This spring’s Asian jumping worm hatch should be the largest and most widespread yet, according to population trends projected by a benchmark survey of the invasive worms taken over the past two summers and published in December 2017.
“We saw a very rapid population expansion and we expect those numbers will grow,” said Katie Laushman, the survey’s lead investigator.
When Laushman began her study two years after the invasive, East Asian earthworm’s 2013 arrival in the UW-Madison Arboretum — the first report of the worm statewide — little was known about its effects on local ecosystems.
“There is a lot of speculation but not a lot of research to back it up. We hoped that this study would help people know what to look for, and what to prioritize,” Laushman said. “We hope that this knowledge base will lay the groundwork for future studies.”
Laushman wanted know how a growing jumping worm population would affect local vegetation and soil conditions. She conducted her survey over sample plots across the Arboretum, and looked for changes in the worm populations, soil profiles and vegetation.
“It was exciting to research what happens when we have a new invasive show up,” Laushman said.
Baseline experiments like this one will help ecologists detect changes in the community later, according to UW Arboretum ecologist and project contributor Brad Herrick.
“You can’t talk about these changes unless you have a starting point,” Herrick said. “That’s why it’s such an exciting opportunity to do this type of monitoring or ecological study. Having this base is really important.”
Laushman reported that a dramatic increase in jumping worms corresponded to a decrease in European earthworms, which are also invasive.
“There were decreases in the European worm, but it’s hard to be sure if that is because of competition or antagonistic relationships between the species,” she said.
Laushman’s field study did not indicate the worm has caused any substantial changes in vegetation so far, but she said the survey didn’t run long enough to detect more subtle landscape changes.
“The lack of data could be because of a very short study, when we’re talking about effects that are really going to take decades to see,” she said.
Those effects could have serious consequences, said Herrick. He worries that the jumping worm could fundamentally change the soil structure in the places it invades, causing disruptions that would ripple across those ecosystems.
“Jumping worms don’t go very deep, and they do all their work in a very small area of the soil profile. They are loading the soil with nutrients and plants aren't able to keep up,” Herrick said. “This may actually deplete the soil over time, and ultimately, the soil may erode away.”
In places like Wisconsin that have no native worm populations, plant communities are not adapted to soils with so many excess nutrients. Changing nutrient composition in the soil changes how plants establish themselves in those soil conditions. Herrick is concerned that changing soil conditions will drive out native plants, and that invasive plants will fill in those voids.
“Hardier plants deal with disturbance better than plants that occupy a specific niche in the ecosystem,” Herrick said. “When you start to see those gaps, you also see other invaders rush in to fill them. This is a common feedback loop that scientists have observed following other worm invasions.”
Over time, Herrick predicts a decrease in plant diversity due to more habitat restrictions related to the ways jumping worms change the soil.
Herrick plans to continue Laushman’s research in seasons to come to establish more conclusive, long term data.