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CSI: WyomingAn interdisciplinary forensic science unit developed by the UW Science Posse

Invertebrates Provide Clues to the Timeline of DeathCSI: Wyoming Question: When did the animal die?

Developed by: Eric M. Anderson, Ph.D. Candidate in Zoology and Physiology

Grade Level: 7–9 (with Enrichment options for higher grad levels)

Estimated Time: 90 minutes

Topics Covered: invertebrate taxonomy/classification, forensic entomology, ecology, decomposition

Standards and Benchmarks:

Content Standard: Concepts and Processes (Life Systems)Benchmarks 8.1.4. Diversity of organisms

(Grade 8): 8.1.5. Behavior and adaptation8.1.6. Interrelationships of populations and ecosystems

Benchmarks 11.1.4. Interdependence of organisms(Grade 11): 11.1.5. Matter, energy, and organization in living systems

11.1.6. Behavior and adaptation

Content Standard: Science as InquiryBenchmarks: 8.2.1. Students research scientific information and present findings

(Grades 8 & 11): 8.2.2. Students use inquiry to conduct scientific investigations8.2.3. Students clearly and accurately communicate the result of

their own work a well as information from other sources

Content Standard: History and Nature of Science in Personal and Social DecisionsBenchmark: 8.3.2. Students explore how scientific information is used to make

(Grades 8 & 11): decisions

Objectives (Enduring ideas):

Upon completion of this lesson, students will understand:1. Levels of taxonomy, distinctions between invertebrates and vertebrates, and between

invertebrates and insects

2. Basic structures of some common invertebrates

3. How differences among invertebrates affect the rates at which they colonize a carcass, and how invertebrate communities can be used to estimate the time of death

4. The need to consider many data sources, including environmental attributes unique to the study location when interpreting results



Vocabulary:

Carrion – The carcass of a dead animal that becomes food for other scavenging animals.Colonization – With regard to entomology, this is simply settlement by insects in a new area.Entomology – The study of insects (or more generally, the study of Arthropods).Frequency distribution – a systematic way to order a set of data from lowest to highest

values showing the number of occurrences (frequency) at each value.Hemimetabolism – A type of metamorphosis in certain insect groups that includes three life

stages: egg, nymph, and adult. There are no larval or pupal stages, and nymphs often resemble adults. Also called incomplete metamorphosis.

Holometabolism – A type of metamorphosis in certain insect groups that includes four life stages: egg, larva, pupa and adult. Larva and pupa generally do not resemble adults. Also called complete metamorphism.

Insect – an invertebrate whose body is comprised of three segments and six legs. Insects (Class Insecta) are a major group within the Phylum Arthropoda. Insects are the most diverse group of animals on the Earth, with over a million described species – more than all other animal groups combined.

Invertebrate – An animal lacking a backbone or spinal column. Includes many phyla of animals, such as Arthropoda, Annelida (segmented worms), Cnidaria (sponges), and Mollusca (including squid, octopi, snails, clams).

Maggot – the common name of the larval phase of flies (Order Diptera). Sometimes used to denote the larval stage of any insect.

Metamorphosis – A biological process in which an animal physically develops after birth or hatching, involving changes in the animal's form or structure. Hemimetabolism and holometabolism are two distinct types of metamorphosis.

Succession – With regard to entomology, this is the process of change in a specific area due to colonization by new species (and possibly departures of existing species).

Materials and Preparation:

Yellowstone Mystery story (Appendix 1) preserved invertebrate specimens (or photos in Appendix 2) copies for student groups or individuals of materials in Appendices 3–10 (and Appendix 11 if doing Enrichment) Solving the Yellowstone Mystery- Case Closed (Appendix 12) *Note: Read only if this is

the last lesson plan of the CSI: Wyoming unit you will be covering with your students dissecting microscopes with light sources blank paper and pencils rulers or calipers (for Enrichment) topographical map of area around Yellowstone National Park (for Enrichment) internet access (optional for acquiring climate data)



Background Information (For Teacher):

The following information details the stages of carcass decomposition used in forensic entomology. This information was summarized from a text on forensic entomology by Byrd and Castner (2001), which is an excellent source for further information. Other references for forensic entomology include Catts and Haskell (1990) and Smith (1986).

Invertebrates and stages of decomposition:Insect activity will generally follow the four stages of decomposition a carcass will

undertake. The initial, or “fresh stage” generally lasts zero to three days. During this stage heterotrophic bacteria work to break down proteins and other easily digestible compounds. Flies are the most common insect present and often include Calliphoridae, Muscidae, and Sarcophagidae. Fly eggs will often be present, with the possibility that a small number of Calliphoridae eggs have hatched into maggots. Fly maggots are generally whitish in color and have mouthparts and an anus, but do not have legs. Smaller number of beetles may also be present, including Silphidae, Histeridae, and Staphylinidae.

The “bloated stage” occurs during the next approximately four to ten days. Anaerobic forces release methane and other gases, leading to the expansion, or bloat of the carcass. Flies are still present, and large numbers of eggs from all types of flies will hatch into maggots. The maggots will often form a feeding mass that roils on the carcass in a circular pattern. As the maggots feed, they burrow deeper into the flesh. This feeding leads to elevated temperatures in the mass of maggots, forcing individual maggots to take turns rotating to the outside of the mass to cool off. The families of beetles mentioned above are still present, with Nitidulidae, Cleridae, and Dermestidae beetles arriving in small numbers during this stage. Wasps and mites may begin to arrive in small numbers. Beetles, wasps, and mites feed on the adult flies and maggots, as well as on the carcass.

The “decay stage” occurs during the next ten to fifty days. During the first ten to twenty days of this stage the body begins to turn black and putrefy. Scarabaeidae beetles may arrive. Adult flies and maggots are still present, although some maggots have developed into pupae. When maggots pupate, they detach from the feeding mass and move to a dark place, usually beneath the carcass or in nearby vegetation or soil. Fly pupae are generally dark in color and shaped like small capsules. Beetles, wasps, and mites are still present. The portion of the decay stage that lasts from twenty to fifty days is often referred to as the “post-decay stage”. Most of the maggots that were present have pupated. Larvae from Silphidae and Staphylinidae beetles may now be present. Cheese flies (Piophilidae) and carcass beetles consume the tougher parts of the corpse including ligaments, small pieces of skin, and hair.

The “skeletal stage”, or “dry stage” begins after about fifty days. Several taxa of adult beetles, as well as larvae of Dermestid and Scarabaeidae beetles may be present. Some moths and mites may remain around the body, although insect activity is usually minimal because there is very little left to feed on.



Procedures:

I. Engage Students will previously have been introduced to the Yellowstone Mystery (Appendix 1). Teachers may choose to review the mystery and findings to date. For instance, what is the carcass? Who are the people involved? What are their stories, and what remains to be done to solve the mystery?.

To begin this lesson, tell the students that a Park Ranger collected samples of some invertebrates found on the carcass. Ask students to define “invertebrate”, and assure that they understand the distinction between invertebrates and vertebrates. This ranger had seen a recent episode of CSI, and knew that in rare cases the numbers and types of invertebrates found on dead bodies could be used to determine the time of death. She hoped that with the assistance of relevant experts, Park Service biologists might use these invertebrate samples to settle the critical question of when the bear died. (Note that if biologists conclude that the bear died prior to the day of discovery, Cody and Kris will only be exonerated from poaching the bear on that day. The possibility that Cody and Kris or other individuals killed the bear on a previous date remains a possibility and will not be addressed in this lesson.)

II. Explore A. Partition the class into groups of 2–4 students. Provide each group with the specimens preserved by the ranger as described in Appendix 8. Specimens should be labeled only with the corresponding number because students will be asked to identify some individuals. If preserved specimens are not available, students may be provided with color photographs (Appendix 2). (Note that the numbers of photographs in Appendix 2 correspond to the numbered specimens in Appendix 8.)

Allow students time to examine the insects with dissecting microscopes. Ask them to notice differences between specimens. Request that students group specimens in what they believe to be related groups. With adequate time, students might be asked to sketch an invertebrate from each of the groups they have defined, noting characteristics they used to distinguish the groups.

B. Provide students with diagrams of two invertebrates collected from the carcass (Calliphoridae, Silphidae), and ask them to label the identified body parts using the terms provided (Appendix 3).

C. Provide students a taxonomy chart (Appendix 4) and work with them to fill in the levels of taxonomy. Ask students to fill in the names for humans. Point out that identifying an organism requires giving both the genus and species names (since some organisms have identical species names), and that genus and species names should always be in italics. Ask students to define the difference between vertebrates and invertebrates, and to distinguish



invertebrates from insects. (Some groups may only be required to understand that insects comprise a very large subset of invertebrates. For advanced groups, students may be required to know that Class Insecta lies within the Phylum Arthropoda, one of several invertebrate phyla.)

D. Ask students to use the dichotomous key (Appendix 5) to identify the two invertebrates above to the level of family. Students should understand that both specimens are insects.

E. Now ask students to again examine all invertebrate samples, and to generate a list of factors that could affect how long it takes the different types of insects to settle on the bear. Ask students for definitions of “colonization”. Students should examine the insect samples using a dissecting scope. During this period, help students generate their list using the following questions:

1. What body structures influence the speed of locomotion, and thus the rate of colonization?

2. How does the number of each type of invertebrate in a particular area affect the rate of colonization?

3. How might the quality of senses (for instance vision, smell) alter the rate of colonization?

III. Explain Tell the students that although the park ranger could not recall the details, she remembered that some invertebrates were known to settle on dead bodies much sooner than others. Provide the definition of succession. Ask the students for ideas about how succession could be used to determine when the bear died. Provide students with a timeline describing the four typical stages of decomposition (Appendix 6). Ask students to identify factors that could speed up or slow down the rate of decomposition. For instance, cold and dry conditions could slow decomposition and invertebrate succession. The presence of many large scavengers such as coyotes could speed decomposition by removing soft tissue.

IV. Elaborate Provide students with the notes taken by the park ranger at the scene where the carcass was located (Appendix 7).

A. Ask to students to estimate the stage of decomposition. They should conclude that there has been little decomposition, and thus that the carcass was in the first, or fresh stage.

B. Tell students that a park biologist identified the invertebrate specimens they were given earlier, and provide them with a list of the identifications (Appendix 8). Ask students to use the park ranger’s notes on the relative



abundances of invertebrates and the succession charts (Appendix 9) to estimate how many days the bear died prior to its discovery. Students should conclude that the bear died near the end of the first stage of decomposition, or about 3 days before discovery.

C. Provide students with a history of average monthly temperature and precipitation from a nearby climate station (Appendix 10). (Alternatively, students may be asked to obtain this data from the following internet site: http://www.wrcc.dri.edu/summary/climsmwy.html; click on the station number, then for 1971–2000 click “Daily Temp. and Precip.”) Assume that the carcass was discovered on September 15. Students should look at a topographical map to determine which climate station is nearest to the Swan Creek Campground, and at a similar elevation. Ask students to modify their conclusion of when the bear died based on recent climate data. In general, students should conclude that the generally cool and dry climate of Yellowstone may have slowed decomposition, and thus that the estimate of the number of days since the bear’s death may be too low.

V. Enrichment If additional time is available, consider having students study patterns of development in invertebrates. Define incomplete and complete metamorphosis. Ask students to identify which of the insects preserved by the ranger go through complete metamorphosis (flies, wasps, mites) and incomplete metamorphosis (beetles). Provide each student group with about ten Calliphoridae maggots, and ask them to use the calipers to measure the length of each maggot. Ask students to calculate the average length of their maggots, and how this information might be used to further estimate how many days the bear had been dead prior to its discovery. Provide students with frequency distributions of maggot lengths grown for two different lengths of time, and under three different temperatures (Appendix 10). Ask students to use these charts to estimate how long the bear had been dead. This will involve students selecting the most appropriate temperature based on climate data (55ºF based on the average September temperature), as well as recognizing that there should be at least a short delay after the bear’s death before fly eggs are laid and develop into maggots. Tell students that this delay is typically 48 hours. Students should conclude that the maggots had been growing for about 24 hours, and thus that the bear had been dead for about 72 hours.

VI. Evaluate If other student groups are considering different components of the mystery, ask the student group attempting to provide a timeline for the bear’s death to present their results to the class. Request that the group use appropriate graphics, and provide relevant background on invertebrates and decomposition. Students should discuss their level of confidence in their conclusions, and may explain how additional circumstances might alter their findings. If all student groups are working on this lesson, teachers may decide

http://www.wrcc.dri.edu/summary/climsmwy.html



to have groups compare their results, or to have individuals or groups write a one-page synopsis of their results.

VII. Mystery Synopsis Based on the prevalence of flies and the relatively small numbers of other invertebrates and fly maggots observed on the carcass, students should conclude that the bear died sometime during the “fresh stage” of decomposition (zero to three days prior to discovery). Students may conclude that the bear died closer to the end of the fresh stage since there were at least some maggots and invertebrates other than flies present. Some students may also conclude that the lack of evidence that large scavengers (which are abundant in Yellowstone) have altered the carcass likely indicates that the bear did not die very long ago. In evaluating the level of certainty in their results, students should explain that the sub-freezing temperatures at this high-elevation site likely slowed the typical rate of decomposition. Thus, the bear could have died somewhat more than three days ago. Students that complete the Enrichment section should also conclude that the average length of Calliphoridae maggots found on the carcass suggest that the bear died about three days ago.

Students should indicate that there is enough evidence, and that their level of confidence in their results is great enough to conclude that the bear died sometime before the day of discovery. So if the gunshots heard that autumn day didn’t kill the bear, how did it die? Was it shot on a previous day? Or are there clues available that suggest a different cause of death?

References:Catts, E. P., and N. H. Haskell. 1990. Entomology and death: a procedural guide. Joyce’s Print

Shop, Inc., Clemson, South Carolina.

Byrd, J. H., and J. L. Castner. 2001. Forensic entomology. CRC Press, Boca Raton, Florida.

Smith, K. G. V. 1986. A manual of Forensic Entomology. Cornell University Press, Ithaca, New York.



Appendix 1.Yellowstone Mystery

It was a beautiful Saturday morning in Yellowstone Park. The sun’s bright shimmer fought the autumn chill, warming the rolling gold meadows and creeping into the coolness of pine forests. Wisps and swirls of steam rose from the numerous geysers peppered throughout the landscape.

In the southern end of the park, a Wyoming family pulled into the parking area for Swan Creek Trail. The two teenage children, Cheyenne and Tim, scrambled out of the van and changed into hiking boots. Tim fiddled with his fishing pole and Cheyenne inspected her new camera. The father packed a large lunch while the mother double-checked the map to the Twin Lakes. Thirty minutes later, they had climbed halfway up a mountain and entered a deep forest with little visibility. Suddenly several gunshots erupted overhead and echoed around them. Then came the sound of distant but loud arguing. The father knew guns were illegal in the park and, fearing for the safety of his family, decided they best hike back to the trailhead and report the incident.

Back at the trailhead, Cheyenne and Tim waited in the car while their parents searched for a park ranger. Cheyenne started taking some practice pictures with her camera when she noticed two tall people dressed in wool shirts dragging something heavy in a burlap sack across the ground to their truck. They heaved the big sack onto the flatbed. Feeling suspicious, Cheyenne decided to play amateur detective and snapped several pictures of the scene. In her rush she didn’t catch a picture of the men but did get a clear shot of the license plate and truck as they were driving away. Tim had sensed what Cheyenne was up to and, putting his face close to the window, caught a few glimpses of one of their faces. Their parents came back with information on a ranger station a few miles down the road near their lodge. Tim and Cheyenne burst into a quick report of the strange event they witnessed.

When they reported the events to the park ranger, they were amazed to hear of another mysterious event that morning. Another group of hikers had reported coming across a dead body, possibly human, on a parallel trail leading to the twin lakes. What did the gunshots and arguing mean? Was there a murder in the park? The park ranger interviewed Tim and Cheyenne carefully, downloaded Cheyenne’s pictures to his laptop, then thanked them for their time and diligence.

After a few phone calls and preparations, three park rangers and a game warden met at Swan Creek Trailhead. They traced the steps of the previous hikers. Two miles up the mountain they discovered a body lying near the trail. It looked human. There were blood stains and dark hairs next to it. Further testing would be necessary. Gunshots had also been reported nearby, so they surveyed the scene and discovered a bullet embedded in a tree ten yards away. They packed up the evidence and headed back to start working on the case. How can you help solve this crime?



Appendix 2.Photographs of invertebrates observed by the park ranger. (Note that the numbers of

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.



Appendix 3.

AntennaeCompound eyeHind wingFore wing3 pairs of legsHeadThoraxAbdomen

For each specimen, label body parts using the terms provided.

AntennaeUnderwingHard outer wing (elytra)3 pairs of legsHeadThoraxAbdomen



Appendix 4. (Student version)

Major TaxonomicLevels

Common Names

Animalia

Arthropoda

Diptera

Insecta

Calliphoridae

Calliphora

Calliphora vomitoria

Blow flyHuman



Appendix 4. (Teacher version)

Major TaxonomicLevels

Animalia

Chordata

Primata

Mammalia

Hominidae

Homo

Homo sapiens

Common Names

Animalia

Arthropoda

Diptera

Insecta

Calliphoridae

Calliphora

Calliphora vomitoria

Blow flyHuman

Kingdom

Phylum

Order

Class

Family

Genus

Species



Appendix 5.

Dichotomous key for insect orders.

STEP FROM CHARACTERS CLASS1a One pair of wings. . . . . . . . . . go to 2

1b Two pairs of wings. . . . . . . . . . go to 3

2a 1a Hind wings reduced to tiny knobs (halteres), tip of abdomen without 2-3 thread-like tails

DIPTERA(Flies)

2b 1a Hind wings not reduced to tiny knobs, tip of abdomen with 2-3 thread-like tails (caudal filaments)

EPHEMEROPTERA(Mayflies)

3a 1b Front and hind wings have similar texture. . . . . . . . . . go to 4

3b 1b Front wings a rigid or leathery covering for clear hind wings. . . . . . . . . . go to 14

4a 3a Wings covered with powdery scales, mouthparts usually a coiled tube (proboscis) for sucking

LEPIDOPTERA(Moths / Butterflies)

4b 3a Wings not covered with powdery scales, mouthparts not a coiled tube. . . . . . . . . . go to 5

5a 4b Wings slope downwards (rooflike) from the center at rest. . . . . . . . . go to 6

5b 4b Wings not held rooflike at rest. . . . . . . . . . go to 9



6a 5a Wings covered with hair

TRICHOPTERA(Caddisflies)

6b 5a Hairless wings. . . . . . . . . . go to 7

7a 6b Sucking mouthparts in the form of a rigid beak, often short and bristley antennae, body may look like a thorn

HOMOPTERA(Hoppers)

7b 6b Mouthparts not in the form of a rigid beak, antennae not short and bristley, body never looks like a thorn. . . . . . . . . . go to 8

8a 7b Wings with many cross veins

NEUROPTERA(Lacewings)

8b 7b Wings without many cross veins

PSOCOPTERA(Bark lice)



9a 5b Front and hind wings similar in size and shape. . . . . . . . . . . go to 10

9b 5b Front and hind wings not similar in size and shape. . . . . . . . . .go to 12

10a 9a Antennae always short and bristley

ODONATA (Dragonflies & Damselflies)

10b 9a Antennae never short and bristley. . . . . . . . . . go to 11

11a 10b Wings held flat over abdomen when at rest, last abdominal segment not enlarged, usually found in colonies

ISOPTERA(Termites)

11b 10bWings not held flat over abdomen when at rest, males with the last abdominal segment enlarged like a scorpion's stinger and held over the body, not found in colonies

MECOPTERA(Scorpionflies)

12a 9b Body very soft, without a narrow "waist". . . . . . . . . . go to 13



12b 9b Body not exceptionally soft, often with a narrow "waist"

HYMENOPTERA(Bees & Wasps)

13a 12a Hind wings wider than front wings, folded underneath like a fan

PLECOPTERA(Stoneflies)

13b 12a Hind wings much smaller than front wings, not folded underneath like a fan

EPHEMEROPTERA(Mayflies)

14a 3bSucking mouthparts in the form of a rigid beak, front wings with clear tips (hemelytra), overlapping at rest, revealing a triangular panel on the back (scutellum)

HETEROPTERA(True Bugs)

14b 3b Chewing mouthparts, front wings without clear tips. . . . . . . . . . go to 15



15a 14b Rigid front wings (elytra) meet in a straight line down the middle of the back

COLEOPTERA(Beetles)

15b 14b Front wings not as above. . . . . . . . . . go to 1616a 15b Head visible from above. . . . . . . . . . go to 17

16b 15b Head hidden from above by a hoodlike structure (pronotum)

BLATTARIA(Cockroaches)

17a 16a Front legs strong with prominent spines for grasping prey, hind legs long and slender

MANTODEA(Mantids)

17b 16a Front legs without spines or with weak spines, the femora of the hind legs are enlarged for jumping

ORTHOPTERA(Grasshoppers & Crickets)



Appendix 6.



Appendix 7.

Park ranger’s description of bear carcass.

The carcass appeared fairly fresh, and had very little odor. The skin had been removed from most portions of the bear, likely with a dull knife provided the rough edges of the remaining skin. Invertebrates had colonized the bear, although they do not appear to have penetrated the flesh to a great extent. The most abundant invertebrates found on the carcass were sample numbers 1, 2, 3, and 5. Samples 4, 6, 7, and 10–14 were somewhat less abundant. Samples 8 and 9 appeared to be larvae of some kind and were common but not abundant. Samples 15–20 were very rare.

Timeline of carcass decomposition

Stage 1:Fresh

Stage 2:Bloated

Stage 3:Decay

Stage 4:Skeletal

Days afterdeath 0–4 4–10 10–50 >50

Carcassdescription

Carcass appearsfresh with little sign

of decay andlittle odor.

Decompositioncreates gases thatenlarge, or bloat

the carcass. Carcassbegins to create odor.

From 10–20 days theCarcass turns black andPortions begin to liquify.During 20–50 days only

coarse parts of the carcassremain, such as bone, hair,

and small pieces of skin.

Only boneremains.



Appendix 8.

Identifications of invertebrate samples completed by a park biologist.

Sample Samplenumber identification

1. Calliphoridae adults (blow fly)2. Calliphoridae adults (blow fly)3. Muscidae (muscid fly)4. Sarcophagidae (flesh fly)5. Muscidae (muscid fly)6. Silphidae (carrion beetle)7. Sarcophagidae (flesh fly)8. Calliphoridae maggots (blow fly)9. Calliphoridae maggots (blow fly)10. Histeridae (clown beetle)11. Staphylinidae (rove beetle)12. Silphidae (carrion beetle)13. Histeridae (clown beetle)14. Staphylinidae (rove beetle)15. Oligochaeta (earthworm)16. Oligochaeta (earthworm)17. Vespidae (wasp)18. Vespidae (wasp)19. Acarina (mite)20. Acarina (mite)



Appendix 9.

Typical succession of adult arthropods on a decaying carcass

Typical succession of larval arthropods on a decaying carcass



Appendix 10.

Temperature and precipitation data from the Western Regional Climate Center. Data are provided for two cites near the Swan Creek Campground.



Appendix 11.

Frequency distributions of the length of Calliphoridae larvaegrown for different times and at different temperatures.

35ºF, 72 hours 35ºF, 24 hours





Appendix 12.Solving the Yellowstone Mystery- Case Closed

Earlier that morning, locals Cody and Kris were hiking up Swan Creek Trail. Cody feared grizzlies, doubted the effectiveness of pepper spray, and was a huge fan of Dirty Harry movies. He ignored park rules and snuck in his .44 magnum handgun.

As they came into a small clearing, Cody and Kris discovered a large bear lying on the trail. Was it dead or simply sleeping? Cody didn’t want to take any chances. He took out his gun and fired a few shots in the air. Just to make sure, he fired one bullet into the bear. When it didn’t move they approached it for a closer look. They poked it a few times with a stick. The bear was dead.

The bear’s coat still looked alright, so Cody decided it would be cool to skin the bear and make a rug out of the pelt. I could tell my friends a heroic story, he thought, of how a bear surprised and charged us but I made a quick, Herculean kill. Kris, however, felt very upset by the whole scene…the dead bear, firing the gun, and now Cody wanting to skin the animal. She also wasn’t sure if this was legal, so they got into a heated argument. Meaner and more aggressive, Cody finally won, and started skinning the bear. Cody had brought a large burlap sack--just in case they found cool stuff they could take from the park--and it worked well to hold the head and skin. They headed down the mountain and back to their truck, Cody dragging the sack and whistling.

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