Materials Included In Kit

Prelab Preparation

1. Use the information in the table below to prepare “maggot samples” for each murder investagation scenario 1–4.
2. The numbers in each column represent the lengths (in mm) of maggots/pupae collected from the body for each murder case. Cut several (2–3) pipe cleaners of each length given to make up the “maggot sample” collected from the body.
3. Place the maggot samples for each murder investigation in separate zipper-type bags.
4. Label each bag with the murder investigation number.
5. Prepare enough samples so each student group receives a bag for all four murder investigations. 

Safety Precautions

Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. All materials may be saved and reused in future classes.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs. All parts of this laboratory activity can reasonably be completed in one 50-minute class period.
• Prior to handing out the materials, discuss the life cycle of insects with complete development (egg, larval instars, pupation and adult). Point out that since colonization and insect development are predictable, insect colonizers can be used to determine the approximate length of time an organism has been dead.
• Point out that some data from the police reports in the murder investigation cases may be useful, and some of it may be irrelevant.
• Several specimens of maggots that are of the same age should be included in each bag. Introduce a little bit of variation in size to simulate natural growth, but keep the sizes within a millimeter or two. This adds a bit of realism to the activity. The lesson is further reinforced due to the fuzzy nature of the pipe cleaners. Students may ask how they should measure maggots—should the length of the wire be measured or the edges of the fuzzy material? State to students that measuring animals in the wild is not always straightforward and that biologists have to make the final decisions on such measurements. Have students make this decision as well.

Teacher Tips

• Since puparia, in reality, are nearly impossible to identify by sight, the puparia for all species in this activity are brown. This means that the only way species of each puparium can be identified is by size. This requires students to make careful measurements and consider the range obtained.
• This is a great activity to introduce during a forensics unit.
• The website http://www.forensic-entomology.com (accessed June 2018) has background information, a good compilation of literature for further study, a standard form filled out by forensic scientists that can be included as part of the exercise. It also has some pictures of maggots and adult flies.

Sample Data

MURDER INVESTIGATION 1

Police Report
Body of a female was found in an alley behind the dumpsters in a major U.S. city. No apparent wounds were observed on the body.

Weather Report
Daytime temperatures have been fairly consistent for the past three weeks ranging from 70 to 74 °F.

MURDER INVESTIGATION 2

Police Report
Body of a young male was found inside an apartment in a major U.S. city. Maggots were found concentrated in the head and chest region. The windows were closed, although the open curtains allowed sunlight to enter, and the air conditioner was set to 72 °F.

Weather Report
Daytime temperatures have been variable over the past three weeks, ranging from 75 to 94 °F. Skies have been sunny. 

MURDER INVESTIGATION 3

Police Report
Body of a young male was found in a field near a small rural town. The autopsy report reveals that cocaine was present in the body.

Weather Report
Daytime temperatures have been unusually warm over the past three weeks ranging from 84 to 86 °F. 

MURDER INVESTIGATION 4

Police Report
Body of an elderly female was found in a dense, evergreen forest far away from any urban area.

Weather Report
Daytime temperatures have been averaged over the past three weeks ranging from 70 to 73 °F. Temperatures in the woods would be approximately 5° cooler due to the lack of sun in the shady environment.

Answers to Questions

MURDER INVESTIGATION 1 

1. Approximately how long has this person been dead?

   11 days.

2. Why are maggots of different ages found in the body?

   Adults of the same species will arrive at the body at different times. Adults of different species may also arrive at different times or they may colonize the body in different stages of succession.

3. Besides temperature, what abiotic conditions should be obtained from weather stations to help confirm the estimation above?

   Humidity, rain, cloud cover, wind, etc.

1. Approximately how long has this person been dead?

   5 days.

2. What effect, if any, does the outside temperature have on your estimation of time of death?

   Since the inside temperature is 72 degrees, the outside temperature has no effect on larval development.

3. How does the fact that the windows were closed relate to the population of flies you observed in and around the corpse? (i.e., is there something different about this population than the population in Investigation 1?) How do you explain the absence of Calliphora vomitoria?

   Since the windows were closed, the only flies that could have laid eggs on the body were those that were already present at the time of death. Thus C. vomitoria must not have been present, even though it is generally an early colonizer.

4. Do you suspect foul play? Explain.

   Yes, the pattern of colonization indicates that an orifice was present in the chest (more maggots were there than would be expected). A stab wound or bullet hole would be consistent with the evidence.

1. Approximately how long has this person been dead?

   7 days (must account for both temperature and drugs when calculating this).

2. What effect, if any, does cocaine have on your estimation of time of death? Explain how you used this information in calculating the post-mortem interval.

   Cocaine speeds up development of Calliphora by 2–3 days.

3. What effect, if any, does the temperature have on your estimation of time of death? Explain how you used this information in determining the post-mortem interval.

   Increased temperature speeds up development, thus we must subtract the number of days of increased development due to the temperature.

4. What insects were found on the victim? Is this consistent with where the body was found?

   All insects but Piophila were found. Yes, this is consistent with where the body was found.

5. Does the location of the body suggest foul play? Explain.

   No, the fact that P. nigriceps was not found on the body is consistent with the location in which the body was found. No other evidence indicates foul play.

1. Approximately how long has this person been dead?

   10 days.

2. What effect, if any, does the temperature have on your estimation of time of death?

   Since it is cooler in the forest, development is slowed down, thus days must be added to the number of days the maggots have been developing. Cooler temperatures slow down the growth by about 2–3 days on average depending on the species.

3. Does the location of the body and the types of insects found suggest foul play? Explain.

   Yes, since Piophilia occur only in urban areas, their presence here indicates that the person must have died in an urban habitat and the body must have been moved to the woods at least five days after death.

References

Special thanks to Lisa Carloye, Washington State University, WA, for sharing this activity with Flinn Scientific.

Carloye, L. The American Biology Teacher. 2003, 5, 360–366.

Introduction

When police arrived at the address given by the frantic caller, they found the body of a young man lying face up on the couch. The man had obviously been dead for some time. Maggots were found concentrated in the head and chest region. The windows were closed, although the open curtains allowed sunlight to enter, and the thermostat was set to 72° F. What had happened? When did the young man die? Was he murdered?

Concepts

• Forensics
• Entomology

Background

When an animal dies, flies (particularly from families Calliphoridae and Sarcophagidae) are among the first to find and colonize the carcass. As the carcass decays, the environmental conditions within it change—it becomes drier, temperature rises, tissues break down, etc. The process of decay is described as a pattern of ecological succession consisting of a series of predictable changes as the carcass progresses from the fresh stage, where the body is intact and decay has barely begun, to the skeletal stage, when all that is left is indigestible hair and bone. The decay process is an example of what is known as secondary succession in which a community begins with the death of an animal and the body represents an isolated, rich source of resources. The body will be colonized by different groups of insects as the resource itself undergoes changes. The process of colonization and utilization of the body continues until decomposition is essentially complete. Because the progression of different insects that colonize a body follows a predictable pattern, and the developmental rates of flies are relatively predictable, investigation of the insect community associated with a corpse is used by forensic scientists to estimate the post-mortem interval. This is called forensic entomology.

The process of decay begins at the moment of death. This is the fresh stage and it lasts until the body becomes bloated. At this stage, the body looks relatively normal—much like a sleeping person. Blow flies (Calliphoridae) and flesh flies (Sarcophagidae) are among the first to find the body and they can arrive within 10 minutes of death. They lay their eggs, from which the maggots hatch quickly and begin to feed on the tissues (the flesh flies do not lay eggs, but rather deposit newly hatched maggots directly onto the corpse). Predatory wasps and/or beetles may arrive to feed on the maggots (but not the corpse). The bloated stage begins when the body becomes visibly inflated due to the production of gases from bacteria that begin to putrefy the body. House flies (Muscidae) now join the other flies and their maggots form feeding masses that help to liquefy the tissues of the body. At this point a lot of maggots are feeding on the body and competition increases, as do the number and variety of predators that come to feed on the maggots.

The decay stage begins when the skin breaks and the gases escape, giving the corpse a deflated look. The maggot masses are large and very active as the maggots continue to develop and grow older and larger. This is the stage of decomposition that smells bad. By the end of this stage, most of the maggots have finished development (they typically molt three times before pupariation) and they begin to leave the corpse in search of a place to pupariate in the soil. The corpse is now devoid of most of its flesh, with only cartilage, bone and skin remaining. At this point the “post-decay” stage begins. This stage is devoid of flies although there may be beetles that continue to feed on the highly desiccated remains.

When the flies arrive to lay their eggs or deposit larvae on the carcass, they search out the natural orifices for doing so. This means that the larvae begin their feeding in the head region first (mouth, nostrils, eyes, ears) followed by the anal/genital region. The trunk of the body is invaded much later in the process. This information is useful for determining if foul play was involved in a death. If maggots are found in the chest cavity early in the decomposition process, this is good indication that there was an opening in the chest present at the time of death. This opening could be the result of a gunshot or knife wound.

Drugs present in the body at the time of death can affect the developmental rate of the maggots as they ingest the drug along with the tissue. Cocaine speeds up development, while arsenic slows it down. This fact can make estimating the time of death difficult due to the presence of large maggots on relatively young corpses or small maggots on relatively old corpses. It also provides an example of the phenomenon of bioaccumulation—as the maggots feed on tissues, they may acquire a high enough concentration of the drug through feeding to detect the presence of the drug in the victim even after the victim’s tissues are decayed and no longer available for testing.

Experiment Overview

In this hands-on activity, the evidence from four death scenarios will be evaluated. A sample of simulated maggots collected from the corpse will be used to determine the post-mortem interval (time after death) and whether or not foul play was involved in the death will be determined.

Materials

Safety Precautions

Follow all laboratory safety guidelines. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

1. Obtain and read the Murder Investigation 1 Worksheet.
2. Obtain the sample of simulated maggots from crime scene 1, a ruler and the Maggot Life History Sheet.
3. Use the ruler to measure the maggots and use the information provided on the Maggot Life History Sheet to estimate how long the victim from whose body the sample was obtained had been dead.
4. Answer the questions in the Murder Investigation 1 Worksheet.
5. Repeat steps 1–3 for Murder Investigations 2, 3 and 4.

Student Worksheet PDF

13529_Student1.pdf