Those masses of webs matted around the tips of tree branches are the work of fall webworms.

“They’re mainly unsightly,” Vincent Cotrone, an urban forester for the Penn State Extension, said of the nests made by the native pest. “Those of us that work with trees generally don’t worry about them.”

Inside the nests, the webworms munch on mature leaves. While not aesthetically pleasing, Cotrone said the critters won’t cause major damage to trees.

“The trees have already stored energy and have set their buds for next year. So for something to come and eat their leaves now, it won’t hurt them. It won’t cause major stress to a healthy plant,” said Cotrone, who covers 18 counties in northeast Pennsylvania.

Webworms feed on almost 90 species of deciduous trees and Cotrone said they’re particularly fond of ash, walnut and hickory trees.

Their nests become noticeable in late summer or early fall.

Because they do little damage, Cotrone’s advice is to let them be.

But those who don’t like seeing the nests in their yards can use a natural bacterium such as Bacillus thuringiensis (Bt) to kill the pests.

“It works great, it’s just too late now,” he said, noting that it’s best applied when the webworms are first spotted in the summer. “They’re done feeding now so it makes no sense.”

When the webbed branches are within reach, they can be pruned and destroyed. People can also spray water onto the nests to knock them to the ground, Cotrone said.

“Again, it is not a health issue or a stressor for the tree,” he said. “My advice is to let it be.”

Folks should be more concerned about spring defoliators, such as the eastern tent caterpillar.

The species acts similar to the webworm but constructs its nests at tree crotches. It, too, eats leaves but does so before trees have a chance to produce food by photosynthesis.

The spongy moth, formerly known as the gypsy moth, is another spring defoliator whose eating habits leave a tree more vulnerable to diseases and other insects.