INSECTS

What happens to a body immediately after death?

What happens to a body immediately after death? 1. Algor mortis - change in temperature after death 2. Livor mortis - setting of blood gives bluish-purple colour 3. Rigor mortis - stiffening of muscles 4. Autolysis - tissue breakdown by enzymes 5. Putrefaction - tissue breakdown by bacteria - characteristic odour 6. Mummification - dehydration/desiccation of tissues

Succession on a corpse Post mortem Processes 1. Initial Decay - body appears ‘normal’ but is decaying internally 2. Putrefaction - cadaver is swollen from internally produced gases 3. Black Putrefaction - exposed skin - black, body collapses 4. Dry Decay - cadaver nearly dry - slow rate of decay

There are two main ways of using insects to determine elapsed time since death : 1. using successional waves of insects 2. using maggot age and development.

Succession on a corpse 1: Within minutes - hours Calliphora and Lucilia spp - primary species -lay eggs in natural body openings (ears, nostrils, eyes or wounds) 1: Within hours-days Chrysosoma and Sarcophaga spp - secondary species face competition from primary species compensation: viviparity

Estimating PMI 1. Temperature dependent development of insects - insect developmental rate  ambient temperature - development will not occur below a species-specific threshold temperature - the accumulation of heat can be expressed as “degree-days” or “degree-hours” Problem: little work done on the daily temperature fluctuations and development

Estimating PMI Development times and temperature Calliphora vomitoria Stage 12.5ºC 23ºC 29ºC 35ºC Egg 64.8 21.6 16.8 12.0 Instar 1- 3 393.6 172.8 117.6 74.4

Estimating PMI 20 Maggot length 10 mm Crop length Time from last feeding (h)

Estimating PMI Experimental Evidence Take larvae from body Raise to adult in lab Mate insects and allow to lay eggs Incubate at field temperatures Note time taken to get to stages collected in field

Two kinds of developmental data 1. Lab Experiments -as in previous slide 2. Field Observations Wind speed & direction Minimum & Maximum temperatures Developmental Degree-days Relative humidity Cloud cover Precipitation

Who are these insects? 1. Calliphoridae (blow flies) 2. Muscidae (muscid flies) 3. Silphidae (carrion beetles)

Who are these insects? 4. Sarcophagidae (flesh flies) 5. Histeridae (clown beetles) 6. Staphylinidae (rove beetles)

Who are these insects? 7. Nitidulidae (sap beetles) 8. Cleridae (checkered beetles) 9. Dermestidae (dermestid beetles)

Who are these insects? 10. Scarabaeidae

Succession of adult insects on cadavers in Tennessee (spring/summer) Succession of larval insects on cadavers in Tennessee (spring/summer) Family Fresh Bloated Decay Dry Calliphoridae Muscidae Silphidae Sarcophagidae Histeridae Staphylinidae Nitidulidae Cleridae Dermestidae Scarabaeidae

Invertebrates Associated with Cadavers

Some case studies: Case 1: Victim: 14-year old prostitute Found: Wooded lane in NW U.S. – 4 June Reported missing 4 days earlier Problem – no precise time of death Data/specimens gathered: Climatic data Adult flies and eggs/larvae from wounds All other insects Entomologists – calculated that first insects got to body on 31 May.

Some case studies: Case 2: Victim: 30 year old female Found: In parking lot at 6 AM (New England) No insects present As day warmed – greenbottle fly (Phaenicia) appeared and fed around woulds Soon after – clusters of eggs Key facts -flies aren’t night active -previous day – ideal for fly activity Conclusion: Victim killed during preceding hours of darkness

Some case studies: Case 3: Victim: 46 year old male alcoholic Found: In bedroom Dead: 5 days Found eggs larvae + red pupae on corpse – incubated them and got Muscina stabulans Determined from rearing experiments that the development time for this species 28 days (egg to adult at 16 C) Tested to see what redness was in pupae – Serratia marcescens Conclusion: Victim was ill with Serratia infection before he died and flies laid eggs while he was still alive

Aquatic insects to establish PMI

Other uses for insects in forensics 1. Detection of poison, drugs and other chemicals Phenobarbitol Mercury Cocaine Heroin Malathion 2. Determination if an insect is the “criminal” 3. Determination of sequence of events in a crime