That bag of worms might just be useful By JIM SHAMP : The Herald-Sun js2@herald-sun.com Sep 2, 2001 : 7:03 pm ET

DURHAM -- Those sacs of gray webworms clutching tree branches in your back yard may look like aliens overtaking the neighborhood, but you probably don’t need to declare war against them.

But wait. They’re worms. They’re eating things. They must be stopped, right? Not necessarily.

"We don’t recommend people do much of anything," said Don Rogers, an insect expert with the North Carolina Forest Service office in Raleigh. "By this time of year the trees are getting ready for winter and they’ve pretty much done their photosynthetic duties, so these worms aren’t hurting anything by eating those leaves."

Another entomologist in Raleigh agreed. Mike Waldvogel, a cooperative extension specialist at N.C. State University, called fall webworms "some of my favorite insects."

"They’re just there," said Waldvogel. "They don’t do a whole lot. Mostly I just hear from my neighbors about them, because I leave mine alone. But then I don’t do anything in my yard. It’s survival of the fittest out there."

"Everybody has an idea about what to do about them," he added. "Mostly it leans toward something like spraying them with kerosene and lighting it. Then they wonder why they get no foliage the next spring. If they’d just leave ‘em alone, the trees would come back fine."

Fall webworm statistics aren’t maintained because the critters don’t represent a threat, the experts said. Their main drawback is that many people consider them unsightly.

"We’re getting more than the usual run of calls from people who are bothered by the aesthetics of the whole thing," said Rogers, "so I take that as an indication we’re running above normal on these late-season defoliator populations this year. But they don’t represent a threat to the trees."

Rogers said every year, insects referred to as "fall defoliators," including fall webworm and the orange-striped oak worm, go through varying population cycles.

Fall webworms, technically known as Hyphantria cunea (Drury), are native to North America and Mexico. That fact, along with the bug’s wide-ranging appetite for more than 100 species of plants and trees, helps the webworm thrive.

They’re not tent caterpillars, which make smaller nests in branch crotches. They’re not bag worms either, though fall webworms are sometimes mistakenly referred to as bag worms.

The North Carolina entomologists explained that fall webworms use their webbed enclosures as protection from flying predators such as parasitic wasps and birds. The webworms build these silky dining halls around clusters of autumnal foliage, adding to the room if the food runs out before winter sends them underground to live through their pupal stage.

The caterpillars typically found in North Carolina are about an inch long with red heads. Their bodies are covered with relatively long tannish to greenish fuzz containing orange to reddish spikes. If you disturb a nest to look at the individual worms, the whole gang might go into a strange jerking dance.

"I guess when their day comes, they just turn loose and fall," said Rogers of the caterpillars’ upcoming transition to become earth dwellers after their one- to two-month web life.

They spin a pupal cocoon in the soil or some other sheltered spot, emerging in the spring as moths to fly and mate. The females then lay about 500 eggs each on the undersides of preferred leaves, and about two weeks later the cycle resumes as the caterpillars emerge to eat and build webs.

"When things are right for them, their populations will boom," said Rogers. "Then the parasites build up, because there’s lots for the parasites to choose from, and that results in a decline in the fall webworm population for a while. It’s nature’s balance."

A surprising array of predators depends on fall webworms for food, said Rogers, including migratory birds. So when homeowners splash insecticides onto the nests, they’re not only killing the beneficial webworms, but they’re also probably killing webworm predators, creating exactly the opposite effect being sought.

"This can be an emotional thing for people," said Rogers. "Some people get all worked up by what they don’t understand. Some even tie this into a fear of gypsy moths or something. But so far gypsy moths have caused no serious defoliation in North Carolina. They’ve only been found in a few spots in the northeastern part of the state."

The abandoned fall webworm nests generally deteriorate from weather, though sometimes they last for many months, giving the impression that they’re occupied more than they are, said Rogers.

"The fact is," said Waldvogel, "by next year the leaves and the caterpillars will be back, annoying the crap out of people, and it’ll be Discovery Channel time all over again -- nature’s bird feeders, hanging out there, all organic and natural, so it must be good, right?"

"North Carolina has a lot of scrub trees along the roadsides, like sweet gums. The darn things have to do something for somebody. Might as well be caterpillar food."

-- Anonymous, September 03, 2001