Virtual Nature Trail
Are all earthworms the same?

No. There are many species of earthworms with a wide range of sizes, activities and ecological roles. In the family "Lumbricidae" (which is the major group of annelid worms that are called "earthworms") there are over 200 species worldwide. Thirty four of these lumbricid species are found in North America. Some of these worms are quite large (well over 100 mm long and up to 6 grams or more in weight), while others are very small and thread-like. Some of these worms burrow deep into their soil habitats (some well over a meter down!), while others live in the decomposing organic debris on the soil surface. 

What do earthworms do?

Earthworms accomplish many important ecological "tasks" within their soil habitats. Some of the larger earthworm species actively consume raw leaves and a great variety of other fresh organic debris from plants and animals that fall to the soil surface. These larger earthworm species help to break up these organic materials and act to facilitate the decomposition and re-cycling of their nutrients. Many of the smaller earthworm species ingest the partially degraded organic materials on and within the soil (the humus) further decomposing these materials and accelerating their eventual decomposition. While the earthworms are feeding and burrowing, they are mixing the organic materials deeply into the mineral soil. These activities helps to a soil to drain surface water more efficiently, they also facilitate the passage of air (which is needed by plant roots etc) deeper into the soil profile. The defecation and excretion of wastes by these active earthworms also contributes to the quality of the soil: these organic "wastes" help to hold soil particles together and greatly improves the "structure" of a soil. A well structured soil is less likely to erode and is capable of supporting a highly productive vegetative ecosystem.

Do earthworms "like" all kinds of tree leaves?

No. Some tree leaves are too tough and are too full of unpalatable chemicals (like polyphenols) to be immediately ingested by earthworms. Before these leaves are palatable to earthworms they must undergo an interval of physical weathering and leaching. Oak leaves and beech leaves are examples of this first category of tree leaves. In the "Nature Trail in Winter" we observed that senescent beech leaves can remain attached to their tree branches through the winter season. This is also true of the leaves of many oak trees if they are in habitats sheltered from the wind. These leaves undergo a significant weathering while they exposed to the wind, cold and moisture of winter tree canopy. When these leaves do fall in the spring they are much more palatable to earthworms and thus decompose much more rapidly. Other tree species have leaves that are more fragile and less infused with protective chemicals. Many of these leaves are also particularly rich in sugars. As soon as these leaves fall to the soil surface, they are rapidly consumed by earthworms. Alder, maple and ash leaves are examples of this second category of tree leaves.

Why are earthworms so hard to find in the summer (when I want to go fishing!)?

The major environmental factor that limits earthworm activity is soil moisture. In the summer, soil moisture levels fall as soil temperature levels rise. In order to conserve their body fluids levels in this increasingly stressful environment, many earthworm species undergo a seasonally timed inactive condition very similar to hibernation (see "Exploring Hibernation"). This "summer hibernation" is called "aestivation". Aestivation is a very efficient survival strategy for these moisture-fragile earthworm species. (sorry about the fishing problems!)

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