Those silky white webs draped over tree branches are almost always the work of caterpillars, not spiders. The two most common culprits are fall webworms and eastern tent caterpillars, and telling them apart is straightforward once you know when and where to look. In most cases, the webs look worse than they are. Healthy trees tolerate them well.
Fall Webworms vs. Eastern Tent Caterpillars
These two insects are responsible for the vast majority of conspicuous webs in deciduous trees across North America, and they occupy different seasons and different parts of the tree.
Fall webworms build loose, messy webs that enclose the foliage at the ends of branches. The caterpillars live and feed inside the web, expanding it outward as they eat. A single web can eventually spread over several branches. Newly hatched caterpillars start by webbing over individual leaves and skeletonizing them, then progressively enlarge the tent. You’ll see these webs from midsummer into fall. In southern states, adults can emerge as early as March and produce up to four generations per year, so webs may appear earlier and persist longer. In northern areas, there’s typically just one generation, with eggs hatching in mid-July and larvae feeding for a month or more before crawling down to pupate in leaf litter or bark crevices.
Eastern tent caterpillars show up in spring. Their webs are thick, tightly woven structures built in the forks and crotches where branches meet, not at branch tips. The caterpillars don’t actually feed inside the tent. Instead, they use it as a shelter, gathering there at night and during rain, then heading out along branches to eat leaves during the day. Eggs overwinter as shiny, dark masses encircling small twigs, each containing 150 to 400 eggs. The larvae hatch around the time buds break in early spring and begin constructing the tent within a couple of days. They add layers as they grow, and feeding generally wraps up by the time the tree is leafing out vigorously.
Both species feed on fruit, shade, and woodland trees. Cherry, apple, and crabapple are particular favorites of eastern tent caterpillars, while fall webworms have been recorded on over a hundred different tree species.
A Third Possibility: Forest Tent Caterpillars
Despite the name, forest tent caterpillars don’t actually build a tent. They create silken mats on branches and trunks where caterpillars cluster together. If you see caterpillars gathering on a flat, shiny pad of silk rather than inside an enclosed web, this is likely the species you’re dealing with. They can cause widespread defoliation in outbreak years, particularly on hardwoods like sugar maple and aspen.
Can Webs Actually Kill a Tree?
The webs themselves do no damage. The concern is the leaf loss from caterpillar feeding. A tree stripped of its leaves looks alarming, but healthy trees can survive two to three consecutive years of defoliation. Trees that lose their leaves early in the season often push out a second, smaller set of leaves by July once the caterpillars finish feeding.
That said, repeated defoliation takes a cumulative toll. It slows growth and chips away at the tree’s ability to handle other stresses like drought, flooding, or secondary pest attacks. In some cases, the stress from defoliation can contribute to a tree’s death eight to ten years after the event, not from the caterpillars directly but because the weakened tree couldn’t recover from additional problems that followed. A single season of webworms or tent caterpillars on an otherwise healthy tree is rarely cause for concern.
Webs on Evergreens Are a Different Problem
If you’re seeing fine webbing on conifers like spruce, juniper, arborvitae, or Douglas fir, caterpillars probably aren’t the cause. Spruce spider mites produce delicate webbing, especially around the base of needles. These mites are tiny, with oval bodies that can be brown, green, or pink depending on the species and host plant. Their feeding causes needles to turn bleached, bronze, reddish, or yellow. The tricky part is that damage to young foliage may not become visible for months, so by the time you notice discolored needles, the mites may have already done their work. Fine webbing plus discolored evergreen foliage points strongly to mites rather than caterpillars.
How to Remove Webs
For webs you can reach, the simplest approach is pruning out the affected branch and destroying it. This works best when the webs are still small. Once a web has expanded across multiple branches, removing it may do more cosmetic damage to the tree than leaving it alone. The goal is to physically remove the caterpillars, so don’t just tear the web open and leave them on the tree.
A pole or stick can be used to open webs on higher branches, exposing the caterpillars to birds, predatory insects, and parasitic wasps, all of which feed on webworms and tent caterpillars naturally. These natural enemies are often the most effective population control over time, especially in landscapes that support diverse bird and insect communities.
For larger infestations, a biological spray containing Btk (a naturally occurring soil bacterium) is an option. It works by disrupting the caterpillars’ digestive system after they eat treated foliage. Timing matters: it needs to be applied while caterpillars are young and actively feeding. Because not all eggs hatch at once, effective treatment typically requires two applications spaced five to ten days apart. Btk is specific to caterpillars and does not harm birds, pets, or beneficial insects like bees, which is why it’s widely used in both residential and public land management programs.
Identifying What You’re Looking At
A quick checklist can help you figure out what’s producing the webs in your trees:
- Loose web at branch tips, summer or fall: fall webworm
- Thick web in branch forks, spring: eastern tent caterpillar
- Silken mat on trunk or branch (no enclosed tent), spring: forest tent caterpillar
- Fine webbing on evergreen needles with discoloration: spider mites
If the web appeared seemingly overnight and is concentrated at the outer tips of branches on a leafy tree in late summer, fall webworms are the most likely explanation. If you spotted it in April or May tucked into a branch crotch on a cherry or apple tree, eastern tent caterpillars are your answer. In either case, the tree will almost certainly be fine.