Abstract
If you're looking for an experiment that will gross out just about everyone, you probably can't do much better than this! This project investigates an important question in the field of forensic entomology. Just make sure to get permission at home before you start.Summary
Andrew Olson, Ph.D., Science Buddies
Sources
This project is based on:
- Koch, E.A., 2003. Controversy in Forensic Entomology and Crime Scene Investigation: The Question that Is Bugging Forensic Entomologists, California State Science Fair Abstract. Retrieved August 29, 2006.
- Kouyoumdjian, S.A., 2006. Maggot Mass Temperature, California State Science Fair Abstract. Retrieved August 29, 2006.
Objective
The goal of this project is to determine if maggot mass temperature increases as the number of maggots in the mass is increased.
Introduction
This project is not for those that are easily grossed out. If this is you, just hit the back button on your browser before reading further, and you'll be fine. If you aren't squeamish, and you think you might be interested in doing a project related to forensic entomology, then keep on reading.
"Forensic entomology is the study of insects and other arthropods in a legal context. The applications are wide-ranging, but the most frequent is to determine the minimum time since death (minimum post-mortem interval, or PMI) in suspicious death investigations. This is done by identifying the age of the insects present on a human corpse, which can provide a relatively precise estimate in circumstances where pathologists may only be able to give a broad approximation. The fundamental assumption is that the body has not been dead for longer than it took the insects to arrive at the corpse and develop. Thus, the age of the oldest insects on the body determines the minimum PMI." (Hall and Brandt, 2006)
All insects start out life as eggs, although some hatch within the body of the mother, who then seeks out a source of food on which to deposit the living larvae (fly larvae are also called maggots). The flesh flies (scientific name Sarcophaga bullata) you will use in this project are an example of this type of insect. Blow flies (family Calliphoridae) are the usual "pioneer" species on an exposed animal corpse. Flesh flies generally arrive a day later. However, since flesh flies are deposited as larvae, and blow fly eggs take about 24 hours to hatch, the flesh fly maggots can develop as quickly as the blow fly maggots (Major, 2003).
As young insects grow and develop, their bodies change in a process called metamorphosis. In a few species, for example silverfish, only size changes. In other species, there is a simple change—development of wings in grasshoppers, for example. In other insect species, such as flies, there is a complete metamorphosis from the larval stage to the adult body form. (Borror and White, 1970; Illinois DNR, 2003)
Insect larvae pass through multiple stages of growth, called instars. Because insects must shed their exoskeleton in order to grow, each growth stage is separated by a molt (also called ecdysis). As shown in Figure 1 (above), fly larvae pass through three instar stages (two molts). At the end of the third instar stage, the maggots disperse, seeking a location in soil before pupation. Pupae are inactive, and do not feed. Adults emerge from the puparium in one to two weeks at room temperature (Figure 2, below). Pupae can hibernate for long periods during colder temperatures, allowing flies to overwinter in the pupal stage and to emerge as adults in warmer spring weather.
Development of fly larvae can be strongly dependent on temperature. Figure 3 (below) shows the total development time for blue bottle blow flies, from egg-laying to emergence of adults (in days), as a function of ambient temperature (in °C). You can see that over the range from 10 to about 17°C, each 1°C increase in temperature results in a significant decrease in development time.
A gradual negative sloping graph shows that as temperature increases the days required for a fly to reach adulthood decreases exponentially.
Flies lay eggs and larvae in clumps, and the developing maggots mass together as they grow. The individuals benefit from shared secretions which aid in digestion and produce an alkaline environment conducive to larval growth. "The larval infestations might look gruesome, but they are a vital component of the natural recycling of organic matter and, on human bodies, they can provide vital clues to the timing and cause of death." (Hall and Brandt, 2006) The mass of maggots can also cause a local increase in temperature. The goal of this project is to determine whether maggot mass temperature increases as the number of maggots in the mass increases. A more advanced project (see the Variations section, below) would also try to determine if increasing maggot mass can lead to decrease in development time, and, if so, over what temperature range.
Terms and Concepts
To do this project, you should do research that enables you to understand the following terms and concepts:
- larva,
- maggot,
- instar,
- molt,
- pupa.
More advanced students should also study:
- degree hour.
Questions
- What are the stages of the fly life cycle?
More advanced students should also study:
- How does ambient temperature affect the development of blow fly larvae?
Bibliography
Here is an introduction to forensic entomology by two scientists from The Natural History Museum in London, England. Please note: This site contains strong graphic images and descriptions.- Hall, M. and A. Brandt. (2006). Forensic Entomology. Science in School. Retrieved August 29, 2006.
- Australian Museum (2009, Nov. 13). Decomposition - Corpse Fauna. Retrieved September 27, 2013.
- Australian Museum (2009, Nov. 12). Decomposition: fly life cycle and development times. Retrieved September 27, 2013.
- Queensland Museum. (n.d.). Flesh flies (family Sarcophagidae). Queensland Government. Retrieved September 27, 2013.
- Kirkman, T. (n.d.). Student's t-Tests. Department of Physics, College of St. Benedict & St. John's University. Retrieved February 23, 2006.
Materials and Equipment
To do this experiment you will need the following materials and equipment:
- flesh fly (Sarcophaga bullata) pupae, available from Carolina Biological, item #: 173480
- pieces of beef liver to feed larvae,
- five large containers with air holes for growing flesh fly larvae,
- digital thermometer, available from Carolina Biological, item #: 745360
- for cleanup at end of experiment:
- Disposable gloves. Can be purchased at a local drug store or pharmacy, or through an online supplier like Carolina Biological Supply Company. If you are allergic to latex, use vinyl or polyethylene gloves.
- water,
- bleach.
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Experimental Procedure
- Do your background research and make sure that you are knowledgeable about the terms, concepts, and questions, above.
- You wll need to plan ahead for this experiment. You need to allow time for ordering the pupae, and then for emergence of the adults and development of the larvae. Remember that it will take about 1 to 2 weeks for the adult flies to emerge from the pupae, and then two or three days more for the adults to mate and lay larvae. It will take a further two days for the larvae to mature to the third instar state which you will use in this study. Note that there is a degree of uncertainty in the development times. Once you receive the larvae, it could be as few as 9 or as many as 16 days until you have third instar larvae to study.
- Forewarned is forearmed: "We also discovered that the smell of rotting beef liver leaves a significant trace of bad odor long after the completion of an experiment." (Kouyoumdjian, 2006) You'll want to think carefully about the best place to conduct your experiment. To simplify the interpretation of your data, it would be best to have a stable ambient temperature. However, this is a smelly experiment, and we don't recommend doing this inside your house.
- Keep pupae at constant temperature in enclosed container with air holes. Adult flies will emerge in 1 to 2 weeks.
- When the flies emerge, provide them with pieces of beef liver. The adults will feed on the liver, mate, and lay larvae. The larvae will feed on the decaying liver. Make sure your container excludes outside insects from entering.
- The larvae will molt twice (about one day of growth for each molt).
- After the second molt you will have third instar larvae. Put on gloves and separate the larvae into several different mass sizes: 25, 50, 100, 200, 400. (We told you this project was not for the squeamish!) Put each mass in its own container, each with its own piece of liver.
- Keep the containers at the same ambient temperature.
- Monitor the ambient temperature and the internal temperature of each maggot mass regularly (every 1–2 hours). For each measurement of maggot mass temperature, take several readings at different places within the mass. Record each location and temperature.
- For each time point, calculate the average and standard deviation of the temperature measurements for each maggot mass.
- More advanced students should use Student's t-test to determine whether any differences in average maggot mass temperature are statistically significant.
- Wear gloves for cleanup. Seal the decomposing liver and remaining larvae and pupae in a 2–3 layers of plastic bags for trash pickup. Disinfect the containers with a 5% solution of household bleach in water before disposal.
Ask an Expert
Variations
- For an alternative (and less smelly!) experiment on temperature and insect development, see the Science Buddies project: Does Temperature Affect the Rate of Butterfly Development?
- Extend the experiment to earlier stages of development. Separate first instar larvae into different mass sizes and take regular temperature measurements. Does increased maggot mass lead to increased temperature for the first and second instar stages?
- Does increased maggot mass lead to a decrease in development time? Design an experiment to find out. Study the temperature dependence of fly development carefully, and select three different ambient temperatures to test.
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