Webworm tents invade region Caterpillar homes unsightly but not harmful, experts say

September 07, 1998|By Erika Niedowski | Erika Niedowski,SUN STAFF

Columbia resident Gini Capuano has just one thing to say when she looks up at the thick, gauzy tents that "webworm" caterpillars have spun on tree branches across the region this year: "Blech."

She also has one thing to ask of her retired husband while he's out in the yard: Prune away the pest-filled eyesores and get rid of them in a plastic bag, securely fastened, just to be sure, with a twist-around tie.

Probably because of the mild winter caused by the weather phenomenon El Nino, it's been a heavier year than normal for the fall webworm -- known scientifically as Hyphantria cunea -- which appears to be wreaking havoc on Baltimore's city and suburban trees alike.

But it turns out there's no need to panic: Experts say the silk tents, which the webworms spin using glands in their mouth for protection while feeding, are far more unsightly than they are harmful. By now, most trees have finished getting their food for the year, and will lose their leaves soon anyway.

Even so, concerned Maryland residents have been seeking tips from horticulture consultants at the Home and Garden Information Center of the University of Maryland Cooperative Extension for weeks.

One gardener-type, writing to The Sun's Backyard columnist in July, seemed to have mobilized for war. "I plan to kill them with diazinon," the gardener wrote.

"You can't walk anywhere without seeing lots of trees that are infested," said Elsie Leonard, a retired librarian from the Village of Oakland Mills in Columbia, who has noticed one webworm tent in a cherry tree in her front yard and two more in the back. "They're just ugly, humongous, intricate spider-webs."

Unfortunately for gardeners -- and plain old landscape aesthetes -- webworms are not finicky eaters. They feed on more than 100 species of shrubs and trees, including hickories, oaks, ash, lilac, apple, pear and box elders. "You name it, they'll eat it," said Michael Pogue, a research entomologist with the Systematic Entomology Lab of the U.S. Agriculture Department's Agriculture Research Service, who has clipped some web-infested branches in his Howard County yard this year.

It's too late to do much more than that. Pesticides such as b.t., insecticidal soap or horticultural oil have to be sprayed before the tents get so big and gauzy.

Trimming branches and soaking the webs in soapy water or disrupting the tents with a stick are probably the best remedies, but beware: The webs usually contain an unseemly mix of frass, or worm waste, as well as dead leaves and shed larval skins.

"People get grossed out by that," explained Dave Clement, director of the Home and Garden Information Center.

Dan Trollinger, who lives on Winterfield Lane in Columbia, took on the webworms several years ago -- and lost.

The retired engineer had an ornamental crab apple tree in his yard that became infested with the hairy caterpillars, so he took out his trimmers and clipped away.

Year after year, though, the webworms would come back, until finally, Trollinger decided it would be easier to chop down the tree altogether than continue eliminating its limbs. "I don't like the way they look," Trollinger said of the tents.

Fall webworms in the Baltimore-Washington area -- so named because their tents usually mark the onset of autumn in the northern United States -- are "two-brooded," meaning two generations of caterpillars each year.

According to Pogue, the entomologist, the first brood goes from egg to adult in about six weeks beginning in the spring. The second -- which is what can be seen in trees now -- hatches around the end of July, spins a silky tent and feeds on leaves, then falls to the ground, spins a cocoon and pupates during the winter months in the crevice of a tree.

The moths, which range in color from immaculate white to white dotted with black and brown spots, emerge in the spring, only to repeat the cycle again.

However bothersome they are, the caterpillars do serve a biological purpose, providing food for birds, beetles and parasites.

But it's difficult to dispute that the sticky tents they call home for a short time leave something to be desired. "They're ugly," said Clement. "I'll give you that."

Pub Date: 9/07/98

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