The Scoop on Worms
Most gardeners consider soil resplendent with earthworms a good sign. Studies on agricultural soils have shown that earthworm burrows can improve soil aeration, water infiltration, relieve compaction, and make nutrients more available to plants. However, there is more to the story.
There are no native earthworms in Wisconsin. Due to glacial activity that scoured the landscape down to bedrock, all native earthworms were destroyed. The earthworms we commonly associate with the garden, the European earthworm (Lumbricus sp), were brought to the United States by settlers. While these earthworms do provide benefit to the gardens, they wreak havoc on forest floors.
On forest floors, decomposition is slow and deliberate, leaving a soft, nutrient rich “duff” that is vital for the ecosystem. This is important for plants such as spring ephemerals to thrive. Earthworms are so efficient at rearranging the soil, eating fungal seed banks, and eating leaf litter that they make conditions hostile for future generations of native plants, allowing invaders to rule.
While the earthworm’s contribution to soil health cannot be argued, everyone should be cautious when entering a forest and potentially introducing these seemingly harmless creatures to this environment. Fishermen should be careful when emptying bait buckets, ensuring they do not do so in a manner where the worms can migrate to a forest.
Of even more concern is “jumping worms” (Amynthas sp). Although in the U.S. since the early to mid-1900s, these non-native, invasive worms were first confirmed in Wisconsin in 2013. They are native to eastern Asia and were introduced inadvertently, but spread rapidly because their very tiny cocoons attach to footwear, equipment, mulch, soil, and potted plants.
European and Asian worms are similar but have distinct differences. The Asian jumping worms congregate in groups; seldom will there be just one in the soil. When disturbed they will trash and wriggle about in almost a snake-like manner. They live in the topmost few inches of the soil and leaf litter, seldom burrowing deeper.
European worms are slightly pink in color while Asian worms are more brown or gray. The clitellum, the distinctive band around the body, on jumping worms completely encircles the body, lies smooth and is closer to the head. European clitellum does not go completely around the body and is slightly raised.
Jumping worms self-fertilize; they do not need a mate to reproduce. Although they live through only one growing season, they produce several generations in one year and the cocoons survive through the winter, hatching the following spring. The cocoons are resistant to drought and cold and are as tiny as a mustard seed, making them almost impossible to detect.
Jumping worms consume nutrients that plants, fungi, and bacteria need to survive. In their place, they leave soil resembling coffee grounds that lacks the structure and support for plants to survive. Invasive plants move in and once again the ecosystem has been altered.
To help mitigate the spread of this invasive species, the Dodge County Master Gardener Association discontinued its plant sale in 2018. While it is still safe to buy nursery plants, it is advised to not trade plants among friends and neighbors that could potentially and unknowingly have jumping worms. Only use plant and landscaping material, including mulch, that appears to be free of jumping worms.
Above all, educate yourself and others about this invasive species that has the potential to negatively alter the ecosystem.
Carol Shirk
Certified Master Gardener