1. Forensic Science Unit 4 Entomology

2. What is Forensic Entomology? Entomology is the study of insects. Insects arrive at a decomposing body in a particular order and then complete their life cycle based on the surrounding temperature. By collecting and studying the types of insects found on a body, a forensic entomologist can predict the time of death

3. What are the different life cycles of insects? Incomplete Metamorphosis 3 stages: Egg Nymph: has appearance of small adult; increases size with each molt Adult Complete metamorphosis 4 stages: Egg Larvae: wormlike stage (caterpillar) Pupa: inactive stage (chrysallis) adult

5. Complete metamorphosis Holometabolous The pig ear in the diagram shows a layer of what looks like a white crust. These are the fly eggs

6. Larva Larva hatch and grow in steps called instars Eventually the larva migrate from the corpse and develop into the pupal stage During this time, the adult insect develops internally Two larval instars

7. Four Main Types of Carrion Species Necrophagous--feed directly on the corpse –Flies (Diptera) –Beetles (Coleoptera) Predators –Burying or Carrion beetles (family Silphidae) –Rove beetles (family Staphylinidae) –Hister beetles (family Histeridae)

8. Four Types continued Species that feed on both the body and other arthropods –Ants –Wasps –Some beetles Arthropods that use the corpse as an extension of their normal habitat –Hunting spiders

9. The Blow Fly Acts as both necrophages and as a predator. One of the most common species on dead bodies Often arrive within 10 minutes Feed on any blood or fluids and then start laying eggs in and around the natural body cavities If the food source is exhausted, they will prey on other species in the same genus (Chrysomya) Black Green

10. Blow Fly continued Blowflies seek moist areas of the corpse to lay their eggs The nose, mouth, armpit, groin and open wounds are favored locations Eggs hatch into maggots within 24 hours Usually reach length of 1cm after 3 days During the next 6 to 10 days they feed, grow and repeatedly molt Become a pupae when their outer covering hardens Approximately 12 days later adult flies emerge

11. Decomposition

12. What are the stages of decomposition? StageDescription Initial DecayCarcass appears fresh externally, but is decomposing internally PutrefactionCarcass swollen by gas produced internally; odor of decaying flesh Black PutrefactionFlesh of creamy consistency with exposed parts black. Body collapses as gases escape; odor of decay very strong Butyric FermentationCarcass drying out. Some flesh remains; cheesy odor develops. Ventral surface moldy from fermentation Dry DecayCarcass almost dried out

13. One day old pig One day old dead pig showing signs of skin changes and bloating

14. One week old pig Advanced stages are seen in one week old dead pig. As the larva develop they migrate from the body and develop into pupa

15. What is the order of decay? Autolysis: nonbacterial; release of gases Putrefication: slippage of skin, etc. Necrophagus arthropods arrival depends on: -Season or climate -Situation of corpse (open air, buried, water, geographic location; cause of death, degree of mutilation) Changes in skin by decomposition

16. What is the effect of temperature on decomposition? Ambient heat plays a role during egg and early larval development After that, its effect decreases rapidly Maggot masses generate their own heat Taking temperature of the maggot mass can find it as high as 125 degrees

17. What is PMI? PMI: Postmortem Interval An estimation of the duration of PMI involves setting the minimal and maximum time between death and corpse discovery Important in narrowing the field of suspects The minimal PMI is determined largely by estimating the age of developing insects collected at time of corpse discovery The maximum PMI is determined from species of insects that are present and the weather conditions necessary for specific activity of these species

18. What body changes occur due to Decomposition? 1.When heart stops, the body turns pale and looks waxy 2.Blood settles & discolors to purplish red. Eyes flatten; extremities turn blue 3.Appearance of burning shows up on drying mucous membranes 4.Body putrefies, turning greenish in color. Bacteria grows & accumulates 5. Rot spreads & a foul odor develops. Body bloats due to bacterial producing gases in intestines 6.Skin blisters from gases, detaches from muscles and bursts. Top layers peel off. 7.In some circumstances, a cheesy substance called “adipocere” forms as fatty tissues harden Left alone in a warm/moist climate, a body can decompose to a skeleton within a few weeks. In other conditions it can take months or even years.