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Presentation on theme: "4/14/2017 FORENSIC ENTOMOLOGY."— Presentation transcript:


2 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. “When one biological clock stops, others begin.” --Neal Haskell, reknown forensic entomologist

3 HISTORICALLY 1235 A.D., a Chinese death investigator named Sung Tz’u wrote a book entitled The Washing Away of Wrongs. It contained one of the first accounts of the use of insects as forensic evidence. A murder, in which a sickle was used, occurred in a Chinese village.

4 HISTORICALLY (cont) There were no suspects, so the investigator had all the men of the village stand in a line with their sickles on the ground in front of them. Flies landed on only one sickle--the one, that although cleaned, still had enough blood to attract the flies. The owner then confessed.

5 Four Main Types of Species that Feed on Dead Organisms
Necrophages - feed directly on the corpse Flies (Diptera) Beetles (Coleoptera) Predators and Parasites – attracted to organisms that are already feeding on the body Burying beetles (family Silphidae) Rove beetles (family Staphylinidae) Hister beetles (family Histeridae) Ants, bees, and wasps (Order of Hymenoptera)

6 Four Main Types of Species that Feed on Dead Organisms
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

7 The First Species Flies are able to detect the smell of decomposition before humans. When a dead body is placed outside a blowfly will generally appear within ten minutes.

8 The Blowfly Blowflies are one of the most common species on dead bodies. Blowflies have a shiny, metallic color so they are often called blue-bottle or green-bottle flies. They feed on any blood or fluids and then start laying eggs in and around the natural body cavities. The female can lay up to 250 eggs at one time. Once the food source is exhausted, they will prey on other species in the same genus (Chrysomya) Therefore, they act as both necrophages and predators.

9 The Blowfly The eggs hatch within 23 hours. The maggots begin feeding on fluids leaking form the body. Later they enter openings on the body and feed on tissues. Other species of flies will begin to arrive and there will be competition for access to the corpse. The maggots are also a source of food for other insects.

10 The maggots become a source of food for other insects such as Beetles
Rove Beetle--Staphylinidae (Lathrobium sp.) Carrion Beetle--Silphidae (Nicrophorus sp.)

11 Minimum Time Since Death
The minimum time since death is determined largely by estimating the age of the maggots at the time the corpse is discovered. The fundamental assumption is that the person has not been dead longer than it took for the flies to arrive, lay eggs and maggots hatch and develop. Therefore, the oldest maggot determines the minimum time since death.

12 Larva Larva hatch from the eggs and increase in size by growth steps called instars. Eventually the larva migrate from the corpse and develop into an inactive pupal stage. During this time, the adult insect develops internally. Two larval instars.

13 The Pupa and Adult Fly Once the maggot have finished feeding, they will pupate. During this process the maggot creates a hard brown shell around itself. Inside of the shell, the maggot turns into an adult fly. When the fly emerges the shell is left behind and becomes another clue.

14 The Cycle of a Blowfly shows the time frame that is used to determine the minimum time since death.

15 Factors that affect maggot growth
Factors such as weather, temperature, heat generated from the maggot mass, clothing and wounds will affect the growth of the maggots. Colder temperatures slow the growth of the maggots. If drugs are present in the body at the time of death, these toxins will also affect the rate of development.

16 Pig Decomposition Pig decomposition is almost identical to human decomposition. Therefore, pigs are used in forensic entomological studies in order to better understand what happens when a human decomposes.

17 Stages of A Pig Decomposition
Complete metamorphosis involves development from egg to larva to pupa to adult. The pig ear in the diagram to the right shows a layer of what looks like a white crust. These are the fly eggs.

18 Pig Decomposition One day old dead pig showing signs of skin changes and bloating. (Picture taken on June 20th, 2002)

19 Pig Decomposition Advanced stages are seen on this one week old dead pig. As the larva develop they migrate from the body and develop into pupa.

20 Collection Procedures
In order to study the maggots, pupa and flies, they must be collected. Collections may be done in three differnet ways: Aerial Hand Live Sampling

21 Aerial Collection Use a net and sweep it back and forth over the decomposing body. Place them in a large jar with ethyl acetate. After a few seconds, use a funnel to move dead flies into a vial of 75% ethyl alcohol with a label of the date, time, case #, location, sample type and collector.

22 Hand Collection Collect a variety of maggots with forceps. Place them in boiling water to stretch them out and fix them. Then place the maggots into a vial of alcohol with a label containing the date, time, case #, location and collector.

23 Live Sampling “Maggot Motels”
Obtain a styrofoam container with a lid. Use sand or vermiculite for the bottom substrate. Place aluminum foil with beef or pork liver for food on top of the substrate. Collect 10 to 15 live maggots of varying sizes and drop them onto the foil. (You may also harvest and develop eggs in the “motel”.) Close the foil around them and allow to develop into pupae and then into adults. THEY MUST BE ADULTS IN ORDER TO IDENTIFY THE SPECIES.

24 More Maggot Information
Maggots collected from a dead body can be ground in a blender and tested for any toxins present in the body at the time of death. When the maggots feed on the dead tissue, they ingest these toxins.

25 Maggot Therapy The medical field uses maggots to eat dead and decaying flesh on wounds. This allows the wound to heal sooner, but many people still find this disturbing!

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