These caterpillars build their own web sites

August 26, 1998

Web wormsBy LAURA ERNDE / Staff Writer

photo: JOE CROCETTA / staff photographer [enlarge]

The silky webs look more like the work of Halloween pranksters than inch-long caterpillars, but drive almost anywhere in the Tri-State area and you're bound to see trees shrouded with them.

The netlike webs, woven by fall webworms, are unusually abundant this year, horticulture experts said.

"This is absolutely the worst I've ever seen," said Henry Hogmire, entomology specialist at the West Virginia University Experiment Farm in Kearneysville, W.Va.

Webworms are abundant this year because a mild winter and wet spring meant good growing conditions for the trees where they make their homes, he said.


Like the dreaded gypsy moth, webworms voraciously eat leaves off trees.

But the good news is, webworms rarely kill trees.

Webworms appear at just the time that trees are beginning to shut down for the fall and don't rely as much on their leaves.

"I think the biggest thing is they look kind of obnoxious. A lot of people think they're decorating their trees for Halloween early," said John Stouffer, a retired horticulture teacher who works as a consultant for Antietam Tree and Landscape in Hagerstown.

They seek out English walnut trees, black walnut trees, fruit trees and flowering cherry trees. But they don't discriminate, even attaching themselves to lilac bushes.

About this time of year, webworms will emerge from their protective netting to seek low-lying places to spin their cocoons, said Sandy Scott, horticulture consultant at the University of Maryland Cooperative Extension Service in Hagerstown.

Eventually, they turn into white moths that sometimes have black dots on their wings.

Because they are essentially harmless, Scott recommends leaving them alone unless they have infested a recently planted ornamental tree.

Stouffer said the tree service has gotten plenty of calls from people who want the unsightly webs removed.

Spraying will kill the worms, but doesn't get rid of the webs. Trimming out the branch is often the only choice, he said.

Scott said too much trimming can be more harmful than doing nothing.

The worms can be killed by spraying inside the web with chemicals or a mixture of one gallon of water and a tablespoon of dish detergent, she said.

Killing the worms doesn't guarantee they won't return next year. That depends more on factors like the weather and predators such as birds, she said.

Although property owners don't need to worry much about webworms, they should keep an eye out for gypsy moths, the numbers of which also have increased this year, Scott said.

This spring, the Maryland Department of Agriculture sprayed about 700 acres in Washington County to keep the larvae from taking hold.

Gypsy moths don't form webs, but instead spin velvety, oval egg cases that hatch in May and eat all summer, she said.

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