Observations and results
Were most of the earthworms in the leaves? Were some in the sand and potting soil? Were none in the gravel?
Earthworms eat dead plant matter, such as fallen leaves, and transform it into a nutritious substance that plants can absorb more readily. So, if they want a tasty meal, they would most likely be in the leaves. However, if there is organic matter (dead plant matter or animal matter, which they also eat) in the other soil types tested, the earthworms might be attracted to those soils as well. But just because an earthworm is in one of the soils does not mean that it is its ideal environment or that it wants to eat that soil. For example, you may find one or more earthworms in the gravel, but this could be due to factors other than the earthworm searching for a food source—the gravel's humidity, for example, might be more appealing or there may be possible chemoattractants on the gravel.
Besides adding nutrients to the soil, earthworms also keep the soil healthy by tunneling. As they eat, earthworms create tunnels that keep the soil open and full of paths for water and air. Without earthworms, the soil would be smashed down, or compacted, making it difficult for water and air to reach the roots of plants. Overall, it would be very hard to grow all the beautiful plants that give us oxygen and food without these wiggly, little creatures.
When you're done with this activity, gently and carefully return the earthworms to some soil outside.
More to explore
Ecology—Reproduction from WormWatch
Plant Nutrients from North Carolina Department of Agriculture & Consumer Services
Earthworms from Colorado State University Extension
Squirmy Wormy: Which Soil Type Do Earthworms Like Best? from Science Buddies
This activity brought to you in partnership with Science Buddies