Entomology Unit
Stages of Decay
-Fresh -Bloated -Decay -Post-Decay
Phaenicia sericata:
green bottle fly
Species Succession
may also provide clues for investigators. Some species may to feed on a fresh corpse, while another species may prefer to feed on one that has been dead for two weeks. Investigators will also find other insect species that prey on the insects feeding on the corpse.
Lividity
pooling of blood
rigor mortis
stiffness of the body that sets in several hours after death
Ambient temperature:
temperature of surrounding air
Entomology:
the scientific study of insects
Climatological
weather related
Factors affecting rigor mortis:
1. ambient temperature a. cooler air slows the onset of rigor b. warmer air speeds up the onset of rigor 2. Clothed body experiences faster rigor 3. If the person was exercising or running prior to death, onset of rigor will be faster due to accumulation of lactic acid and lack of oxygen
Loss of body temperature at rate of 1.4° F per hour for the first twelve hours after death.
1.4 degrees/hour x 12 hours = 16.8° F lost in the first 12 hours Loss of body temperature continues after the first twelve hours at a rate of 0.7° F per hour.
2nd instar
10 mm long after 2.5 days
3rd instar
14-16 mm long after 4-5 days
When does lividity begin?
2 hours after death
When does rigor mortis begin?
2 hours after death
When does rigor mortis disappear?
After 36 hours
Things that affect rigor mortis?
Ambient temp. -> warmer temp = faster onset Body weight -> more fat = more stored oxygen Clothing type -> warm/thick = faster Illness-> fever/ hyperthermia = faster Physical cond. -> if in exercise rigor occurs faster Sun exposure -> faster
Lividity can be impede by?
Belts and watches
When do blowflies arrive?
Blow flies are attracted to dead bodies and often arrive within minutes of the death of an animal. They have a complete life cycle that consists of egg, larva, pupa, and adult stages.
initial decay (first)
Corpse appears normal on the outside, but is starting to decompose from the actions of bacteria and autolysis.
black putrefaction (third)
Due to the breakdown of flesh, the gases have escaped thus making the odor of decay very strong.
2nd
Eggs hatch into larva (maggots) in 12-24 hours.
Most insects used in investigations are in two major orders:
Flies (Diptera) and Beetles (Coleoptera)
Forensic Entomologist
Forensic entomologists use their knowledge of insects and their life cycles and behaviors to give them clues about a crime.
stomach contents
If undigested stomach contents are present, then death occurred zero to two hours after the last meal. If the stomach is empty but food is found in the small intestine, then death occurred at least four to six hours after a meal. If the small intestine is empty and wastes are found in the large intestine, then death probably occurred twelve or more hours after a meal.
How do you record the temperature in rigor mortis?
In the liver
putrefaction (second)
In this second stage, the abdomen is swollen due to internal gases formed by bacteria and the odor of decay is produced.
What causes rigor mortis?
It is caused by lack of oxygen to the body, which locks muscle fibers in place. Rigor begins in small muscles then gradually moves to larger ones. (Ex. First facial/fingers, then legs/glutes)
3rd
Larvae continue to grow and molt (shed their exoskeletons) as they pass through the various instar stages.
Postmortem interval:
PMI, time since death
4th
The larvae (17 mm) develop into pupa after burrowing in surrounding soil.
Urban
This aspect deals with the arthropods that affect man and his immediate environment. This area has both criminal and civil components and mostly includes litigations and civil law actions involving insects in dwellings or as garden pests or a loss of revenue due to insect damage. It also involves lawsuits dealing with the misuse of pesticides. For example, an argument between a landlord and tenant over whom is responsible for infesting a house with bedbugs
Medicolegal
This aspect is what is commonly thought of when forensic entomology is mentioned. It focuses on arthropod involvement in felony criminal cases. The most widely known aspect is the use of necrophagous insects (those that eat dead flesh) to help police detectives and investigators determine time of death and various other aspects of homicide (for instance, if the body was moved after death). However, it also can involve physical abuse and drug trafficking. This aspect is the only one we will cover in lab.
Stored Product
This deals with arthropod infestation or contamination of a variety of commercial products. The forensic entomologist may serve as an expert witness during both criminal and civil proceedings involving food contamination. For example, if a fly is in someone's ketchup bottle, the entomologist can try to determine if it got into the bottle at the factory or at the buyer's home.
Butyric (fourth)
This fourth stage is the drying out stage. The exposed skin may start to mould and a cheesy odor develops. As the body becomes drier, conditions are less conducive to rearing young insects.
Phormia regina
black blow fly
Oviposition:
egg deposition, especially for insect
Adult
21-24 days
1st instar
5 mm long after 1.8 days
Pupa
8-5 days
5th
Adult flies emerge from pupa cases after 6-8 days.
1st
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.
What may drugs do?
Slow down or speed up the process.
Body heat is lost at a rate of -1.4 F for the first 12h following death, then -.7F after those 12 hours.
Solution:98.6 -93.6 = 5 F of body temp. lost 5 / 1.4 = 3.57 = PMI Body dead at least since 12:30pm on 6/11/17
What are the two types of death?
Somatic death and cellular death
somatic death
Somatic death occurs when the individual is irreversibly unconscious- what we consider "dead." This does not mean all functions immediately cease. In fact, after somatic death, the body's cellular processes continue.These factors affect when rigor mortis occurs and when the body begins to decay.
Eggs
Soon after death
Dual lividity indicates what?
That the body has been moved
What is the body farm?
The "Body Farm" in Knoxville, Tennessee is a university research facility to investigate human decomposition under various conditions in order to understand the factors which affect its rate.
Dry Decay (fifth or final)
The body is pretty much dry and the odor is very minor to nonexistent; bones are exposed.
Algor Mortis
The cooling of the body after death
PRACTICE SCENARIO A lady became concerned when she did not see her neighbor for a few days. She called the police on Aug 16th. Around 5pm, they forcibly entered the home and found the woman dead in her kitchen. She was in her bathrobe and there were no signs of violence. There were adult metallic flies on the kitchen walls and there were maggots in her mouth. Investigative teams collected live flies for identification and several maggots to rear in the laboratory. Laboratory temperatures are a constant 25 deg C. You are the authority on forensic entomology- you must determine, "When was PMI (When did she die)?" Note: to get the correct answer, you need to know when the flies oviposited. Why does time of oviposition give you PMI?
Total time (egg to adult) - rearing time (larvae to adult) = age of fly at time of collection The flies emerged 9 days and 1 hour after collection; this equals 217 hours. (9 x 24 + 1) We know the rearing time was 217 hrs at 25 deg C. Multiply the two and get 5425 ADH We know that it takes a total of 7225 ADH for C. vicina to go from egg to adult Subtract rearing time from total time (7225 ADH - 5425 ADH = 1800 ADH) Therefore, the flies were 1800 ADH old when we collected them. BUT, we collected them at 22 deg C (not 25) so we need to convert at THIS temperature to get true hours. 1800 ADH / 22 deg C = 81.8 hours old (this is ~3 days and 10 hours old) Subtract 3 days 10 hrs from time of collection to get PMI This equals 7 am on Aug 13th. Since Calliphorids can only oviposit after the sun rises, it is logical to assume she was already dead by sunrise. Answer: She died sometime early morning on Aug 13th or late night on Aug 12th (as evidenced by her bathrobe and presence in the kitchen).
Lividity speeds up during what weather?
Warm weather
Other factors that might affect PMI?
Was the body enclosed in an area or wrapped in a material that would have prevented flies from finding the corpse and laying eggs? Were other insect species present that may have affected the development of the collected species? Were there drugs or other poisons in or on the body that might have affected the larvae's development?
Stomach contents
We don't use digestive content to tell us PMI, but rather to give us an idea when/what the victim ate prior to death If undigested stomach contents are present death occurred 0-2hrs after their last meal. If food is in the small intestine, death occurred 4-8hrs after their last meal. If food is all the way to the large intestine, death occurred 12 or more hours after a meal.
Weather used
Weather data is also an important tool in analyzing insect evidence from a corpse. Investigators will make note of the temperature of the air, ground surface, the interface area between the body and the ground, and the soil under the body as well as the temperature inside any maggot masses. They will also collect weather data related to daily temperature (highs/lows) and precipitation for a period of time before the body was discovered to the time the insect evidence was collected.
Accumulated degree hour (ADH):
a given amount of thermal energy needed to develop from one stage of an insect life cycle to the next
Medical Examiner:
a medical doctor who ascertains cause of death, especially for those deaths not occurring under natural circumstances
Forensic entomology:
a scientific study of insects as it applies to criminal cases to help determine the postmortem interval (time since death), possible movement of the body and other clues to the circumstances before and after death
Factors affecting heat loss include:
a. Cooler air temperature (body loses heat faster) b. Warmer air temperature (body loses heat slower) c. If the body is clothed, heat loss is slower. d. If the body is overweight, heat loss is slower. e. If the body is thin or small, heat loss is accelerated. f. In water, body cools faster than on land.
When does lividity become permanent?
after 8 hours
