Fall web worms thriving after mild winter

SANGERVILLE – Examine a deciduous tree this fall, and chances are you’ll find more than one icky-looking web that could serve as a backdrop for a horror movie.

While they appear downright unsightly, those thick, grayish silk webs that stretch from one branch to another, and the caterpillars that weave them, do little damage to most of the trees they frequent, according to Jim Dill, the University of Maine Cooperative Extension pest management specialist.

The fall web worm has been so abundant this year – likely because of the mild winter – that Cooperative Extension has fielded more calls than usual from homeowners wanting advice on how to eradicate the pest, Dill noted this week.

“There seems to be lot more around this year, and we’ve gotten a lot more calls,” Dill said. In a normal year, there are one or two webs in a clump of trees, but this year there are a lot more than usual, he said.

The webs, which first appear in late July or early August, are spun by the fall web worm caterpillars to encase their colonies of larvae as well as foliage on which to feed. Females can lay as many as 1,000 eggs on the foliage of host trees. The larger the larvae grow, the larger the web becomes.

The fall web worm should not be confused with the eastern tent caterpillar, whose web appears in early spring. Wintering as a pupa under debris on the ground, the fall web worm emerges the following summer as a snow-white moth, known by old-timers as a “miller,” Dill said. The moth then lays its eggs, typically beneath leaves, which are later encased in webs.

In Maine, the native fall web worm produces one generation, but in southern states, there can be up to four generations a year, according to Dill. The fact that some of the webs this year have been spun on the tops of trees has nothing to do with any weather prediction, he noted.

Common throughout the United States and southern Canada, the fall web worm typically is not a serious threat to most trees. They are of concern to property owners, however, when they infest ornamental or fruit trees.

For the second consecutive year, organic apple grower Leigh Wiley of Sangerville has tangled with the creepy, thick webs. His trees off Route 23 are dotted with the webs despite his efforts to keep them pest-free the natural way.

“They seem to have gotten worse in the last couple of years,” Wiley said Tuesday. “You’re looking at an economic threshold.”

He said that as an organic farmer, he has to determine if there is enough damage to hurt the tree or to hurt him economically. The caterpillars reduce the leaf cover, which weakens the tree’s ability to produce food for itself, a process called photosynthesis, he said.

Typically, when he sees the small webs in July, Wiley eliminates them by knocking them down, but a few more than anticipated escaped his inspection this year.

The grower said, however, that he didn’t think this year’s crop had been affected by the fall web worm. The wet spring has had a more serious impact, he said.

For this year, the fall web worms have “pretty well run their course,” Dill said. For those homeowners who dislike the webs, a long stick with a nail sticking out of the end is the tool of choice, Dill said. After poking the nail into a web, a homeowner can twist the stick and the webs will stick to the pole, he said. He does not recommend burning the web, as it may be harmful to the tree.

Where webs have been established this fall, homeowners should carefully inspect those trees in late July or early August for little webs and small caterpillars, Dill said. That is the easiest time to rid the tree of the pests by removing the webs, he said.