Jeremy Clark is walking through a section of 海角换妻鈥檚 Housatonic State Forest that鈥檚 had a rough couple of years.
鈥淢ost of the trees are dead,鈥� Clark says, pointing out the telltale signs. 鈥淵ou can see all these oak trees basically have limited [or] no small, fine branches on them.鈥�
It was about four years ago when Clark, the lead forester here, realized he had a problem on his hands. He was walking the woods, drawing up a forest management plan.
鈥淚 was actually out inventorying when I first noticed the caterpillars in 2021 falling on me, and I was like, 鈥楾his is not good,鈥欌�� he recounts.
The black, bristly caterpillars raining down on him were young spongy moth larvae. They鈥檙e a longstanding invasive insect with a . In their larval stage, the bugs are ravenous 鈥� and they love oak. They can devastate an oak forest.聽
They can leave woodlands more susceptible to fire. Within their range 鈥� which encompasses all of New England 鈥� they鈥檝e done to trees. Here in this forest, they stressed or killed up to 90 percent of the oaks in some sections.
鈥淚t鈥檚 always amazing to see how much damage such a tiny insect can cause on a single tree and a whole forest,鈥� Clark says. 鈥淚t鈥檚 impressive.鈥�
How it got here
The spongy moth, native to Europe, originally landed in North America in the 1800s, brought to Massachusetts by an amateur entomologist.
鈥淚t was a Frenchman,鈥� explains Gale Ridge, an entomologist at the 海角换妻 Agricultural Experiment Station. 鈥淚n 1869, he brought the spongy moth in from England, wanting to crossbreed it with silk moths here in the United States. He was raising the spongy moths in his oak trees in his backyard and they got out, and they've been out ever since.鈥�
Since then, the moth has spread as far west as Minnesota and as far south as North Carolina, according to the . Outbreaks can be dramatic and devastating to forests. Ridge remembers the first major outbreak she saw, in 1981.
鈥淐ars were sliding on the roads because so many caterpillars were moving, and trains were actually having trouble stopping on the tracks because they were sliding on the caterpillars. It was just remarkable,鈥� she recalls. 鈥淓ntire areas of 海角换妻 were completely defoliated. It looked like winter in June.鈥�
Ridge says trees that lose their leaves to the caterpillars can end up in a battle for their lives.
鈥淭hey're stressing the trees,鈥� she says. 鈥淎nd so if you have several years where trees have been fed on鈥� they're drawing this reserve of energy from their roots, and that lessens every year until the tree basically dies from exhaustion.鈥�
In 1989, though, another non-native organism became a game changer in the fight against the spongy moth.
A killer fungus
The fungus Entomophaga maimaiga is from Japan, and it鈥檚 unclear how it arrived in the spongy moth鈥檚 range in North America. Anecdotally, Ridge says it鈥檚 possible a 海角换妻 scientist who had returned from a spongy moth-infested area in Japan brought it back on his boots. One thing was clear, though: the fungus was adept at killing spongy moth caterpillars.
鈥淲hen the caterpillars are infected with this, they die,鈥� says Katherine Dugas, another entomologist at the experiment station. 鈥淭hey cling to the tree and they slowly liquefy. It鈥檚 pretty gruesome, but if you see it, that鈥檚 good news.鈥�
The dead caterpillars on trees become 鈥渓ittle spore factories,鈥� Dugas says, spreading the killer fungus to their compatriots.
鈥淚t鈥檚 lights out,鈥� says Greg Dwyer, a professor of ecology and evolution at the University of Chicago. 鈥淎lmost right away, starting in 1989, it started causing huge amounts of mortality鈥� among spongy moth populations.
But the fungus needs the right weather to activate.
鈥淚f it鈥檚 wet enough, the higher the relative humidity and if the temperature鈥檚 not too hot, then the pathogen will spread like wildfire, and it can wipe out a population of spongy moths in just a few weeks,鈥� Dwyer explains.
Competing climate impacts
Climate change will likely play a big role in the extent to which the fungus will help control the spread of spongy moths in New England.
鈥淐limate change is not just about polar bears not being able to walk out on the ice to hunt for seals,鈥� Dwyer says. 鈥淐limate change is about oak trees in people's backyards.鈥�
Dwyer is the senior author of a January in the journal Nature Climate Change titled 鈥淐limate change drives reduced biocontrol of the invasive spongy moth.鈥�
He and his team project that overall warmer and less humid conditions in the moth鈥檚 range will lead to a decline in conditions conducive to activating and spreading the fungus, leading to greater defoliation of trees by spongy moth caterpillars.
鈥淭he effects of climate change on webs of interaction among species are hard to think through, and our research provides one glaring example of such an effect,鈥� he says.
But Ridge, the 海角换妻 entomologist, has hope. She notes springs in the northeast to see more precipitation due to climate change. Wetter springs, in theory, could lead to the activation of the fungus at the time of year when caterpillars begin to emerge from their spongy egg masses, from which the moth draws its name.
鈥淐ertainly, everything is going to be affected鈥� by climate change, Ridge says. 鈥淭he dynamics in our ecosystem are going to be shifting and changing and adapting as the weather dictates. Yes, spongy moth will certainly be affected 鈥� I鈥檓 hoping with wetter springs.鈥�
鈥楢t the mercy鈥� of a changing climate
It was a wet spring in 2023 that activated the fungus and curbed the spongy moth outbreak in Housatonic State Forest. Clark, the forester, remembers it well.
鈥淲e saw a huge kill-off of the caterpillars. There were dead caterpillars everywhere. It was gooey. It stank. But I was happy to see it nonetheless,鈥� he recounts.
Looking to the future, Clark is unsure what to expect from a changing climate when it comes to spongy moth outbreaks and the health of the forest.
鈥淲e鈥檙e kind of at the mercy of what the weather is going to give us,鈥� Clark says. 鈥淲e鈥檝e forecasted wetter springs, so that might activate the fungus. We鈥檙e also forecasted to have more droughty, drier summers, which could then further stress the trees out.鈥�
鈥淪o will that offset? Will it balance out?鈥� Clark wonders aloud. 鈥淚 think that just remains to be seen.鈥�
Entomologists say there鈥檚 not a lot any of us can do, though some locals are getting creative in their attempts to save the oaks.
鈥淥ne of the funniest anecdotes I was told by a landowner who had a significant amount of acreage was that he was collecting some of these [caterpillars infected by the fungus], putting them in a blender, making caterpillar soup, and then spraying it on his trees to basically spread the spores as far and wide as possible,鈥� Dugas says. 鈥淚 just thought that was a clever way to distribute this.鈥�
鈥淵ou know, I'm not recommending that everybody sacrifice a blender,鈥� Dugas says. 鈥淎nd do not mix up your smoothie-making blender with your caterpillar blender,鈥� she adds.
