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Entomology
Estimating Post Mortem Interval (PMI)
Insect Succession
• The blow flies show up first• Then other species of flies including
soldier flies• The predacious species arrive after the fly
eggs have hatched and feed on the maggot masses
• Then beetles show up once the corpse begins to dry
• Mites, ants, and spiders along with others are present
Role of the Entomologist
• The Forensic Entomologist assists in estimating the time of death by studying which insects are present and in what life stage
• At a crime scene the entomologist collects samplings of the types and stages of insects present
• Some are preserved at the scene and others are kept alive for rearing to adulthood for identification
Know the stages in order of a fly life cycle. Times are based on 70 degrees F. Changing the temp. will alter the times.
Adult insects are collected using a net.
Insect samples are placed in jars containing KAA or alcohol solution. KAA is used for eggs, larvae, and pupae. Alcohol is used for adults. The jars need to be labeled with the name or initials of collector, date, time, area from which they were collected, and location.
Factors that Affect Insect Development
The weather affects the time that the insects arrive and inhabit the body. Insects are less active in the rain. Much less active in winter or snow. Cloud cover also slows them down. Temperature has an affect on the life cycle times.
Factors that need to be considered when estimating PMI are location of the body. Sun vs. shade, inside vs. outside, terrain, or inside a vehicle. It takes some time for insects to get inside a house or vehicle.
Whether the body has been buried, or is above ground, or was buried and dug up will make a difference. Urban area. Time of day – insects are less active at night.
Varying types of terrain or tundra make a difference on rate of decay and succession of insects. Aquatic areas have different insects.
Season matters
Geographic locations influence insects, progression of insects, and climatological information. So state or country will matter.
Insect RearingSome of the larvae and pupae collected are not put into KAA solution but kept alive and reared to adulthood to make species identification easier.
Insect Identification
Blow flies and maggots
Soldier flies and maggots
Types of beetles found on corpses. Beetles prefer the body when it has dried out.
