Webspinners are the larvae of certain moths, primarily the Fall Webworm and, less frequently, the Tent Caterpillar. These insects weave dense, silken nests around tree branches to protect themselves while feeding on leaves. While a healthy, mature tree can usually withstand the resulting defoliation, the large, unsightly webs diminish the aesthetic value of the landscape. Addressing infestations requires correct identification, timely physical removal, and precise biological control methods.
Identification and Action Timing
Differentiating between the two primary web-producing pests is important because their distinct activity periods guide intervention timing. The Eastern Tent Caterpillar is active early, with webs appearing in the spring, often in the crotches of host trees like cherry and apple. The Fall Webworm is a late-season pest, with messy webs appearing toward the tips of branches in late summer and autumn. Fall Webworm larvae feed inside their silk nest, while Tent Caterpillars leave their nest to forage.
Successful control hinges on treating the larvae when they are small and confined within the protective silken nest. For Tent Caterpillars, the treatment window is generally limited to April and May. For Fall Webworms, action is most effective when small, new webs are first noticed in July or August. Once the larvae grow larger and disperse to pupate, chemical and biological treatments become largely ineffective, making early detection the most important step.
Immediate Physical Removal Techniques
The most straightforward way to manage accessible webspinner nests is through physical removal, which avoids the use of products. For small trees or low-hanging branches, pruning the infested limb entirely is highly effective. Cut the branch below the web base and immediately seal the removed section in a plastic bag to prevent larvae from escaping and re-infesting the tree.
When webs are too high or large to prune, a long pole, broom, or rake can be used to physically tear open the silken structure. This action immediately exposes the clustered larvae to natural predators like birds and wasps, and to weather elements. Simply breaking the web apart eliminates the protective barrier the larvae rely on for survival.
Another method involves using a strong, focused jet of water from a garden hose to dislodge the nest and the feeding larvae. This technique works best on smaller, newer nests that have not yet become too dense. Physical removal offers instant results and removes the web, which functions as a barrier against sprays.
Targeted Biological and Chemical Controls
When webs are out of reach or the infestation is widespread, a targeted application of biological control products is the preferred next step. Bacillus thuringiensis subspecies kurstaki (B.t.k.) is a naturally occurring soil bacterium highly effective against caterpillars. When larvae ingest B.t.k.-treated foliage, the bacteria produce a toxin that paralyzes their digestive system, causing them to stop feeding immediately and die within a few days.
B.t.k. must be sprayed directly onto the leaves inside the web, requiring the nest to be torn open or sprayed aggressively to ensure penetration. This treatment is highly selective, harming only the caterpillar and moth family of insects, making it safe for beneficial insects like bees and ladybugs. For severe infestations, a product containing Spinosad, an organic compound derived from another soil bacterium, offers an alternative control.
Spinosad works through both ingestion and contact, providing a more robust treatment option for large populations. Although naturally derived, Spinosad can be harmful to beneficial insects, including honeybees, while the spray is still wet. Applications should be scheduled for the late evening when pollinators are less active, and it should only be used as a last resort when B.t.k. proves insufficient.
Long-Term Prevention and Landscape Management
Reducing the likelihood of future webspinner infestations begins with maintaining the overall health of host trees. Well-watered and properly fertilized trees are better equipped to withstand and recover from defoliation damage. Healthy trees possess the vigor to produce new foliage and tolerate pest pressure.
Sanitation is an important preventative practice, requiring the removal of debris around the base of trees where some webspinners overwinter. During the dormant season (late fall through early spring), inspect susceptible branches for overwintering egg masses. Tent Caterpillars lay eggs in a dark, foam-covered band wrapped around small twigs.
These egg masses can be scraped off the branch with a dull knife or sandpaper and destroyed, significantly reducing the pest population before it hatches in the spring. Consistent monitoring of host plants, especially during egg-laying periods, allows for the mechanical removal of the first, smallest nests, preventing a larger population explosion later in the season.