This story begins: GristGrist’s Get the weekly newsletter here.
Take a few steps into the densely wooded forests of New York’s Hudson Valley, close your eyes and listen: you won’t hear the rain, but the chewing and excreting of millions of caterpillars.
On clear spring days, birdsong drowns in the sound of sponge-like moth larvae flopping about feeding on oak, maple, crabapple, linden and aspen trees. Fragments of green leaves scatter to the ground like confetti, evidence of the insatiable feeding going on in the tree canopy above. Hundreds of larvae bob up and down on long, thin silk threads, waiting to be blown by the breeze to carry them to new trees.
Northeast and Midwest Some areas are enduring the worst sponge moth outbreaks on record. One factor stimulating the proliferation of hungry caterpillars is drought caused by climate change, which allows the moths to reproduce uncontrollably. Up to 1 million caterpillars per acreAlthough the trees are resilient, this outbreak has been particularly long and destructive. After two consecutive years of intensive feeding by sponge moths, Up to 80 percent Trees in deciduous hardwood forests die. The current sponge moth epidemic has been ongoing in some parts of the United States for five years.
“When leaves fall at this exact time of year, trees use the energy stored in their trunks and roots to fuel a second wave of growth,” says Brian Eschenault, a plant pathologist with Cornell University’s Integrated Pest Management Program. “If the tree has to do this two years in a row, it’s using up all of its stored energy.”
Caterpillars aren’t the only forest pests benefiting from climate change: Many invasive species in the US are expanding thanks to milder winters brought about by warmer-than-average global temperatures. Hemlock Woolly Adelgidemerald ash borer, Japanese beetle and spotted lantern fly are devouring the nation’s trees at a record pace. Widespread tree mortality and forest stress They are prone to drought and disease. No single species can destroy the country’s forests. Approximately 60 billion tons of carbonHowever, the rise of invasive species is causing serious cumulative damage.
Sponge moths have been in America since 1869, when French artist and amateur entomologist Étienne Léopold Trouvelot imported them from Europe and began raising them in nets in his backyard near Boston. Trouvelot wanted to breed silkworms suited to the American climate for commercial fiber production. The sponge moths, then called gypsy moths, float from leaf to leaf and tree to tree on long, strong silk threads. But they soon escaped captivity, likely due to violent storms. Broke Truvro’s net.Some of the insects then migrated to the forests of Massachusetts.
Twenty years later, in the midst of the first recorded outbreak of sponge moths, one resident of Trouvelot’s town described a world carpeted with the fuzzy black caterpillars: “It is no exaggeration to say that there was no place outside the house where you could put your hand without touching a caterpillar.” a resident told the Boston Post in 1889.(The caterpillars do not bite humans, but some people develop an itchy, painful rash if they come into contact with their sharp hairs.)
Over the century since its initial appearance, the sponge-like moths have spread across parts of New England, the Mid-Atlantic, the Midwest and the South at a rate of about 13 miles per year, devouring 300 species of leafy trees and shrubs and denuding entire forests. A cumulative 81 million acres of foliage were lost between 1970 and 2013.Because of the damage they cause to trees, controlling sponge moth populations has been one of the U.S. Forest Service’s top priorities. The economic cost of controlling sponge moths has averaged $30 million per year over the past 20 years.
Climate change is making it worse: Outbreaks typically occur every eight to 12 years, with each surge lasting one to three years, and this latest outbreak has lasted longer than usual, said Tom Coleman, a Forest Service entomologist who manages insects for the service. Slow the spread of infection The sponge moth eradication program is being driven in part by drought conditions in some of the areas where the moths live.
Drought influences the spread of fungal pathogens Entomophaga gypsy moth The fungal pathogen, which suppresses sponge moth populations, was originally found in Japan and introduced to the United States by researchers in the early 1900s as a way to control sponge moths. The pathogen is very effective at killing the moths in their larval stage, but it needs cool, wet springs to thrive. Periodic outbreaks of sponge moths often occur after drier-than-usual years, when the pathogen is less prevalent in the environment. “Without the fungal pathogen suppressing the population, we would have these massive outbreaks,” Coleman said.
In the eastern part of the country where the sponge moth outbreak is occurring, climate change is Weather patterns become more erraticMost of the eastern U.S. Rainfall is predicted to increaseAs the Earth warms, on average Climate change is also affecting drought-stricken areas In these regions, during the warm seasonDrought expected to affect parts of Northern Virginia, Southern Pennsylvania, Wisconsin and Michigan in 2023 and early 2024 This year’s epidemic was fuelledA major drought, like those common in the Western U.S., isn’t a prerequisite for sponge moth outbreaks in the East. “You don’t have to have drought all year,” Coleman says. “You could just have a warm, dry spring.”
It’s unclear whether rising temperatures will lead to more frequent sponge moth outbreaks, but it’s safe to assume that warmer, drier conditions will cause periodic outbreaks to intensify over time. Fortunately, the Forest Service 100,000 pheromone traps to capture pests heading westThe agency also plans to deforest 10 million acres of forests. A biological insecticide that kills larvaeThis will prevent insects from establishing themselves in new locations.
Still, experts worry about the multifaceted threat that pests and climate change pose to America’s trees, and how the two dangers overlap. “Climate change not only affects insects, but it can also make native trees in certain regions less suitable for their habitat,” Eschener says. “Many trees in the Northeast cannot tolerate high temperatures and extended drought, which makes them more susceptible to new, invasive pests.”
This article was originally published on Grist in https://grist.org/science/whats-behind-the-record-outbreak-of-spongy-moths-in-the-eastern-us/.
Grist is a nonprofit, independent media organization dedicated to telling stories about climate solutions and a just future. For more information, Grist
