A surprising invasive species threatens the maple sugar industry.

A Michigan Technological University scientist studies upper Midwest maple groves showing die-back and empty branches. She discovered earthworms are the common factor.

All earthworms in the upper Midwest are exotic species from Europe and Asia. These species target the soft leaves of maple trees, consuming the forest floor litter layer.

“Earthworms when they come in, they eat all of that stuff up and pull it down in the ground and it is gone a lot faster than it would be naturally,” Research Professor Tara Ball said. “A tree could maybe handle some drought, but when earthworms are present, it just makes it far worse for the trees."

Without the litter layer, trees are more vulnerable to winter weather. Earthworms also speed up the flow of nutrients to the trees, leaving fewer nutrients for the forest in the long run.

The only current solution is slowing the spread of earthworms. Loggers and hikers can clean off equipment, vehicles and shoes. Fishermen should dispose of fishing worms in the trash, not on the ground or in the water.