How Do Carnivorous Plants Digest Insects?

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Updated on Oct 05, 2011

Grade Level: High School; Type: Biology


This science project examines how carnivorous plants digest insects, and whether the plant can use nitrogen in the soil to compensate for lack of insects.

Research Question:

  • How does the pitcher plant digest insects?
  • What role to pH and enzymes play in insect digestion?
  • Do the plant’s nitrate levels vary after digesting insects?
  • What happens when a pitcher plant is grown in nitrogen-rich soil and not fed insects?


  • At least four pitcher plants (available from suppliers online)
  • Six additional plants are helpful if you are also performing Experiment #2
  • pH paper
  • Live insects
  • Nitrate kit (available online or from scientific supply outlets)
  • Cheesecloth
  • Electrophoresis equipment (optional)
  • Rhizobia (nitrogen fixing bacteria) – needed for experiment #2

Experimental Procedure

Experiment #1

  1. Grow four pitcher plants and maintain them for three weeks. These plants require a low pH and no direct sunlight. During this period, keep them covered with cheesecloth so that they cannot feed upon insects. Before you put cover them with cheesecloth, observed whether there are insects in the liquid found in the inverted tube-like structure (hereafter called the bell). Waiting three weeks before beginning your experiment will allow all old insects to be digested.
  2. Test the pH and nitrate content of the liquid in the bell. If you have access to electrophoresis equipment, run a gel to separate the proteins found in a sample of this liquid.
  3. Feed each plant an insect.
  4. Repeat step 2 every two or three days, starting the day after the plant was fed. Keep the plant swathed in cheesecloth. Watch for changes in pH, and nitrate content. If you are running the electrophoresis gels, look for evidence of increased enzyme levels. Continuing making and recording your observations for three weeks.

Experiment #2

  1. Identify your plants. Two plants should be low nitrogen plants, two should be high nitrogen plants, and two should be insect fed. Low nitrogen plants need no special care other than to swath them in cheese cloth so they are unable to trap insects.
  2. Feed the high nitrogen plants periodically with plant food. Be careful to follow the package directions on the plant food because too much nitrogen can burn the leaves.
  3. Dust the soil of the high nitrogen plants with rhizobia. Swatch these high nitrogen plants in cheese cloth. The insect-fed plants are fed one insect every week. They can remain unswathed.
  4. Keep the plants on this regimen for at least one month. During this time, take regular photographs of the plant and measure the leaves and bell.

Terms/Concepts: nitrates, insectivorous plants, proteolytic enzymes, nitrate cycles ugar, starch; why green plants have sugar and fungi doesn’t.

References: Wayne's World: Carnivorous Plants

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