Insects used to determine TOD Forensic Entomology Insects used to determine TOD

Insect Biology Insects are the most diverse and abundant life forms on earth Existed for over 250 million years How long have humans existed? There are over a million described species More than 2/3 of all known organisms There is more total biomass of insects than humans Insects under either incomplete or complete metamorphosis Humans 300,000 years

Metamorphosis Complete has four distinct life cycle stages Egg Larva - Can be worm-like; can see six legs; eat constantly and grow rapidly Pupa - Hard protective case Adult Incomplete only has three life cycles Egg Nymph - Looks like a smaller, wingless version of the adult Adult

Forensic Entomology Use of insects and other arthropods that feed on decaying remains to aid in legal investigations Used to determine PMI or time since death

Arthoropoda Invertebrate/exoskeleton/segmented body/joint appendages Insects Chitinous exoskeleton, a three-part body, three pairs of jointed legs, compound eyes and one pair of antennae Arachnids Eight (4 pair) legs, 2 additional with adaptation (feeding, sensory); no wings, body is cephalothroax and abdomen Myriapods Many, many legs Crustaceans Appendages split in two; mostly aquatic

Medicolegal Forensic Entomologist Focus on violent crimes Determination of PMI or site of death based on identification of arthropods collected near corpse

Post Mortem Interval (PMI) Forensic Entomology is used to determine time since death Also used to determine Movement of corpse Manner and cause of death Association of suspects with death scene Detection of toxins, drugs, or DNA of victim through insect larvae analysis

Forensic Entomology - Applied Forensic Entomologists… Identification immature insects at various stages of life cycles Determine size and development of insects Calculations growth of insects and passage through life cycles in the lab Compares growth to weather conditions to estimate time of oviposition

Succession of Insects on a Corpse PMI estimates based on insects present Time required for a given species to reach a particular stage in life cycle Comparison of all insect species on the corpse at the time of examination Ecological succession The first invasion by insect species will alter the habitat by their activities These changes make the habitat more attractive to a second wave of organisms who in turn the habitat for yet another organism

Ecology of Decomposition Necrophages First species feeding on corpse tissue Diptera (rue flies) Coleopter Carrion (beetles)

Ecology of Decomposition Omnivores Species such as ants, wasps, and some beetles that feed on the corpse and associated maggots Large populations of omnivores can slow the rate of corpse decomposition by reducing populations of necrophage species

Ecology of Decomposition Parasites and Predators Beetles and true flies and wasps that parasitize immature flies Incidentals Pillbugs, spiders, mites, and centipedes use corpse as an of their natural habitat

Life Cycle of a Fly

Decay Rates are Variable Decay rates of 150 human corpses studied at the Body Farm in Tennessee Most important environmental factors Temperature Access by insects Depth of burial Other factors Chemicals Embalming agent, insecticides, lime, etc… Animals disrupting the corpse

Five Stages of Decomposition Fresh Bloat Decay Post-decay Dry (skeletal)

Five Stages of Decomposition Fresh Days 1-2 Begins at death Flies begin to arrive Temperature falls to that of ambient temperature Autolysis occurs

Five Stages of Decomposition Bloat Days 2-6 Swells due to gases produced by bacteria Temperature of corpse rises Flies still present

Five Stages of Decomposition Decay Days 5-11 Gasses subside, decomposition fluids seep from body Bacteria and maggots break through skin Unpleasant odor Larvae begin to pupate Corpse reduced to 20% of original mass

Five Stages of Decomposition Post-Decay Days 10-25 Carcass reduced to hair, skin and bones Fly population reduced and replaced by other arthropods Hide beetles are dominant in dry environments Mite and predatory beetle populations increase

Five Stages of Decomposition Dry Days 25+ May not occur if corpse in wet region Maggots stay longer and hide beetles will not appear In wet regions hide beetles replaced by nabid and reduviid insects Corpse reduced to at least 10% of original mass Only bone and hair remain