Turning over a shovelful of soil and finding earthworms was always a good thing. We were taught that earthworms improved soil structure by increasing air and water movement. However, in many parts of the country, including Pennsylvania, the situation has changed with the introduction of Asian species of earthworms (Amynthas spp.)
There are still native species in a few areas of North America, but in states where glaciation occurred, the native worms were wiped out. Forests developed without them but in time, European earthworms appeared. However, now the European worms are being displaced by the more aggressive Asian worms, also known as jumping earthworms.
How do you know if you have Asian worms?
Scratch the upper surface of the soil in your garden. If you uncover many worms writhing and twisting like snakes, you most likely have jumping earthworms. These worms, which can reach 6 inches in length, are much more active than European earthworms.
The clitellum — the prominent band around the body of an earthworm — is also different. On a jumping worm, the band completely encircles the body and is creamy white to light gray. In comparison, the clitellum of European earthworms does not wrap entirely around the body and is slightly raised.
While European earthworms mix nutrients as they burrow deeply into the soil, the Asian species live in the upper layer, which protects the soil from erosion. They are voracious feeders, quickly consuming much of the organic matter where tree roots establish and wildflowers grow.
In shaded areas with high populations of jumping worms, fallen leaves and organic matter are rapidly consumed, leaving behind soil with a loose texture similar to coffee grounds. The remaining worm castings are rich in nutrients; however, they are leached through the soil too quickly for plants to utilize. The soil has fewer available nutrients and is unable to support plant growth. Where there was once lush vegetation and wildflowers, there is only bare soil. That provides an opportunity for invasive plant species such as garlic mustard or stilt grass to move in.
It is very difficult to remove an invasive species once it is well-established, so the focus must be on preventing the spread of Asian earthworms. What can we do to keep these wriggling invaders out of our forests and home landscapes?
• Only plant, purchase, sell or trade plants that appear to be free of jumping worms. If you identify them in your landscape, do not share plants with friends and neighbors.
• Only purchase or share compost that has been properly heat-treated to reduce pathogens.
• Do not release unused fishing bait in the environment.
• Remove and destroy adult Asian worms by bagging and throwing them in the trash.
Research has focused on forests and the effects of this invasive species. To date, there is no approved product to eliminate them. However, researchers are now looking at several products as possible controls.
Nancy Knauss is the Penn State Master Gardener Coordinator. This volunteer program supports the outreach mission of Penn State Extension and provides research-based information on best practices in sustainable horticulture and environmental stewardship. For more information, contact the Penn State Extension of Allegheny County at alleghenymg@psu.edu or 412-482-3476.
First Published: July 27, 2018, 12:00 p.m.
