Forensic entomology Flashcards
(28 cards)
What are the questions to be answered at a suspected homicide?
-Who is it?
-How did they die?
-When did they die?
-Where did they die?
-When did wounds to the body occur?
What does any discussion of forensic entomology mention?
‘Washing away of wrongs’, by Sung Tzu, 1235
What are blowflies?
-Arrive within minutes of death
-Most common organism in FE
What do the 5 stages of post mortem decomposition associate with in FE?
‘Waves of colonisation’ by insects
What are problems with estimating PMI from species composition?
-No stage has a fixed duration and different body regions decay at diff rates
-Season and weather can affect colonisation sequence
What colonisation occurs during the fresh stage of decomp?
First insects to arrive are blowflies, e.g. calliphora vicina
What colonisation occurs during the bloat stage of decomp?
-Gases released by body attracts blowflies
-Predators that feed on blowfly larvae are attracted
-E.g. Burying beetles, Rove beetles
What colonisation occurs during the active decay stage of decomp?
-Putrfaction of the body occurs and fermentation products are produced attracting more insects
-E.g. Histerid beetles, muscid flies
What colonisation occurs during the post decay stage of decomp?
-Blowfly larvae departing
-Species of fly larvae that feed on dry remains
-Dermestid beetle larvae dominates
What colonisation occurs during the skeletonisation stage of decomp?
-Few insect species found
-E.g. Nitidulidae beetles
How can we estimate time of death from species composition?
Consider:
-Time of year
-Temperature
-Species of insect
What is the minute time since death?
Reflects the least time it would take for invertebrate to reach a particular stage of development
How are blowfly eggs layed?
-Female chooses natural openings and under bodies
-Up to 180 eggs laid
What do blowfly eggs hatch into?
-1st instar larva
-Feeds on tissues and bacteria from decaying bodies
What occurs 24-48 hours after blowfly eggs hatch?
-Moults to 2nd instar
-Feeds and dramatically increases in size over 3-4 days
What happens when blowfly reach 3rd instar?
-Reach optimal size
-Empty gut contents
-Crawls away
What occurs after blowflies empty their gut contents?
-Burrow in the soil
-Adult fly then emerges
What is the life cycle of an adult blow fly?
-Body hardens and wings expand
-Fly off for food
-Live for several weeks-months depending on temperature
What must you allow for when calculating the minimum time since death?
Temperature effect
*Time taken to develop increases with temperature
How do you calculate the minimum time since death?
-Calculate accumulated degrees hours/days
=Time taken to reach stage x (temp - base temp)
What are invertebrates?
Those that infest wounds or live on the body surface
What is ‘wound myiasis’?
Infection of wounds with diptera larvae
What occurs when infested wounds are untreated?
-Extends and more flies attract to lay their eggs
What is septicaemia?
-Infections of the blood
-Potentially fatal
