Instant Flies: Can Worms Grow From Decaying Bananas?

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Author: Janice VanCleave


Can worms grow from decaying bananas?


  • Masking tape
  • Marking pen
  • 2 1-quart (1 liter) jars
  • Banana


Note: This experiment works best during warm weather.

Instant Files

  1. Use the tape and marking pen to label the jars #1 and #2.
  2. Peel the banana and place the fruit inside jar #2.
  3. Leave the jars open and undisturbed for two weeks.
  4. Observe and record your observations daily. Things to look for:
    • changes in the color of the banana
    • any insects, such as flies, inside the Jars
    • presence of maggots

Instant Files


You can use a chart like the one shown to record your daily observations for fourteen days. It will indicate the exact day that these results were observed:

  • Brown spots appeared on the banana.
  • The entire banana looked dark brown and moist.
  • Flies appeared and were seen inside each jar. (Record about how many flies.)
  • The maggots appeared.


Because maggots appeared in the jar with the rotting fruit and not in the empty jar, a popular theory until the eighteenth century was that living organisms such as maggots came from dead matter. The theory that living organisms come from nonliving material is called spontaneous generation. This theory was disproved about 100 years ago, and, through further experimentation, it was proved that gases released by the rotting fruit attract the flies. The flies lay their eggs in the fruit, and the eggs hatch into tiny, white worms called maggots. Given enough time, the maggots grow into adult flies. Thus, the maggots observed in the jar with the fruit are just one stage in the life of a fly.

Let's Explore

  1. Would the maggots appear if the jar with the banana was closed? Repeat the experiment with a third jar. Label it jar #3 and place a peeled banana in it. Seal jar #3 with a lid. Observe and record the daily results.
  2. Does the limited amount of air in jar #3 prevent spontaneous generation? Repeat the experiment, but this time seal jar #3 by putting a cotton handkerchief over the mouth of the jar and securing it with a rubber band. (You use a handkerchief because it allows air in the jar, but nothing else.) Observe and record the daily results.
  3. Will the rotting of other fruits result in the appearance of maggots? Repeat this experiment replacing the banana with other fruit. Keep daily records of your observations for display.

Show Time!

Instant Files

  1. Use the procedure of a famous experiment designed by Francesco Redi (1626-1697) to confirm that decaying food does not produce living organisms. Place small pieces of fruit in three separate jars. Leave one jar open, seal one with a lid, and cover the third jar with a cotton handkerchief. Keep daily records of your observations for display. Find out more about Redi's experiment and use it in your project report.
  2. Use biology texts to discover different popular spontaneous-generation beliefs, and represent them with drawings. A recipe for producing mice was created by a man named Van Helmont. It is given below. The drawing shows an example of how this can be used as part of a project display.

Note: Do not try this at home!

Van Helmont's Recipe for Mice


  • 1 dark container
  • 1 cup (250 ml) wheat grains
  • 1 dirty shirt


  1. Put the dirty shirt and the wheat grains together in a dark container.
  2. Wait several days.
  3. Yields many mice.

Van Helmont's Recipe for Mice

Checkt it Out!

Antonie van Leeuwenhoek's discovery of microorganisms made scientists question whether these tiny creatures that appeared so quickly in rotting food might arise spontaneously. Discover how an Italian priest named Lazzaro Spallanzani tried to disprove this. Why was his experiment not respected by other scientists?

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