The fall webworm (Hyphantria cunea), a native moth of North America, is commonly found across Iowa during late summer and early fall.
“We expect higher populations of fall webworm south of Interstate 80,” explains Tivon Feeley, Iowa DNR Forest Health forester.
The caterpillars of the moth spin webbed nests that cover the ends of tree branches, providing protection as they consume foliage. Dozens of caterpillars can be found in a single nest. Webbing can cover multiple branches and occasionally an entire tree.
Fall webworms are not picky eaters. Their webs can be found on a variety of hardwood trees such as hickory, walnut, birch, cherry and willow. As caterpillars mature, they abandon their host tree to search for protected locations to pupate during the winter. These spiky-haired caterpillars may be seen crawling on decks, houses and sidewalks, sometimes by the hundreds.
The webbing and defoliation caused by fall webworms is mostly aesthetic and rarely causes long-term damage to trees. An effective control method is to open the webbed nest with a long stick that has a nail driven through the end to expose the caterpillars to natural predators. Use caution when trying to open nests on branches that are difficult to reach. Never use fire to burn webs from trees as this can damage twigs and buds.
Fall webworm is often confused with the eastern tent caterpillar, which also builds silken tents in tree branches. Eastern tent caterpillars are found in spring and early summer.