Paul W. Alfke, 82, first detected sinister-looking black-shelled bugs about two weeks ago crawling up and down cedar trees in the backyard of his Black River home. But now boxelder bugs cover the entire southern side of his house, where the sun shines the most. He can’t seem to get rid of them.

“There’s nothing you can really do,” he said of the bugs with red and orange stripes that are attracted to buildings exposed to the sun. “I’ve sprayed them off the side of the house with a hose, but they just come back.”

Though he’s lived in the house since 1973, he said, “This is the first time I’ve ever seen them. There’s now close to a thousand of them on the side of the house.”

Educators say Mr. Alfke’s story is not a rarity this fall among homeowners in Jefferson, Lewis and St. Lawrence counties. He’s one of about 500 residents who have called Cornell Cooperative Extension of Jefferson County during the past three weeks after spotting the uncommon bug, said horticulture educator Susan J. Gwise.

“People want to know what the heck they are,” she said Thursday morning after fielding a handful of calls from residents. “They say they don’t want to go out the front door because they’re all over.”

Unnerved residents who call her usually calm down, though, when they learn the harmless bugs can’t damage their homes, Mrs. Gwise said. During the late summer, the bugs gravitate to female boxelder trees that produce wing-shaped seeds, but they cause only marginal feeding injury. As the temperatures drop in the fall, they flock to homes to seek warmth and shelter during the winter by crawling through cracks and crevices.

Mrs. Guise attributed the barnstorm of bugs to the hot, dry summer in which temperatures consistently hovered above 90 degrees. The mild winter that led up to the summer also contributed.

“It’s been like a perfect storm,” she said. “More eggs were laid during the mild winter, and the hot, dry summer has sped up their life cycle to create a huge storm of bugs.”

While a frost this fall would kill outdoor bug populations instantly, Mrs. Gwise said, Watertown’s long-term weather forecast shows temperatures aren’t expected to dip below 40 degrees. In other words, she said, the invasion could have time to balloon further “unless something changes drastically.”

Black River resident Patricia M. Walton, though, isn’t waiting until the frost destroys the population of bugs crawling along the perimeter of her home.

“The front of my house was covered with them yesterday,” she said, “but I sprayed the whole front with Raid and they’re all dead right now.”

Her suspicion is that there’s still a population of bugs lurking inside the crevices at the front brick wall of her house exposed to the sun.

“I’ve lived 60 years in the same house and had never seen these bugs before,” she said, adding she was alarmed before learning they are harmless.

Like Mrs. Walton, most residents are surprised when they see the bugs, which haven’t been this widespread for decades, said Joseph R. Lawrence, educator for Cornell Cooperative Extension of Lewis County.

“It’s definitely in high populations in Lewis County, and I’ve had some questions from people here,” he said. “Most residents are afraid they could be a nuisance, but if some do get inside they can’t cause any harm and you can suck them up with a vacuum cleaner.”

To eradicate boxelder bugs, homeowners can try the following:

■ If found inside, suck them up with a vacuum and dispose of the bag.

■ Spray infected areas with outdoor insecticides as a targeted perimeter treatment.

■ Spray insects off the sides of buildings with a water hose as a temporary solution.

■ In extreme cases, remove female boxelder trees in the yard. These trees can be identified by their seeds shaped like wings.

For more information, contact Mrs. Gwise from Jefferson County’s extension office at 788-8450, ext. 243, or at sjg42@cornell.edu.

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