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Fall Webworms on Trees and Shrubs

Fall Webworms are pretty white moths that cause a lot of unsightly problems in their larval stage.  Most fall webworm infestations are not harmful to a tree, but they look terrible and homeowners are eager to be rid of them!  You’ll see them in late summer and early fall, unless we have an unusually large outbreak, and then you may see them earlier.

Northern areas, approximately north of the 40th parallel (around the Kansas/Nebraska border) see one generation of fall webworms per year.  Farther south, there are two or more generations.  The farther south you go, the earlier you see them.  Unfortunately, our service area is south of the 40th parallel.

Webworms are actually native to North America, from Canada to Mexico.  They’re one of the few pests from North America that was inadvertently introduced to other countries. In the 40’s, they turned up in Europe as well as in Japan, spreading to China and Korea, and are now found pretty much over all the northern continents of the world (whose residents probably aren’t thanking us for that.)

Fall webworms should not be confused with tent caterpillars, although they are both defoliators. 

Fall webworms (Hyphantria cunea)

  • Are yellowish white or yellowish green, with black dots along their length
  • Turn into white moths
  • Appear later than tent caterpillars
  • Make webs on the ends of branches and feed on the leaves
  • Eat inside their web
  • First hatch in spring, but barely noticeable until late summer/fall hatching
  • Mostly a nuisance – rarely damage trees

Tent caterpillars (Malacosoma americanum)

  • Are black with a white stripe and blue dots
  • Turn into light brown moths
  • Appear earlier than fall webworms
  • Make webs in the crotch of the tree
  • Eat outside their web, returning to the web for protection
  • Appear in spring
  • Can damage trees during heavy infestations

Fall webworms make webs on the ends of branches, feed on leaves, and gradually increase the size of the webs to enlarge their eating area.  In heavy infestation years, you can see trees on the side of the road that are nearly engulfed in webs.  Most trees can stand to lose leaves in the late summer and early fall, unless they are already heavily stressed as from drought or disease.  But trees in your yard usually receive more care and water, and sometimes spraying, as we provide with our tree and shrub service.  Spraying will kill the webworms, but the webs will remain until wind and rain dismantle them.

If you notice webs in your trees, it’s best to use a stick or rake or hard stream of water to break open the web, leaving the webworms vulnerable to birds and other predators that feed on them.  However, if the trees are tall, reaching the web may be difficult or impossible, in which case you should consider having them treated professionally.

Having your trees sprayed not only kills the worms, but prevents them from spreading to other trees in your landscape.

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