Forensic Entomology

Maggots and Time of Death Estimation

Entomology is the Study of Insects

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

Insect Biology

• Insects are the most diverse and abundant forms of life on earth.

• There are over a million described species- more than 2/3 of all known organisms

• There is more total biomass of insects than of humans. of 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 “maggots”

What is Forensic Entomology?• Forensic Entomology is the

use of the insects and other arthropods that feed on decaying remains to aid legal investigations. – Medicolegal (criminal)– Urban (criminal and civil)

• “legal proceedings involving insects and related animals that affect manmade structures and other aspects of the human environment”

– Stored product pests (civil)

Medicolegal Forensic Entomology

• Often focuses on violent crimes– Determination of the time (postmortem interval

or PMI) or site of human death based on identification of arthropods collected from or near corpses.

– Cases involving possible sudden death– Traffic accidents with no immediately obvious

cause– Possible criminal misuse of insects

Postmortem interval (PMI)

• Forensic Entomology is used to determine time since death (the time between death and corpse discovery)

• This is called postmortem interval or PMI).• Other uses include

• movement of the corpse• manner and cause of death• association of suspects with the death scene• detection of toxins, drugs, or even the DNA of the

victim through analysis of insect larvae.

Forensic Entomology is Applied Biology

• If it weren’t for decomposition of all living things, our world would fill up with dead bodies.

• When an animal dies, female insects will be attracted to the body. They enter exposed orifices or wounds and lay eggs or larvae.

• A forensic entomologist:– identifies the immature insects– determines the size and development of the insects– calculates the growth of the insects and passage through

stages of the life cycle in laboratory– compares the growth against weather conditions to

estimate time of oviposition

Succession of Insects on the Corpse

• Estimates of postmortem intervals based on insects present on the remains are based on:• The time required for a given species to reach a particular stage of

development.• Comparisons of all insect species present on the remains at the time

of examination.• Ecological succession occurs as an unexploited habitat (like a

corpse) is invaded by a series of different organisms. • The first invasion is by insect species which will alter the

habitat in some form by their activities. These changes make the habitat attractive to a second wave of organisms which, in turn, alter the habitat for use by yet another organisms.

Ecology of Decomposition• Necrophages - the first species feeding on corpse tissue.

Includes rue flies (Diptera) and beetles (Coleoptera). • Omnivores - species such as ants, wasps, and some beetles

that feed on both the corpse and associated maggots. Large populations of ominvores may slow the rate of corpse’s decomposition by reducing populations of necrophagous species.

• 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

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

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

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

Decay Rates Are Variable

• Studies of decay rates of 150 human corpses at in the Anthropological Facility in Tennessee (The Body Farm)

• Most important environment factors in corpse decay: • Temperature• Access by insects• Depth of burial

• Other Factors• Chemical-- embalming agent, insecticides, lime, etc.• Animals disrupting the corpse

http://www.jeffersonbass.com/video_body_farm_tour.html

Time of Death can be broadly estimated up to about 36 hours

Temperature Stiffness Time of deathTemperature Stiffness Time of deathWarm Not stiff Dead less than three hoursWarm Not stiff Dead less than three hours

Warm Stiff Dead between 3 to 8 hours Warm Stiff Dead between 3 to 8 hours

Cold Stiff Dead between 8 to 36 hoursCold Stiff Dead between 8 to 36 hours

Cold Not stiff Dead in more than 36 hoursCold Not stiff Dead in more than 36 hours

Differentiate between PMI and Time of Death

• These may not always equate. • Post mortem interval is restricted to the time

that the corpse or body has been exposed to an environment which would allow insect activity to begin. – Closed windows– Body in box or bag– Cold temperatures– Deeper burial

Insect species arrive at a corpse in waves like clockwork

• Calculate the heat/thermal energy (accumulated degree hour) required for each stage of the Green Bottle Fly’s life cycle.

• Possibly the greatest potential source of error in using arthropod successional patterns lies in the collection of speciments.

• Must only be done correctly to accurately sample the insects.

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

Calculating PMI from Accumulated Degree Hours (ADH)

From To Temp

Hours

ADH Cumulative ADH

Egg 1st Instar 70° F 23 23 x 70=1610 ADH

1610

1st Instar 2nd Instar

70 ° F 27 27 x 70=1890 ADH

1610+1890

2nd Instar

3rd Instar

70 ° F 22 22 x 70=1540 ADH

1610+1890+1540

3rd Instar

Pupa 70 ° F 130 130 x 70=

9100 ADH

1610+1890+1540+9100

Pupa Adult Fly 70 ° F 143 143 x 70=

10010 ADH

1610+1890+1540+9100+10010

Initial decay - 0 to 3 days after death

► From the moment of death flies are attracted to bodies.► Bacteria and the body's own digestive enzymes (normally in the intestine)

spread through the body, contributing to its decomposition. ► Without the normal defenses of a living animal, blowflies and house flies are

able to lay eggs around wounds and natural body openings (mouth, nose, eyes, anus, genitalia) and any wounds.

► These eggs hatch and move into the body, often within 24 hours. The life cycle of a fly from egg to maggot to fly takes from two to three weeks. It can take considerably longer at low temperatures.

Flesh flies - Family Sarcophagidae

Blowflies - Family Calliphoridae

Blowfly Larvae

Stage 2: Putrefaction - 4 to 10 days after death

► Putrefaction begins; gases produced by anaerobic bacteria; considerable bloating; seepage of fluids;

► Larval activity speeds up decomposition - the smells and body fluids that begin to emanate from the body attract more blowflies, flesh flies, beetles and mites.

► The later-arriving flies and beetles are predators, feeding on maggots as well as the decaying flesh. They are joined by parasitoid wasps that lay their eggs inside maggots and later, inside pupae.

Stage 3: Black putrefaction - 10 to 20 days after death

► Abdominal wall is broken and carcass deflates ► By this stage, several generations of maggots are present on the body and

some have become fully grown. – They migrate from the body and bury themselves in the soil where they become

pupae. ► Predatory maggots are much more abundant at this stage, and the pioneer

flies cease to be attracted to the corpse. ► Predatory beetles lay their eggs in the corpse and their larvae then hatch out

and feed on the decaying flesh. ► Parasitoid wasps are much more common, laying their eggs inside maggots

and pupae.

Hister Beetles Prey on Blowfly Larvae

Stage 4: Butyric fermentation - 20 to 50 days after death

► All the remaining flesh is removed over this period and the body dries out. It has a cheesy smell, caused by butyric acid, and this smell attracts a new suite of corpse organisms.

► The reduction in soft food makes the body less palatable to the mouth-hooks of maggots, and more suitable for the chewing mouthparts of beetles. Beetles feed on the skin and ligaments. Many of these beetles are larvae. They hatch from eggs, laid by adults, which fed on the body in earlier stages of decay.

► The cheese fly consumes any remaining moist flesh at this stage, even though it is uncommon earlier in decay.

Stage 5: Dry decay - 50-365 days after death

► The body is now dry and decays very slowly. Eventually all the hair disappears leaving the bones only.

► Animals which can feed on hair include moths, and micro-organisms like bacteria. Mites, in turn, feed on these micro-organisms.

► They remain on the body as long as traces of hair remain, which depends on the amount of hair that covers the particular species. Humans and pigs have relatively little hair and this stage is short for these species.

Making Calculations► Step 1. Determine temperature history at crime scene ► Extract weather bureau records of maximum and minimum daily temperatures at the

weather station nearest to crime scene, over the general period the body has been exposed.

► Calculate the average temperature that the body has been exposed to. ► Step 2. Rear maggots to adulthood to identify species ► Collect a range of maggots, (particularly those that might be the oldest) from the

body and rear them (on ox-liver) at constant temperature. ► Record time taken until larvae pupate. ► Identify fly species from adult characteristics. (For some species, identification from

larval features may be possible or they can be identified from DNA samples, if a DNA library is available.)

► Step 3. Estimate time of egg laying ► Using knowledge of development rate of the particular species at rearing

temperature, count back to estimate age of maggots when body found. ► Using knowledge of development rate of the particular species at the average crime

scene temperature, count back to determine date of egg laying. ► This is the latest time at which the body died. (It may have died earlier if there was a

delay between death and egg laying. This depends on weather conditions and accessibility of the body to insects).

Case Study► Establish PMI:

– Body found – all larvae collected are Lucilia sericata – The biggest and oldest are mid 3rd in-star larvae– Weather reports from the crime scene indicate the average temp was 21

C°– This species does not colonize bodies for 48 hours after death

► Development rate of Lucilia sericata (in hours) at three different temperatures

Solution► Use 21 C° ► It takes 21 hours to hatch from the egg, plus 31 hours for 1st

instar, plus 26 hours for 2nd instar, plus roughly 25 hours for mid-3rd instar

► Add 48 hours colonization time

► Total:Total: 21 + 31 + 26 + 25 + 48 = 151 hours 21 + 31 + 26 + 25 + 48 = 151 hours► 151 hours/24 hours per day = 6.29…roughly 6 days pmi151 hours/24 hours per day = 6.29…roughly 6 days pmi

Fresh

• Begins at death• Flies begin to arrive• Temperature falls to

that of the ambient temperature.

• Autolysis, the degradation of complex protein and carbohydrate molecules, occurs.

Bloat

• Swells due to gases produced by bacteria

• Temperature rise of the corpse

• Flies still present

Decay• Gases subside,

decomposition fluids seep from body.

• Bacteria and maggots break through the skin.

• Large maggot masses and extreme amounts of fluid.

• Unpleasant odor• Larvae beginning to

pupate.• Corpse reduced to about

20% of it’s original mass.

Post-Decay• Carcass reduced to

hair, skin, and bones.• Fly population

reduced and replaced by other arthropods.

• Hide beetles are dominant in dry environments.

• Mite and predatory beetle populations increase.

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 nabid and reduviid insects.

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

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

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 …

The End