Forensic Entomology

Insects in the Forensic Sciences

What is Forensic Entomology?

• The application of insects and other arthropods to legal issues and court proceedings

What is it used for?• Applications

– Estimation of time of death– Cases involving possible sudden death– Traffic accidents with no immediately

obvious cause– Possible criminal use of insects

How does FE work?• Fact – insects feed on humans after

death. Yup – not good news, but we are part of the cycle of life!

• If insects are found on a corpse, the life stage of the insect can be used to determine time of death– This calculation is known as the

POSTMORTEM INTERVAL (PMI)

PMI ConditionsPMI must take into consideration many

environmental variables• Temperature• Time of day death occurred • Time of year death occurred • Whether the corpse is submerged in soil or

water.

Divisions of Forensic Science• Urban – Relates insects to human

structures and environments• Stored Products – Insect infestations

of stored food and beverages• Mediocriminal – The only division that

has a criminal aspect. Relates to insects feeding on human tissue in the postmortem period.

After Death• As the body decays, odors attract insects to

the dead body. Levels of putricine (decomp. enzyme,) sulfur and methane compounds send up an “open for dinner” flare.

• The flies (order Diptera) are the first to arrive. Blowflies (F. Calliphoridae) and flesh flies (F. Sarcophagidae) are flesh feeders and will be the first in line.

• Flies can arrive within minutes or up to a couple hours after death.

• In many cases flies arrive before the completion of a crime and are silent witnesses.

Phylum Athropoda• Not as large of a biomass as bacteria – but

run a respectable second!• Unifying Characteristic – hard exoskeleton• Class Insecta includes bees and wasps

(Order Hymenoptera,) flies (O. Diptera,) butterflies (O. Lepidoptera,) dragonflies (O. Odanata,) beetles (O. Coleoptera,) etc.

• “True Bugs” are Order Hemiptora. No hemiptorans have any consequence for forensic science – so erase “bugs” from your vocabulary!

Fly Life Cycle• If no trauma is present on the body, female

blowflies will lay eggs in exposed body openings (ears, nose, mouth, anus, genitalia.)

• Flesh flies don’t lay eggs, they deposit larvae.

• The colonization pattern is due to the mouth parts of adult flies. – Blowflies and flesh flies have spongy mouth

parts. They lack piercing apparatus that can cut through unbroken human skin. The body openings provide a moist, warm environment for larvae development.

BlowfliesBlowfly ClassificationKingdom: AnimaliaPhylum: ArthropodaSubphylum: UniramiaClass: InsectaOrder: DipteraFamily: Calliphoridae

Blowfly Eggs• Small, 2-3 mm length, elongated shape,

white to yellow color• Found in large clusters in and around body

openings as well as injuries• Clearly visible to naked eye• Colder months may see fewer in numbers• Can be found in more hidden locations such

as under eyelids or in nostrils• Eggs typically hatch within hours but may

take up to 2-3 days depending on conditions

Blowfly Larvae• One fairly small and featureless larvae

hatches from each egg• The body tapers from anterior to

posterior – Mouth at the anterior, spiracles at the posterior

• Posterior contains breathing apparatus called spiracles– Spiracles, along with body size and

shape provide important info for identification

Blowfly larvae• Large numbers of blowfly

typically hatch at a time and remain together while they feed on a corpse

• These maggot masses generally form in the head region and move down the torso as they feed.

• As they feed the larvae secrete digestive enzymes which allows them to consume nearly all the soft tissue on the corpse

Blowfly life cycle• Blowfly larvae go through three instars

(molts)• They are considered fully grown at the

third instar• This can occur in several days or

several weeks depending on species, environmental conditions and number of larvae present

Pupa Stage• After the 3rd instar

larvae go through a drastic behavioral change– they crawl away from the

corpse and burrow down into the soil to transform into the pupal stage and complete the life cycle

Pupa• The pupa form when the outer larval skin

hardens and shrinks• Inside this “case” the adult blowfly will form• Once the adult fly emerges, the pupal case

does not decompose. It can remain under a corpse for hundreds of years

• Pupal cases can provide valuable forensic info to investigators long after a crime has been committed.

Postmortem Interval (PMI)• Entomological evidence collection can

be done in a variety of ways• For our purpose we will:

– Identify the species– Document larvae length– Determine the instar– Determine postmortem interval estimation

• Depending on species we will use extrapolation of instar length or the accumulated degree day theory

Post Mortem Intervals• PMI – The use of insect life cycles to

estimate the time a corpse has been in the location where it was found

• PMI does not DETERMINE the time of death– Time of death is established by the

medical examiner• Forensic entomology can provide value

information for the M.E.

Forensic Applications• Time of injury vs. death• Estimation of time of death• Whether or not a corpse has been moved• Instances of insects as weapons• Child and elderly abuse and neglect• Single vehicle car accidents (insect stings

and path vehicles have traveled)• Aircraft crashes (instrument obstruction and

engine and fuel line clogging)

F.E. Applications – Blood Evidence

• “Roach Track” Confusion– Roaches are notorious for confusing

blood spatter analysis– Blood trajectory is often critical to forensic

investigations– Roaches, silverfish and other household

insects often travel through bloodstained areas• “Roach tracks” frequently confuse forensic

investigators that are untrained in how to identify them

Blood Spatter Confusion – Fleas and Flies

• Flies also track through blood, but “fly specks” are a far greater problem for investigators

• Flies ingest blood and can leave large undigested droplets behind in previously uncontaminated areas. These droplets can enlarge a crime scene unneccessarily.

• Fleas also leave behind undigested blood in their feces (commonly known as “flea dirt.”)– Flea dirt in a heavily infested dwelling can falsely

suggest blood “evidence”

Roaches, Flies, Fleas • It is becoming more clear that household

insect infestations need to be included as a variable in forensic investigations

• Proper identification of household pests can save valuable time and resources for technicians and investigators

• Best for juries to hear about insect “confusion” from CSI’s rather than from attorneys for the defense!

Insects and Illegal Drugs• Shipments of illegal drugs often

contain insect infestations, especially cannabis and heroine (derived from poppy plants.)

• Analysis of insect “stowaways” can allow investigators to track country of origin, and in many cases the local area of cultivation.

• PMI used to detect illegal drugs/poisons in fly larvae (consumed from corpses)

The moral of the story…• Insects are becoming invaluable in the

investigation of crime• Forensic entomology is one of the

fastest growing specialties in forensic science.

• All Crime Scene Investigation Units MUST be prepared to include insect collection, identification and analysis in their investigations.