Most earthworms feed on dead leaves. Some earthworm species live above ground in the leaf litter layer, while others live underground and dig tunnel systems. In doing so, these subterranean earthworms drag leaf litter from the surface into deeper soil layers. This improves aeration, water supply and nutrient availability in the soil, thus promoting plant growth. Earthworms also create new habitats for other soil animals and microorganisms by digging. They are thus often referred to as ecosystem engineers.
What is good for us here is a problem in the deciduous forests of North America. These forests have been free of earthworms since the last ice age and are not adapted to these animals. Earthworms introduced from Europe disturb the ecological balance in North America, reducing the diversity of plants and soil animals. Scientists at the iDiv research centre are investigating this phenomenon. The exhibits explain the phenomenon in more detail.