Entomology in Action

Description: Lesson 1 introduces students to the blow fly's life cycle and the accumulated degree hour (ADH) used by forensic entomologists for estimating the time of death. Lesson 2 introduces Dr. Krinsky's entomological work in solving a murder case in 1986. Students access several primary-source documents related to Dr. Krinsky's entomological work. Both lessons help students expand their understanding of a forensic entomologist's work and appreciate how scientists account for environmental/variable factors in forming a conclusion in a scientific study.

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National science education standards

Science as Inquiry

• use appropriate tools and technology to gather, analyze and interpret data.
• use mathematics in all aspects of scientific inquiry.
• think critically and logically to make the relationship between evidence and explanation.

• all organisms are composed of cells.
• all organisms must be able to obtain and use resources, grow, reproduce, and maintain stable internal conditions.

Science in Personal and Social Perspectives

• societal challenges often inspire questions for scientific research.

History and Nature of Science

• work of science relies on scientific habits of mind as well as on basic human qualities such as reasoning, insight, energy, skill, creativity, etc.
• scientists formulate & test their explanation of nature using observation, experiments, and theoretical and mathematical models.

Learning outcomes

Lesson 1

The student will be able to:

• list different stages of the blow fly's life cycle.
• perform appropriate mathematical functions to calculate accumulated degree hour (ADH).
• understand how insect life cycle and ADH are applied in estimating time of death.

Lesson 2

The student will be able to:

• relate aspects of an insects living and behavioral patterns (entomology) to the estimation of time of death.
• describe how the forensic entomologist combines environmental factors, such as weather, and location, etc., with his or her knowledge of an insect's life cycle to note changes.

Background information

Lesson 2 uses a real murder case where Dr. William Krinsky was asked to help establish a time of death for a murder case. His investigation of this murder case involves gathering entomological evidences; rearing larvae to the adult stage; and answering various questions regarding anything that might have affected the insects' access to the body and the progression of their life cycle. The Case Summary (66KB, PDF) of the detailed investigation conducted by Dr. Krinsky also contains information for developing additional classroom discussions or student research projects.

Time needed

One or two 40–45 minute class periods

Materials

• pen or pencil
• calculator
• overhead projector and transparencies
• the following documents:
  Lesson 1:
  • Entomology Worksheet (72KB, PDF)
  • Teacher’s Entomology Worksheet (PDF)
  • Blow fly introduction (48KB, PDF)
  • Blow Fly Life Cycle (98KB, PDF)
  • ADH Worksheet (76KB, PDF)
  • Teacher’s ADH Worksheet (PDF)
  • Entomology Case Worksheet (51KB, PDF)
  • Teacher’s Entomology Case Worksheet (PDF)
  • "Jurors shown result of stabbing" (181KB, PDF)
  • Dr. Krinsky's note (170KB, PDF)
  • Climatological Data (275KB, PDF)
  • Case Summary (66KB, PDF)
  • Dr. Krinsky's letter stating his findings (159KB, PDF)

  Vocabulary

  Accumulated degree hour (ADH): a given amount of thermal energy needed to develop from one stage of an insect life cycle to the next Ambient temperature: temperature of surrounding air Climatological: weather related Entomology: a scientific study of insects Forensic entomology: a scientific study of insects as it applies to criminal cases to help determine the postmortem interval (time since death), possible movement of the body and other clues to the circumstances before and after death Medical Examiner: a medical doctor who ascertains cause of death, especially for those deaths not occurring under natural circumstances Oviposition: egg deposition, especially for insects Phaenicia sericata: green bottle fly Phormia regina: black blow fly Postmortem interval: PMI, time since death

  Procedures

  Lesson 1 (6–9 grades):

  1. Assess students' prior knowledge about forensic entomology by reviewing the following terms: entomology, entomologist, insect life cycle, postmortem interval (PMI, time since death).
  2. Introduce blow fly information by reading aloud the Blow fly introduction (48KB, PDF) to students.
  3. Hand out a copy of the Blow Fly Life Cycle (98KB, PDF) and Entomological Worksheet (72KB, PDF) to each student.
  4. Place a Blow Fly Life Cycle (98KB, PDF) transparency on an overhead projector, and ask a volunteer to read question 1 of the worksheet.
  5. Have students review the Blow Fly Life Cycle (98KB, PDF) and answer question 1.
  6. Ask students to share their answers to question 1 and review different stages of the life cycle and its scientific and common name.
  7. Ask students how they interpret the temperature and hours noted.
  8. Explain that the entomologists have researched and found evidence that insects require a given amount of heat/thermal energy to develop from one stage to the next of its life cycle. And this is called accumulated degree hour (ADH) or accumulated degree day (ADD).
  9. Have students read question 2 of the worksheet. Review the first calculation of the ADH (temp.Xhours) in Table 1 using the overhead projector, and have students complete Table 1 on their worksheets.
  10. Review the calculations with the class, and tell students that they will use the information from the Table 1 to answer questions 3a-3d of the worksheet.
  11. Have students work with a partner to complete question 3a–3d for 5 minutes.
  12. Have students share their answers and how they have come up with the answers, while noting answers on the worksheet transparency. For 3d, review or define what variables and constants are in a scientific study—life cycle stages (constant), temperature (variable), time between the life cycle stages (variable), and ADH (constant).
  13. Given what students know about the insect life cycle and ADH, conduct a discussion on how entomological knowledge such as the blow fly life cycle may be used in a criminal investigation? What kind of information do entomologists gather and help determine—i.e., insect collection, insect identification, environmental factors which may influence the insect's life cycle, etc.
  14. Record the types of information the entomologist would gather in a criminal case from the discussion on a flip chart or a black board.
  15. Review the list with students and categorize whether each item would be a constant or a variable in a scientific study of insects.
  16. Ask students to describe in their own words how entomologists may use the ADH data to help estimate the time of death using the insect evidence found on or near the body. [Teacher's Note: The ADH data, combined with other entomological evidence and environmental data, help entomologists calculate the most likely time of egg deposit by an adult insect—oviposition. This information can corroborate other evidence establishing the possible earliest time when the body became accessible to insects.]
  17. Ask students to work individually and complete worksheet item 4.
  18. Collect the completed worksheets at the end of the class for evaluation.

  Lesson 2 (9–12 grades)

  [Teacher's Note: For older or advanced students, Lesson 1 can be condensed to review the blow fly life cycle and introduce accumulated degree hour before Lesson 2.]

  1. Modify or use part of Lesson 1 to review and/or introduce the blow fly life cycle and the accumulated degree hour using the Entomology Worksheet (72KB, PDF) .
  2. Tell students that they are going to explore the work of a forensic entomologist Dr. William Krinsky, and introduce him using the transparency of "Jurors shown result of stabbing" (181KB, PDF) and reading aloud the article to students.
  3. Provide each student with a set of print-outs of Dr. Krinsky's notes (170KB, PDF) , Climatological Data (PDF) , the whole or a part of Case Summary (66KB, PDF) , and the Entomology Case Worksheet (51KB, PDF) .
  4. Use an overhead projector to review the questions in the Entomology Case Worksheet (51KB, PDF) .
  5. Group students in three and provide 15 minutes for them to review the handouts and complete the worksheet.
  6. Have groups share their answers to the worksheet questions. Afterwards collect the completed worksheet for evaluation.
  7. Distribute a copy of ADH Worksheet (76KB, PDF) to each student, and read aloud the first two questions.
  8. Ask students to review the weather report from the Climatological Data (275KB, PDF) handout to answer these two questions. Have students share their answers.
  9. Review or introduce the accumulated degree hour—refer to Lesson 1 Step 7 and Entomology Worksheet (72KB, PDF) .
  10. Have students read question 3 and Table 1 of the ADH Worksheet (76KB, PDF) . Review the calculation of the first 3 rows by asking students to come up with the formula for calculating ADH for each date—average temperature X hours. [Teacher's Note: The ADH on September 22 is calculated with 17 hours instead of 24 as Dr. Krinsky took the specimen to his laboratory at 5 p.m. on that day.]
  11. Using a transparency complete Table 1 based on the groups work.
  12. Now ask students to work in their groups of three to complete questions 4 and 5. Tell students that each group will present their findings at the end of the class.
  13. Have groups share their findings while asking students how they determined the answer to question 5.
  14. Use a transparency of Dr. Krinsky's letter stating his findings (159KB, PDF) and read aloud Dr. Krinsky's conclusion. Tell students that Dr. Krinsky used various entomological references and other factors in order to come to his conclusion on the estimated time of death.
  15. Collect the completed ADH Worksheet from students for evaluation.

  Evaluation

  Lesson 1

  The Worksheet questions serves as evaluation tools. Students demonstrate their understanding of how an insect's life cycle information is applied in estimating the time of death. Students also correctly identify the variable factors affecting the insect life cycle.

  Lesson 2

  Classroom discussions and completed worksheets serve as evaluation tools. Students are able to revise or correct their thoughts about the work of entomologists; use mathematics and reasoning to complete worksheet questions; and demonstrate their understanding of how an insect's life cycle information is applied in estimating the time of death. Students also correctly identify the variable factors affecting the insect life cycle.

  Extension

  • Read about Body Farm and write a paper on the value of studying the decomposition process.
  • Research and write about the life cycle and characteristics of at least three different insects involved in the decomposition of a dead body.