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Eat Like a Housefly- Eat Barf!

Use jello and vinegar to introduce students to how house flies feed. Our way of eating is rather boring compared to the technique used by flies!

Without barfing frequently, a housefly would not survive! Houseflies don’t have mouths that bite, chew or jab. When a fly lands on something, it tastes with its feet. Then, if the fly finds something tasty, it will barf on it. Fly vomit contains digestive enzymes, which break down the food so that the fly can use its sponge-like tongue to mop up the barf soup.

Other animals also eat vomit. doves, finches, penguins and herons all vomit into the mouths of their hungry babies. The food that baby birds receive doens't actually come from the parent's stomach at all. When the parent bird swallows, their food goes down the throat and into a storage sack called the crop. At the nest, the food comes out of storage and becomes the babies' meal.

Human vomit is different: It contains:

  • Anything not digested from the last meal
  • ​Acids that kill bacteria
  • Enzymes that break down food
  • Mucus that protects the stomach itself from those acids and enzymes

​The lovely green colour comes from bile which is produced by your small intestine and whose job it is to help break down the fats in the food.

Puking is useful to humans because it gets rid of stuff that your body thinks could be dangerous to you. In fact, throwing up is so potentially helpful that there is a part of the brain called the vomit centre that induces vomiting. Different things can excite the vomit centre to bring on barfing in humans. For example:

  • Something bothering the lining of the stomach.
  • Confusing information from body position sensors.
  • Hormones.
  • Unpleasant sights or smells.

Next time you complain about what’s put in front of you at dinnertime, just be glad you’re not eating barf!


  • Regurgitate: The expulsion of material from the mouth, pharynx, or esophagus, usually characterized by the presence of undigested food or blood.
  • Proboscis: Is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate.
  • Vomit: The forceful expulsion of the contents of one’s stomach through the mouth.


  • Describe why vomiting is beneficial to both humans and other animals.


  • Prepared Jello, cut into small pieces in a shallow plate
    Turkey baster
    A fake fly head or fly head diagrams

Key Questions

  • Why do flies vomit before eating when humans might vomit after eating? What other animals rely on vomiting to survive? Why? Why do humans vomit? What part of the brain triggers humans to vomit?

What To Do

  1. Start a discussion on how flies eat. Has anyone observed what flies do after they land on your plate? Use a video to have the whole class make some observations — one example is this video.
  2. Using the fly head (or diagrams) highlight the proboscis and its role in a fly’s feeding process.
  3. Demonstrate how a fly uses vomit to break down its food. Pour a little “fly vomit” (vinegar) onto the Jello, and stir it lightly. The vinegar will break down the Jello into a soupy mess that can be sucked up by the proboscis (turkey baster). Note: Cutting up the Jello into smaller pieces before you start makes this process faster.
  4. Discuss why humans vomit and when. What are the differences between the role that vomit plays between flies and humans?


Other Resources

Science World Resources | Full Lesson & other activities | Animal Grossology
Science World at TELUS World of Science | School Programs | Grossology