Biologist warns of tent caterpillar-like tree pest

Sarah Eames | The Daily Star A fall web worm nest is shown Wednesday, Sept. 2, on a Franklin Mountain tree on state Route 28.

Those who have noticed the web-like insect nests popping up in local tree branches may think it is the wrong season for tent caterpillars.

That thought would be correct, according to Hartwick College biology professor Allen Crooker. The silken dwellings are actually home to a different species of insect, commonly known as the fall webworm.

“The fall webworm kind of crops up at this time of year, late summer to early fall,” Crooker said. “After developing for about six weeks from July on, they pupate and start their cycle again next spring.”

Crooker, who has been at Hartwick for more than two decades and lists entomology among his specialties, said that a keen eye can differentiate between the nests, even without knowing what season it is.

“Tent caterpillars, the tents are smaller and confined to the crotches of trees more than the fall webworms. The caterpillars stay in the nest except to eat, but then they’ll make their way out,” Crooker said. “These guys (webworms) show up in the fall and make a messy-looking nest that usually covers a larger area. They do most of their feeding in the nest.”

Crooker went so far as to describe the webworm nests as “obnoxious,” and said that they can cover as much as a whole tree branch.

The webworms may appear at a more inopportune time than the caterpillars, at least for humans hoping to see flawless fall foliage. But Crooker said the level of damage to the trees is similar between the worms and the caterpillars.

The state Department of Environmental Conservation said it takes about three years of heavy defoliation to kill a tree. Crooker echoed that approximation.

“The hazards are not a lot different. They aren’t great to a tree for either one,” he said. “Repeated nests in the same tree for two or three years could cause some problems for the tree, but usually there isn’t real damage to the tree. They don’t cause much of a problem unless they are persistent on the same tree for two or three years.”

He said that he hadn’t noticed a larger population of webworms this summer, but also said that it is a species prone to variations in prevalence year to year.

Jared Bomba, staff writer, can be reached at or 607-441-7229.

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