Human decomposition and insect succession

Human decomposition and insect succession

1. Human Decomposition and Insect Succession Submitted to- Dr. Sapna Sharma Submitted By- Nitesh Roll.no-1323

2. Ecology of Decomposition Four categories of insects can be found on decomposing carrion : Necrophages - the first species feeding on corpse tissue. Includes true flies ( Diptera ) and beetles ( Coleoptera ). 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 – P ill bugs , spiders, mites, centipedes that use the corpse as an extension of their normal habitat. The succession waves in which the arthropods colonize the carrion depends on the state of decomposition of the carrion

3. Decomposition Stages

4. Stages Involved in Decomposition Decomposition process was best divided into five stages on the basis of physical appearance of carcasses, internal temperatures and characteristic insect populations : Fresh stage: Blowflies have detected the cadaver,Eggs are being laid , often around the eye, nostrils, mouth, followed by anus or genital . At death: Flies begin to arrive . The estimation of the time of death by entomological data after 24 hrs is more accurate than medical examiner's estimation based on the soft tissue examination. Cellular breakdown occurs during this stage without morphologic alterations.

5. Fresh Decay Stage

6. Bloated stage (Days 2-7) Putrefaction begins at this stage. Gases produced by the metabolic activities of anaerobic bacteria cause an inflation of the abdomen and the carcass forming a balloon-like appearance during the later part. Arthropod activities combined with the putrefaction processes cause internal temperatures of the carcass to rise .

7. Decay stage (Days 5-13): Abdominal wall is penetrated, resulting in the deflation of the carcass and ending the bloated stage. The internal temperature rises to 14 degrees above the ambient temperature followed by a drop signifying the end of the decay stage . There is a steady decrease in the weight of the carcass by 10th day. There is a conversion of carcass biomass to dipteran larval biomass . The larvae subsequently depart from the carcass to pupate.

8. Post-decay stage (Days 10-23) The post-decay stage begins when most of the Diptera larvae leave the carcass, leaving behind bones, cartilage, hair , small portions of tissue, and a large amount of wet, viscous material known as byproducts of decay (BOD).

9. Dry stage (days 18-90) This stage is characterized by bones with little cartilage remaining and the BOD has dried up. The transition from post - decay to dry stage is gradual, with declining adult and larval Diptera populations .

10. Factors Affecting Decomposition Body-  The first factor is related to body itself; its body size or mass.  Large bodies  take longer to decompose than small bodies. -The second important consideration related to body is whether or not the body is  intact . Environment  – Weather, climate, humidity, all have affects on the decomposition rate. For example; Cold weather slows the rate;  hot weather accelerates  it, On the other hand Frozen bodies do not decompose. Direct sunlight and High humidity also accelerates decomposition. Insects –  Nothing affects the rate of body decomposition more than insects.Insect activity varies area to area and season to season.

11. Soil-  A buried body will decompose slowly than one found on the surface, yet acidic soil and high soil moisture content can accelerate decomposition of buried bodies. Flora   and Fauna-  Plants also can accelerate deterioration of the body. Scavengers tend to devour a corpse in a characteristic sequence beginning with the torso and viscera. They may drag parts of the body to secluded areas for feeding; dis -articulating the body.

12. Insect succession Insects colonize cadavers in a predictable sequence, also known as insect succession. After the initial decay, and the body begins to smell, different types of insects are attracted to the dead body. The insects that usually arrives first is the Diptera , in particular the blow flies or Calliphoridae and the flesh flies or Sarcophagidae . The females will lay their eggs on the body, especially around the natural orifices such as the nose, eyes, ears, anus, penis and vagina. If the body has wounds the eggs are also laid in such. Flesh flies do not lay eggs , but deposits larvae instead.

13. After some short time, depending on species, the egg hatches into a small larvae. This larvae lives on the dead tissue and grows fast. After a little time the larva molts, and reaches the second larval instar . Then it eats very much , and it molts to its third instar . When the larvae is fully grown it becomes restless and begins to wander. It is now in its prepupal stage. The prepupae then molts into a pupae, but keeps the third larval instars skin, which becomes the so-called puparium . Typically it takes between one week and two weeks from the egg to the pupae stage. The exact time depends on the species and the temperature in the surroundings.