What Are Those Webs in My Tree? Fall Webworm in Clark County

Late August, and a grey bag of webbing shows up at the end of a branch on the cherry tree. By the weekend there are four more, they are getting bigger, and the leaves inside them are skeletons. The phone calls start about a day after that.

It is fall webworm, it turns up in Clark County every year around now, and the short version is that it looks far worse than it is. The longer version is worth knowing, because there is one very popular piece of internet advice about it that will cost you the tree.

Fall webworm or tent caterpillar? Look at where the web is

These two get confused constantly, and telling them apart takes about five seconds from the driveway.

• Location. Fall webworm builds at the branch tips, wrapping the leaves it is eating right inside the web. Western tent caterpillar builds in the crotches and forks where branches join, and leaves the tent to go feed.
• Timing. Tent caterpillars are a spring and early summer problem. Webworm webs show up in August. If it is late summer, it is webworm.
• The web itself. Webworm webbing is loose, dingy, and full of chewed leaf fragments and droppings. A tent caterpillar tent is tighter and cleaner.
• The caterpillar. WSU describes mature fall webworm larvae as yellowish or tawny and about an inch long, with a dark stripe down the back, rows of black and orange-yellow bumps along each side, and long fine pale hairs.

There is one generation per year here. The insect overwinters as a pupa in a cocoon in ground debris, adults fly in summer, and each female lays an egg mass of 300 to 400 eggs on a leaf. That is why a single web becomes a colony the size of a beach ball in a couple of weeks, and why webs can end up two feet long by the end of the season.

Which trees get it around here

Fall webworm feeds on almost all fruit, forest, and shade trees, with one useful exception: not conifers. Your Douglas fir, cedar, and arborvitae are not on the menu.

In Clark County yards it turns up most on cherry, apple, and other fruit trees, alder, cottonwood, birch, walnut, willow, maple, and linden. Shade trees take the most visible damage. If you are looking at webbing in a fir, you are looking at something else and it is worth a closer inspection.

The honest answer on damage: it is mostly cosmetic

This is the part that surprises people, so here is the reasoning rather than just the verdict.

A leaf's job is to make and store energy for the tree, and by late August a deciduous tree in the Pacific Northwest has already banked most of what it is going to bank this year. Those leaves are a few weeks from dropping anyway. A branch stripped in the last week of August loses the tree a fraction of what the same branch stripped in May would cost it. Fall webworm can completely defoliate a small tree or an individual limb on a big one, and it still rarely kills anything.

So for most healthy trees, the correct response to a couple of webs high in the canopy is to leave them alone. Birds, parasitic wasps, and predatory insects work these colonies hard, and a web you cannot reach safely is a web that is doing its job as bird food.

The exception is a tree that is already in trouble. Four consecutive drought years have left plenty of trees in this county running on reserves, and repeated defoliation year after year on a tree that is also thinning, dying back, or struggling for water is a different conversation. Damage stacks. If the same tree webs up heavily every August and looks worse each spring, that is worth an inspection rather than a shrug. The same stacking logic is what is killing Douglas firs across Clark County right now.

Do not burn the webs

Every year this advice circulates: put a rag on a pole, soak it in fuel, light it, and burn the nests out of the tree. Every year an arborist has to talk somebody out of it.

Burning does more damage to the tree than the caterpillars ever would. Fire kills living bark and cambium, and a scorched branch union is a permanent structural defect on a tree that was going to shrug off the defoliation on its own. On top of that, you would be holding an open flame up into a dry canopy in the driest weeks of the year, in a county sitting inside a statewide drought emergency, usually within a few feet of a house. There is no version of this that is worth it.

What to do instead

1. Break the web open. A pole, a rake, or a hard jet from the hose tears the webbing apart and exposes the caterpillars to every bird and wasp in the neighborhood. This is the highest-value two minutes you can spend on it.
2. Prune out what you can safely reach. A pole pruner handles most low webs. Make a proper cut back to a branch union, not a stub in the middle of a limb, and do not remove a major limb to chase a cosmetic web. That is how a small pest problem turns into a topped tree.
3. Bag what you take down. Bag the webs and put them in the trash rather than leaving them on the ground under the tree.
4. Treat only if it is genuinely warranted. Products based on Bacillus thuringiensis subspecies kurstaki or spinosad work while caterpillars are small and are gentler on beneficial insects than a broad-spectrum insecticide. On a mature shade tree in late August, treating is usually effort spent on a problem that is about to solve itself.
5. Leave the high ones. Nothing about fall webworm justifies a ladder with a saw on it, and nothing about it justifies paying someone to climb a healthy tree.

When it is worth having someone look

Call if the webbing is on a tree that also shows real problems: dieback in the upper crown, thinning that got worse over the last two summers, mushrooms or conks at the base, cracks, or a lean that has changed. In that combination the webworm is a symptom you noticed rather than the thing that is wrong.

Call as well if a small or newly planted tree is being stripped repeatedly, if the webs are tangled up with a hedge or ornamental planting you want kept clean, or if you simply want the low webs pruned out properly during other work. Our tree trimming and pruning crews handle it as part of a visit, and hedge and shrub work covers the ornamentals. If you want a written opinion on a tree's overall condition, that is an arborist report.

Otherwise, knock the webs down, put the pole away, and let the tree get on with dropping its leaves. It was going to do that in a month regardless.

Sources reviewed August 25, 2026: WSU Tree Fruit, fall webworm, OSU Nursery Pest Management, fall webworm, PNW Insect Management Handbook, and Washington Department of Ecology drought response.