Some fun and simple science experiments with earthworms involve studying earthworm behavior. For example, you can perform an experiment to test earthworms' preference for moisture by placing a wet paper towel on one half of a container and a dry paper towel on the other half. Place a few worms in the middle and wait ten minutes to see which environment they prefer. Or you can test the worms' reaction to odor by performing a similar experiment using one paper towel dampened with water and another paper towel dampened with ammonia.
Other interesting earthworm science experiments deal with the diet of the earthworm. For example, you can set up four different colonies of earthworms in flowerpots filled with soil. Weigh the earthworms and take pictures of them at the start of the experiment. Feed the four different pots of earthworms four different diets: eggs shells, fruits or vegetables, coffee grounds, and grass or leaves. After several weeks, compare the size and weight of the worms to determine which type of food helped the worms to grow the fastest.
Earthworms' effect on soil is another interesting topic of earthworm study. A simple experiment to investigate this topic involves filling six pots with soil and adding three seeds to each pot. Place two earthworms each into three of the pots. Do not add earthworms to the other three pots. Allow all six pots to grow with the same light and watering conditions for 4 to 6 weeks. Observe and record the outcome and draw conclusions based on the results.
The effect of light on earthworms is another topic to experiment with. An example of this type of experiment involves creating an earthworm habitat, covering it with different colored transparencies for one day each and then observing the behavior of the earthworms in reaction to the different colors. You could also choose to give the earthworms natural light for one day and no light at all for one day. Record your observations and draw conclusions based on the outcome of each type of light.