CHAPTER 13 FORENSIC ENTEMOLOGY OBJECTIVES understand the stages of death describe the role insects play in the decomposition of the carrion describe and calculate the PMI articulate the life cycle of insects 1
TAXONOMY method of orderly classification of biological systems (Carl Linnaeus late 1700 s) kingdom is the broadest category and species the smallest entomology interested in arthropods - animals with jointed legs, a segmented body and a hard, non-living exoskeleton beetles (Coleoptera) eat carrion (carcass of a dead / decaying animal) flies (Diptera) 2
forensic entomology is the use of insects and other arthropods to aid in legal investigations three areas of application urban entomology affects man and his environment (insect damage to structures) stored product entomology insects infecting foodstuffs medicolegal entomology (forensic medical) deals with necrophagous (carrion feeding) insects that inhabit human remains post mortem interval (PMI) time elapsed since a person dies to solve a crime, investigators answer the five W s Who was the victim / perpetrator? What happened? When did it happen? Where did it happen? Why did it happen? 3
The Process of Death death is a process, not an event different tissues and organisms in a living body die at different rates (brain cells die within 3-7 min / skin cells can live up to 24 h) definition of death varies (cardiac / brain) algor mortis the cooling of body temp after death the body cannot metabolically maintain its temp 98.6 F (37 C) equalizes its temp to the environment theoretically follows Newton s law of cooling (exponential temperature decay) - rate of change of the temp of an object is proportional to the difference between its temp and the ambient temp (applies to small, inorganic substances) 4
Glaister equation formula used for determining the approximate time period since death based on body temp hours of death = 98.4 F internal body temp 1.5 the equation can be used 1-36 h after death most accurate within 12h body cools 1-1.5 F per hour until it reaches ambient temp when calculating approx time of death, considerations must be given to temp of environment types of clothing on body / layers wetness of clothing air movement surface area ( surface area, faster the body cools) 5
livor mortis a purple / red discoloration of the skin due to pooling of blood in the body due to gravity after death (heart stops) can give an indication of the position of the body at the time of death (does not move) does not occur in areas that are in contact with a hard surface (ground) begins within 1/2h of death and most evident within 12h rigor mortis rigidity (stiffness) of the skeletal muscles after death ATP breaks down, fluid concentrations change and muscles become rigid begins in small muscles (face and jaw) occurs within a few hours of death gone within approx 30h leaving the body limp affected by environmental factors temp, dehydration, condition of muscles and use prior to death 6
Rule of thumb when estimating TOD Temp of Body Stiffness of Body Time since Death Warm Not stiff Dead > 3h Warm Stiff Dead b/t 3-8h Cold Stiff Dead b/t 8-36h cold Not stiff Dead >36h decomposition begins within 4min of death cells deprived of O 2, CO 2 in the blood, ph, and waste accumulates, poisoning cells enzymes dissolve cells from inside out causing them to rupture (autolysis the process by which a biological cell self-destructs) autolysis (step 1 of decomposition) is observed after a few days appearance of fluid-filled blisters on the skin and skin slippage putrefaction (step 2 of decomposition) the decomposition of animal proteins (soft tissues of the body primarily by bacteria (anaerobic microorganisms) first visible sign is a greenish tint (cast) to skin gases (methane, ammonia) are released by continued decomposition of tissues bloating foul odor (volatile butyric and propionic acids) further decay of proteins and fats produce more odiferous compounds (skatole, methyl disulfide, cadaverine and putrescine) body is a mass of fluid and extremely foul smelling - black putrefacation 7
adipocere (grave wax) insoluble fatty acids left as residue on decomposing cadavers formed by the slow hydrolysis of fats in wet ground (can occur in both embalmed and untreated bodies) occurs months to years after death saponification (alkaline hydrolysis of fatty acid esters the reaction of a base with fat to form soap) of fatty acids catalyzed by bacteria mummification is the result of dehydrated tissue (skin) that has survived decay develops in hot dry conditions with low body fat content diagenesis (final stage) process of chemical and physical change in deposited sediment during conversion to rock bone is chemically altered by moisture and ph of soil Stages of Decomposition (p380) Stage Initial / fresh decay (autolysis) Description - cadaver appears fresh externally decomposing internally due to activity of bacteria (0-4d) Putrefaction / bloating - cadaver is swollen by gas produced internally accompanied by odor of decay (4-10d) Black putrefaction - flesh of creamy consistency exposed body parts black body collapses as gases escape fluids drain from body and odor or decay is very strong (10-20d) Butyric fermentation - Cadaver drying out some flesh remains; cheesy odor from butyric acid (20-50d) Dry decay (diagenesis) - Cadaver almost dry slow rate of decay (may mummify) (50-365d) 8
the rate of decomposition is variable dependent the environment, temperature and the presence of scavengers body decays twice as fast under water and half as fast under ground number of days to become skeletonized = 1285 average temp o C - if the average temp is 20 o C (68 o F) it will take approx 64d to skelotonize - if the average temp is 30 o C (86 o F) it would take approx 30d to skeletonize due to heat and humidity Life Cycle of Insects many insects are carrion eaters four principal stages of metamorphosis of a fly (Musca domestica) egg, larva (maggot), pupa and winged adult 3days 9mm 24-48h 17mm 12h 6mm 12-24h 12h 1.2mm 12h 3mm female deposits 100-150 eggs at a time hatch as larvae which eat, grow fast (slightly rigid exoskeleton) and molt (1 st,2 nd and 3 rd instar) larva moves away from food source (prepupal) and pupates (hard brittle casing from which an adult fly emerges) 9
Forensic Entomology knowing the stage of insect inhabitation of a corpse and the duration of stages in the insect s life cycle lead to an estimate of time since colonization as body undergoes successive stages of decomposition attracts a succession of insects some feed on the products of decomposition and others feed on the feeders the succession of insect predators on a corpse follows a predictable pattern Influenced by geography and local conditions insects vary from region to region, habitat to habitat and season to season The Insects of Death most common are flies (Diptera) and beetles (Coleoptera) adult flies (Diptera) have one pair of wings, three pairs of legs larvae are worm like complete metamorphosis 10
Major Families of Diptera found on / near carrion Family Examples Calliphoridae blowflies (blue / greenbottle flies) early stages of decomp most abundant larva different species have preference for oviposition (shade / light) and habitat (urban / rural) Sarcophagidae flesh flies large flies that lay live larvae instead of eggs present shortly after death larvae eat blowfly maggots Muscidae large family ubiquitous housefly sometimes found in later stages of decomposition Piophilidae dark, shiny flies (cheese skipper) larvae are scavengers late stage of decomposition blowfly flesh fly housefly cheese skipper 11
adult beetles (Coleoptera) have two pairs of wings (top wing is hard for protection, lower wing for flight) and three pairs of legs larvae of different shapes (worm-like with legs / soft and c-shaped (grubs)) pupae pale, mummified versions of adult complete metamorphosis Most are nocturnal may be found under the body / in the soil surrounding the remains Major Families of Coleoptera found on / near carrion Family Examples Staphylinidae rove beetles can be present within hours of death months later adults and larvae feed on eggs and larvae of other species Siphidae carrion / burying beetles (sexton beetle) early stages of decomp adults and larvae feed on maggots and carrion Histeridae clown / hister beetles present from early stage to start of dry stage decomposition adults and larvae feed on maggots and pupae / larvae of Dermestes beetles Dermestidae Scarabidae Cleridae skin / hide beetles feed on dried skin and tissue during later stages of decomp hide beetles dry stage of decay Ham / checkered beetles predators of flies and other beetles Carabidae ground beetles larva and adults are predatory all stages of decomp Tenebrionidae darkling beetles larva and adults are predatory 12
rove beetle carrion (sexton) beetle clown / hister skin / hide beetle ham beetle ground beetle darkling beetle 13
Insect timeline. blowflies and flesh flies arrive at body first (shortly after death) attracted by molecules of decay female fly lays eggs within natural body openings / wounds fly eggs hatch as larvae (maggots) that feed on soft, mushy body parts maggots can form large, moving masses that with bacterial decomposition raise the temp around them to above ambient temp (environmental) maggots account for loss of body mass predators (ants, wasps and beetles hister, rove, burying) are attracted to the corpse beetles feed on carrion and other arthropods lay their eggs on or under the corpse blowflies and flesh flies thrive in a semifluid environment (fresh decay) as corpse dries, cheese skippers and coffin flies take over ham / checkered beetles feed on flies and other beetles corpse is reduced to <20% of original weight skin and bones remaining flies and maggots are gone rove beetles remain hide beetles arrive In the soil, under the corpse, mites (tiny, 8-legged) end of decay stage of decomp no insects corpse is reduce to <10% of original weight 14
Temperature Dependence : degree-days insect development dependent on temp ( temp, growth) above and below a temp threshold (too hot / too cold) halts insect development within the development temp range, insect growth is regulated by the amount of thermal energy absorbed (per unit of heat) growth rate expressed in temp-time units (degree-day (a unit of measure of energy absorbed by a biological system, causing growth) / degree-hour) accumulated units represent the energy needed to effect a change of form (eggs to larvae 3 rd instar) using the life cycle of a housefly (diagram 13.5 p383) assuming a constant temp 68 F (20 C), it takes 36h to grow from eggs to 3 rd instar 36h x 20 C = 720 accumulated degree-hours (ADH) this is the total amount of energy required to effect the change of a housefly at 10 C it will take twice as long to get to 3 rd instar 720 degree-hours / 10 C = 72h 15
How do forensic entomologists use this concept to find PMI (post mortem interval)? (p 389) 9/16 two squirrel hunters find a body under an oak tree lots of maggots on body largest 18mm prepupae on ground around the corpse Entomologist decides developmental stage was end of 3 rd instar ambient temp 74 C specimens collected to raise into flies several weeks later identified as blue blowflies (Calliphora vomitoria) took 536h at 68 F (20 C) for collected maggots to become adult flies life cycle (egg to eclosion) of 555h at constant temp 27 C prefers shady places with a low threshold temp (from literature) entomologist needs to know temp that corpse experienced under the oak tree (find max/min temps for the month) estimate PMI published life cycle: 555h x 27 C = 14 985 ADH lab study(3 rd instar to eclosion): 536h x 20 C = 10 720 ADH thermal energy needed from eggs to third instar 14 985 10 720 = 4265 ADH the average median temp for first 20d Sept = 70.9 F (21.6 C) therefore 4265 ADH / 21.6 C = 197 hours (8d 5h) the amount of time since the bluebottle flies deposited eggs on the body (Sept 8 th at 10am approximate PMI) 16
variables that may skew PMI estimation time it takes for flies to find corpse (dependent on location, amount of blood and temp) parts of body exposed (liver, heart, lungs attract flies) burn victims clothes can retard colonization burial, water, plastic coverings delay oviposition maggots feed in masses that generate own heat above ambient temp decay toxins / drugs consumed can / decomp traces of drugs can be identified in maggots Habitat fly species vary geographically according to climate, season and habitat knowledge of fly habitats (what flies are present in specific areas, seasons and at defined temps) helps forensic entomologists corroborate field evidence, infer postmortem movement of a corpse, or infer prior burial, freezing or wrapping of a body 17
Other Uses of Insects in Forensic Science presence of wounds can be observed by maggot activity away from usual body orifices (activity on forearms may indicate defensive wounds) Insects can place a suspect at the scene of the crime (suspect has chigger bites, identical to bites investigators got at crime scene chiggers are localized to that specific area) Contraband trafficking can be traced to by identifying trapped insects (seized marijuana carrying beetles specific to Mexico) species of insects found on grill of vehicle investigators can refute a suspect s alibi (may indicate travel to an area outside of alibi) presence of drugs can be identified by testing maggots Collection of Evidence (diagram p401) description of habitat, temp and weather conditions (sunny, shady, cloudy) climatological data at site temp, humidity, evidence of rain and weather data (1-2 weeks before victim s disappearance to 3-5 days after body discovered) temp recording of ground by the body, beneath the body and of the maggot mass all the different types of insects on the body, in the body, beneath the body and flying over the body should be collected and labeled collection of largest maggot to be reared for identification and calculation of degree-days 18
New Developments in Forensic Entomology remember PMI is estimated based on many variables and not all experts will agree DNA fingerprinting of adult fly species can be used to ID eggs and early instar maggots computer modeling of the life-cycle of flies may decrease the number of variables and unknowns analyzing chemicals released into soil and air during decomp to determine PMI research toward improving the measurement of relevant body temp in algor mortis may be a relationship between electrical conductance of tissue and time since death with all new developments in forensic science, the Daubert ruling must be satisfied especially true in forensic entomology 19