Post by Jiangxiao Qiu
Known as ecological powerhouses, earthworms have proven their worth as best friends to gardeners and farmers. As worms burrow through the ground, they loosen and aerate the soil, create air and water passages, and add nutrient-rich castings to the soils, making conditions more ideal for plants to grow and thrive.
However, too many earthworms can be a problem, especially if they live and flourish in a novel environment, where there are no competitors. The recent and shocking discovery of a new invasive earthworm, the Asian jumping worm (Amynthas agrestis), in the Yahara Watershed has presented the region with this possibility. The worm’s abundance, voraciousness, and ability to spread has caused concern over whether it may alter the region’s soil and vegetation, which may then have important, and most likely negative, implications for water quality and quantity, as well as for other benefits that nature provides us.
Within less than a year since it was first discovered in the UW Arboretum, there have been many reports of their appearance around Madison. I completed a field survey in July and roughly estimated that where the worms are present in the Arboretum there are about 100-120 individuals per square meter. Their population may grow even more in August or September, when their numbers peak.
A ravenous eater, the Asian jumping worm can consume all of the organic matter at the soil surface within a very short period of time, and it may outcompete many European earthworms, such as Lumbricus rubellus, with its superior feeding ability.
Native to Japan and the Korean Peninsula, the Asian jumping worm first arrived in the United States with nursery plants intended for landscaping. It has since been found primarily in the Southeast and along the Eastern seaboard. Now, Wisconsin has become a northern frontier for the worm, and they could potentially migrate to more states, especially in a changing climate.
Though they have existed in 18 states for decades, surprisingly very little is known about the worm’s behavior, biology, and ecological consequences, as well as what measures might be effective to control or manage their populations.
In response to the invasion, we have been conducting an experiment this summer to understand how the Asian jumping worm might affect our region’s forest and prairie soil systems, as well as the extent to which such alterations might degrade soils and water quality. This experiment involves two complementary parts.
One is called a mesocosm experiment, in which intact soil cores have been collected from a variety of forests and prairies all around the Yahara Watershed and brought to a common facility at the University of Wisconsin Arboretum. We measured soil characteristics at the beginning of the experiment, and then introduced worms into half of the soil cores, each of which is paired with a control core that gets no worms. We are monitoring the worms and their activities through the summer and will then re-analyze the soil characteristics at the end of the summer. Thus, we can compare changes in the soils with and without the worms to determine the extent to which they can alter soils in one season.
The second is an observational study for which, on a monthly basis throughout the summer, we will measure the soil characteristics of various locations within the Arboretum, comparing soil where the worms have invaded with similar soil where they have not invaded.
With these two components, we will be able to see how soils change following an invasion in both a natural setting and under controlled experimental conditions. The experiment will run until late fall, when the worms die off (this species has a yearlong life cycle).
Through this experiment, we are hoping to get an initial estimate of how vulnerable our soils may be to this new invasion or whether any of these soils are more resistant to the worms’ effects.