Nature Takes Its Course

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Davidson College professor of biology and environmental science Chris ParadiseFor a period of three weeks, the campus and Town of Davidson was plagued with cankerworms suspended from the trees by strands of nearly invisible web. As countless people learned, the tiny green worms are double trouble for pedestrians.

A silky strand to the face might trigger shock and disgust, and victims often don’t realize they’re carrying the little freeloaders until the worm crosses from clothing to exposed skin.

While most people tried to avoid the worms at all costs, Associate Professor of Biology and Environmental Studies Chris Paradise delighted in the opportunity to map out spatial distribution of worm populations and evaluate control methods through a partnership with the Town of Davidson’s Public Works Department, the college’s grounds crew and the Davidson Lands Conservancy.

The project focused on the most popular method for reducing worm numbers—tree banding.

Paradise launched the study after the Town of Davidson sent out a newsletter recommending that residents band their trees to resolve the cankerworm problem. That sounded extreme to Paradise, whose trust in natural control gives value to all creatures great and small, including inchworms.

Subsequently, Paradise met with the town council and representatives of the Davidson Lands Conservancy to discuss whether banding was the appropriate response. “We don’t even know whether banding is effective,” Paradise explained. “I’ve found no conclusive literature to suggest that it is.”

Young cankerworm larvae begin their lives emerging from eggs in trees and feed voraciously on leaves as they grow. They may eventually eat entire leaves, leaving only the major leaf veins. Although low populations do not damage healthy trees, high populations can defoliate trees, causing them to expend considerable resources to refoliate.

Eventually the cankerworms spin down to the ground from the trees on a strand of silk and bury themselves in the ground to pupate.

In theory, adhering sticky bands around tree trunks will trap and kill the wingless female moths as they climb up the trees to lay eggs, thereby disrupting the life cycle of the insect.

Paradise and his team of student researchers began their investigation in the winter by identifying trees that had been banded by individuals or the town; others without bands were designated control trees. The research team collected worm density data by comparing the numbers of worms found under both banded and unbanded trees. Lightly infested trees might have about a dozen worms in a specific area, while heavily infested trees might have more than 100 on a six-foot branch.

Their preliminary counts suggested that there is no significant difference between banded and unbanded trees. “There are many other factors that play a role,” Paradise explained. “For example, trees in tree canopies tend to have more worms than isolated trees, and this may have a greater influence on worm population than banding.”

Paradise acknowledged that banding is less environmentally harmful than other forms of pest control (like spraying), but he doesn’t condone it. “I think we should just let nature run its course,” he said. “Many insect species have boom and bust periods depending on factors like food source availability or environmental change. If we banded trees and it worked, there’s a good chance we would affect the populations of beneficial insects or even small mammals that could get stuck in the bands.”

—Cathryn Westra

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