Forensic Science Unit 4 Entomology
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
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 What are the different life cycles of insects?
Complete metamorphosis • Holometabolous • The pig ear in the diagram shows a layer of what looks like a white crust. These are the fly eggs
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
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)
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
The Blow Fly Black • 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) Green
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
One day old pig One day old dead pig showing signs of skin changes and bloating
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
What is the order of decay? • Autolysis: nonbacterial; release of gases • Putrefication: slippage of skin, etc. • Necrophagus arthropodsarrival 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
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
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
When heart stops, the body turns pale and looks waxy Blood settles & discolors to purplish red. Eyes flatten; extremities turn blue Appearance of burning shows up on drying mucous membranes 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 Skin blisters from gases, detaches from muscles and bursts. Top layers peel off. In some circumstances, a cheesy substance called “adipocere” forms as fatty tissues harden What body changes occur due to Decomposition? 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.