An aggressive, invasive species of earthworm has been making its way from the southeast to the Midwest.
Asian Jumping Worms, consisting of various species from multiple genera (including: Amynthas agrestis; the smaller Amynthas tokioensis; and Metaphire hilgendorfi) of earthworm, have been around in a number of eastern and southeastern states for decades.
Also known as crazy worms, Alabama jumpers and snake worms — they are native to Southeast Asia, but were accidentally introduced to the southeast United States in the 19th Century.
In 2013, species from the genus Amynthas were confirmed for the first time in the Upper Midwest, at the University of Wisconsin-Madison Arboretum. Last year, they were discovered to have wriggled their way into eastern Iowa when they were found in Dubuque and Muscatine counties.
The worry is they may make the jump from Iowa into Nebraska and cause problems for agribusiness.
“Earthworms change the environment to suit their needs,” said Brad Herrick, ecologist and research program manager at the University of Wisconsin-Madison Arboretum. “When they are introduced, they make a host of physical, chemical and biological changes to the soil environment.”
The worms are competitive with other species and grow rapidly. They’re parthenogenetic: They can reproduce without fertilization. The introduction of a single individual is enough to launch a jumping worm invasion, Herrick said.
These worms are unlike the common Lumbricus terrestris or European earthworm (aka nightcrawler). They live in the top part of the soil, they don’t make channels which plant roots can exploit; they grow more quickly, reproduce more rapidly and thus consume more nutrients, which starves other invertebrates; and they leave behind an inhospitable environment for plants.
That is the big reason these worms are a major concern. Instead of nutrient-rich castings being left behind that help the soil, they fundamentally transform the ground into a field of soft, dry soil pellets. Soil hit by Asian jumping worms has nutrients, but it’s all on the surface, and is easily washed away by rain. It’s not a sustainable way to keep the soil rich and healthy — bad for crops, and good for weeds.
Jenelle Wempner, a geoscientist at the University of Wisconsin in Madison, studied the worms’ voluminous production of excrement — called “aggregates”— and found that they may be eroding and leaching nutrients from soil.
Wempner was able to corroborate that finding by examining aggregates under a scanning electron microscope. Her team found high levels of iron, aluminum, potassium and calcium in the aggregates, confirming that the worms are decreasing the availability of key nutrients in their ecosystems and increasing the likelihood of soil erosion.
“Unfortunately at this time, there are no good control measures,” Herrick said. “The important thing now is to the stop the spread. Everyone can help.”
While fire has been shown to be somewhat promising as a way of reducing the worm population, it has to be the right temperature to kill their offspring, said Allison Zach, coordinator of the UNL Nebraska Invasive Species Program.
It can be difficult to identify jumping worms until a few months into the growing season because the young worms are small (less than half an inch long when they hatch from the cocoon). The cocoons are inconspicuous and a similar size (1/10 of an inch in diameter) and color of soil aggregates. Jumping worms have a flexible diet and are suited to surviving in less-opportune environments, such as below hardwood mulch. Their unnoticed presence in plant, soil and bark products, combined with the cocoons’ resilience to cold and drought, may explain how they spread.
The Iowa Department of Agriculture and Land Stewardship recommends against acquiring compost, mulch and topsoil from potentially infested areas or acquiring plants from the infested counties.
“They are not currently regulated but they maybe in the future,” Zach said. “I suggest not bringing them here as they can have negative consequences to soil and water resources.”
People who think they’ve spotted one of the worms are urged to call the Nebraska Invasive Species Program at 402-472-3133 or report it through www.neinvasives.com.