TWIN FALLS, Idaho (AP) - Chinch bugs likely numbering into the billions have invaded south-central Idaho as they seek out weeds to eat.

They're covering homes in the Twin Falls area, and though University of Idaho bug experts say the tiny false chinch is harmless, residents are still grossed out.

"There was so many of them that the ground looked like it was moving," said Gordon Greaves, whose home was inundated starting Friday.

His wife, Kerma, waged war inside with her vacuum cleaner.

"They just kept coming," she said. "There must be millions of them."

Kelly Tindall, a University of Idaho entomologist, says there's a good explanation for the chinch bug invasion: A wet spring produced lots of weeds of the mustard family, and chinch bugs love to eat them, she said. As they migrate toward their meals, they cover everything: fence posts, lawns, Gordon Greaves' driveway, his shoes.

"The calls started coming in last Friday," Tindall said. "Ive been getting five or more calls a day."

The chinch bugs marching through Twin Falls are wingless, immature creatures. They range from pinhead size to about an eighth of an inch.

The extension service in Maricopa County, Arizona says once they reach such large numbers, about the only thing homeowners can do is seal off their doors and try to keep them outside.

The bugs will move away in a short time, according to a posting on the agency's Web site.

When crops or fields with weeds are cut, the bugs go searching for another food source, often running across homes, lawns and trees in their path like some Biblical scourge - with all the creepiness but fortunately without the Old-Testament-style destruction.

"They do have piercing-sucking mouth parts, but are harmless to humans and animals," Tindall said. "There can be millions or billions of the bugs when they are migrating looking for food."

Greaves says he's lived in Twin Falls for more than three decades and has never seen anything like the infestation that emerged last week.

"I had the whole day planned for something else," he said, standing in his yard Saturday with a garden hose and piles of dead chinch bugs around him. "I don't like to use spraying, but I didn't have a choice. I even used a weedburner around my driveway."