A new study has uncovered an unexpected ecological chain reaction that could put vast stretches of North American forests at risk. As climate change drives hotter and drier conditions, a natural fungal enemy of the spongy moth, an invasive species notorious for defoliating millions of trees, is struggling to survive. With this natural control mechanism weakening, spongy moth populations could skyrocket, leading to widespread destruction of forests.

For decades, the Entomophaga maimaiga fungus has been a crucial defense against these pests, infecting and killing moths before they can multiply. But this delicate balance is now being disrupted by shifting weather patterns. Researchers warn that even a slight decline in fungal activity could allow moth numbers to surge, overwhelming forests and accelerating their decline. As the climate continues to change, this study highlights the growing challenge of preserving ecosystems in an increasingly unstable world.

A Natural Defense Against Invasive Moths Is Failing

The findings, published in Nature Climate Change, come from researchers at the University of Chicago and Argonne National Laboratory. Their study examined how rising temperatures and declining rainfall are affecting the ability of Entomophaga maimaiga to control spongy moth populations.

For years, this highly specialized fungus has been one of nature’s most effective tools in limiting moth outbreaks, keeping infestations from reaching devastating levels. However, the fungus thrives in cool, moist conditions, and as those conditions become rarer, its ability to curb moth populations is weakening.

Greg Dwyer, a professor of ecology and evolution at the University of Chicago and lead author of the study, explained the dangerous implications of this shift. “Even small reductions in mortality rate for the moths lead to big increases in defoliation,” Dwyer said. “If they don’t get killed off when they’re at low density one year, then the next year they’ll be back at higher density. You get this multiplication process going on.”

In other words, without the fungus keeping the moth population in check, infestations could spiral out of control, putting millions of trees at risk.

How the Spongy Moth Became One of North America’s Most Destructive Pests

Originally introduced to New England’s hardwood forests in 1869, the spongy moth has since become one of the most destructive invasive species in North America. The caterpillars strip trees of their leaves, leaving them vulnerable to disease, drought, and even wildfires. Over time, repeated defoliation weakens forests, making them less resilient to other environmental threats.

The Entomophaga maimaiga fungus has long been the best natural counterbalance to this destruction. It infects the caterpillars before they can reach outbreak levels, stopping population booms before they start. However, as climate change alters temperature and precipitation patterns, this once-reliable control method is starting to fail.

Dwyer emphasized that the impact of climate change is unfolding faster than expected. “Our projections were pessimistic, but probably not pessimistic enough. It’s very concerning,” he said. Below-average rainfall and above-average temperatures in recent years have already led to increased moth outbreaks, confirming that this crisis is not just a distant possibility—it’s already happening.

Why This Study Changes How We Predict Climate Change’s Impact

One of the most significant takeaways from this research is how climate change doesn’t just affect individual species—it disrupts entire ecosystems. Many climate models focus on single-species responses to environmental changes, but this study shows that small shifts in one species can trigger cascading effects across multiple organisms.

“The vast majority of previous climate change studies look at individual organisms, but a small amount of climate change can have a big effect when you compound it across multiple species,” Dwyer explained. “So, computer models are crucial for understanding the effects of climate change on species interactions.”

This means that forests, wildlife, and agricultural systems could be facing a wave of unforeseen challenges, as the delicate checks and balances of ecosystems break down under the stress of climate change.

What Can Be Done to Prevent a Forest Crisis?

With spongy moth populations poised to surge, scientists and conservationists are working to develop alternative methods to control outbreaks. While pesticides and biological control agents are currently used, they come with environmental trade-offs and may not be effective at the scale needed to replace the role of Entomophaga maimaiga.

A potential solution could be developing new fungal strains or identifying other natural predators that can survive in hotter, drier climates. Early detection and rapid-response forestry strategies may also help slow the spread of infestations before they reach crisis levels.

The findings from this study make it clear: climate change is reshaping ecosystems in complex and unpredictable ways. Scientists will need to move beyond single-species models and focus on the interactions between species to develop strategies that protect forests and other vital ecosystems from unexpected ripple effects.