White, silky and seemingly appearing out of nowhere webs are starting to cover leaves and even entire branches of trees around the state. But while it might look like something out of a scary spider movie, in this case the real web builders are quite benign.
The insect responsible for the large webs is the fall webworm. And there’s good news: they pose no real danger to trees, humans or pets.
“The fall webworms are on the march,” according to James Dill, pest management specialist with University of Maine Cooperative Extension. “Calls are coming in and this pest seems to be abundant this year.”
Numbers not withstanding, the only danger the webworms pose to trees are foliage is purely aesthetic.
“They make things very unsightly,” Dill said. “Their nests can envelope the whole branch and you can see a tree with as many as 10 nests on it, and while it won’t kill the tree, it is one nasty looking tree.”
This can be especially discouraging for people with ornamental trees who suddenly find their gorgeous tree covered with white webs.
The webworms create their tightly woven, weather-proof silken nests as caterpillars and feed on any leaves inside that web. Unlike the eastern tent caterpillar that builds similar nests earlier in the summer, the webworms never go outside their nests to feed.
In Maine, the webworm’s preferred tree is chokecherry, Dill said, though they also build nests and feed on the leaves of apple, ash, willow, oak, birch and elm trees.
“Sometimes you will see the whole chokecherry tree completely wrapped up in [fall webworm] webs,” Dill said. “Even that won’t kill the tree.”
However, Dill said if webworms build nests and feed on the same tree year after year, that can eventually kill a tree. Luckily, the adult webworm moths are not territorial and don’t necessarily lay eggs in the same tree from which they emerged from their nest.
Any tree that the webworms are currently building their nests has already built up enough nutrient stores to survive the winter, so it can afford to lose any leaves still attached to its branches at this point in the season.
If having all those communal webworm nests in your tree is just too much to look at, there are ways to get rid of them.
You can simply pull them off by hand or cut off the entire branch and destroy the web anyway you can, according to the Maine Department of Agriculture, Conservation and Forestry. To remove larger webs take a forked stick or one with a nail stuck through it and poke it into the web. Then twist it loose from the tree.
Chemical pesticides are also an option, but only ones clearly labeled for use against webworms and tent caterpillars. The biologic non-chemical agent Bacillus thuringiensis — or Bt — can also be used.
Whatever you do though, don’t use a torch or flamethrower to burn the nests in the tree because you can easily set the entire tree on fire.
As far as Dill is concerned, if you can handle looking at the nests and if a tree has not been a webworm home over the past several seasons, why not take a live and let live attitude.
“There is no reason to panic if you see them on your trees,” he said. “You may see some brown leaves and your tree may look ugly, but it will be fine.”