Using Pig Carcasses as Model Corpses INQUIRY & INVESTIGATION. To Teach Concepts of Forensic Entomology & Ecological Succession

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1 INQUIRY & INVESTIGATION K ENNETH G. SCHOENLY NEAL H. HASKELL DAVID K. MILLS CARINE BIEME-NDI KRISTIE L ARSEN YER L EE RECREATING DEATH S ACRE IN THE SCHOOL YARD: Using Pig Carcasses as Model Corpses To Teach Concepts of Forensic Entomology & Ecological Succession 402 THE AMERICAN BIOLOGY TEACHER, VOLUME 68, NO. 7, SEPTEMBER 2006

2 Table 1. Environmental and biological variables that are known to influence carcass decay rates, successional processes, and/or arthropod species composition. VARIABLE(S) COMPARISON SUGGESTED REFERENCE Sunlight and Heat Sun-Exposed vs. Shaded Carcasses Shean, B.S. et al J. Forensic Sciences 38: Season Spring vs. Summer Tabor, K.L. et al J. Medical Entomology 41: Dwellings and Shade Indoors vs. Outdoors Goff, M.L J. Forensic Sciences 36: Diel Activity Diurnal vs. Nocturnal Schoenly, K.G J. N.Y. Entomological Soc. 91: Concealment and Burial Surface-Exposed vs. Buried Carcasses VanLaerhoven, S.L. and G.S. Anderson J. Forensic Sciences 44: Clothing and Vertebrate Clothed/Scavenged vs. Clothed/ Komar, D. and O. Beattie J. Forensic Sciences 43: Scavenging Unscavenged Carcasses Fire Burnt vs. Unburnt Carcasses Avila, F.W. and M.L. Goff J. Forensic Sciences 43: Water Submersed vs. Unsubmersed Carcasses Payne, J.A. and E.W. King J. Georgia Entomological Society 73: Insect Accessibility Insect-Open Cages vs. Insect-Proof Cages Payne, J.A Ecology 46: Insect Predators Fire-Ant Presence vs. Fire-Ant Absence Wells, J.D. and B. Greenberg J. Medical Entomology 31: PIG CARCASSES AS MODEL CORPSES 403

3 Table 2. Materials list and vendor sources for constructing the mock crime scene and for sampling and processing carcass-frequenting arthropods. ITEM, QUANTITY, SIZE AND CATALOGUE NUMBER VENDOR A. Mock Crime Scene (about $250) 1" 1" mesh welded wire (3' high 30' long) Local hardware stores hog rings (#H1), ringer pliers (#RR-HM) Seymour Manufacturing 4 rubber tie downs (79 cm long), 8 S-hooks Ozark Trail 4 sections (152 cm long) of 13 mm diam. reinforcement bar or rebar Local hardware stores 4 plastic tent stakes Local hardware stores 4 sections of PVC pipe (10 cm diam. 20 cm long) Local hardware stores 4 canning jars and metal lids (1 pint size) Local supermarkets 4 plastic funnels (10 cm max. diam.) Local supermarkets mailbox address frame (17 cm long), 2 sets of metal digits, letters `d-a-y (see Figure 1) Cole Consumer Products Rain gauge (#88991), maximum/minimum thermometer (#89024) Forestry Suppliers 4" 4" vertical post (2 m long), signboards, plastic wood for day marker (see Figure 1) Local hardware stores B. Field Sampling (about $75) knapsack, workman s gloves Ask students to bring 4 canning jars and metal lids (1 pint size) Local supermarkets 70% ethanol* Bioquip Products aerial sweep net (#7112NA) Bioquip Products penetration (=turkey) thermometer Local supermarkets miscellaneous (forceps, magnifying lens, disposable gloves, self-sealing bags, clipboard, pencils, permanent markers, camera) Ask students to bring Figure 1. Experimental layout of the mock crime scene. Drawing by Margaret Tosti. rubber tie downs (4) rebar (4) day marker welded wire cages (2) photographic station max/min thermometer pitfall traps (4) S-hooks (8) tent stakes (4) 4" x 4" vertical post sign boards (2) rain gauge C. Specimen Processing (about $150) 70% ethanol* Bioquip Products rustproof insect pins (#1202B), insect examination stage (#6185), insect pinning block (#1144), insect storage drawer kit (#1010B or 1012B) Bioquip Products dissecting microscope School small kitchen strainer Local supermarket cafeteria trays (for sorting out daily catch) School one graduated cylinder (100 ml) School LaserJet printer, card stock (specimen labels made in 4-pt fonts) Ask students to make miscellaneous (pencils, permanent markers, baby food jars with leakproof lids) Ask students to bring *rubbing alcohol (70% isopropanol) can be substituted for ethanol if the latter is unavailable. 404 THE AMERICAN BIOLOGY TEACHER, VOLUME 68, NO. 7, SEPTEMBER 2006

4 Table 3. General checklist of field procedures for gathering entomological, climatic, and photographic data in the model corpse study. 1. In the lab, fill each of the four pint jars 3-cm deep with alcohol. 2. Put on leather gloves and work in pairs to remove and set aside cages. 3. Remove jars from the pitfalls and seal with lids. Replace old jars with new jars containing fresh alcohol; re-position funnels over the jars. 4. To collect flying insects, apply the net back and forth over the body with a rotation of the net opening 180 for each of five successive passes. Alternatively, holding the tail of the net above the insects while swatting downward is also effective. 5. Transfer collected arthropods from the net bag into one or more coded jars containing alcohol. Allow insects to resettle on remains before taking a second net sample. 6. Check the nine body orifices (i.e., eyes, nostrils, mouth, ears, anus, urogenital opening) for sites of egg laying by colonizing adult flies. If one or more maggot masses are present, collect several hundred and record their internal (center) and edge temperatures using the penetration (turkey) thermometer, and compare with ambient air temperatures recorded from the max/min thermometer. 7. Inspect and collect handfuls of soil around remains for post-feeding larvae, pupae, and other soil invertebrates. Place any collected specimens in a coded vial. 8. Lift up remains for any additional insects that may not have been trapped by either pitfall traps or sweep nets. Possible taxa include silphid (carrion) beetles, trogid (skin) beetles, scarab (dung) beetles, and other arthropods that may tunnel under or use the remains for shelter or mating. 9. Record maximum and minimum temperatures and report any precipitation on data sheet. Reset the max/min thermometer and dump out any accumulated water from the rain gauge. 10. Revise the day marker and photograph the remains making sure to include the day marker in the camera s visual field (lower left corner). Photograph any unusual events (e.g., animal tracks, predator-prey behavior, maggot masses, recently eclosed adults, etc.). Record the number of photographs taken on the data sheet. 11. Replace cages and re-secure tarp straps. Figure 2. Students and instructor (in background) collecting arthropod samples, weather data, and photographs. Photo by Steve Wolf. PIG CARCASSES AS MODEL CORPSES 405

5 Table 4. Table of carrion-arthropod succession recorded by CSU-Stanislaus students from one 50-lb pig carcass in spring Timetables are based on recorded observations and counts from aerial sweeps and pitfall traps. Bar shading indicates relative abundance of each taxon at different times: light shading = 1-5 individuals, medium shading = 6-20 individuals, dark shading = >20 individuals. Unless otherwise stated, all taxa are adults. DAY IN THE SUCCESSION INSECT STAGE, FAMILY OR ORDER CARRION FEEDERS Calliphoridae Sarcophagidae Diptera (sm. misc.) Scarabaeidae Cleridae Diptera larvae Dermestidae Dermestid larvae Teneral flies PREDATORS Staphylinidae Formicidae Carabidae Araneida Histeridae Staphylinid larvae SOIL FAUNA Acari Dermaptera Isopoda Pseudoscorpionida 406 THE AMERICAN BIOLOGY TEACHER, VOLUME 68, NO. 7, SEPTEMBER 2006

6 Figure 3. Day 0: The first blow fly (at arrow) appeared on the carcass within 3 minutes after placement. Photo by Kenneth Schoenly. Figure 4. Day 3: Greenish marbling on abdomen marks the putrefaction process caused by hemolysis of blood vessels and the reaction of hemoglobin and hydrogen sulfide. The fauna present included blow flies, flesh flies, predatory rove beetles (staphylinids), and ants (formicids) (Table 3). Photo by Kenneth Schoenly. Figure 5. Day 6: Carcass bloating has everted the intestinal tract (at arrow), causing a feeding frenzy by flies and beetles. Fluids emitted from the mouth and nose originated from the stomach and lungs. Small numbers of adult clown beetles (histerids) were collected. Maggot masses were discernible around the natural orifices (eyes, nose, mouth). Photo by Colleen Blackburn. PIG CARCASSES AS MODEL CORPSES 407

7 Figure 6. Day 13: Large maggot masses have begun to skeletonize the head; their combined wriggling motions emit a faint but uniform rustling sound. Partial collapse of the abdomen has released trapped gas pockets that emit a foul and sickening smell. At or near this period, the number of arthropod families reached peak richness. Photo by Kenneth Schoenly. Figure 7. Day 18: A light shower the day before has caused a mass migration of postfeeding maggots to overfill the pitfall trap at the posterior end of pig (see arrow). On this day, over 33,000 individual insects were collected in the four pitfall traps. Photo by Kenneth Schoenly. Figure 8. Day 23: The carcass is noticeably drier, no maggot activity was seen, and few flies were caught, while several dermestid larvae were collected underneath the carcass. Photo by Colleen Blackburn. Figure 9. Day 25: Large numbers of newly emerged adult flies (tenerals) perched on the cages and the nearby vegetation (at arrows) signaled their completion of one full generation on the carcass. Breakup of the skeleton (disarticulation) began with separation of the lower jaw from the rest of the head. Photo by Colleen Blackburn. Figure 10. Day 30: The dried remains resemble parchment and are riddled with insect emergence holes as skeletal disarticulation continues. Photo by Kenneth Schoenly. becomes the definitive taxon for the lower limit because its arrival coincided with the Day 3 lower limit and Taxon D becomes the definitive taxon for the upper limit because its last day in the succession coincided with the Day 5 upper limit. Discussion & Study Questions The public s fascination with forensic science is both a challenge and an opportunity for teachers. Although entomology-based PMI estimation is one of the most powerful and promising techniques of modern forensic science, it is also one of the least understood (Greenberg & Kunich, 2002). One source of confusion is why forensic entomologists require whole carcasses, rather than butchered meats, as model corpses. For this alternative to be effective, it needs to simulate the whole animal but only if the underlying scientific principles are already well understood. When the principles themselves are being scrutinized and validated, as they still are in forensic entomology, this alternative falls short. Moreover, research has shown that butchered meats (e.g., drumsticks, fish filets, pork ribs) desiccate quickly, favor some blowflies over others, deny insect larvae natural refuges to escape from predators and parasites (Smith, 1986), and lack the gastrointestinal apparatus that generates chemical cues for attracting many necrophilous species. Except for cases involving dismemberment and scattering of remains, butchered meats do not capture the realistic elements investigators-in-training will face when processing real crime scenes. Using whole carcasses invites an endless number and variety of crime scenes inspired from actual cases in the primary literature (i.e., Journal of Forensic Sciences, Forensic Sciences International, Journal of Medical Entomology, American Journal of Forensic Medicine and Pathology). An important lesson in this activity is that death scenes are special habitats in the sense that human and other animal remains have shrinking and uneven borders whose close confinement promotes a feeding and reproductive frenzy by colonizing invertebrates. Fresh carcasses function initially as empty islands that rapidly concentrate regional biodiversity, attracting up to 150 invertebrate families (Payne & Crossley, 1966). When approached, many carrionarthropod species fly off or slither away, becoming what forensic entomologists call disappearing evidence (Catts & Haskell, 1990). For teachers seeking inexpensive, replicable, and compact systems for introducing biodiversity concepts, carcasses are hard to beat. 408 The AmeriCAn BiOLOgy TeACher, VOLume 68, no. 7, SePTemBer 2006

8 Table 5. A hypothetical occurrence matrix for illustrating the method of succession-based PMI estimation (1 = presence, 0 = absence). CORPSE BASELINE POSTMORTEM INTERVAL (PMI) FAUNA FAUNA Taxon A Taxon B Taxon B Taxon C Taxon D Taxon D Taxon E Taxon F Taxon G Taxon G Taxon H Taxon H PMI estimate: Days 3 to 5 with a width of 3 days. PIG CARCASSES AS MODEL CORPSES 409

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