Mistaken for gypsy moth, webworms cause little damage
Mistaken for gypsy moth, webworms cause little damage
Those webs in the trees are mostly not a return of the gypsy moth, a plague of decades last century that defoliated many trees in the region.
You might say the webs are harbingers of fall. They are not the voracious treekilling gypsy moths, but fall webworms (Hyphantria cunea).
They spin webs in tree branches to protect themselves from predators while they munch on leaves. They can feed on almost 90 species of deciduous trees commonly attacking hickory, walnut, birch, cherry and crab apple.
The large conspicuous webs contain caterpillars, dead partially eaten leaves and fecal droppings.
In a few weeks, they will emerge and crawl to the ground, find a crack in the soil, spin a cocoon and pupate through the winter and spring. In June, adult moths will emerge, breed and lay eggs on branches — and the larva will spin their webs again.
Fairly harmless
It’s not clear if there are more fall webworms this year, said Beth Finlay, master-gardener coordinator for Penn State Extension. Her area includes Adams, Berks, Cumberland/Perry, Dauphin, Franklin, Fulton, Huntingdon, Lebanon, Lancaster, Mifflin, Juniata and York counties.
“We have no way of sampling the whole county,” Finlay said.
Finlay said the population rises and falls over the years depending on weather and predators. More could have survived since winter 2019-20 was quite mild.
They don’t do much damage, though they may be unsightly. Finlay said webworms eat leaves that were going to fall off the trees anyway and don’t eat buds.
The branches where they nested will produce leaves in the spring.
“Those leaves have done their jobs,” Finlay said.
She said the impact they have is primarily cosmetic as well as sending residents into a panic because they think they are gypsy moths.
Native insect
Webworms are also confused with tent caterpillars. Eastern tent caterpillars create their nests in the spring in the crotches of trees, whereas webworms prefer the ends of branches and emerge in the fall.
“The main role of the webs is presumably to protect the caterpillars from their many predators and parasites,” according to North Carolina Cooperative Extension. “Birds, spiders and predatory insects like wasps will sometimes raid the web to eat the caterpillars inside.”
Finlay said homeowners really don’t have to do anything about the webs. If you are bothered by how they look, you can just get a long stick and twirl it around the nest. Then plunge it into a bucket of soapy water. “
According to the Penn State Extension, pesticides should not be used on fall webworms in areas that could contaminate forage, streams or ponds.
Interestingly, webworms are a native insect that was exported from the U.S. to Europe and Asia and have caused problems there.
The North Carolina’s extension says they were accidentally introduced to Yugoslavia in the 1940s. Since then, they have invaded most of Europe and spread to China, Korea and Japan.
The webworm is a major pest in those regions.
In Europe, the fall webworm is more destructive than the European gypsy moth caterpillar is in the U.S.
The European gypsy moth was intentionally introduced to the U.S. in 1869 with the hopes of interbreeding with silk worms to develop a silk industry in the U.S.
The interbreeding never occurred, but the moths have spread from Massachusetts to the North CarolinaVirginia line.