“Lo and behold we found another worm that until that moment we didn’t believe was in the state,” Herrick said.

Bernie Williams, an invasive species specialist with the Department of Natural Resources, was on the trip and confirmed the mystery worm’s identity.

The worm is darker in color than the pale and pinker European earthworm, the common worm found all across the state. It also has a smooth and flat band of milky white, unlike the raised, ridged band found on European earthworms.

The find came near the Arboretum’s visitor center. In spring more of the species were found there and in a few adjacent areas. The total area of coverage is about an acre so far, Herrick said.

It is believed the crazy worm first came to the U.S. from its native Japan and Korea in the soil of plants imported for landscaping. Wisconsin’s representatives likely hitched a ride aboard some nursery plants headed here from the eastern U.S., Herrick said.

Arboretum staff don’t know to what extent the crazy worm is in the grounds beyond the areas where it’s already been spotted. Boots, tools and vehicles are being washed regularly to keep the worm from spreading, and Arboretum employees are avoiding areas where the worm has already been found.