Officials discover highly invasive 'spongy moth' wreaking havoc on trees: 'I knew right then that we were doomed'

The absence of researchers at an outdoor site during the coronavirus pandemic may have resulted in an unexpected infestation.

In 2021, when a research team at the University of Wisconsin–Madison returned to a stand of aspen trees after an absence in 2020, they realized there was a big problem, as the Daily Cardinal reported. Spongy moth egg masses were everywhere.

"Each egg mass contains 400 to 600 larva — and we were not anticipating that," entomology professor emeritus Rick Lindroth said, per the Cardinal. "I knew right then that we were doomed to have a major defoliating outbreak of spongy moths."

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The invasive species arrived in Wisconsin two decades ago, though it had entered North America in 1869 from Europe, according to the newspaper. The moths can eat up the leaves from most trees in their path, leaving the plants vulnerable to disease, drought, and other insects.

The trees at UW–Madison's Arlington Agricultural Research Station, planted in 2010 for other experiments, quickly became a different type of testing ground, the Cardinal reported. The researchers changed course to study the impact of the spongy moth on the native polyphemus silk moth, which feeds in mid- to late summer, after the spongy moth.

They found that the defoliation caused the aspens to produce more salicylate-like compounds as a defense against the bugs when they regrew leaves. The aspirin-like substance "can be highly toxic at high levels," per the Cardinal, and the silk moths consumed leaves with eight times more salicinoids than they previously had, overwhelming their guts and causing septicemia, hemorrhaging, and death.

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The spongy moth's defoliation also hurt the trees, which were using their energy to defend themselves.

"I think we can make the argument that invasive species like spongy moths can negatively affect the capacity of aspen forest to sequester carbon by removing leaves so the trees aren't photosynthesizing, and when the leaves reflush, they're busy making defense compounds rather than growing," Lindroth told the Cardinal.

Websites such as Invasive.org may help in identifying the spongy moth and its caterpillar form from other species.

The federal Slow the Spread program teaches people to keep from transporting firewood and other items that can harbor the moth's egg masses, allowing the creatures to spread to new areas. Started as a pilot program in 1992, it has cut the spongy moth's rate of spread by over 60% via trapping, aerial spraying, and mating disruption. According to a program website, this results in a four-to-one benefit-to-cost ratio, factoring in reduced management and quarantine costs overall, as well as avoided recreation and tourism losses.