Presentation on theme: "Forensic Entomology “ We fat all creatures else to fat us, and we fat ourselves for maggots. Your fat king and your lean beggar is but variable service-"— Presentation transcript:
1Forensic Entomology“ We fat all creatures else to fat us, and we fat ourselves for maggots. Your fat king and your lean beggar is but variable service- two dishes, but to one table. That’s the end.”….Hamlet(Act 4: Scene 3)
2China 200 BC- Sung Tz’uThe death of Sung Tz’u, a poor farmer in China, represents the first time insects were used in a death investigation.The investigator asked all neighboring farmers to bring their sickles (70-80)Flies gathered at one sickle due to the presence of blood and tissue remains. The man was determined to be guilty of the murder.
3Forensic EntomologyForensic Entomology has been used in all of the following:Determine the time of death of a rotting corpseProvide evidence in abuse cases: (Open wounds in elderly)Analyze “Spatter” evidence from insects walking through blood.Check for drugs, poisons (toxins will build up in the insects feeding on a corpse)Determine the identity of insects hidden in shipments of products from other countriesDetermine the types of insects that can cause crop damageDetermine the types of insects that can be used as biological controls in place of pesticides.
4Flies: Order DipteraFlies are usually the first insects attracted to a dead body.Their life cycle can provide important clues: particularly for time of death.Life cycle of flies:EggLarvae : 1st, 2nd, 3rd instarsPupaAdult
5Finding a CarcassFlies can detect smell of decomposition (as little as a few parts per million) by using special hairs called sensilla trichoidea that are equipped with chemical receptors.Flies must find carcass early, before it turns to mush
6Egg Laying Flies must lay eggs in a moist area. Clothing that sops up blood and other fluids.. becomes a nursery for the eggs.Females cannot pierce skin.Lay eggs in mucous membranes of nose, mouth, eyes, open wound, scratches.
7Egg LayingA female fly has chemoreceptors on soles of her 6 feet to locate the proper location to lay her eggs.Eggs are released through the ovipositor on the tip of her abdomen.A single female can lay up to 400 eggs in 6 minutes
8Maggots: Larva Eggs will hatch within10-24 hrs. Maggots will nurse on liquid protein before their mouth hooks grow large enough to tear through flesh.
9MaggotsLarvae tear at exposed flesh with a pair of tiny mouth hooks
10Mouth Parts of MaggotsAs seen with an electron microscope
11Maggots Maggots breath through anal spiracles (butt breathers) These can be used to help determine the larval stage:1st instar = 1 anal spiracle2nd instar = 2 anal spiracles3rd instar = 3 anal spiracles
12The Feeding MassMaggots use collagen splitting enzymes to break through connective tissueLarvae bury heads in fleshThe feeding mass generates a lot of metabolic heatThe mass will periodically move to the surface to cool.Some insects will remove most maggots by eating them.This delays the decomposition of the carcass
13As maggots grow, they put on their own layer of fat that eventually hides all internal organs except for the crop (feeding tube) – seen as dark red line extending back from mouth
14Pre-pupa FliesMaggots will stop feeding once they reach the 3rd instar stage (about 1/2 inch long)They will then drop to ground, and seek darkness; moving their light sensitive heads right and left as they move.
15Determining the Species Determining the species of maggot is difficult and requires the third instar.Often, forensic entomologists will collect half and grow the others in lab to determine the species after pupation.If maggots not well preserved: rely on simple length of maggots: compare to day to day growth
16PupaWhen ready to pupate, maggots will bury themselves in soil, or move under leaves or carpetsThey will contract into short, thick plugs and wait for larval skin to hardenThey will then metamorphosize into adultsNew flies emerge within 1 week to 6 months later (depending on environmental conditions)Pupa stages of the house fly
17Emergence of Adult Flies A fleshy sac pops out of slit above the eyesThe sac fills with fluid and presses against the top of the pupal caseThe case pops open along a fracture lineThe adult fly will fully emerge within thirty minutesBlow fly emerging (as seen withan electron microscope)
18Typical infestation:First to arrive are usually blow flies: aka bottle fliesThey will appear within a few minutesThey have shiny, metallic colors
19Flesh fliesFlesh flies will be attracted to the site within a day or two.They are recognized by their large red eyes.
20Rove beetles and Soldier Flies Rove beetles and soldier flies will appear once the fly eggs have hatched and maggots are present.They will feed on the developing maggotsRove BeetlesSoldier Fly
21Cheese Skippers and Scuttle Flies Cheese Skippers and Scuttle Flies will appear towards the end of the infestation to feed on the fermented protein of the later stages of decompositionCheese SkipperScuttle Fly
22Mites, Moths and Spider Beetles Mites show up very late in the infestation. They prefer a dry cadaverClothes moths and spider beetles will be the last to clean up the completely desiccated remainsMothMitesSpider Beetle
23Other Insects Commonly Scene Include: Carcass beetleCarrion BeetleHide beetle
24Example of Post-Mortem Interval (PMI) 8-14 hrs for eggs to hatch8-14 hrs to finish 1st instar2-3 days 2nd instar7-8 days- third instarThird instar of Maggot
25PMI Converted to hours: 8-14 hours 8-14 hours 48-72 hrs 168-192 hrs Totals to: 232 – 292 hrs(this represents the total time needed to reach 3rd instar)In days: days
26PMI estimates PMI estimates are affected by: Temperature Time of day Time of yearExposure
27Rate of development of immature blow flies vs temperature Cooler weather- choose later range of 12 days; insects develop slowerWarmer weather – pick early part of range, 9 days; insects will develop faster
28Jobs at the sceneThe following information should be documented or collected at the scene:Observations and notesClimatological dataSpecimens from the bodySpecimens from near the bodySpecimens under and near the body after the body is removed
29Observations What is the setting: rural, urban, aquatic Estimate # and kind of flying and crawling insects visible and already presentWhich types appear to be the cause of the major infestations of the body
30Observations What is the compass direction that the body is facing? Is the body in sunlight or shade?What is the position of body?Take photos
31Climatological dataThe following temperatures should be documented at the scene:Ambient tempGround tempBody surface tempUnder body tempMaggot mass tempSoil temp after body removed
32Climatological dataOnce an approximate time frame is established, it should be adjusted by gathering additional weather data from local weather stationsMaximum and minimum temperatures during the presumed time period and amount of precipitation should be traced back to the time when the victim was last seen
33Taking field samples½ of the sample is generally collected and preserved in alcohol (70-80% solution of ethyl alcohol)The other ½ is kept alive and raised to adulthood in the lab to help with identification and confirm timing.