Grades 3–5 · Organisms
How can earthworms move and mix soil material?
A worm's tunnel and nearby cast show soil material being moved into new places. An earthworm changes soil by pushing particles aside or taking material through its body as it burrows. It rearranges existing matter rather than making soil from nothing.
The pictured worm feeds on a mixture containing soil and dead plant fragments. Material moves through its gut, where mineral particles and organic material can become mixed. The material it leaves afterward is called a cast. Different worms place casts underground or at the surface.
This creates a connection between feeding and the soil's arrangement. Plant fragments that began near the surface can end up mixed with mineral material elsewhere. A cast is therefore more than a sign that a worm passed: it is existing material released in a changed mixture and location.
Dead plant material begins near the surface, while the burrow leads toward a Cast elsewhere. The cast represents soil and plant material mixed through the worm's gut and released in a changed location.
In the diagramA burrowing worm can move soil materialDead plant materialCastMixed material is left in a new place.Species and habitats differ; effects are not always beneficial.
A burrow opens passages that can change air and water movement, while casts rearrange nearby particles. Effects depend on species and habitat: worms do not all feed or burrow alike, and their activity is not helpful everywhere. One worm's route shows material moving, not a universal benefit.
About this explanation
Starting knowledge: Recognize soil, dead plant material and an earthworm; distinguish moving material from creating it.
Sources
- Penn State Extension — Earthworms
- USDA Agricultural Research Service — Earthworms and Soil Structure