Honors Forensic Science Chapter 8 Entomology

Forensic Entomology – The study of the insects associated with a human corpse related to legal issues. 1. Purpose of Forensic Entomology A. Determine elapsed time since death – Not an exact time, only a close estimate.

B. Factors that affect insect deve- lopment: (1) Temperature (2) Moisture (3) Wind (4) Season

(5) Variations among individual insects (6) Exposure to the elements (7) Time of day

C. Insect evidence may show that. the body has been moved to a C. Insect evidence may show that the body has been moved to a 2nd site after death

D. Insect evidence may show that. the body has been disturbed at D. Insect evidence may show that the body has been disturbed at some time, either by animals or by the killer returning to the crime scene

2. Most cases that involve a forensic 2. Most cases that involve a forensic entomologist are 72 hours or more old   A. Up to 72 hours after death – Other forensic methods are equally or more accurate than the insect evidence.

B. 3+ days – Insect evidence is. often the most accurate and B. 3+ days – Insect evidence is often the most accurate and sometimes the only method of determining elapsed time since death.

Two Main Ways of Using Insects to Determine Elapsed Time Since Death 1. Using succession waves of insects   A. Used when the corpse has been dead between 1 month and up to a year or more

2. Using maggot age and develop- ment: A. Used when death occurred less than a month prior to discovery

Insects of Forensic Importance Fly – Often the first insects to come in contact with a dead animal 1. Attracted to two gases of decompo- sition: A. Putrescine B. Cadaverene

2. Prefer a moist corpse for the maggots to feed on – Easier to chew

Blow-Fly 1. Lays eggs in carrion, wounds, or dung

Life Stages of Blow-Fly 1. Egg Stage A. Size – 2 mm B. Color – White C. 1st Appearance – Within 10-15 minutes after death D. Stage Duration – 8 hrs

E. Characteristics: (1) Found in moist, warm areas of the body

2. Larva 1 (Instar 1) A. Size – 5 mm B. Color – White C. 1st Appearance – 41-45 hours D. Stage Duration – 20 hrs

E. Larva 1 Characteristics (1) Black mouth hooks visible (anterior side) (2) Thin body (3) One spiracle slit near anus

3. Larva 2 (Instar 2) A. Size – 10 mm B. Color – White C. 1st Appearance – 2 ½ days D. Stage Duration – 15-20 hours

E. Larva 2 Characteristics (1) Black mouth hooks (anterior side) (2) Actively feeding (3) Dark crop seen on anterior dorsal side (4) 2 spiracle slits near the anus

4. Larva 3 (Instar 3) A. Size – 17 mm B. Color – White C. 1st Appearance – 4-5 days D. Stage Duration – 36-56 hrs

E. Larva 3 Characteristics (1) Black mouth hooks (2) Crop not visible – Crop is covered by fat deposits (3) Fat body   (4) Three spiracle slits near the anus

5. Pre-Pupa A. Size – 9 mm B. Color – Light brown C. 1st Appearance – 8-12 days D. Stage Duration – 86-180 hrs   E. Pre-Pupa Characteristics (1) Larva migrates away from the body to a dry area

6. Early and Late Pupa A. Size – 9 mm B. Color – Light brown & changes to dark brown C. 1st Appearance – 18-24 days D. Stage Duration – 6-12 days

E. Characteristics of Early and Late Pupa: (1) Immobile (2) Does not feed (3) Changes to dark brown with age

(4). Filled air “balloon” to help. split open pupa case prior to (4) Filled air “balloon” to help split open pupa case prior to emerging as adult  

Early / Late Pupa

7. Adult A. Size – Varies B. Color – Black or green C. 1st Appearance – 21-24 days D. Stage Duration – Several weeks

E. Characteristics: (1) Incapable of flight for first few hours

Flesh Fly 1. Medium-sized flies with black and gray longitudinal stripes on the thorax & checkering on abdomen 2. Do not lay eggs – Deposit newly hatched maggots directly onto the corpse.

House Fly 1. Characterized by a thorax that is gray with 4 dark longitudinal lines on the back; Abdomen is yellow   2. Breeds in moist or decaying organic matter

Beetles – Generally found on the corpse when it is more decomposed 1. In drier conditions – Beetles can be replaced by moth flies

Rove Beetles 1. Elongated bodies with small wing covers and large jaws 2. Have very fast larval development 3. Feed on larvae of all species of fly 4. Common only during the later stages of decomposition

Hister (Burrowing) Beetles 1. Usually shiny (black or metallic- green) beetles 2. Only become active at night – Feed on the maggot infested part of the corpse

A. Day – Hide under the corpse. unless it is sufficiently decayed A. Day – Hide under the corpse unless it is sufficiently decayed to enable to hide inside it

Carrion Beetles 1. Don’t feed on carrion, but are carnivorous A. Often carry mites on their bodies (1) These mites feed on fly eggs

B. Arrival at the corpse before any fly eggs hatch into maggots: (1) The 1st eggs are eaten and maggot development is delayed (2) May lead to an incorrect estimate in time of death

Other Uses for Insects in Forensic Science 1. Has the body been moved after death? A. Some insects on the body may be native to the 1st habitat and not the 2nd

(1) Will show that the body has been moved following death   (2) Give an indication of the type of area where the murder actually took place

2. Has the body been disturbed after death? A. Did the killer return to the scene of the crime (1) This may disturb the insects cycle

(a) The entomologist may be able to determine the date of death   (b) The entomologist may be able to date the return of the killer

3. Presence and position of wounds: A. Decomposition may obscure wounds

B. Insects colonize remains in a. specific pattern – Usually laying B. Insects colonize remains in a specific pattern – Usually laying eggs first in the facial orifices, unless there are wounds, in which case they will colonize these first, then proceed down the body

(1). Maggot activity that is cen-. tered away from the natural (1) Maggot activity that is cen- tered away from the natural orifices – This is likely the site of a wound   (2) Maggot activity on the palm of the hands or on the arms – Defensive wounds

4. The presence of drugs: A. There is often not enough flesh left to determine the presence of drugs

(1) Bioaccumulate – The accu- mulation of substances (2) Maggots can be analyzed to determine the type of drug present

5. Place a suspect at the scene of a crime: A. Insects found on a certain type of vegetation can connect a suspect to a specific location

6. Child or Senior Abuse / Neglect: A. Cutaneous Myiasis – Insect colony on wounds/unclean areas on a living person

(1) Victim is still alive, but maggot infested (2) Entomologist will be able to tell when the wound or abuse occurred

Limitations of Forensic Entomology: 1. Temperature 2. Seasonal – Insects are only com- monly used in spring, summer, and fall  

A. Victim found in the spring with. little to no insect presence – May A. Victim found in the spring with little to no insect presence – May have died during the winter

3. Body Disposal – Can exclude insects A. Freezing the body B. Burial – If a body is buried deeply would exclude most insects

C. Wrapped – A victim that is. tightly wrapped would delay C. Wrapped – A victim that is tightly wrapped would delay insect infestation

4. Drugs – May affect the develop- ment of the insects

Life History of Flies Table 1: The development of body length (in mm) of some fly species during their metamorphosis at 72oF (L = Larvae; P = Pupae; A = Adult Fly).

Days after Death House Fly Blow Flesh Skipper Fly 1   Egg L 9 – 11 2 L 12 – 16 3 L 17 – 20 4 L 6 L 21 – 25 5 L 26 – 30

D.A.D. House Blow Flesh Skipper   11 L 31 – 35 L 26 – 30 P 38 – 40 L 10 – 13 12 P 26 – 29 L 14 – 16 13 P 13 – 15 14 P 31 – 34 15 16 17 18 A 30 – 32

* Pupae Species cannot be determined except by the size of the Pupae

Temp. House Fly   Blow Fly 50-54 Delay 5 days 55-65 Delay 4 days 55-60 66-69 Delay 2 days 61-65 Delay 3 days 70-74 Delay 1 day 66-70 75-79 No Effect 71-75 80-81 Accelerate 1 day 76-79 82-84 Accelerate 2 days 80-84 85+ Accelerate 3 days

Ecological Traits House Fly Blow Flesh Skipper Habitat Urban and Rural Urban and Rural   Urban Lighting Full to Partial Sun Partial Sun to Shade Prefers Sun Drugs No Effect Sensitive to Drugs