chapter 12 forensic entomology © 2012 cengage learning. all rights reserved

Chapter 12

Forensic Entomology

© 2012 Cengage Learning. All Rights Reserved

2 Forensic Science II: Forensic Entomology, Chapter 12


Introduction—Objectives

1. Define forensic entomology.2. Describe the anatomy of an arthropod.3. Discuss the life cycle of insects.4. Estimate time of death using insect

evidence.5. Examine the effects of insects on human

remains.



Introduction—Objectives

6. Evaluate the use of entomological evidence to solve crimes.

7. Describe the impact of weather on metamorphosis.

8. Demonstrate proper procedures for collection and preservation of entomological evidence.



Introduction—Vocabulary

o Arthropod—a phylum of animals with jointed appendages and an exoskeleton (from the Greek arthros–jointed; podes–feet)

o chitin—a tough polysaccharide; the major component of an arthropod’s exoskeleton

o exoskeleton—a rigid external structure made of chitin and protein (protects, provides a point of attachment for muscles; prevents water loss)

o forensic entomology—the study of insects in legal situations



Introduction—Vocabulary

o invertebrate - organism lacking a backboneo larva (larvae, pl) - immature, feeding stage of insects

that undergo complete metamorphosis; the stage between the egg and pupa

o maggot - legless larvao metamorphosis - the changes an organism

undergoes as it develops into an adulto pupa (pupae, pl) - nonfeeding and relatively inactive

developmental stage of some insects



Bugs Don’t Lie

o July 9, 1997 Champaign County, Ohioo Stepfather, Kevin Neal, claims stepchildren are

missing from their back yardo Bodies discovered on September 6th were in the late

stages of decompositiono Autopsies revealed

• Maggot infestation• Absence of blowflies and screwworms• Presence of cheese skipper fly in its 3rd instar stage

o How were these insects evaluated?



Introduction (Obj 12.1, 12.2)

o Arthropod—an invertebrate



History



Insects & Forensics (Obj 12.2)



Insects

o 29 orders, or related groups, of insectso 2 orders are important to forensics

• Flies (Diptera)• Beetles (Coleoptera)



Insects at Work (Obj 12.3, 12.5)

o Metamorphosis—the maturation process for insects)• Eggs• Larvae• Pupa• Adult



Postmortem Interval (Obj 12.4, 12.6)

o Postmortem Interval—the time elapsed since a person died

o When longer than 72 hours after death, entomology becomes important

o Within 48 hours the female blowfly lays eggs in moist areas of the body



Collecting & Preserving Evidence (Obj 12.6, 12.7, 12.8)

o Observe and record all pertinent factors• Weather patterns (rainfall, wind, humidity,

temperature, and exposure to light) during the PMI

o Avoid disturbing insects within several feet of the body

o Measure distance from body to insectso Collect samples of all insect stages on, near,

and under the body




1. Estimates on the types and number of insects2. Key insect colonizations on and near the body3. Exact positioning of the body using fixed points, if

possible: placement of the arms and legs, the position of the head, and parts of the body in the shade and in the sunlight

4. Locations of eggs, larvae, and pupae on the body




5. List of opportunistic feeders and other insects (such rove beetles, ants, wasps, and insect parasites)

6. Insect movements (within 20 feet of the body)7. Natural and artificial influences that might affect the

speed of decomposition, such as burning, covering, or burying the body



Collecting & Preserving Evidence



Factors Affecting Insect Activity

o Natural environment and natural lighto Natural environment and artificial light

o Artificial environment and natural lighto Artificial environment and artificial light



Temperature Readings

o Ambient air• 1 foot above the body• 4 feet above the body

o Ground Soil• Surface• 10 centimeters below• 20 centimeters below

o Center of a large infestation (if present)



More on Collecting and Preserving

o Capturing live flies with netso Pin flies to a board, oro Preserve with 80% alcohol and 20% water

• Adult flies• Eggs• Largest larvae



More on Collecting and Preserving

o Label vials with• case number• collection time • date• geographic location • the location of the insects on the victim • the initials of the investigator



Chapter Summary

o Forensic entomology is the analysis of insect evidence in legal cases.

o Insects belong to the phylum Arthropoda, a group of organisms with jointed appendages, segmented bodies, and an exoskeleton.

o The first documented use of insects to solve a homicide case was in China in AD 1235

o Since, scientists have added to the knowledge of insect behavior and life cycle.



Chapter Summary

o Insect evidence is valuable in estimating the postmortem interval.

o There are more than 700,000 known species of insects, but only a few have forensic value.

o Female blowflies are usually the first insects to colonize a dead body.

o The extent of decomposition—especially if it is unevenly distributed on the body—provides information for estimating the time (and perhaps manner) of death.



Chapter Summary

o Entomologists record and analyze climate and weather information related to the insect samples.

o Temperature, humidity, and other weather and climate elements affect the insects that colonize remains as well as the progression of the insect life cycle.

o Processing and preserving insect evidence requires special care, techniques, and materials.

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