Silken webs in tree branches signal an infestation by leaf-eating caterpillars. While the webs are primarily a cosmetic issue, the feeding activity within the nests can cause significant defoliation, especially on young or stressed trees. Understanding the source of the webbing is the first step in successful removal, as the timing and placement of the nests indicate the right treatment strategy. Addressing this problem promptly prevents widespread leaf loss and maintains the tree’s overall health.
Identifying the Weaving Pests
The appearance and location of the silken structures distinguish between the two most common culprits: Eastern Tent Caterpillars and Fall Webworms. Eastern Tent Caterpillars are active in early spring when tree buds open. Their characteristic nests are tightly woven and found in the crotches or forks of branches, typically closer to the trunk.
Fall Webworms become active much later, usually from late summer through the fall. These pests construct a looser, more sprawling web generally located at the tips of branches, often encompassing a cluster of leaves. Identifying the pest dictates the window for manual removal and the timing of biological controls.
Physical Removal Methods
Mechanical removal is the safest and most immediate way to eliminate webs, especially for accessible infestations on smaller trees. For nests on outer branches, the simplest approach is pruning the entire affected branch tip, ensuring the web and all caterpillars are removed. The severed branches should be immediately sealed in a plastic bag or dropped into soapy water to destroy the pests.
For nests that are out of reach or too large to prune, use a long stick or a pole pruner to tear open the webbing. Target removal during early morning or evening hours when the larvae are resting inside the nest. Tearing the web exposes the caterpillars to natural predators like birds and parasitic wasps, and allows for better penetration of subsequent spray treatments. Never attempt to burn the webs out of the tree, as the resulting flame causes severe damage to the living wood.
Biological and Chemical Control Options
Targeted treatments are used when physical removal is impractical due to the tree’s size or the extent of the infestation. The most effective biological control option is a naturally occurring soil bacterium called Bacillus thuringiensis subspecies kurstaki (Bt-k). This product is a stomach poison that is harmless to beneficial insects, pets, and humans, but the caterpillar must ingest it to work.
Application is most effective when the larvae are small, ideally in their first or second developmental stage, and actively feeding outside the web. Since Bt-k degrades rapidly in direct sunlight, applying the product in the late afternoon or evening maximizes effectiveness. For severe or hard-to-reach infestations, a chemical insecticide containing ingredients like spinosad may be necessary, requiring careful application to ensure the product reaches the caterpillars inside the protective webbing.
Long-Term Prevention Strategies
Maintaining the tree’s health increases its natural resistance to pests and helps it recover from defoliation. Ensuring the tree receives proper watering and seasonal fertilization gives it the resources needed to withstand and recover from an attack. This cultural care is a defense against recurring infestations.
A proactive approach during the dormant season can prevent the problem from starting. Eastern Tent Caterpillars, for example, overwinter as a shiny, dark egg mass encircling small twigs. Inspecting the branches in winter and scraping these masses off the bark before they hatch in spring reduces the population of new caterpillars. Encouraging natural enemies, such as by installing bird feeders or planting diverse vegetation that attracts predatory insects, provides continuous, non-chemical control.