The way animals and plants behave is so complicated because it not only depends on climate, water availability, competition for resources, nutrients available, and disease presence but also having the patience and ability to study them close-up.

We’re going to build an eco-system where you’ll farm prey stock for the predators so you’ll be able to view their behavior. You’ll also get a chance to watch both of them feed, hatch, molt, and more! You’ll observe closely the two different organisms and learn all about the way they live, eat, and are eaten.

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This experiment comes in two parts. The materials you need for both parts are:

  • four 2-liter soda bottles, empty and clean
  • 2 bottle caps
  • one plastic lid that fits inside the soda bottle
  • small piece of fruit to feed fruit flies
  • aluminum foil
  • plastic container with a snap-lid (like an M&M container or film can)
  • scissors and razor with adult help
  • tape
  • ruler
  • predators: spiders OR praying mantis OR carnivorous plants (if you’re using carnivorous plants, make sure you do this Carnivorous Greenhouse experiment first so you know how to grow them successfully)
  • soil, twigs, small plants

Fruit Fly Trap

In order to build this experiment, you first need prey. We’re going to make a fruit fly trap to start your prey farm, and once this is established, then you can build the predator column. Here’s what you need to do to build the prey farm:

Download Student Worksheet & Exercises

Did you know that fruit flies don’t really eat fruit? They actually eat the yeast that growing on the fruit. Fruit flies actually bring the yeast with them on the pads of their feet and spread the yeast to the fruit so that they can eat it. You can tell if a fruit fly has been on your fuit because yeast has begun to spread on the skin.

When you have enough fruit flies to transfer to the predator-prey column, put the entire fruit fly trap in the refrigerator for a half hour to slow the flies down so you can move them.

If you find you’ve got way too many fruit flies, you might want to trap them instead of breed them. Remove the foil buckets every 4-7 days or when you see larvae on the fruit, and replace with fresh ones and toss the fruit away. Don’t toss the larvae in the trash, or you’ll never get rid of them from your trash area! Put them down the drain with plenty of water.

Predator-Prey Column

You can use carnivorous plants, small spiders, or praying mantises. If you use plants, choose venus flytraps, sundews, or butterworts and make sure your soil is boggy and acidic. You can add a bit of activated charcoal to the soil if you need to change the pH. Since the plants like warm, humid environments, keep the soil moist enough for water to fog up the inside on a regular basis. You know you’ve got too much moisture inside if you find algae on the plants and dirt. (If this happens, poke a couple of air holes.) Don’t forget to only use distilled water for the carnivorous plants!

Keep the column out of direct sunlight so you don’t cook your plants and animals.


  1. What shape is the head of the mantis?
  2.  How many eyes does a praying mantis have?
  3.  How else has the mantis head evolved to stalk their prey?
  4.  How does a praying mantis hold its food?
  5.  Do fruit flies eat fruit?
  6.  How do predators and prey change over time?


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2 Responses to “Predator-Prey: Who Eats Whom?”

  1. lizeth_buffington says:

    how long does a fruit fly live