies will begin oviposition as soon as they discover a body
  • Succession on a corpse is predictable
  • Insect development is predictable
58
Q

Factors that are used to determine time since death

A

Four Factors must be taken into account
1. Oldest stage of blow fly associated with the body
▪ Look at old pupal cases.
2. Species of insects
▪ Each species develop at different rates so each species of insects at the scene need to be collected.
3.Temperature data
▪ Must be able to determine temperature of crime scene for a period of time.
4. Developmental data
▪ Must know how fast or how slow the specific species develop.

59
Q

Steps in determining the PMI?

A

Step 1. Collect samples of the insects present.
Step 2. Determine temperature history at crime scene
Step 3. Estimate time of egg laying
Step 4. What other insect evidence is available?

60
Q

Why is it important to collect the largest maggots on the cadaver during the insect collection stage of determining PMI?

A

There is often not enough flesh left to determine drug presence, but maggots bioaccumulate so an can be analyzed to determine type of drug present.

61
Q

What is the purpose of rearing some of the preserved maggots to adulthood during the insect collection stage of determining PMI?

A

The growth rate of larvae can be studied by rearing them in the laboratory and this can give a reliable definition of time since death. As well as to confirm species ID’s.

62
Q

How does temperature history at a crime scene affect the determination of PMI using insects?

A

Look for ‘windows’ of insect opportunity.

63
Q

What are some sources of temperature data that can be used to estimate the temperature history at a crime scene during the determination of PMI using insects?

A

Air temperature for general area (airport readings, etc.).

64
Q

How do species present and their age help to estimate PMI during the determination of PMI using insects?

A

Given the species present and their age (size), eggs can tell how long did it take them to develop to that point at the temperatures occurring in the area.

65
Q

What do examiners do in the Step 4. What other insect evidence is available?

A

Look for other insect evidence that might corroborate or contradict your PMI estimate.

66
Q

How can you determine whether a body has been moved?

A

Insects present on the deceased body that are not prevalent to the crime scene can indicate that the victim was murdered elsewhere and was dumped at another location.

67
Q

How can insects help determine the presence of wounds on a decomposing body?

A

Insects are attracted first and foremost to wounds, so the first instar larvae will have access to liquid protein for nutrition.

68
Q

What is the significance of the position of wounds in relation to insect colonization on a cadaver?

A

Wound sites in individuals that have completely decomposed are shown by irregular or atypical insect colonization.

69
Q

How can insects link a suspect to a crime scene?

A

Sometimes, criminals carry entomological evidence on them unknowingly
This evidence can place them at the crime scene by examining the life cycles of the insects.

70
Q

How does the presence of a maggot mass on a cadaver complicate the use of insect evidence for estimating the PMI, and what factors contribute to this complication?”

A
  • Metabolic activity by large numbers of maggots raises temperature of the cadaver significantly.
  • Generally increases with larval density
  • May result in dramatically shorter development times
  • Most important at cooler temperatures
  • Very difficult to determine the heat regime experienced by an individual maggot.
71
Q

How does the age of assessment of the maggots complicate the use of insect evidence for estimating the PMI?

A

Are the biggest maggots the oldest?
▪E.g., A Phaenicia or a Phormia oviposits one day before a Calliphora but by day 4, the Calliphora are the largest.

72
Q

How does the sun of effect complicate the use of insect evidence for estimating the PMI?

A
  • Sunny vs. shady sites may have a greater effect than air temperature alone.
  • Changes with cadaver size
  • Presence / absence of clothing
  • Changes with substrate (sand vs. soil. vs concrete)
73
Q

How does the bioaccumulation complicate the use of insect evidence for estimating the PMI?

A

Insects that feed on the body of individuals that have been poisoned can be examined to determine what type of drug or toxin the person was poisoned with
▪It is important to note that specific drugs either
speed up or slow down larval development
▪Can influence entomologist’s final report

74
Q

How should one collect entomological evidence?

A
  1. Evidence should be collected by an entomologist
    ▪ If not available, a police death investigator should collect the evidence
  2. Different stages of larval growth should be collected and bagged separately
  3. Sample of soil should also be collected from just outside the area marked by body fluids
75
Q

Three challenges that face forensic entomological ?

A
  1. Temperature
    - Temperature of crime scene and the temperature that the insects have been exposed to us unknown.
  2. Season
    - Entomology is valuable only in spring, summer, and fall
  3. Exclusion of insects
    - Insects are excluded based on condition of body

Environmental Forensics (10 decks)

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