Critters that put the creep in creepy crawlers have returned.

However, two state bug experts say people shouldn’t worry about what appears to be a population explosion among fall webworms as evidenced by their unsightly silken nests found in trees around the state.

“For some reason, they’re really bad this year. They’re definitely heavier and locally abundant,” said Don Ouellette late last week of the native tree-defoliating insects.

“But the good news is, they’re not a serious pest because the damage they do occurs late in the season,” said Ouellette, a forest entomologist with the Maine Forest Service’s Insects and Disease Lab in Augusta.

Likewise, Clay Kirby, an insect diagnostician with the University of Maine Cooperative Extension’s Pest Management Office in Orono, said he also tells people not to get too anxious about the yellowish, inch-long hairy caterpillars.

“The biggest problem people have with them is aesthetics,” Kirby said of their loosely constructed nests, which can totally disrupt the appearance of a well-manicured yard.

The caterpillars are essentially harmless to most people, but some folks with sensitive skin could develop a rash-like reaction by brushing against the crawlers. Both bug experts advised anyone sensitive to webworms to avoid them.

Affected trees won’t experience long-term effects from fall webworms, but, if the pests return to the same area for a few consecutive years, Kirby said some branches might die.

Fall webworms feed on more than 85 species of trees, including ornamentals, apple, cherry, ash, willow, oak, birch, elm, and other deciduous species.

According to the Maine Forest Service Web site, fall webworm caterpillars, or larvae, hatch within two weeks after adult snow-white moths deposit their eggs in late June or early July on the undersides of leaves.

The caterpillars spin silky nests capable of engulfing a branch. By August and September, the webs get very large and can join together, Ouellette said.

Examples can be seen along Route 4 in Livermore and in the Augusta area, where nests have enshrouded small trees.

A nest or colony can have several hundred writhing worms inside, munching leaves as early as late July.

“Little trees, I’ve seen totally enveloped with nests. It looks like something from a Stephen King novel. It’s not unusual for a small tree to be stripped of leaves in a couple of weeks. I’ve seen that. It’s quite impressive,” Kirby said.

Ouellette agreed.

“I’ve seen some trees recently on I-295 heading south between Richmond and Augusta that look like they’ve been stripped. I’ve never really seen badly infested trees like I’ve seen this year,” he said.

Exploding populations are kept in check by predators, parasites and diseases, Kirby said.

Still, if people want to rid their trees of the nuisances, both entomologists said don’t torch the nests, because it damages the trees.

Instead, Ouellette said he uses a stick to gather the webbing, drawing most of the caterpillars to the ground. He then puts them in a sudsy solution, steps on them or feeds the worms to his chickens.

“You can remove them by hand early, but you have to be persistent,” Ouellette said.

Kirby recommended using a microbial product, Bacillus thuringiensis, or Bt for short, if people seek an organic approach.

“It’s most effective when the caterpillar is small,” he said.

Pole pruners can also be used to disrupt the nests. Kirby recommended early monitoring from mid June on, to nip the nests when they’re small.

By early fall, killing frosts arrive and the worms disappear, spending the winter as pupa in leaf litter and soil then emerging in the summer as small white moths, Ouellette said.

“The most troublesome pests we have are the introduced species like the gypsy moth,” he added.

But fall webworms are one of the few American insect pests that have been introduced into Europe and Asia, Kirby said.

“I guess that’s retaliation for the Japanese beetle,” he added, laughing.