Here’s a tale from the annals of globalizing insect problems and solutions.

In mid-June, I was taken aback twice during a walk in the woods near our home in the Hudson Highlands. First, I realized I was hearing a steady, quiet pitter-patter, like that from a drizzle, but on a sunny day. Glancing down, I saw thousands of tiny green leaf fragments on the forest floor and realized the rain was droppings and table scraps from countless caterpillars munching the newly emerged canopy far above.

This was clearly a bad outbreak of the gypsy moth, an invasive species whose occasional arboreal ravages were familiar to me from childhood days in Rhode Island long ago. (In fact, this year’s infestations, which the Associated Press described as perhaps the worst since the 1980s, are particularly bad in my home state.)

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Most residents of the Northeast know at least some of the story of the French-American artist and silkworm enthusiast Étienne Léopold Trouvelot, who brought gypsy moths from Europe to his Massachusetts home in the 1860s for an ill-fated interbreeding effort.

After some escaped and defied an aggressive eradication effort, he moved to France, where his main legacy was illustrations of astronomical phenomena like eclipses.

Trouvelot’s North American legacy has been the mounting impact on forests of a pest that is so firmly established federal agencies make no bones about being able to wipe it out. Their campaign is to “ Slow the Spread.”

That brings me to the second surprise that day.

Looking around at the tree trunks, I saw dozens, then hundreds, of gypsy moth caterpillars clinging to the bark. But on closer inspection, it became evident they were desiccated caterpillar carcasses.

Right there and then, through a Facebook Live video, I asked for help, which quickly came from Tom Kimmerer, a friend of a friend who’s an expert on saving “venerable” urban trees. The likely cause? Entomophaga maimaiga, a fungal antagonist of the Asian gypsy moth variant that scientists tried to use against Trouvelot’s European imports several times starting in 1910.

Those efforts were deemed a failure. But in 1989, as scientists at the Connecticut Agricultural Experiment Station examined a gypsy moth die-off, they found that E. maimaiga was, in fact, the caterpillar killer. In a paper the following year, they described how a potential biological weapon that had long been written off had somehow established itself in the ecosystem. In an interview this week, Kirby Stafford, the chief entomologist at the agriculture station, said there’s no way to know how the fungus gained that foothold.

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Since then, the fungus has spread through much of the gypsy moth’s range, and — at least in spots where weather is wet enough at the right time — appears to be restoring some semblance of control.

This is particularly welcome given that this cuts down on the need for pesticides or the like. Happily, the fungus doesn’t seem to harm other moths and butterflies. A 2014 study of the fungus’s impacts in Bulgarian forests, for instance, concluded, “E. maimaiga is a host-specific pathogen of gypsy moth and its introduction is not dangerous for the non-target insect species in these oak forests.” There are other natural antagonists of the gypsy moth, although during a big outbreak they tend to be overwhelmed, as the Minnesota Department of Natural Resources explains.

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After that June walk, I tweeted how the unexpected victory of a lowly fungus over a seemingly-invincible alien invader brought to mind H.G. Wells description of the surprising source of the demise of the victorious Martian invaders in “The War of the Worlds”: “…slain by the putrefactive and disease bacteria against which their systems were unprepared; slain as the red weed was being slain; slain, after all man’s devices had failed….”

But as news reports on this summer’s infestations indicate, dry spring and early-summer conditions both last year and this year have limited the impact of the fungus.

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Indeed, when I walked in the woods again on Tuesday, I saw an unnerving display of resilience in the gypsy moths, spying dozens, then hundreds, of newly emerged moths mating or laying masses of eggs, some right next to the skins of their dead kin, preparing for next year’s feast.

Learn more about the gypsy moth problem in Kirby Stafford’s 2016 fact sheet on gypsy moths and much more about the E. maimaiga fungus in a great post on a Cornell mycology blog.

And please watch and share my video report on the running battle between the gypsy moth and the fungus on YouTube or Facebook.