Forensic Entomology

What is Forensic Entomology?•The use of insects that inhabit decomposing remains to aid in legal investigations.•An entomologist can aid in investigations by:•Determining PMI (Post Mortem Index)•Helping interpret distributed blood spatter•Helping interpret disturbed evidence

Body Decomposition

A body goes through 2 decay processes after death.1.Autolysis: The internal digestion of itself (decomposition within)2.Putrefaction: The decay process which entails bacterial and fungi breaking down the organism

PMI

Postmortem Index- The time interval of death estimated for a person•2 things needed to figure this out• Types of insects found on the body and their stages of development• Temperature the insects were found in

Larvae and Pupae

•Larva (plural- larvae): Immature form of an insect that undergoes metamorphosis (ex. Maggot)• Instar: 1 of 3 larval stages of insect development

•Pupa (plural- pupae): The stage in an insects life cycle when the larva forms a capsule around itself and changes into an adult.

How do bugs aid in determining PMI?

•Using the life cycle of common insects one can determine how long a person has been dead.•Entomologists look at the oldest insect on the body and the time periods at which they come to the body to determine the time since death.

How do you calculate PMI?

•Example: Blow flies come to the body and lay eggs within an hour or so after death.•They are attracted to gases (putrescine and cadaverene)•If a body is found with larvae on the body, the entomologist can conclude that the body has been there 23-72 hours (1-3 days).

Blow Fly Life Cycle

•6 Stages:• 1 Egg (Laid directly after death) – 0-23 hours• 2 First instar larvae – 23 hours• 3 Second instar larvae – 50 hours• 4 Third instar larvae – 72 hours• 5 Pupae – 202 hours• 6 Adult – 345 hours (14-15 days)

Other Insects Used to Determine PMI

•Beetles •Roaches•Flesh flies•Wasps•Cheese Skippers•Mites

Beetles

•Many beetles are also used to determine time of death because they go through the larvae stage like the blow fly.•The species of beetles are too diverse to name all of them but using them to determine time of death is the same as that of the blow fly.

Hairy Rove Beetle

•Arrives within a day or a few days of blow flies.•Adult and larvae rove beetles prey upon the fly larvae.

Hide Beetle

•Found Worldwide•Feed on dried remains• Hair and skin• Show up weeks to months after death

Roaches

•Roaches are capable of producing damage to human skin that resembles abrasions or chemical burns.•These abrasions appear as small pits in the skin.•They often consume human hair, removing the entire hair shafts during their feeding.

Flesh Flies

•Deposit living larvae.•They “skip” the egg stage so egg masses will not be visible on remains.•An adult female fly deposits less larvae.•There are not as many of these flies found on remains.

Other Insects

•Tiny wasps come to lay eggs on the maggots already present. (parasites)• Live off of the larvae

•Cheese skippers arrive once putrefaction starts (attracted by the seepage of bodily fluids)•Mites also like the body dry like beetles.

What else can be determined by bugs?•Since bugs feed off of human fluids and soft tissues it does not take long to lose specimens needed for toxicology reports.•However, bugs’ larvae can be used to run a standard toxicology analysis.•Bugs are crushed up into a “milkshake” and a tox screen is run on the fluid mixture.

What else can be determined by bugs?•Was the body moved?• A body killed in one location and moved to another might have insects on it that only come

from the location it originated.