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Forensic Entomology

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Title: Forensic Entomology


1
Forensic Entomology
  • Chapter 9

2
What is Forensic Entomology?
  • Forensic Entomology is the use of the insects,
    and their arthropod relatives that inhabit
    decomposing remains to aid legal investigations. 
  • The broad field of forensic entomology is
    commonly broken down into three general areas
    medicolegal, urban, and stored product pests. 
  • The medicolegal section focuses on the criminal
    component of the legal system and deals with the
    necrophagous (or carrion) feeding insects that
    typically infest human remains.
  • The urban aspect deals with the insects that
    affect man and his immediate environment.

3
What is Forensic Entomology?
  • This area has both criminal and civil components
    as urban pests may feed on both the living and
    the dead.
  • The damage caused by their mandibles (or
    mouthparts) as they feed can produce markings and
    wounds on the skin that may be misinterpreted as
    prior abuse.
  • Urban pests are of great economic importance and
    the forensic entomologist may become involved in
    civil proceedings over monetary damages.  
  • Stored product insects are commonly found in
    foodstuffs and the forensic entomologist may
    serve as an expert witness during both criminal
    and civil proceedings involving food
    contamination.

4
How diverse is forensic entomology?
  • The diverse applications of forensic entomology
    include the detection of abuse in children and
    neglect of the elderly. 
  • There have been many published cases that detail
    parents intentionally using wasps and bees to
    sting their children as a form of punishment. 
  • Entomological evidence has been used to prove
    neglect and lack of proper care for wounds
    existing on the elderly under both private and
    institutional care.

5
How diverse is forensic entomology?
  • It is theorized that the stings (or mere
    presence) of bees and wasps may be responsible
    for a large number of single occupant car
    accidents that seem to lack a definitive cause.  
  • Insects have been suspected of causing aircraft
    crashes through the obstruction of essential
    instrumentation, and even implicated in the
    obstruction of fuel lines causing engine
    failure. 
  • Forensic entomologists are also requested to
    examine the fragmented remains of insects that
    have impacted and lodged on the front fascia,
    windshield, and radiator of automobiles. 
  • Analysis of such remains can yield evidence to
    the probable path of an automobile through
    particular areas when pinpointing the location
    and areas of travel are of unique importance.

6
How diverse is forensic entomology?
  • Insects can also affect the interpretation of
    blood spatter pattern analysis.
  • Roaches simply walking through pooled and
    splattered blood will produce tracking that may
    not be readily recognizable to the untrained
    observer.
  • Specks of blood in unique and unusual areas (such
    as on ceilings) may mislead crime scene
    technicians unless they are aware of the
    appearance of blood contaminated roach tracks.
  • Similarly, flies and fleas may also track through
    pooled and spattered blood.
  • However, flies will also feed on the blood and
    then pass the partially digested blood in its
    feces, which are known as "flyspecks". 

7
How diverse is forensic entomology?
  • Flies will also regurgitate and possibly drop a
    blood droplet on a remote surface, which may
    serve to confuse bloodstain analysis. 
  • Fleas feeding on the living pass a large amount
    of undigested blood (used as the larval food
    source) on many household surfaces. 
  • If a crime occurs in a heavily infected
    apartment, fecal drops already present would
    serve to confuse analysts as those droplets would
    test positive for human blood. 
  • Therefore it is important to recognize and
    properly document the natural artifacts that may
    occur from the presence, feeding, and defecation
    of roaches, flies, and fleas. 
  • Insects that feed on living, decomposing, or
    dried vegetable material are submitted to the
    forensic entomologist in an effort to determine
    the country or point of origin.
  • This is particularly important with vegetative
    material such as imported cannabis.

8
Importance of Bugs
  • Insects have existed on earth for about 250
    million years comparatively humans have existed
    for about 300,000 years. 
  • Such an enormous amount of time has allowed
    insects to attain a wide diversity in both form
    and development. 
  • There are currently about 700,000 described
    species and it is estimated that there may be
    more than 10 million species of insects yet to be
    described. 
  • Some insects have evolved a gradual or
    "paurometabolous" development in which there is
    an egg that hatches into an immature or "nymph",
    which resembles the adult form, but is smaller
    and lacks wings. 

9
Importance of Bugs
  • Most forensically important insects undergo a
    complete or "holometabolous" development.
  • There is an egg stage (except for a few insects
    such as the flesh flies that deposit living
    larvae) which hatches into a larval form and
    undergoes a stepwise or incremental growth. 
  • This pattern is caused by the successive molts
    (shedding of the outer skin that has become too
    small) that the larva must undergo before it
    finally enters the inactive pupal stage. 
  • The pupa is simply the hardened outer skin of the
    last larval stage and the adult will develop
    inside of this protective skin.

10
Blowflies
  • Blowflies often are an attractive blue-green,
    metallic color, leading to the common English
    names, blue-bottles and green-bottles - and the
    common Australian name, blue-arsed flies.
  • They also come in a non-metallic, brown form, but
    all blowflies are usually relatively large flies.
  • Blowflies can pick up faint traces of the odor of
    decay and can fly up to 10 miles from their
    birth-place in search of a suitable corpse in
    which to lay their eggs.

11
Blowflies
  • Female blowflies will often use their tongue-like
    mouthparts to feed on the protein secretions
    oozing from a corpse, prior to laying their eggs
    through their pointy ovipositor.
  • Blowfly eggs are 2 mm long and are laid in clumps
    that resemble miniature rice balls.
  • A single female can lay nearly 2,000 eggs during
    her life, and 5,645 eggs have been counted from a
    small piece of meat (150 g) after five hours
    exposure.
  • The eggs hatch after between 12 hours and 2 days,
    depending on the temperature.

12
Blowflies
  • Blowfly maggots are of two forms smooth maggots,
    and 'hairy' maggots.
  • The smooth maggots belong to pioneer flies that
    are purely corpse feeders.
  • 'Hairy' maggots will often feed on corpses, but
    they are also active predators that feed on
    smooth maggots.
  • Although they look hairy, the 'hairs' are really
    papillae (protrusions of the body), which deter
    other predators from consuming them. Because they
    are predators, the arrival of the secondary flies
    that produce hairy maggots is normally later that
    of the pioneer maggots.

13
Blowflies
  • Blowfly larvae feed using their mouth hooks and
    rapidly increase in size.
  • They shed their skins (molt) two times during
    their development.
  • Each stage of development is called an instar and
    the time it takes to develop between instars is
    fairly constant, although it is dependent upon
    temperature.
  • The identification of larvae of a particular
    instar, combined with a knowledge of recent
    weather conditions, allows forensic entomologists
    to determine the time of death in murder
    investigations.

14
Blowflies
  • When the third-instar larva has finished growing,
    it leaves the corpse and burrows into the ground
    where it develops into a pupa.
  • It takes around 14 days for the pupa to
    reorganize itself and emerge as an adult fly, but
    can take much longer in cold weather.

15
Blowflies
  • The pupae of blow flies are often overlooked, as
    they closely resemble rat droppings or the egg
    case of cockroaches. 
  • The pupal stage is an extremely important stage
    to the forensic entomologist and a thorough
    search should be made for the presence of pupae
    at any death scene. 
  • If the adult insect has not emerged, the pupa
    will appear featureless and rounded on both ends. 

16
Blowflies
  • If the adult insect has emerged, one end will
    appear as if it has been cut off, and the hollow
    interior will be revealed.   
  • Most adult blow flies appear a metallic green or
    blue and are easily recognizable. 

17
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18
Screw Worms
  • The adult secondary screwworm, Cochliomyia
    macellaria, emerging from the puparium. 
  • This newly emerged adult will attain its typical
    bright green coloration and will be ready for
    flight in a few hours. 
  • The empty case that it leaves behind will remain
    in the environment for extended periods of time. 
  • Therefore, a careful search should always be
    conducted for the presence of the puparium. 
  • Its presence is often useful in establishing the
    maximum postmortem interval estimation. 
  • Since the puparium is composed of the outer skin
    of the larvae, many identifying characteristics
    are retained and a species identification may be
    obtained even though the adult fly is not
    recovered.   

19
Blowflies
20
1st Instar
21
2nd Instar
22
3rd instar
23
Age based on Mouth Hooks
1st instar maggot
2nd instar maggot
24
Mouth sphericales
25
Maggots at Work
Maggots can consume 60 per cent of a corpse in
less than a week.
26
Life Cycle
  • Eggs
  • present in clumps of up to 300
  • laying to hatching takes 1 day
  • Larva - 1st instar
  • initially feeds on fluid exuded from the body
  • migrates into body
  • hatching to first molt takes 1 day
  • Larva - 2nd instar
  • moves around in maggot mass
  • first molt to second molt takes 1 day

27
Life Cycle
  • Larva - 3rd instar
  • still moves in mass
  • greatly increases in size
  • second molt to pre-pupa takes 2 days
  • Pre-pupa
  • migrates away from the corpse seeking a suitable
    pupation site, (usually in soil)
  • does not feed
  • transforms into pupa
  • pre-pupa to pupa takes 4 days

28
Life Cycle
  • Pupa
  • resides within puparium
  • undergoes transformation from larval body form
    adult fly
  • does not feed
  • pupa to emergence takes 10 days
  • Adult fly
  • mates on emergence from pupa
  • feeds on protein from body fluids
  • lays eggs on corpse
  • emergence to egg laying takes 2 days

29
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30
Beetles
  • The beetles (order Coleoptera) are one of the
    largest groups of animals and they also undergo
    complete development. 
  • Because of their development the larvae appear
    very different from the adult form. 
  • Although the larvae or "maggots" of a large
    number of blow fly species may look almost
    identical the larvae of beetles may look very
    different from one species to the next. 
  • Beetle larvae recovered from corpses can be
    easily differentiated from maggots as they have 3
    pairs of legs and the maggots found on
    decomposing remains will not have any legs. 

31
Beetles
  • Once a larva as been identified as that of a
    beetle, further field identification can be
    accomplished because of the wide diversity of
    larval forms. 
  • The bodies of beetle larvae may range from almost
    white, robust, and hairless to dark brown,
    slender, and quite hairy. 
  • Others may appear almost black and have armored
    plates on their back. 

32
  • The larvae shown here are from four different
    beetle families, and are representation of the
    body types that can be found in each of the
    respective families. 
  • The families are (from left to right)
    Dermestidae, Staphylinidae, Silphidae,
    Scarabaeidae.  Larvae such as these are typically
    found later in the stages of insect succession,
    after the early arriving flies. 
  • The Dermestids are commonly called skin beetles
    and their larvae are commonly used in museums to
    clean bones of their associated tissues. 
  • Staphylinds (commonly called rove beetles) and
    Silphids (called carrion, sexton, or burying
    beetles) are both predaceous on maggots.  Their
    larvae are commonly found on carcasses in the
    late stages of decay.

33
What information can a forensic entomologist
provide at the death scene?
  • Forensic entomologists are most commonly called
    upon to determine the postmortem interval or
    "time since death" in homicide investigations. 
  • The forensic entomologist can use a number of
    different techniques including species
    succession, larval weight, larval length, and a
    more technical method known as the accumulated
    degree hour technique which can be very precise
    if the necessary data is available. 
  • A qualified forensic entomologist can also make
    inferences as to possible postmortem movement of
    a corpse.  Some flies prefer specific habitats
    such as a distinct preference for laying their
    eggs in an outdoor or indoor environment.  

34
What information can a forensic entomologist
provide at the death scene?
  • Flies can also exhibit preferences for carcasses
    in shade or sunlit conditions of the outdoor
    environment. 
  • Therefore, a corpse that is recovered indoors
    with the eggs or larvae of flies that typically
    inhabit sunny outdoor locations would indicate
    that someone returned to the scene of the crime
    to move and attempt to conceal the body.

35
What information can a forensic entomologist
provide at the death scene?
  • Similarly, freezing or wrapping of the body may
    be indicated by an altered species succession of
    insects on the body. 
  • Anything that may have prevented the insects from
    laying eggs in their normal time frame will alter
    both the sequence of species and their typical
    colonization time. 

36
What information can a forensic entomologist
provide at the death scene?
  • This alteration of the normal insect succession
    and fauna should be noticeable to the forensic
    entomologists if they are familiar with what
    would normally be recovered from a body in a
    particular environmental habitat or geographical
    location. 
  • The complete absence of insects would suggest
    clues as to the sequence of postmortem events as
    the body was probably either frozen, sealed in a
    tightly closed container, or buried very deeply.

37
What information can a forensic entomologist
provide at the death scene?
  • Entomological evidence can also help determine
    the circumstances of abuse and rape.
  • Victims that are incapacitated (bound, drugged,
    or otherwise helpless) often have associated
    fecal and urine soaked clothes or bed dressings. 
  • Such material will attract certain species of
    flies that otherwise would not be recovered. 
  • Their presence can yield many clues to both
    antemortem and postmortem circumstances of the
    crime. 

38
What information can a forensic entomologist
provide at the death scene?
  • Currently, it is now possible to use DNA
    technology not only to help determine insect
    species, but to recover and identify the blood
    meals taken by blood feeding insects. 
  • The DNA of human blood can be recovered from the
    digestive tract of an insect that has fed on an
    individual. 
  • The presence of their DNA within the insect can
    place suspects at a known location within a
    definable period of time and recovery of the
    victims' blood can also create a link between
    perpetrator and suspect.

39
What information can a forensic entomologist
provide at the death scene?
  • The insects recovered from decomposing human
    remains can be a valuable tool for toxicological
    analysis. 
  • The voracious appetite of the insects on corpses
    can quickly skeletonize the remains. 
  • In a short period of time the fluids (blood and
    urine) and soft tissues needed for toxicological
    analysis disappear. 
  • However, it is possible to recover the insect
    larvae and run standard toxicological analyses on
    them as you would human tissue. 
  • Toxicological analysis can be successful on
    insect larvae because their tissues assimilate
    drugs and toxins that accumulated in human tissue
    prior to death.

40
Death Scene Procedures
  • It is important to note that the collection of
    insects and other arthropods from a death scene
    may disturb the remains. 
  • Therefore, the forensic entomologist (or the
    crime scene personnel charged with making the
    collection) should contact the primary
    investigator and make plans for the collection of
    entomological evidence. 
  • Once a course of action as been determined,
    utmost care should be taken during insect
    collection so that the remains are disturbed as
    little as possible. 
  • Before collections are made notes should be taken
    as to the general habitat, ambient weather
    conditions, and location of the body.  
  • Observations should also be made to describe the
    microhabitat immediately surrounding the body.

41
Scene observations and weather data
  • Observations of the scene should note the general
    habitat and location of the body in reference to
    vegetation, sun or shade conditions, and its
    proximity to any open doors or windows if
    recovered within a structure. 
  • Locations of insect infestations on the body
    should be documented as well as noting what
    stages of insects are observed (such as eggs,
    larvae, pupae, or adults). 
  • It is also useful to document evidence of
    scavenging from vertebrate animals and predation
    of eggs and larvae by other insects such as fire
    ants. 

42
Collection of climatological data at the scene.
  •   Such data should include
  • Ambient air temperature at the scene taken
    approximately at chest height with the
    thermometer in the shade.  DO NOT EXPOSE
    THERMOMETER TO DIRECT SUNLIGHT!
  • Maggot mass temperature (obtained by placing the
    thermometer directly into the larval mass
    center).
  • Ground surface temperature.
  • Temperature at the interface of the body and
    ground (simply place the thermometer between the
    two surfaces).
  • Temperature of the soil directly under the body
    (taken immediately after body removal).
  • Weather data that includes the maximum and
    minimum daily temperature and rainfall for a
    period spanning 1-2 weeks before the victims
    disappearance to 3-5 days after the body was
    discovered.  Such information can be gathered by
    contacting the nearest national weather service
    office, or your state climatologist.

43
Collection of insects from the body at the scene
  • The first insects that should be collected are
    the adult flies and beetles. 
  • These insects are fast moving and can leave the
    crime scene rapidly once disturbed. 
  • The adult flies can be trapped with an insect net
    available from most biological supply houses. 
  • They are inexpensive and readily obtainable. 
  • Once the adult flies have been netted, the closed
    end of the net (with the insects inside) can be
    placed in the mouth of a "killing jar" (which is
    a glass container with cotton balls or plaster
    soaked with ethyl acetate, or common fingernail
    polish remover). 
  • The jar is then capped and the insects will be
    immobilized within a few minutes.
  • Once they are immobile they can be easily
    transferred to a vial of 75 ethyl alcohol. 
  • Beetles can be collected with forceps or gloved
    fingers and placed directly into 75 ethyl
    alcohol.  

44
Collection of insects from the body at the scene
  • It is extremely important that the collected
    specimens are properly labeled. Labels should be
    made with a dark graphite pencil, NOT IN INK. 
    The label should be placed in the alcohol along
    with the specimens, and alcohol can dissolve the
    ink from the paper!   However, pencil is not
    affected by alcohol and should be used for
    labeling purposes.   The collection label should
    contain the following information
  • 1). Geographical Location
  • 2). Date and hour of collection
  • 3). Case number
  • 4). Location on the body where removed
  • 5). Name of collector
  • A duplicate label should be made and affixed
    to
  • the exterior of the vial

45
Collection of insects from the body at the scene
  • Once the adults have been collected the
    collection of larval specimens from the body can
    begin. 
  • First the investigator should search for the
    presence of eggs, which are easily overlooked. 
  • After this step, the larvae should be readily
    apparent on the body. Generally speaking, the
    largest larvae should be actively searched for
    and collected.  
  • Additionally, a representative sample of 50-60
    larvae should be collected from the maggot mass. 
  • These insects can be placed directly into a
    killing solution or ethyl alcohol. 
  • However, the specimens are better preserved if
    they are placed in boiling water for about 30
    seconds. 
  • Obtaining boiling water at a scene is difficult,
    so boiling of the larvae upon returning to the
    proper facility is satisfactory.

46
Collection of insects from the body at the scene
  • If the larvae are boiled with about 48 hours of
    initial preservation, a good specimen should
    result.  
  • It is important to note that some forensic
    entomologists prefer not to have the submitted
    larvae boiled. 
  • Therefore, the investigator should discuss
    preservation techniques with their cooperating
    entomologist. 
  • In any case the exact preservation techniques
    should be documented and forwarded to the
    forensic entomologist. If the body has more than
    one area of colonization (more than one maggot
    mass) each site should be treated separately.

47
Collection of insects from the body at the scene
  • Once the preserved collections have been made,
    duplicate samples should be made for live
    shipment. 
  • Living specimens can be placed in specimen
    containers or Styrofoam cups with tight fitting
    lids along with some moist paper toweling, or
    most preferably a food substrate such as beef
    liver or pork meat. 
  • Tiny air holes should be poked in the lid using
    an ice pick or similar instrument. 
  • This cup should be placed into a slightly larger
    container that has about 1/2 inch of soil or
    vermiculite in the bottom to absorb any liquids
    that may accumulate and leak. 
  • This entire container should be enclosed in an
    appropriate shipping container and shipped
    overnight to a forensic entomologist.

48
Collection of insects from scene after body
removal
  • Many of the insects that inhabit a corpse will
    remain on, or buried, in the ground after the
    body has been removed. 
  • The steps listed above should be followed when
    collecting insects from the soil (i.e. both a
    preserved and a living sample should be taken). 
  • Soil and litter samples should also be taken both
    immediately under where the body was positioned,
    and from the immediate surroundings. 

49
Collection of insects from scene after body
removal
  • It is not necessary to dig deeply. 
  • A good technique is to collect the leaf litter
    and debris down to the exposed upper surface of
    the soil, and then make a separate collection
    from about the first two or three inches of
    topsoil. 
  • Each soil collection area should be about 4-6
    inches square, and be taken from underneath the
    head, torso and extremities. 
  • All soil samples should be placed in a cardboard
    container for immediate shipment to a forensic
    entomologist. 
  • These collections should be labeled and forwarded
    to the forensic entomologist along with the
    insects collected from the body.

50
The End!!!
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