The Aggressive, Insatiable Asian Crazy Worm Has Invaded Wisconsin

They may look tame, but these worms decimate forests and are starting to spread across the United States.

(Photo: "Invasive Asian crazy worms found in Madison"/

Jul 23, 2014· 2 MIN READ
John R. Platt covers the environment, wildlife, and technology and for TakePart, Scientific American, Audubon, and other publications.

Look out, Wisconsin: The Asian crazy worm has arrived.

These voracious and invasive earthworms from Korea and Japan (scientific name Amynthas agrestis) have already caused ecological problems in several other American states, and now they're poised to spread into new territories.

Asian crazy worms—also known as Alabama jumpers or Jersey wrigglers for their speed and snakelike agility—first turned up in the United States more than a century ago when they were accidentally imported with ornamental plants. Today they remain popular as bait or as composting aids. (You can buy 1,000 Alabama jumpers for less than $80 online.) But their real damage occurs when the worms or their cocoons spread from home gardens into the wild.

"They're voracious," said Bernie Williams, invasive plants and earthworm specialist for the Wisconsin Department of Natural Resources. "When you find it in the understory of a forest, it's the only worm species you'll find. You can just lightly move the fallen leaves or the soil, and they're just swarming."

Unlike typical earthworms—which were imported to the U.S. from Europe—Asian crazy worms reproduce rapidly and don't take the trouble to mate (a process called parthenogenesis). They lay cocoons in 60 days, compared with about 120 days for the European varieties. The hungry Asian worms eat up all the leaf litter and other organic matter they can find, leaving no nutrients for the forest's plants to consume.

European earthworms are also technically invasive species, Williams pointed out. "We've all been told that earthworms are our friends, that they're great for your garden, and that they're nature's recyclers," she said.

But when they get outside gardens, they can cause a great deal of harm. In the Great Lakes region, for example, earthworms have damaged millennia-old hardwood forests by robbing them of their rooting soils.

The trees aren't the only species to suffer. Ground vegetation also disappears, as do the animals that depend on it. Soil at this point becomes more erosive, which can then expose it to even more invasive species.

Asian crazy worms have the potential to be much worse because they reproduce so quickly and easily. "All you need is one," Williams said.

Their voraciousness has an even more damaging effect on the soil than European earthworms, leaving the dirt balled up and granular, which can make it hard for new plants to germinate from seeds.

So far the crazy worms have only turned up in Wisconsin at the University of Wisconsin–Madison Arboretum. The worms were discovered there last October. "At first we thought they wouldn't be able to overwinter in our climate," Williams said.

That was not the case. The worms survived until this spring. Researchers are now watching to see how they spread.

Wisconsin had anticipated the worms' arrival. In 2009, crazy worms were added to the state's list of banned wildlife under its invasive species law. As a result, Williams reports, the arboretum changed its annual plant sale this spring by moving the venue, inspecting the nursery stock, and alerting people to the crazy worm menace in its newsletter.

Public attention like that is important for controlling the spread of the species, Williams said. "We need people to start thinking about the worms that they always thought were good and to realize that they are actually aggressive."

Scientists still don't know much about Asian crazy worms and their long-term impact on the environment, let alone how to control them. Williams said Wisconsin hopes to participate in an experiment with Vermont, where the worms have already turned up, to see if certain types of fertilizer that golf courses use to control earthworms will also kill the crazy worms. "We need a lot more information and studies to take place," she said.

Until then, Williams recommends that people look at any soil they purchase and avoid buying Asian crazy worms for bait or composting: "They have an incredible effect that we're just starting to understand."