If you’re seeing silky webs in your trees during spring, you’re almost certainly looking at eastern tent caterpillars, not true webworms. The insect most people call a “webworm” is the fall webworm (Hyphantria cunea), which doesn’t appear until mid-summer at the earliest. This mix-up is one of the most common in backyard pest identification, and telling the two apart matters because their timing, behavior, and the threat they pose to your trees are all different.
Why “Spring Webworm” Is Usually a Tent Caterpillar
Eastern tent caterpillars are the web-building insects active in spring. They build thick, tightly woven webs in the forks and crotches of tree branches, typically starting in March or April depending on your region. Fall webworms, by contrast, show up in summer and fall, with their loose, messy webs appearing on branch tips from late July onward. If you’re seeing webs in April or May, tent caterpillars are your culprit.
The web location is the fastest way to tell them apart. Tent caterpillar webs sit in the V-shaped joints where branches split. The caterpillars don’t actually feed inside these webs. They use them as a home base, heading out during the day to eat leaves and returning to the web at night or during rain. Fall webworms do the opposite: their loose, dirty-looking webs enclose branch tips, and the larvae feed on leaves right inside the web. As the caterpillars grow, they expand the web outward to cover more foliage, sometimes creating enormous silken tents by August and September that can even merge together across branches.
Other Webworms Active in Spring and Summer
A few true webworm species do feed during spring, though they’re less conspicuous than tent caterpillars. The cotoneaster webworm is active in spring and summer, primarily in coastal California. Its larvae are dark brown, about half an inch long, and they web together groups of leaves on cotoneaster shrubs, feeding within silken tubes while skeletonizing the undersides of leaves. The mimosa webworm feeds on mimosa and sometimes honeylocust, with young larvae grouping together under silk and turning foliage brown. Cypress webbers and cypress leaftiers attack arborvitae, cedar, cypress, and juniper, mostly in southern California.
All of these species share a basic habit: they spin silk over foliage near the tips of branches and feed within that protective covering.
How Much Damage Webworms and Tent Caterpillars Cause
The good news is that neither tent caterpillars nor most webworm species cause lasting harm to otherwise healthy trees. Both feed on leaves, and heavy infestations can strip a tree bare in spots, but deciduous trees typically push out a second flush of leaves and recover fully by the following year. The webs look alarming, especially when they grow large, but the cosmetic damage is usually worse than the biological damage.
The exceptions are young or stressed trees, which may not have the energy reserves to regrow lost foliage. Trees weakened by drought, disease, or repeated defoliation over multiple years can decline. Evergreen hosts like arborvitae and cypress are also at greater risk because they don’t replace foliage as readily as deciduous species.
Physical Removal
For most homeowners, physical removal is the most effective and practical approach. You can tear open tent caterpillar webs by hand or with a stick, exposing the caterpillars to birds and other predators. On smaller trees, pruning out webbed branch tips works well. Hand-picking larvae or destroying their nests can significantly reduce a local population without any chemical intervention. The best time to do this is early in the season, while the webs and caterpillars are still small.
One popular but bad idea: burning webs with a torch. This damages bark and can kill the branch you’re trying to save. Stick with pruning or manual destruction.
Biological and Chemical Options
A bacterial insecticide called Bt (Bacillus thuringiensis var. kurstaki) targets caterpillars specifically without harming other insects. It works by disrupting the larvae’s digestive system after they eat treated foliage. The key limitation is timing: Bt only works on young, early-stage larvae. Once caterpillars are close to full size, it’s largely ineffective. It also breaks down rapidly in sunlight and washes off leaves easily, so you may need repeat applications. After spraying, avoid watering the treated area for at least two days.
Broader insecticides are available for severe infestations but are rarely necessary for healthy landscape trees. The silk webbing actually shields caterpillars from contact sprays, so any treatment works best when applied early, before the webs grow large and dense. If the webs are already big and well-established, physical removal is more reliable than spraying.
Identifying What’s in Your Tree
Here’s a quick reference for the three most commonly confused web-building caterpillars:
- Eastern tent caterpillar: Active in spring (March through May). Thick, compact webs in branch forks. Caterpillars leave the web to feed. Prefers cherry, apple, and crabapple trees.
- Fall webworm: Active late summer through fall (July through September). Loose, messy webs enclosing branch tips. Caterpillars feed inside the web. Attacks over 100 species of deciduous trees. Mature larvae are yellowish, about an inch long, with tufts of long hair and black and brown markings.
- Sod webworm: A completely different group that feeds on turfgrass, not trees. If you’re seeing brown patches in your lawn with small moths fluttering above the grass at dusk, that’s a sod webworm problem, not a tree issue.
Whichever species you’re dealing with, the pattern is the same: early intervention is easier and more effective than waiting. Small webs are simple to prune out or treat. Large, mature webs are harder to manage but also signal that the caterpillars are nearly done feeding for the season anyway. In most cases, the tree will recover on its own.