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Fall Webworms

9-10-18 fall webworm nest_U1A9376

For several weeks white webs on the tips of branches have been apparent on many trees.  These silken tents are the work of the Fall Webworm (Hyphantria cunea), a moth most associated with its larval stage. Fall Webworm caterpillars construct a web over the end of a branch, enclosing leaves on which they feed.  As the hairy, white caterpillars grow, they enlarge the web to encompass more leaves, with tents sometimes extending two to three feet.

Often mistaken as the work of Eastern Tent Caterpillars, the tents of these two moths can be distinguished by the season they appear (ETC are active in the spring, Fall Webworms in the fall) as well as the location of the tents (ETC are usually in the crotches of trees, Fall Webworms at the tip of branches). As soon as the eggs hatch in early summer, the Fall Webworm larvae begin to spin small silk webs over the foliage of the deciduous trees on which they feed (over 90 species). By fall the tents are conspicuous. A look inside one  reveals caterpillars, dead partially-eaten leaves, and fecal droppings.

The larvae feed together inside the increasingly large web for roughly six weeks, at which point they often start feeding independently before pupating in the ground over the winter and emerging as adult white moths the following summer.

If your favorite tree has one or more Fall Webworm nests in it, there’s no cause for alarm. These caterpillars may defoliate a tree occasionally, but rarely kill it, and usually only build tents on a handful of branches, if that. The larvae have more than 50 natural predators and 36 parasites that help control them. Also bear in mind that Fall Webworms do not eat the buds of next year’s leaves and the leaves they are feeding on will soon to drop to the ground. Next year leaves will appear on the currently affected branches with no sign of last year’s damage.

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8 responses

  1. Thanks for making this distinction.

    September 10, 2018 at 9:08 am

  2. Alice Pratt

    Great info! They certainly can’t be considered ‘picky eaters’ 🤣

    September 10, 2018 at 9:08 am

  3. Gina

    Thank you for this timely article as I’d been lecturing my family about the ETC thinking we were in for another cycle. I was wrong and relieved to learn there is another caterpillar that makes tents. {o:

    September 10, 2018 at 9:32 am

  4. Kathryn

    Thanks, Mary. Your post just saved the lives of the worms in the web that I was going to take down today!

    September 10, 2018 at 3:13 pm

  5. John O'Brien

    Thanks for this, Mary; I had mistaken these for hickory tussock moths. What sort of nests do they make? We have tons of them in western Maine this year.

    September 11, 2018 at 3:15 am

    • Hi John,
      To my knowledge, HIckory Tussock Moth larvae do not make silk nests. They feed on hickory and walnut leaves, often congregating in large groups, but I don’t believe they spin a silk web.

      September 11, 2018 at 9:24 am

  6. Bill on the hill

    To think I have called them tent caterpillars for my entire adult life… Needless to say they are unsightly and I would not hesitate to snip the branch they are attached to & throw them in the fire. Done…

    September 11, 2018 at 11:13 am

  7. Thanks for this post. Just a note that in the southern half of Maine we’re dealing with a significant expansion of the nonnative browntail moth (BTM). BTM also creates small webs on the tips of branches at this time of year, which persist through the winter till the tiny larvae emerge in spring. BTM’s toxic hairs cause a more or less severe, itchy rash, and can trigger respiratory issues in some people .

    Since pruning and destroying winter webs is by far the most effective treatment for BTM, we try to educate people about how to identify their webs, including how to distinguish them from fall webworm (which as you point out don’t need to be pruned).

    Much more info is on the Maine Forest Service website, https://www.maine.gov/dacf/mfs/forest_health/invasive_threats/browntail_moth_info.htm.

    September 14, 2018 at 9:56 am

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