All about earthworms

Did you know that there are over 100 species of earthworms across the continental US? Here are the important differences between kinds of worms and what you need to know for your garden and lawn!

Epigeic earthworms: compost digesters. These types of worms aren't likely to be in your yard, since their natural habitat is the litter layer of fallen leaves and other organic debris on the forest floor. But you might have them around if you're into vermiculture -- feeding worms food scraps for them to digest into a rich, composted, organic fertilizer. The most common worm used for this is known as the red wiggler (Eisenia foetida).

A red wiggler. Image attribution: Rob Hille

Endogeic earthworms: topsoil dwellers. These worms live in the top few inches of soil. They ingest soil, mix it with organic matter and microbes in their guts, and excrete it in a stable, nutrient-rich form called earthworm castings. They also create horizontal burrows when moving around, which assists in soil aeration. These are the kinds of worms you'll notice coming to the surface of the soil after a good rain.

Anecic earthworms: deep-burrowers. These worms also digest soil and create castings similar to endogeic worms, but their burrowing style is different. They live 5 or 6 feet below the surface at the bottom of a permanent, vertical burrow, but they come to the surface to collect organic matter and to excrete castings. Their up-and-down activity mixes the soil, like a natural version of tillage! The most famous worm in this category might be the nightcrawler (Lumbricus terrestris).

An earthworm at the bottom of its burrow. Image attribution: common domain (Royal Albert Memorial Museum & Art Gallery)

Invasive earthworms: fishing bait! Native worms are an important part of ecosystems and soil health because they facilitate organic matter breakdown, aeration, and water drainage. However, invasive worm species can wreak havoc by excessively mixing the soil and over consuming organic matter, which destroys leaf litter habitat and leads to soil depletion. The farther north you are on the continent, the worse of an issue invasive earthworms are: in in the lower 48 and Mexico, around one in 3 earthworms are non-native, while in Canada and Alaska the vast majority of earthworms are non-native. One example is the jumping worm (Amynthas agrestis), which can spread when anglers dump unused bait. This distructive species is prohibited in several states. Make sure to stick with non-invasive options for household use, and never release extra live bait worms into the wild!

An Asian jumping worm. Image attribution: John Abrams.

Learn more about the benefits of earthworms for soil health and how to protect earthworms in your farm or yard here (Penn State Extension).