Intruders got into Donna Howry's swimming pool, thousands upon thousands of them.
They crept through a fence along the three-acre lot north of Empire and made their way toward the house and the fruit trees.
Howry couldn't figure out why these inchlong creatures, which appeared to be some kind of caterpillar, infested her yard last Friday through Wednesday.
She could only scoop them from the pool and pour laundry detergent along the fence in an attempt to keep them at bay.
"This has been a nightmare, an absolute nightmare," Howry said Wednesday morning at the Church Street house. "They're crawling everywhere."
Just as mysteriously, the plague diminished Wednesday night and was mostly gone Thursday morning.
"I guess maybe they just went through their little cycle," Howry said.
So what was it?
"It is a yellow-striped armyworm," said Gary Caseri, agricultural commissioner for Stanislaus County, after The Bee e-mailed him close-up photos of the pest. "Quite common and sometimes can result in severe outbreaks."
The armyworm in its larval caterpillar form can infest alfalfa fields, which are common in the county because of its many dairy farms. Caseri said the economic losses are not large compared with other pests his office monitors.
He urged residents facing armyworm outbreaks to look in stores for pesticides designed for this pest. He also said the University of California Cooperative Extension has information on control measures.
Howry, who lives at the home with her husband, Marlen, said a residential pest-control company could not identify the caterpillar nor guarantee a permanent solution.
She said the owner of the alfalfa field is willing to spray it once the latest cutting of the crop is picked up.
The pest appeared en masse for about an hour twice a day, first about 8:30 a.m., then about 7 p.m.
"We see them migrating across the cement," said Shannon McCleary of Salida, the couple's daughter. "They're all headed in one direction. It's just bizarre."
She visited Wednesday morning with son Douglas, 8, and daughter Jaycie, 7. They helped pour liquid Tide, which they stirred into suds that trapped and killed the armyworms.
Donna Howry shoveled up the tiny, soggy corpses.
"They stink," she said. "I know Tide makes things smell good, but not them."
Douglas likes to study bugs but was as confounded as his grandmother by this species.
"I've never seen one of these in my book, never," he said as a caterpillar creepy-crawled along his finger.
The pest started to damage the Howrys' tomato plants, grapevines and fruit trees. They have stayed out of the house.
Howry said she plans to keep watch to make sure the pest really is gone. Six days of battling the masses of bugs was enough.
"It's ridiculous," Howry said Wednesday. "We're supposed to be camping right now."
Bee staff writer John Holland can be reached at 578-2385 or firstname.lastname@example.org.