What Are the White Webs in My Trees? Identifying the Fall Webworm

From late July through fall, homeowners across North America notice the same thing: loose, dirty-white webs appearing at the tips of tree branches, sometimes wrapping several feet of foliage. The panic reaction is understandable — it looks like something is smothering the tree. In almost every case these are the nests of the fall webworm (Hyphantria cunea), a native caterpillar that is far more of an eyesore than an actual threat to a healthy tree.

How to Identify a Fall Webworm Nest

Fall webworm webbing has a few telltale features that separate it from other silk you might find in a tree:

• The web is built at the ENDS of branches, enclosing the leaves the caterpillars are eating — not in the crotches where branches meet
• It is loose, messy, and grayish-white, and it grows larger as the caterpillars expand it over dead, partially eaten leaves
• Inside are dozens to hundreds of pale, fuzzy caterpillars, usually yellowish to pale green with black or orange heads and long white hairs
• They appear from mid-to-late summer into fall — the "fall" in the name is the giveaway to timing

The most common mix-up is with the eastern tent caterpillar, but the two are easy to separate by season and location. Tent caterpillars build their tight, dense webs in the forks and crotches of branches in the SPRING; fall webworms build loose webs at the branch TIPS in late summer. Bagworms, another look-alike, make small individual spindle-shaped bags covered in bits of leaf, not open communal webs.

Are Fall Webworms Harmful?

To people, no — they do not sting or bite and are harmless to handle. To trees, they look far worse than they are. Fall webworms feed late in the season when leaves have already done most of their work for the year, so even when they strip a few branches bare, an established, otherwise-healthy tree tolerates it fine and leafs out normally the next spring. They attack a huge range of hardwoods — pecan, walnut, birch, cherry, crabapple, and many others — but the damage is almost always cosmetic.

What to Do About Them

For most trees, the honest answer is: nothing. The webs weather away over the fall and the tree is unaffected. If a nest is low and bothering you, the simplest fix is to prune out the affected branch tip and dispose of it, or use a pole to pull open the web so birds and predatory insects can get at the caterpillars — they are a favorite food of many songbirds and wasps.

One thing not to do: burning the webs out of a tree with a torch, a piece of advice that circulates every year. It causes far more harm to the tree than the caterpillars ever would, and it is a genuine fire risk. Skip it.

When to Take a Closer Look

It is worth confirming the ID if the webbing is dense and packed into branch crotches (which points to a spring tent caterpillar instead) or if a young or already-stressed tree is being heavily defoliated year after year. Not sure whether the webs in your tree are harmless fall webworms or something that needs attention? Take a photo and Spotter will identify what made them and tell you whether you need to act.