Yes those are earthworm castings. There are many species of earthworms that produce different size castings and occur in various numbers. Nightcrawlers produce larger castings and larger piles of castings, but are present in fewer numbers in most cases. Smaller species produce smaller castings and casting piles, but can occur in such large numbers that the entire soil surface is covered. In such cases the soil gets a soft, spongy feel when you walk on it.
There is no need to worry over earthworm activity. They help build the soil and tend to come and go over time. When the weather heats up you should see much less of them.
Thanks for the question. Please feel free to stop in again with another question any time we can help!
Q&A Library Searching Tips