Entomology is the Study of Insects

Images from: www.afpmb.org/military_entomology/usarmyento/files/ArmyEntomology.ppt

/

Warning: Some material in this presentation and related videos may be too graphic for some people.

What do they do?Forensic entomologists apply their knowledge of entomology to provide information for criminal investigations.

A forensic entomologist’s job may include:

• Identification of insects at various stages of their life cycle, such as eggs, larva, and adults.

• Collection and preservation of insects as evidence.

• Determining an estimate for the postmortem interval or PMI (the time between death and the discovery of the body) using factors such as insect evidence, weather conditions, location and condition of the body, etc.

• Testifying in court to explain insect-related evidence found at a crime scene.

Did you know? Maggots can be used to test a corpse for the presence of poisons or drugs. Some drugs can speed up or slow down the insect’s development.

Insects as Evidence

Forensic entomologists use their knowledge of insects and their life cycles and behaviors to give them clues about a crime.

Most insects used in investigations are in two major orders:1 – Flies (Diptera) and2 – Beetles (Coleoptera)

Blow Fly

Carrion Beetle

Images: Top Right - http://www.insectinvestigations.com/aboutfe.htm, Chart - http://www.clt.uwa.edu.au/__data/page/112507/fse07_forensic_entomology.pdf

Species succession may also provide clues for investigators.

Some species may to feed on a fresh corpse, while another species may prefer to feed on one that has been dead for two weeks.

Investigators will also find other insect species that prey on the insects feeding on the corpse.

Examples of Diptera (Flies)

Informational Source: http://naturalsciences.org/files/documents/csi_tg_overview.docImages: Top Left - http://www.scienceinschool.org/repository/images/issue2forensic3_large.jpg, Middle-Left: http://forensicfact.files.wordpress.com/2008/04/blowfly053.jpg, Top Right - http://users.usachoice.net/~swb/forensics/P1.jpg, Bottom - http://www.deathonline.net/decomposition/corpse_fauna/flies/index.htm

Flesh Fly(Sarcophagidae)

Striped thorax

Blow & Greenbottle Flies(Calliphoridae)

Metallic thorax and abdomen

House Fly(Muscidae)

Cheese Skipper (Piophilidae)

Early Stage Decomposition

Late Stage Decomposition

Life Cycle of a Calliphoridae Fly

Examples of Coleoptera (Beetles)

Informational Source: http://naturalsciences.org/files/documents/csi_tg_overview.doc Images: http://www.cals.ncsu.edu/course/ent425/library/spotid/coleoptera/coleoptera.html & http://www.forensicflies.com/beetles.htm

Carrion Beetles (Silphidae)Adults & larvae feed on fly larvae

Early to Late Stage Decomposition

Late Stage Decomposition

Rove Beetles (Staphylinidae)

Predator of fly eggs

Early Stage Decomposition

Hide Beetles (Scarabidae)

Usually the last to arrive

Clown Beetles (Histeridae)

Predator of fly eggs

Ham & Checkered Beetles (Cleridae)

Predator of flies & beetles; also feed on dead tissue Skin Beetles (Dermestidae)

Feed on dried skin & tissues

Weather data is also an important tool in analyzing insect evidence from a corpse.

Investigators will make note of the temperature of the air, ground surface, the interface area between the body and the ground, and the soil under the body as well as the temperature inside any maggot masses. They will also collect weather data related to daily temperature (highs/lows) and precipitation for a period of time before the body was discovered to the time the insect evidence was collected.

Other factors that might affect their PMI estimates:

1. Was the body enclosed in an area or wrapped in a material that would have prevented flies from finding the corpse and laying eggs? a. Was the body (wrapped in a material, in a closed room, exposed to outside conditions, etc.)?

2. Were other insect species present that may have affected the development of the collected species? a. Not all fly species are found everywhere, and this can provide important information also.

For example, the skipper fly, Piophila nigriceps (pie-oh-FEEL-ah NYE-greh-cehps), is found only in urban settings. House flies, blow flies, and flesh flies can be found in both urban and rural settings.

3. Were there drugs or other poisons in or on the body that might have affected the larvae’s development? a. A drug like cocaine speeds up development, while some poisons, such as arsenic and

glycosides, slow it down.

Did you know…The “Body Farm” in Knoxville, Tennessee is a university research facility to investigate human decomposition under various conditions in order to understand the factors which affect its rate.

Click the image to view a video about the Body Farm!

Image: http://www.umext.maine.edu/images/FlyLife.jpgInformation: http://www.kathyreichs.com/entomology.htm and http://www.forensicentomologist.org/

Blow Fly Metamorphosis

1st – Adult flies lay eggs on the carcass especially at wound areas or around the openings in the body such as the nose, eyes, ears, anus, etc.

2nd – Eggs hatch into larva (maggots) in 12-24 hours.

3rd– Larvae continue to grow and molt (shed their exoskeletons) as they pass through the various instar stages. 1st Instar - 5 mm long after 1.8 days 2nd Instar - 10 mm long after 2.5 days 3rd Instar – 14-16 mm long after 4-5 days

4th – The larvae (17 mm) develop into pupa after burrowing in surrounding soil.

5th – Adult flies emerge from pupa cases after 6-8 days.

Blow flies are attracted to dead bodies and often arrive within minutes of the death of an animal. They have a complete life cycle that consists of egg, larva, pupa, and adult stages.

It takes approximately 14-16 days from egg to adult depending on the temperatures and humidity levels at the location of the body.

Adult

EggsPupa

3rd Instar Larva

2nd Instar Larva

1st Instar Larva

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

• Flies, beetles, and many other insects have complete metamorphosis, which consists of four stages – egg, larva, pupa, and adult.

• After the adults mate, the females lay eggs onto corpses - usually near natural body openings or wounds.

http://www.cmnh.org/site/Img/ResearchandCollections/InvertZoo/124_blowflylifecycleRW.jpg

Metamorphosis

• Feeding activity is usually seen in the head region first (mouth, nostrils, eyes, ears), followed by the excretory and reproductive openings. The trunk of the body is invaded much later in the process.

• The length of the life cycle varies between different fly species and is dependent on temperature.

The maggot has a pointy end (mouth parts) and a blunt end.

a. The posterior segment of the blunt end containsspiracles that are used for breathing

b. The pointy end is the anterior and has the mouthparts..Diagram courtesy of Dr Ian Dadour, Centre for Forensic Science, UWA

The Maggot

Figure 3: A diagram showing a cross-section of the posterior segment of a maggot.

A pair of spiracles is shown, each with 3 slits indicating a third stage maggot.

Diagram courtesy of Dr Ian Dadour, Centre for Forensic Science, UWA

The Posterior End of a Maggot

Phormia regina

Spiracles are incomplete

Third-instar larvae

Phaenicia species

Spiracles are complete

Third-instar larvae

Maggots commonly found on cadavers

Unemerged Pupa

Emerging Adult from Pupa

Adult Blowfly

Adult Blowfly

Things to Remember …• The progression of insect life follows a pattern, and the developmental rates of flies are relatively predictable.

• The rate of insect development is influenced by temperature because insects are ectothermic (“cold blooded”), which means their body temperatures are largely dictated by the outside temperature. Only when the outside temperature warms an insect’s internal body temperature to its critical level can the insect become active (and eat and grow).

As discussed previously:• The postmortem interval—the time between death and discovery of the corpse – can be estimated using insect evidence and temperature data along with other factors, such as the presence of drugs in a corpse and conditions related to the corpse itself (wrapped in a material, in a closed room, exposed to outside conditions, etc.). •Any drugs present in the corpse at the time of death can affect the rate of maggot development, as they ingest the drug along with the tissue. A drug like cocaine speeds up development, while some poisons, such as arsenic and glycosides, slow it down.

• Not all fly species are found everywhere, and this can provide important information also. For example, the skipper fly, Piophila nigriceps (pie-oh-FEEL-ah NYE-greh-cehps), is found only in urban settings. House flies, blow flies, and flesh flies can be found in both urban and rural settings.

STAGES OF DECAY AND DECOMPOSITION

1. Fresh Stage

• Begins at the moment of death and lasts until the body becomes bloated.

• Blow flies and flesh flies are among the first to find the body.

• Predatory wasps and beetles may arrive later to feed on the maggots (but not the corpse).

Bloat Stage

• Begins when the body becomes inflated due to the production of gases from bacteria that begin to putrefy the body or cause it to decompose.

• House flies now join the other flies and their maggots form feeding masses that help to liquefy the tissues of the body.

 

Decay Stage• Begins when the skin

breaks and the gases escape.

• Maggot masses are large and very active as they grow older and larger.

• This is the stage of decomposition that smells bad.

• At the end of this stage, the maggots leave the corpse in search of a place to pupate in the soil.

Post-Decay Stage

• Most of the flesh is gone from the corpse, with only cartilage, bone, and skin remaining.

• This stage is devoid of flies. Some beetles continue to feed on the highly desiccated or dried remains.

Dry (Skeletal)

• Does not always occur especially if corpse is in a wet region.

• Maggots will stay longer and hide beetles will not appear.

• In wet environments the hide beetles are replaced with reduviid insects such as the (assassin bug) etc.

• The corpse is reduced to at least ten percent of the original mass.

• In the last stage (Skeletal Stage), only bone and hair remain.

Two Different Maggot Generations

• These are distinguishable by

the length and obvious size difference.

• • The photograph was taken

at a time consistent with the influx at 132 hours.

The End

Click the image above or click here to visit the website at http://www.pbs.org/wnet/nature/episodes/crime-scene-creatures/interactive-determine-the-time-of-death/4390/

Let’s give it a try …

T. Trimpe 2009 http://sciencespot.net/

Presentation developed for use with the Crime Solving Insects activity available at http://ipm.ncsu.edu/4-H/CSIfinal.pdf.

Image: http://www.animals-in-distress.net/files/photos/coriander2.jpg

What happened to Porky?

Case Studies

For each case:

1 – Review the police report and weather report.

2 – Examine & document the collected evidence.• Measure the length of the maggots & pupae. Record your data in the chart.• Consult the Species Key and the tables on your lab page to determine the

various fly species that were found on the corpse and their ages.

3 – Use the information from the reports and your examination to answer the questions.

Case #1: Oh, Deer!Police Report: The body of a female deer was found behind a fence along a busy two-lane road on the edge of the city limits of Charlotte. Animal Control was called and reported no apparent wounds on the body. It was not hunting season.

Weather Report: Daytime temperatures have been fairly consistent for the past three weeks, ranging from 70 to 74º F.

Questions:1. Approximately how long has this animal been dead?

2. Why are maggots of different ages found in the body?

3. Other than temperature, what abiotic (external to the corpse) conditions would you want to obtain from the weather station to help you to be more confident of your time of death estimation?

Species & Stage

Size(mm) Age

Case #2: Canine CaperPolice Report: The body of a large pit bull terrier was found inside a walk-in basement at a home in Cary. Maggots were found concentrated in the head and region behind the shoulder. The windows were closed, although the open curtains allowed sunlight to enter, and the air conditioner was set at 72º F.  Weather Report: Daytime temperatures have been variable over the past three weeks, ranging from 75 to 94º F. Skies have been sunny.

Questions:1. Approximately how long has this animal been dead?

 2. What effect, if any, do the outside temperatures have on your estimation of time of death in this case?

3. How does the fact that the windows were closed relate to the populations of flies you observed in and around the corpse?   4. Do you suspect foul play? Explain. 

Species & Stage

Size(mm) Age

Case #3: Dandy’s DeathPolice Report: The body of a young male horse was found in a pasture in a small town near Wilmington. The autopsy from the vet school reveals that the cardiac glycoside, oleandrin (a powerful heart stimulant), was present in the body. Oleandrin is found in the oleander plant. Oleander is a common ornamental shrub in this area, but none grows within 200 feet of the pasture.  

Weather Report: Daytime temperatures have been unusually warm over the past three weeks, ranging from 84 to 86º F.

Questions:1. Approximately how long has this animal been dead?  

2. What effect, if any, does oleandrin have on your estimation of time of death?

3. What effect, if any, does temperature have on your estimation of time of death in this case?   4. Do you suspect foul play? Explain. 

Species & Stage

Size(mm) Age

Case #4: Porky’s PerilPolice Report: The body of a large pot-bellied pig was found in a dense stand of evergreen trees far from any urban area in Buncombe County. Hairs around the pig’s neck were worn away in a band pattern. Weather Report: Daytime temperatures have been average over the past three weeks, ranging from 70 to 73º F. Temperatures in the woods would be approximately 5 degrees cooler due to the lack of sun in the shady environment.

Questions:1. Approximately how long has this animal been dead?  

2. What effect, if any, does temperature have on your estimation of time of death in this case?  

 3. Do you suspect foul play? Explain. 

Species & Stage

Size(mm) Age

• Crime Solving Insects Case Cards• Crime Solving Insects Scenarios• Crime Solving Insects

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