Chapter 13 Forensic Entomology
Terms in this set (21)
Carl Linnaeus established the current classification system for identifying biological systems.
Forensic entomology mainly deals with the orders: Coleoptera (Beetles) and Diptera (Flies)
Types of Forensic Entomology
Urban, Stored Product, & Medicolegal
The Process of Death
All methods used to determine time of death work better if a body is discovered within 24 hours. The location a body found also determines how difficult applying these methods will be.
After death, the body cools at a predictable rate of about 1.25 degrees Fahrenheit per hour. The Glaister equation is used to determine time of death based on cooling.
The Glaister equation works best if applied within the first 12 hours. It can be used within 36 hours of death, but is less accurate at this point.
Rate of Cooling
Factors like temperature of the environment, types of clothing, layers of clothing, moisture content of clothing, air movement, & the ratio of surface area to body mass all affect this process. Hours since death = 98.6 degrees F - internal body temperature / 1.25
After the body dies, the blood pools due to gravity. This begins a half hour after death & is most visible for the first 12 hours after death. It appears as a purplish red discoloration of the skin. Livor mortis does not occur in areas where the body is compressed, & does not change location if a body is moved after it appears. It often gives information on if a body was moved post mortem as a result.
After the body dies, muscles relax, tense, then relax again over time. Factors like temperature, dehydration, condition of muscles, & use of muscles prior to death all affect this process.
Time of Death
In general the following chart can estimate time of death.
Warm/relaxed muscles - dead less than 3 hours
Warm/ stiff muscles - dead 3-8 hours
Cold/ stiff muscles - dead 8-36 hours
Cold/ relaxed muscles - dead 36 or more hours
Stages of Decomposition
Body cells begin to decompose within 4 minutes of death. Cells are deprived of oxygen, CO2 levels rise, pH levels fall, wastes accumulate, & enzymes destroys the cell eventually rupturing them. The body essentially changes state from a solid to a liquid/gas when decomposing.
Stages of Decomposition (Autolysis)
Occurs 0-4 days after death. The cadaver appears fresh externally, but is decomposing internally. The only external signs are fluid filled blisters & skin slippage.
Stages of Decomposition (Putrefaction)
Occurs 4-10 days after death. The cadaver swells as the gases of decomposition build up causing a slight odor. The external sign are a greenish tint to the skin & bloating.
Stages of Decomposition (Black Putrefaction)
Occurs 10-20 days after death. The body collapses as the gases in it escape causing a strong odor. The body begins to liquefy.
The external signs are creamy consistency flesh, with exposed skin taking on a black color.
Stages of Decomposition (Butyric Fermentation)
Occurs 20-50 days after death. The body begins to dry out, some flesh is still present in early stages, & there is a cheese-like odor caused by butyric acid production.
Stages of Decomposition (Dry Decay)
Occurs 50-365 days after death. The body is almost dry, & undergoes a slow rate of decay & then results in skeletonization.
Rate of Decomposition
Factors like environment, temperature, & presence of scavengers all affect this process. # of days to skeletonization = 1,285 / avg temp degrees C
Insect life cycles vary based on temperature. To accurately predict the time it took an insect to change from one stage to another, the average temperature in an area must be considered. How to calculate degree days: calculate the average temperature for the day by adding the low & high temperature & dividing by 2.
If the result is greater than the threshold temperature for the insect, subtract the threshold from the average temp. If the result is lower than the threshold, the insect did not grow at all on the day in question. Formula: (Max temp + Min temp - Threshold temp x 1 day / 2)
Insect Life Cycles
Insects have 4 stages to their life cycle:
egg, larvae, pupa, & adult
Knowing the timing of an insect's life cycles helps establish time of colonization. Time of colonization & estimated time of discovery are added together to establish Post Mortem Interval.
Insects at a crime scene
Calliphoridae (Blow flies): usually the first species to arrive at a crime scene, sometimes within minutes of death.
Sarcophagidae (Flesh flies): Arrive shortly after the blowflies & begin feeding on the corpse as well as on blowfly larvae.
Muscidae (House flies): Arrive later in the decomposition process & lay eggs in natural body openings & wounds.
Piophilidae (Cheese flies): Arrive in the late stages of decomposition, & prefer a non moist corpse to feed on.
Staphylinidae (Rove Beetles): Are present on corpses within hours, but stay for a long period of time, in some cases months. Feed on the eggs & larvae of other species not the body itself.
Silphidae (Carrion Beetles): Adults eat other insect larvae & carrion. Often dig tunnels under the body to lay their eggs, & bury the body in the process.
Histeridae (Clown and Hister Beetles): Present throughout the majority of decomposition. Adults feed on the larvae of other insects.
Dermestidae(Skin beetles): Feed on dry skin & tissues during later stages of decomposition.
Scarabidae(Hide beetles): Feed on the body during the dry decay stage when flies have abandoned the corpse.
Cleridae (Checkered beetles): Predators that feed on other beetles &late stage flies.
Insects and Corpses
Insects create a complex inhabitation that weaves the arrival & departure of various species according to degree of decay.
Insects will reduce a corpse to about 10% of its original weight by the time they finish feeding on it.
Describe the habitat (sunny, shady, cloudy), research climate data (temperature, humidity, weather patterns esp. if rainy), record temperatures (body, ground, maggot mass.), take soil samples (esp. from under the corpse at a depth of 10 cm.), & collect insects: Use nets to capture flies in the air, collect maggots on body , collect pupa from within 3-10 meters of the corpse, collect beetles on & underneath corpse, label all collected insects & place them into killing jars for transport.
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