Forensic Entomology

The Role of Insects in Medico-legal Death Investigation

Forensic Entomology

Forensic Entomology

Forensic Entomology is the use of insect knowledge in the investigation of crimes.

Forensic Entomology is not only a useful tool to decide how long human remains have been undetected, but forensic entomology can also be used to find out whether the corpse has been moved after death, the cause of death and also solves cases of contraband trafficking (Catts, 1995).

Forensic entomology can be divided into three categories

UrbanStore-productMedicolegal

Urban forensic entomology deals with insects that affect man and his immediate environmentMay deal with pest infestations where there might be litigation, for example, landlord and tenants.

Stored-product forensic entomology concentrates on commonly found insects in contaminated foods.Legal issues on insect infesting stored products

Medicolegal, which we primarily focus on, deals with the criminal component of the legal system and with insects that typically infest human remains or corpses.Use of insect development and insect colonization to solve crime(s)

Medico-legal Entomology

Helps determine postmortem intervalMovement of body???Determine scene of deathProves or disproves suspect, witness or corroborating statements regarding death

http://www.smithsonianchannel.com/site/sn/show.do?episode=141561

http://www.smithsonianchannel.com/site/sn/show.do?episode=141561 - measuring-time-with-maggots

Some History1200s – Sung Tz’u, a Chinese “death investigator” uses the behavior of flies to solve a murder. Everyone in the small town where the murder took place is gathered together with their sickles (blades used for cutting grass). Though no obvious blood stains appear on the tools, Tz’u releases flies into the area which, drawn to the scent of blood, buzz around the murder weapon. The guilty person confesses.

1668- Francesco Redi disproves the theory of spontaneous generation of maggots in rotten meat. The prevailing thought of the day was that maggots appear from nowhere in the spoiled food, as if by magic. His experiment showed that the life cycle of the maggot is associated with the rate of decay, allowing scientists to better estimate a deceased person’s time of death.

1750s – 1780s – Carolus Linnaeus published a standardized system of biological classification. Scientists use this system to determine the location of a murder, as fly species live in certain habitats.

1855 – Dr. Berger d’Arbois, France’s premier coroner of the day, proves the innocence of residents of a home in which a body is found. By studying fly larvae and mites in the body he determines that they were laid before the body was sealed inside the home of the accused well before the current residents moved in.

1894 – Dr. Jean-Pere Megnin publishes. The Fauna of Corpses, describing eight stages of bodily decomposition. Included in these are the types of insects each stage attracts. This further aids scientists in determining a victims time of death and if the body has been moved.

1935 – Dr. Alexander Mearns of Glasgow University uses the development of maggot larvae in a body to determine the victim’s time of death. This, in conjunction with witness testimony and other evidence, allows a suspect to be convicted in court.

1986 – The first textbook devoted to forensic entomology, A Manual of Forensic Entomology, is published. This makes information on this branch of forensics readily available, allowing standardized training for aspiring scientists.

Maggot Mass

Medicolegal Entomology

Typically focuses on violent crimesDetermination of time of deathDetermination of crime scene

Identifies the immature insectsDetermines the size and development of the insects

Calculates the growth of the insects and the stages of the life cycle

Compares the growth against weather conditions to estimate time of ovipositions (egg laying)

A Forensic Entomologist:

Corpse as Insect Food Source

Bodily decomposition attracts fliesFlies and related insects have highly sensitive

olfactory receptor sites on top of head.Attracted to protein-rich environment which corpse

provides Insect activity on the corpse within minutes of

deathDeposits eggs in natural or unnatural openings,

a.k.a., orifices or exposed wounds – eyes, ears, anus, etc.

Deposits eggs in orifices during daylight

Forensic EntomologyAfter 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 are the Necrophages, which includes flies (Diptera) such as the blowfly (Calliphoridae) and the flesh flies (Sarcophagidae).

Blowflies and flesh flies are very important to the forensic entomologist

Calliphorid Flies Adult flies can be identified by the iridescent blue, green colors

Sarcophagid Flies

These flies are grayish with longitudinal dark stripes on the dorsum

Omnivores, which include wasps, beetles and ants feed on the corpse along with the maggots left by the flies.

Omnivores may slow the rate of decomposition by decreasing the population of necrophages

Parasites and Predators – beetles and wasps eat immature flies

Others – spiders, mites, pill bugs and others use the corpse as a source of habitat

Omnivores Parasites and Predators

Forensic EntomologyEggs are laid 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.

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

Insect Evidence

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

Cleoptera

Forensic Entomology

The usual sites of oviposition on dead humans are natural openings. Blowflies will most often lay their eggs in the facial region, and more seldom in the genitoanal region. If there is a sexual assault prior to death, leading to

bleeding in the genitoanal region, blowflies will be more likely to oviposit in these regions.

If there’s blowfly activity in the genitoanal region, a sexual crime is suggested.

Forensic Entomology

The sites of blowfly infestation on the corpse may be important in determining the cause of deathFor example: if there has been trauma or mutilation of the body prior to death, this may lead to heavy infestation of other body parts than the usual sites when the victim is not mutilated.

Under a knife attack, it is usual to guard oneself with arms in front of thorax and head. This may lead to injury on the lower part of the arm. After death, blowfly may oviposit in these wounds.

EggsLaid on a host which is typically dead. May be laid within

minutes of death. Eggs typically hatch within 24-hours of depositing

Blow Fly Life Cycle:

Blow Flies

Insects are cold-blooded so their development is temperature dependentAs temperature increases, they develop more rapidly

As temperature decreases, they develop more slowly

Fly Eggs

Fly eggs look like parmesan cheese and accumulate in moist areas

Fly Larva

Eggs hatch within 24 hours after being laid

Fly larva are also known as maggots1st Instar Stage – 1.8 days (5 mm long)

The larva will eat until it gets so big it needs to shed its skin

First Instar

Initially feeds on fluid exuded from the body

Migrates into body

Hatching to first molt takes 1.8 days

Fly Larva

2nd Instar Stage – 2.5 days (10 mm long)For another 24 hours these maggots will grow until they shed their skin again

Third Instar

Still moves in mass

Greatly increases in size

Second molt to pre-pupa takes 2.5 days

Fly Larva

3rd Instar Stage – 4 –5 days (17 mm long)Feeding 3rd instar – maggots are eatingMigrating 3rd instar – maggots stop eating and start moving to the soil under the bodyMaggots are in the 3rd instar for about 100 hours

Pupa

Once the maggots are deep within the soil they will go through the pupation in order to become an adult fly.

10 –14 days after oviposition (lay eggs) Pupa (made of chitin; a hardened protein based

substance to protect developing insect that is encased)Many investigators overlook the dried, hardened outer

skin of the larva that is left in the environment when the fly emerges.

PUPA

Fly pupae are often discovered away from the body since maggots migrate. These pupae should be recovered at the death scene if time of death is questionable.

Blow FliesAnalysis of the oldest insect stage on the body, together with knowledge of the meteorological conditions at the scene, can be used to determine how long insects have been feeding on the body, and hence, how long the victim has been dead

Almost complete skeletonization of the head by maggots

Young maggots resemble fly eggs but are mobile.

Fly pupa and other insects present on decedent.

Post-morten ant and roach Activity leaves a typical

grouped pattern that looks like an abrasion

Post Mortem Interval

PMI – time interval from actual death to discovery of the body.

Cadavers decompose in four stages: Fresh Bloated Decay Dry

Certain insects are attracted to the corpse in each of the four stages of decomposition.Succession = the order in which insects are attracted to

the decomposing bodySuccession pattern is useful to determine PMI

Post Mortem IntervalBlowflies are attracted to a fresh corpse in order to lay their eggs

Carrion flies are attracted to the bloated corpseThere is a succession database that can be used to estimate PMI

Factors Used to Determine Time Since Death

4 factors must be taken into account Oldest stage of blow fly associated with the body Look at old pupal cases

Species of insects Each species develop at different rates so each species of

insects at the scene need to be collectedTemperature data Must be able to determine temperature of crime scene

for a period of timeDevelopmental data Must know how fast or how slow the specific species

develop

Degree HoursDegrees since death

The life cycle of the insect is measured by degree-hours because temperature effects the cycle

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

Calculating ADH from Climate Data

Using the Data3928 ADH in these three days (952+1488+1488). How many ADH of 70º are there in these 3 days? 3928/70=56.11 hours72 hours at 70º would have the insects passing to

the 3rd instar. But 72 hours at colder temperatures and insects will only be at 2nd instar stage.

Determining Whether the Body has been Moved

Insects present on the deceased body that are not prevalent to the crime scene can indicate that the victim was murdered elsewhere and was dumped at another location

Linking Suspect to SceneSometimes, criminals carry entomological evidence on them unknowingly

This evidence can place them at the crime scene by examining the life cycles of the insects

DrugsInsects that feed on the body of individuals that have been poisoned can be examined to determine what type of drug or toxin the person was poisoned withIt is important to note that specific drugs either speed up or slow down larval developmentCan influence entomologist’s final report

Forensic EntomologyAnalysis of larvae can assist in the identification of drugs used by decedent as well as their DNA•Triazolam •Oxazepam •Alimemazine •Chloripriamine •Phenobarbitol •Malathion •Mercury •Amyltryptiline •Nortriptyline •Cocaine •Phenycyclidine •Heroin

Forensic EntomologyMany of these chemicals will also influence the life-cycle of the maggot. Cocaine accelerates the development of some sarcophagids.

Malathion, an insecticide, is commonly used in suicide, and is usually taken orally.

Amitriptyline, an antidepressant, can prolong the developmental time up to 77 hours, at least in one species of Sarcophagidae.

Collection of Entomological Evidence

Evidence should be collected by an entomologist If not available, a police death investigator should collect the evidence

Different stages of larval growth should be collected and bagged separately

Sample of soil should also be collected from just outside the area marked by body fluids

Challenges to Forensic Entomology 3 challenges exist

Temperature Temperature of crime scene and the temperature that

the insects have been exposed to us unknown Season

Entomology is valuable only in spring, summer, and fall Exclusion of insects

Insects are excluded based on condition of body

Forensic Entomology

Blow fly pupae were collected from a body found. The ambient temperature was approximately 75°F and the humidity was 20%.

Larva found on the body were approximately 10mm long.

Estimate time since death.

Case Study (Decomposition)

On a hot August day (90°F), the body of an elderly man was discovered in a ditch next to a country road. He was lying supine dressed in overalls, a short-sleeved work shirt, and socks without shoes. His abdomen and legs were covered by a blanket. There was marked maggot infestation of the head and neck, partially obscuring a posterior scalp defect, and a ligature around his neck.

Case Study (Decomposition)

The skin of the upper chest, neck, and head were markedly darkened. The rest of the body was not decomposed. There was a slight greenish tinge to the abdominal area. There was no apparent blood on the ground surrounding the victim.

Case Study (Decomposition)

The scalp defect was a four inch gaping laceration with no underlying bone or brain injury. The ligature was a small towel tightly compressing the neck and knotted in the back. There was no rigor mortis and livor mortis was posterior. When the body was turned the livor did not move with gravity.

Case Study (Decomposition)

Stomach contents revealed fragments of sausage pieces, brown liquid and white semi-solid food particles. At least ten maggots were saved in a container of alcohol. The largest maggot was 4mm in length. A diagnosis of ligature strangulation was rendered and the death was ruled a homicide.

Case Study (Decomposition)When the wife came in to view his body she made a spontaneous statement, “I don’t understand, he looks fatter than normal.”

Case Study (Decomposition)

The next day a deputy sheriff called the pathologist to ask about the time of death. The deputy was holding a man in custody who had been seen with the decedent two days before the body was discovered. The suspect claimed that he was out of town the day before the man was found dead. The suspect had a good motive for the murder because of a soured business deal with the victim.

Case Study (Decomposition) Prior to making a formal arrest, the officer needed to make sure the postmortem interval was consistent with two days. What should the pathologist say about the postmortem interval in this case and why?