LOCAL

Fall webworm nests spotted in Pennsylvania

Teresa Boeckel
York Daily Record

YORK, Pa. — They’re back!

No, not the eastern tent caterpillars. Those make their nests in the spring in the area where branches meet together or connect with the tree trunk.

These are fall webworms, which make their nests in late summer and early fall, defoliating parts of trees and blotching the landscape.

They are easy to spot because they spin their nest at the ends of the branches, said Michael Skvarla, an assistant research professor of arthropod identification at Penn State University.

This marks the second year in a row that the unsightly nests have been plentiful. Some trees are covered with nests while others only have a few.

One spot in central Pennsylvania where it’s easy to see them this year is along Interstate 83 near Lake Redman.

Fall webworms follow a “boom and bust” cycle, Skvarla wrote in an email. They will increase in numbers for a few years, reach a peak, and crash when predator and parasitoid populations catch up with them.

The predator and parasitoid populations crash when they don’t have any food left, which then allows the webworms to increase in population again.

“So it may be that the webworms are just on the upswing of a normal cycle,” he said.

The Yellow-billed Cuckoo is one that eats fall webworms, said Kelsey Frey, manager of education with York County Parks.

“We have been hearing a lot of cuckoos this year (way more than usual),” she wrote in an email.

They rarely do much damage or affect the long-term health of trees, Skvarla said.

That’s because the fall webworms appear late in the season, just before the deciduous trees drop their leaves. The trees do not have to expend energy to grow a whole new set of leaves at this point.

Frey said the fall webworms are primarily eating walnut trees, which are common and grow quickly. They shouldn’t be damaging to the forest overall.

“The caterpillars are also feeding primarily in edge habitats (side of the road, edge of the parking lot), not in the interior of the forest,” she said.

“Fall webworms are found throughout much of North America, including all of the United States, southern Canada, and northern Mexico,” Skvarla said.

They also have been introduced into other countries, including China, North Korea and Yugoslavia.

Fall webworms can be found throughout Europe after being introduced in Yugoslavia in the 1940s, he said.

In Europe and Asia, they’re an invasive species because the parasitoids that attack and keep the fall webworms under control have not been introduced there.

There’s no need to get rid of them, but if you want to, just take a stick and poke some holes in the nest. That will allow natural predators, such as birds, bees and wasps, to get into the webs and eat them.

“There’s no need to cut down that branch. There’s no need to burn it or spray chemicals,” Frey has said. “All you got to do is cut open a hole in the nest, and it lets predators get into them easier.”

“The adult moths range in color from all white to white with many black spots,” Skvarla said. “The color varies by latitude, with individuals in northern areas being mostly all white and individuals in the south being mostly white with black spots.”

Fall webworms, which make their nests in late summer and early fall, defoliate trees and blotch the landscape.