The web-spinning caterpillars most people call “silkworms” in their trees are almost never actual silkworms. They are tent caterpillars or fall webworms, and the good news is that you can get rid of them with a combination of well-timed manual removal, targeted sprays, and a bit of patience. The approach that works best depends on which caterpillar you’re dealing with, how large your trees are, and how bad the infestation has gotten. Most homeowners can handle the problem themselves if they catch it early enough.
What You’re Actually Looking At
True silkworms (Bombyx mori) are domesticated insects raised for silk production and don’t infest landscape trees. The caterpillars spinning silk in your yard belong to one of a few common species, and telling them apart matters because their habits and timing differ.
Eastern tent caterpillars (Malacosoma americanum) build dense, white silk tents in the forks and crotches of branches, usually on cherry, apple, and crabapple trees. You’ll spot these tents in early to mid-spring, and the caterpillars use them as a base camp, venturing out to feed during the day and returning at night. Forest tent caterpillars (Malacosoma disstria) are close relatives that look similar but don’t actually build a proper tent. Instead, they lay down silk mats on trunks and branches where they cluster together.
Fall webworms (Hyphantria cunea) are the ones that enclose entire branch tips in loose, messy webs later in summer. Their webs expand outward as the caterpillars eat, eventually engulfing large sections of foliage. These caterpillars are less picky about host trees and will colonize everything from pecans to elms. Interestingly, research has shown that fall webworms tend to avoid trees that were already used by tent caterpillars earlier in the season, so a spring tent caterpillar problem and a late-summer webworm problem on the same tree is less common than you might expect.
Why Timing Is Everything
The single biggest factor in controlling these caterpillars is catching them at the right stage. Young caterpillars are far easier to kill than older ones, and removal is simplest before webs grow large.
Eastern tent caterpillars hatch from egg masses in early spring, often before the host tree’s leaves have fully opened. Research tracking the relationship between caterpillar hatching and leaf emergence has found that hatching often precedes budbreak, which means the tiny caterpillars may already be spinning their first tent while the tree is still mostly bare.
1PubMed. Warming affects hatching time and early season survival of eastern tent caterpillars That’s your first window of opportunity: look for small, shiny egg masses wrapped around twigs during winter or early spring, and the beginnings of tiny tents as soon as warm weather arrives.
Young caterpillars that hatch out of sync with their host tree’s budbreak face a harsh penalty. Studies on forest tent caterpillars found that larvae hatching well after budbreak needed nearly three times as many degree-days to complete their first stage of development, and that prolonged feeding period left them far more vulnerable to predators.
2Environmental Entomology. Budbreak Phenology and Natural Enemies Mediate Survival of First-Instar Forest Tent Caterpillar (Lepidoptera: Lasiocampidae) The practical takeaway: nature already stacks the deck against late-emerging caterpillars. Your job is to push them over the edge by removing nests and colonies while they’re still small and concentrated.
Manual Removal
For small to medium trees, physical removal is the most straightforward method and the one with zero chemical concerns. During winter, inspect your trees for egg masses. Eastern tent caterpillar eggs look like dark, varnished bands wrapped tightly around pencil-thin twigs, each mass holding a few hundred eggs. Pruning off these egg masses and destroying them before spring eliminates the problem before it starts. Egg masses are easiest to spot when leaves are off the tree.
3Journal of Integrated Pest Management. Biology and Management of the Forest Tent Caterpillar (Lepidoptera: Lasiocampidae)Once caterpillars have hatched and begun building tents, you can remove the tents by hand or with a stick. Early morning or late evening is the best time because the caterpillars are clustered inside the tent rather than scattered across the tree feeding. Twist the tent around a stick or gloved hand, pull it free, and drop it into a bucket of soapy water. Some people suggest burning tents with a propane torch while they’re still in the tree, but this is a genuinely bad idea. Open flame near tree bark causes cambium damage that can wound the tree far worse than the caterpillars would have. Soapy water does the job without the fire risk.
For fall webworm nests later in the season, the same stick-and-bucket approach works. Because webworm nests enclose branch tips rather than sitting in branch forks, you can also prune off the infested branch tip if it’s small enough. Bag it and throw it away rather than leaving the clipping on the ground, since the caterpillars will simply crawl back up.
Biological Sprays
When manual removal isn’t practical because the tree is too tall, the infestation is too widespread, or you simply have too many trees, Bacillus thuringiensis var. kurstaki (Btk) is the go-to biological pesticide. Btk is a naturally occurring soil bacterium that produces proteins toxic to caterpillars but harmless to people, pets, birds, and beneficial insects like bees. It’s sold under brand names like Dipel and Thuricide and is widely available at garden centers.
Btk works by being eaten. The caterpillar ingests treated foliage, the bacterial protein destroys its gut lining, and it stops feeding within hours and dies within a few days. Because it has to be consumed, Btk must be sprayed onto the leaves the caterpillars are actively eating, and it degrades in sunlight within about a week, so timing and reapplication matter. Research on tent caterpillars and related species has confirmed that Btk formulations provide effective forest-level protection against these pests.
4REDIA. Evaluation of different Bacillus thuringiensis sv kurstaki formulations against Lymantria dispar and Malacosoma neustria larvae infesting Quercus suber treesOne nuance worth knowing: the tree species the caterpillar is feeding on can affect how well Btk works. Research on forest tent caterpillars found that the concentration needed to kill half the larvae was roughly 100 times greater when the caterpillars were feeding on aspen compared to sugar maple. Older caterpillars were also harder to kill, with the effective dose roughly doubling between third and fifth instar.
5Journal of Economic Entomology. Variation in the Susceptibility of the Forest Tent Caterpillar (Lepidoptera: Lasiocampidae) to Bacillus thuringiensis variety kurstaki HD-1: Effect of the Host Plant The practical lesson: spray early, when caterpillars are young and small. Waiting until they’re large and well-fed makes any treatment less effective.
Chemical Insecticides
If Btk isn’t cutting it, or if the infestation is severe enough that you need faster knockdown, conventional insecticides are an option. Bifenthrin and spinosad have both been tested specifically against eastern tent caterpillars and proven effective as foliage sprays against all larval stages, with residues remaining active for at least a week after application.
6PubMed. Managing Eastern tent caterpillars Malacosoma americanum (F) on horse farms to reduce risk of mare reproductive loss syndromeSpinosad sits in an interesting middle ground: it’s derived from a soil bacterium and is approved for organic use in many contexts, but it’s more broadly toxic than Btk and can harm beneficial insects on contact. Bifenthrin is a synthetic pyrethroid and a more conventional chemical option. Both work on contact and by ingestion, giving them an edge over Btk when caterpillars are older or harder to reach with thorough spray coverage.
For tall trees, getting spray to the canopy usually requires a hose-end sprayer or a professional applicator with high-pressure equipment. If you’re dealing with a large shade tree and can’t reach the canopy yourself, this is one of those situations where hiring an arborist or pest control professional is worth the cost. Spraying from the ground with a pump sprayer simply won’t reach a 40-foot canopy.
Trunk Barriers
You’ll sometimes see advice to wrap tree trunks with sticky bands or barriers to trap caterpillars as they move up and down. The idea is sound in theory, since tent caterpillars travel between their resting sites and feeding areas, and a band of sticky material (like Tanglefoot applied to duct tape or a similar wrap) can intercept them. In practice, the results are modest. Studies on gypsy moth caterpillars using sticky trunk barriers found that larval density in the canopy dropped by roughly 27 to 28 percent.
7Environmental Entomology. Effects of Trunk Barriers on Larval Gypsy Moth (Lepidoptera: Lymantriidae) Density in Isolated- and Contiguous-Canopy Oak Trees8Journal of Economic Entomology. Sticky Barrier Bands Affect Density of Gypsy Moth (Lepidoptera: Lymantriidae) and Damage in Oak Canopies
That sounds decent, but the researchers also found that this reduction didn’t consistently translate into less leaf damage or fewer egg masses the following year. The caterpillars that made it past the band still did enough eating to defoliate the tree. Trunk barriers work best as a supplementary measure alongside other controls, not as a standalone solution. If you do use them, place the barrier at chest height, apply the sticky material to a removable wrap rather than directly to bark (which can damage the tree), and check it periodically since debris and dead insects can create bridges that let caterpillars walk across.
Trunk Injection for Large Trees
A more targeted approach for high-value shade trees is trunk injection, sometimes called endotherapy. Instead of spraying pesticide across the canopy and surrounding area, a professional injects the product directly into the tree’s vascular system through small ports drilled into the trunk. The tree then distributes the insecticide through its own water-conducting tissue to the leaves where caterpillars feed.
A comprehensive review of trunk injection found that the technique can deliver products with next to no water consumption, a strong reduction in pesticide use compared to broadcast spraying, and treatment persistence lasting one to two years in some cases.
9PubMed Central. Tree Endotherapy: A Comprehensive Review of the Benefits and Drawbacks of Trunk Injection Treatments in Tree Care and Protection The downsides are cost and access: trunk injection requires specialized equipment and is typically performed by certified arborists, not homeowners. It also involves drilling into the trunk, which creates small wounds that the tree must compartmentalize. For a large, mature tree in a prominent spot in your yard, it may be worth the investment. For a row of wild cherries at the back of your property, it’s overkill.
Natural Predators and Letting Nature Help
Before you reach for any spray, it’s worth considering that tent caterpillars have a long list of natural enemies that often keep populations in check without human intervention. Birds, parasitic wasps and flies, ground beetles, spiders, and predatory bugs all feed on tent caterpillars at various life stages. Research examining predation on forest tent caterpillars found that generalist predators, both arthropods and birds, were responsible for the majority of natural-enemy-caused mortality across the caterpillar’s immature stages.
10Ecological Entomology. Generalist predation on forest tent caterpillar varies with forest stand composition: an experimental study across multiple life stagesTent caterpillar populations are famously cyclical. In many regions, outbreaks build over several years, peak, and then crash as disease, parasites, and starvation catch up. If your infestation is mild and the trees are healthy, doing nothing may actually be the right call. A single season of moderate defoliation rarely kills a mature tree. That said, if the same trees are getting hit year after year, or if the trees are already stressed by drought, disease, or other factors, active intervention becomes more important.
Will Your Trees Recover?
Most healthy deciduous trees can tolerate a single season of heavy caterpillar defoliation and bounce back by producing a second flush of leaves in midsummer. The real danger comes with repeated years of severe defoliation, which drains the tree’s stored energy reserves.
Research on sugar maples defoliated by forest tent caterpillars found that growth rates dropped by nearly 40 percent during the years of active defoliation compared to unaffected trees nearby. Trees that ultimately recovered had significantly greater starch reserves in their sapwood than trees that continued to decline and die.
11The Forestry Chronicle. Dieback and growth loss of sugar maple associated with defoliation by the forest tent caterpillar In other words, a well-nourished tree with deep energy reserves can weather the storm; a tree already running on empty cannot.
Defoliation also affects the chemistry of sap and sugar production in maple trees. Research has found that the timing of defoliation matters: early-season defoliation tends to have less impact on root starch reserves by autumn, while late-season defoliation causes greater depletion. Severe defoliation in mature trees can lead to measurable declines in both sap volume and sugar concentration the following spring.
12Forest Ecology and Management. Tamm review: The impact of forest tent caterpillar defoliation on maple fitness and syrup productionTo give your trees the best chance of recovery, water them deeply during dry spells, avoid fertilizing during active defoliation (forcing new growth when the tree is already stressed can do more harm than good), and hold off on heavy pruning until the tree has had a full growing season to replenish its reserves. Mulching around the base helps retain soil moisture and moderate root temperature.
Safety When Handling Caterpillars
Most tent caterpillars and fall webworms in North America aren’t medically dangerous to people, but they can cause skin irritation. Many caterpillar species have fine hairs (called setae) that can break off on contact and trigger itchy rashes, and some species are far worse than others. Contact with caterpillar hairs can cause reactions ranging from mild local skin irritation to, in rare cases with certain species, more serious effects.
13PubMed Central. Caterpillar Venom: A Health Hazard of the 21st CenturyWear gloves when removing nests by hand, and avoid rubbing your eyes or face while working around caterpillar webs. The hairs can become airborne when nests are disturbed, so if you’re sensitive or working with a large nest, long sleeves and safety glasses aren’t a bad idea. Wash your hands and forearms afterward. If you develop a persistent rash, applying tape to the affected skin and peeling it off can help remove embedded hairs. People with severe allergies or asthma should be cautious around large infestations where airborne hairs could be inhaled.
14PubMed Central. Skin Reactions to pine processionary caterpillar Thaumetopoea pityocampa SchiffA Seasonal Game Plan
Putting it all together, here’s what an effective year-round approach looks like:
- Winter: Inspect dormant trees for egg masses on small twigs. Prune off and destroy any you find. This is the lowest-effort, highest-reward step.
- Early spring: Watch for tiny tents forming in branch crotches as soon as buds begin to swell. Remove small tents by hand immediately.
- Mid-spring: If caterpillars are spreading faster than you can remove them manually, apply Btk to the foliage while larvae are still young. Reapply after rain or after about a week.
- Late spring: If large caterpillars persist, consider bifenthrin, spinosad, or a professional application for tall trees.
- Summer: Watch for fall webworm nests appearing on branch tips from midsummer onward. Prune out or treat as needed.
- Fall: Support tree recovery with deep watering. Avoid unnecessary pruning. Note which trees were affected so you can prioritize winter egg-mass scouting.
Consistency across seasons matters more than any single dramatic intervention. A homeowner who scrapes off egg masses every winter and removes small tents every spring will rarely face a serious outbreak. The people who end up with trees draped in caterpillar silk are typically those who ignored two or three years of smaller infestations until the population exploded. Tent caterpillars breed in cycles, but in a residential setting, you can break that cycle by staying one step ahead.