Beijing authorities are intensifying efforts to control an outbreak of the invasive North American fall webworm (Hyphantria cunea) that has heavily infested trees across the city and surrounding regions this summer. The caterpillars have enveloped foliage in large swaths of greyish-white webs, posing a threat to a wide variety of plant species.

While the larvae do not harm humans, they feed aggressively on the leaves of hundreds of trees, including common urban species such as mulberry, ash, and plane trees. The pest is native to North America, where natural predators typically keep its population in check, but it has spread extensively across Europe and Asia since its accidental introduction to Europe in the 1940s. In China, the fall webworm was first identified in 1979 and now affects 13 provincial-level areas.

Experts link this year’s severe infestation to favorable weather conditions. Chen Min, a professor at Beijing Forestry University, said that a mild winter followed by a rainy summer has created an optimal environment for the larvae to thrive. Chen also noted that the wet weather has diminished the effectiveness of pesticide applications, complicating control efforts.

To address the outbreak, municipal teams have implemented a variety of measures, including physically removing the webs, trapping adult moths, and conducting pesticide spraying campaigns. Approximately 3,000 monitoring sites have been established throughout Beijing to inform and coordinate these efforts.

In addition to official actions, community participation is being encouraged through caterpillar-catching competitions and public appeals to report affected trees. Beijing has also released 1.1 billion parasitic wasps of the species Chouioia cunea, a natural enemy of the fall webworm discovered in the 1980s, aiming to reduce the pest’s population biologically.

Chen emphasized the challenges posed by this year’s outbreak, describing it as the third generation of fall webworms appearing this season, with the first generation emerging around May considered the most critical target for control. The professor stressed that the concentrated infestation has revealed weaknesses in the coordination and timing of current pest management strategies, highlighting a need for improved synchronization and adaptation of control measures.