The web-spinning caterpillars people call “silkworms” in their yards are almost never actual silkworms. They are tent caterpillars or fall webworms, and getting rid of them starts with physical removal of the webs and, when possible, destroying the egg masses before larvae ever hatch. The good news is that most infestations are more ugly than dangerous, and a combination of well-timed manual removal and a few preventive measures can keep them under control without heavy pesticide use.
They Are Not Silkworms
True silkworms are domesticated moth larvae (Bombyx mori) raised commercially for silk production. They do not live in North American or European trees and would not survive in the wild. The caterpillars building conspicuous silk structures in your cherry, apple, or walnut trees are one of two common species: eastern tent caterpillars (Malacosoma americanum) or fall webworms (Hyphantria cunea). Both spin silk shelters, but they behave differently and show up at different times of year.
Eastern tent caterpillars build their tents in the forks of branches, usually in spring. Fall webworms enclose the tips of branches in loose, baggy webs, typically from late summer into fall. Knowing which one you have matters because it changes when and how you intervene. Eastern tent caterpillars feed primarily on cherry, apple, and other trees in the rose family, while fall webworms are less picky and will colonize a wide range of hardwoods.1Entomologia Experimentalis et Applicata. The Effect of Variation in Host Plant on the Growth of an Oligophagous Insect, Malacosoma americanum and Its Polyphagous Relative, Malacosoma disstria
When to Act and Why Timing Is Everything
The single most important factor in controlling these caterpillars is timing. Eastern tent caterpillars lay their eggs in dark, shiny masses that wrap around thin twigs, typically on exposed sides of branches in the lower canopy. Those egg masses sit on the tree all winter, doing nothing. If you spot and scrape them off between November and early March, you prevent the problem entirely. Larval emergence begins around mid-March, though the exact timing depends on spring temperatures. In a cool spring, emergence can be drawn out over three to four weeks; in a warm spring, the caterpillars hatch more or less all at once.2PubMed. Managing Eastern tent caterpillars Malacosoma americanum (F) on horse farms to reduce risk of mare reproductive loss syndrome
Fall webworms operate on a different calendar. Their webs appear in summer and grow progressively larger through August and September. Because they show up later in the season, the trees they attack have already done most of their growing for the year, which is why fall webworm damage tends to be cosmetic rather than life-threatening for the tree.
The practical takeaway: for tent caterpillars, winter egg-mass removal is your easiest win. For fall webworms, you usually deal with them after the webs appear.
Physical Removal of Webs and Nests
The most straightforward approach, and often the most effective for a homeowner with a few affected trees, is tearing the webs out by hand or with a pole. For tent caterpillar nests in branch forks, a stick or a long-handled tool can pull the silk tent apart. Do this on a cool morning or in the evening when the caterpillars are clustered inside the tent rather than spread across the tree feeding. Once you pull the nest down, drop the caterpillars into a bucket of soapy water to kill them.
For fall webworm webs at branch tips, pruning the affected branch tip is often the cleanest solution. Cut below the web and dispose of the branch. On small or young trees, this alone can eliminate the infestation. On larger trees where the webs are out of reach, you may need a pole pruner or simply accept that the caterpillars will run their course. Burning webs with a torch, a method you will see recommended in old gardening books, is a bad idea. Open flame damages bark and cambium tissue far more than the caterpillars themselves would.
For egg masses, a putty knife or similar flat tool works well. Scrape the shiny egg band off the twig and crush it or drop it in soapy water. Each egg mass can contain a couple hundred eggs, so removing even a few has a real effect on the next spring’s population.
Do Sticky Bands and Trunk Barriers Help?
Wrapping a band of sticky material around a tree trunk is a common suggestion for stopping caterpillars from climbing into the canopy. The idea makes intuitive sense: if caterpillars cannot walk up the trunk, they cannot reach the leaves. In practice, the protection is modest at best. Research on sticky trunk barriers used against gypsy moth caterpillars, which behave similarly to tent caterpillars in their climbing habits, found that the bands reduced larval density by about 25% and leaf loss by roughly 30%. The researchers concluded that sticky barriers provide some foliage protection but should not be relied on as the primary defense against caterpillar damage.3Arboriculture & Urban Forestry. Management of Gypsy Moths Using Sticky Trunk Barriers and Larval Removal
The limitation is that caterpillars are resourceful. They can balloon on silk threads from neighboring trees, drop from above, or simply pile up on the sticky surface until later arrivals walk across their dead siblings. Sticky bands also trap beneficial insects and can damage bark if left on too long. If you use them, treat them as one tool among several rather than a standalone fix, and remove them once caterpillar season ends.
Biological Controls and Sprays
For larger infestations or situations where manual removal is not practical, a spray containing Bacillus thuringiensis var. kurstaki (Btk) is the standard recommendation. Btk is a naturally occurring soil bacterium that produces a protein toxic specifically to caterpillars. When a caterpillar eats a leaf coated in Btk, it stops feeding within hours and dies within a few days. Btk does not harm bees, birds, pets, or people, which makes it a far better option than broad-spectrum insecticides for a backyard setting. It is available at most garden centers under various brand names. The key is applying it while the caterpillars are small and actively feeding, because older caterpillars are harder to kill and because Btk breaks down in sunlight within a few days.
Spinosad, another microbial insecticide derived from a different soil bacterium, also works against web-spinning caterpillars and is approved for organic use. It has a broader activity window than Btk but can be more harmful to some beneficial insects, so timing applications for evening hours when pollinators are less active helps reduce collateral damage.
On the purely biological side, tent caterpillars and fall webworms have plenty of natural enemies. Parasitoid wasps, tachinid flies, and predatory beetles all attack them at various life stages. Research on deploying parasitoid wasps for caterpillar control has shown that a managed release of the right wasp species can knock down about 80% of a caterpillar population within two months.4Semantic Scholar. Eco Control of Agro Pests using Imaging, Modelling & Natural Predators That kind of structured biocontrol is more relevant to agriculture than a backyard, but the principle still applies at a smaller scale: avoiding broad-spectrum insecticides lets the existing population of parasitoids and predators do much of the work for you. Cuckoos, orioles, and other birds also feed heavily on tent caterpillars, and encouraging bird activity with nesting boxes or feeders near affected trees can make a noticeable dent.
Which Trees Are Most Vulnerable
Eastern tent caterpillars are choosy. They strongly prefer trees in the rose family: wild cherry, black cherry, crabapple, apple, and plum. Among those, black cherry (Prunus serotina) is a particular favorite.1Entomologia Experimentalis et Applicata. The Effect of Variation in Host Plant on the Growth of an Oligophagous Insect, Malacosoma americanum and Its Polyphagous Relative, Malacosoma disstria If you have a wild cherry growing at the edge of your property, it is almost certainly the staging ground for tent caterpillars that then spread to your ornamental trees. Removing or treating that source tree can reduce pressure on everything nearby.
Fall webworms are far less particular. They colonize hickory, walnut, persimmon, sourwood, birch, and dozens of other species. Because of that generalist appetite, preventing fall webworm problems by changing what you plant is not really an option.
Trees do have their own chemical defenses. Research on red alder trees attacked by western tent caterpillars found that higher concentrations of certain defensive chemicals in the leaves, including tannins and a compound called oregonin, were consistently associated with reduced caterpillar feeding. Trees with enough of these compounds appeared to reach a threshold that discouraged the caterpillars from eating.5Canadian Journal of Forest Research. Red alder defense mechanisms against western tent caterpillar defoliation For the homeowner, the practical lesson is that healthy, well-watered, properly fertilized trees mount a stronger chemical defense than stressed ones. You cannot control the genetics of a mature tree, but you can keep it in good shape so it fights back on its own.
Will They Kill Your Trees?
A single season of defoliation almost never kills an otherwise healthy deciduous tree. The tree pushes out a second flush of leaves, and while it will look ragged for the rest of the summer, it usually recovers fully by the following year. The danger comes from repeated defoliation over multiple consecutive years, especially if the tree is already stressed by drought, poor soil, or disease.
Research on trees that suffered severe defoliation shows how serious the long-term consequences can be when recovery is disrupted. Trees that were heavily defoliated and did not recover quickly had mortality rates up to five times higher than trees that escaped the initial damage, and they were twice as susceptible to secondary pest attacks, such as bark beetles that move into weakened wood.6Europe PMC. Pathogen-induced defoliation of Pinus sylvestris leads to tree decline and death from secondary biotic factors Even a decade after the initial defoliation event, severely affected trees in that study had not restored their crowns and still showed stagnated growth.
That study looked at pine trees defoliated by a pathogen rather than caterpillars specifically, but the mechanism is the same: a tree that loses its leaves loses its ability to photosynthesize and store energy, and if it gets hit again before it rebuilds those reserves, the downward spiral accelerates. For a homeowner, this means that one year of tent caterpillar webs is not an emergency, but if the same trees are being stripped year after year, active intervention is worth the effort to break the cycle before secondary problems set in.
Concerns for Horse Farms and Livestock
Most people looking to remove web-spinning caterpillars are worried about aesthetics or tree health, but there is one context where the stakes are significantly higher. Eastern tent caterpillars have been linked to mare reproductive loss syndrome, a condition that caused thousands of foal losses in the Ohio Valley in 2001 and 2002 and resulted in enormous economic damage to the horse industry.2PubMed. Managing Eastern tent caterpillars Malacosoma americanum (F) on horse farms to reduce risk of mare reproductive loss syndrome The exact mechanism involves pregnant mares ingesting caterpillars or their shed skins along with pasture grass, which then triggers bacterial infections in the uterus.
If you keep horses and have wild cherry or other host trees near your pastures, controlling tent caterpillars is not optional. The management approach developed for horse farms focuses on removing wild cherry trees from fence lines and within a reasonable buffer zone around pastures, destroying egg masses in winter, and applying Btk to remaining host trees in spring before caterpillars disperse.2PubMed. Managing Eastern tent caterpillars Malacosoma americanum (F) on horse farms to reduce risk of mare reproductive loss syndrome During years with large caterpillar populations, keeping pregnant mares off pastures near infested trees during the peak caterpillar season (mid-March through May, depending on your climate) adds another layer of protection.
Preventing Next Year’s Infestation
Because tent caterpillar populations tend to boom and bust on roughly ten-year cycles driven by disease and parasitoid buildup, a terrible year does not necessarily mean the next year will be equally bad. But you can tilt the odds in your favor.
Walk your trees in late fall or early winter and look for egg masses. On cherry and apple trees, they look like shiny, dark bands wrapped around pencil-thin twigs, usually on the lower and outer parts of the canopy where the branches get the most sun.2PubMed. Managing Eastern tent caterpillars Malacosoma americanum (F) on horse farms to reduce risk of mare reproductive loss syndrome Scraping those off is fifteen minutes of work that can prevent weeks of caterpillar management the following spring.
Minimize outdoor lighting near susceptible trees during the summer months when adult moths are flying. Like most moths, tent caterpillar and fall webworm adults are drawn to light, and a porch light next to your prized crabapple effectively advertises it as an egg-laying site. Switching to yellow or amber bulbs, or simply turning off unnecessary lights, reduces how attractive your yard is to egg-laying females.
Encouraging predator and parasitoid populations also pays dividends over time. Avoid spraying broad-spectrum insecticides unless you have a genuinely severe infestation. Those sprays kill the wasps, flies, and beetles that would otherwise keep caterpillar numbers in check, and you can end up with worse outbreaks in subsequent years because the natural enemies take longer to recover than the caterpillars do. If you must spray, Btk or spinosad are far more targeted and leave most beneficial insects unharmed.
Finally, consider whether wild cherry trees growing along your property line are worth keeping. They are the primary reservoir for eastern tent caterpillar eggs in most landscapes. If a weedy wild cherry on the back fence is the source of annual infestations on your ornamental trees, removing it may be more effective than any spray program.