https://phys.org/news/2018-11-invasive-earthworm-feces-soils.html

"The way that these worms change the soil is something new. You can see very clearly that they have been there," said geoscientist Jenelle Wempner of the University of Wisconsin in Madison. "They leave little balls of soil. Imagine a soil surface covered with coffee grounds."

The little balls, or aggregates, left behind by the Asian earthworms are essentially worm feces, and they are a target of Wempner's research.