Body Decomposition Watch me! April 17 2014

Stages of Decomposition Fresh The body begins to decay (complex molecules, cells, and tissues break down) immediately, but visible signs are limited to those already discussed: lividity, rigidity, and cooling. Flies begin to arrive. Time line varies enormously. First 3 days? Stages of Decomposition

Stages of Decomposition 2. Bloat Bacteria found in digestive tract multiply, producing gasses that swell the abdomen. Temperature of the body will actually rise slightly, due to the metabolic activity of the bacteria. Some smell and some signs of decay (ruptured skin, etc). Flies still present, some maggots may hatch 3 – 5 days? Stages of Decomposition

Stages of Decomposition Putrefaction Strong smell, obvious signs of decay Bloat is no longer present, because gasses have escaped through broken skin Fluid seepage Lots of maggots, some pupae, ominivorous & predatory bugs (wasps & beetles) Corpse mass reduced to 20% of original mass Stages of Decomposition

Stages of Decomposition Post Decay Body is reduced to hair, skin, and bones. Fly population declines and is replaced with beetles Body dries out in dry environments; may have mold growth in wet environments Skeletal Body is reduced to bones & hair <10% of original mass What are some circumstances that might alter these stages? Stages of Decomposition

Name stages and put in order C Name stages and put in order B E

Entomology is the Study of Insects Images from: www.afpmb.org/military_entomology/usarmyento/files/ArmyEntomology.ppt

Insects are the most diverse and abundant forms of life on earth. The total biomass of insects is ~30 times greater than the biomass of all humans Insects undergo either incomplete or complete metamorphosis (Egg to larva to pupa to insect) Larva have a soft tubular body and look like worms. Fly species larvae are called maggots. Insect Biology

By examining insects found on or around a body or other pieces of evidence or bite/sting marks, forensic investigators can help determine: Time since colonization (a minimum estimate of PMI) Where a body or vehicle has been / whether its been moved Whether unexplained sudden death or car accident was caused by insects Abuse / neglect of elderly Fun Fact: Forensic entomologists usually have a PhD and are board-certified. Most work as university professors, and assist police part-time. Forensic Entomology

Time Since Colonization Forensic entomologists can estimate time since colonization by examining the type, life stage, and size of insects found in and around the body. Different types of bugs colonize the body in a regular successional pattern. It takes predictable lengths of time for insects to grow and mature to specific stages. Flies are most often used for this purpose. In what other places do we see ecological succession? Why does succession occur? Succession occurs anywhere new habitat is formed – newly formed land, after a fire, a newborn digestive tract, etc. It occurs because each species alters the habitat. Time Since Colonization

Necrophages – species that feed on dead tissue arrive first Necrophages – species that feed on dead tissue arrive first. Includes blow flies, flesh flies, and hide beetles. Blow fly Fun Fact 1: Blow flies arrive within minutes after death. Flesh fly Fun Fact 2: Taxidermists use hide beetles to clean skulls of their hair. Hide beetle Insect Succession

Necrophages – species that feed on dead tissue arrive first Necrophages – species that feed on dead tissue arrive first. Includes blow flies, flesh flies, and hide beetles. Omnivores - species such as ants, wasps, and some beetles that feed on both the corpse and associated maggots. Flesh fly Hister beetle Yellow jacket wasp Hide beetle Insect Succession

Necrophages – species that feed on dead tissue arrive first Necrophages – species that feed on dead tissue arrive first. Includes blow flies, flesh flies, and hide beetles. Omnivores - species such as ants, wasps, and some beetles that feed on both the corpse and associated maggots. Parasites and Predators - beetles, true flies and wasps that parasitize immature flies. Incidentals – pill bugs, spiders, mites, centipedes that use the corpse as an extension of their normal habitat Rove beetle Braconidae wasp Insect Succession

Fly life cycle Because they are the first to arrive on a corpse, and because they have very predictable life-cycles, fly eggs, larvae, and pupae can be very helpful in identifying time since colonization.

Fly life cycle The adult female fly lays her eggs on the exposed tissue within minutes of death. She lays all eggs in one sitting, but may return to the same site to lay again several times over the course of her 2-3 week lifespan. adult egg

Fly life cycle The eggs hatch within approximately 24 hours of being laid. Fly larvae, known as maggots, are now in the first instar stage. They crawl to the closest food source and begin to eat. adult egg 1st instar

Fly life cycle The first instar maggots are small and do little more than eat to support their rapid growth. Over the next 27 hours, they will double in size until their skin literally can’t hold them anymore. adult egg 1st instar

Fly life cycle The maggots shed their old skin and are now considered second instar maggots. This stage is very similar to the first instar in that the maggots continue to devour their food source and grow rapidly. adult egg 1st instar 2nd instar

Fly life cycle After another 22 hours, these maggots will have reached the maximum size their current skin will allow and they will shed once more. They are now in their third instar adult egg 1st instar 3rd instar (feed) 2nd instar

Fly life cycle The third instar stage is divided into two halves, the feeding third instar and the migrating third instar During the first half, the maggots continue to eat, storing up as much energy as possible. adult egg 1st instar 3rd instar (feed) 2nd instar

Fly life cycle The second half of the third instar begins when the maggots stop eating and begin to move away from their food source. The maggots will move to a patch of soil where they can burrow and begin the next life stage. Overall, the maggots spend about 100 hours in their third instar. adult egg 1st instar 3rd instar 2nd instar

Fly life cycle Once burrowed, the maggots enclose themselves in a hard shell and begin the metamorphosis (change) that will result in an adult fly. At this stage, the maggots are now known as pupae. adult egg Pupae 1st instar 3rd instar 2nd instar

Forensic Entomologists can estimate the earliest PMI by utilizing the fly life cycle. All stages and species of fly found on the corpse are carefully collected, identified, and measured The time required for each species to reach a certain developmental stage/size is known from laboratory studies Insect development is temperature-dependent so it is measured in accumulated degree hours – the number of hours at a certain temperature. Fly life cycles & ADH

Image: http://www.nlm.nih.gov/visibleproofs

Accumulated Degree Hours (ADH) Calculating PMI from Accumulated Degree Hours (ADH) From To Temp Hours ADH Total Egg 1st Instar 70° F 23 1610 2nd Instar 27 1890 3500 3rd Instar 22 1540 5040 Pupa 130 9100 14140 Adult Fly 143 10010 24150

Crime Scene Creatures We do

Closure What were our objectives today, and what did you learn? What was our learner profile trait, and how did we demonstrate it? How does this relate to our unit question? Closure

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