A scorpion stung David Sullivan on the back of his right leg, just below the knee, then continued up that leg and down the other, he believes, before getting him again in the shin.

It wasn't what he was expecting on a flight from Chicago to Vermont.

Sullivan, a 46-year-old builder from Stowe, was aboard the United Airlines flight on the second leg of his Jan. 3 trip home from San Francisco, where he and his wife Helena had been visiting their sons. He awoke from a nap shortly before landing and noticed something strange.

"My right leg felt like it was asleep, but that was isolated to one spot, and it felt like it was being jabbed with a sharp piece of plastic or something."

The second sting came after the plane had landed and the Sullivans were waiting for their bags at the luggage carousel. Sullivan rolled up his cuff to investigate, and the scorpion fell out.

"It felt like a shock, a tingly thing. Someone screamed, 'It's a scorpion,'" Sullivan recalled. Another passenger stepped on the two-inch arachnid, and someone suggested Sullivan seek medical help.

He scooped up the scorpion and headed to the hospital in Burlington. His wife stopped at the United counter and was told the plane they were on had flown from Houston to Chicago. The Sullivans surmised the scorpion boarded in Texas.

"The airlines tell you can't bring water or shampoo on a plane," Helena Sullivan said. But the scorpion did make it aboard, she said.

United spokeswoman Robin Urbanski said the incident "is something that we will investigate and look into. We're very sorry for what happened. Our customer safety and security is our No. 1 priority." She said the airline would offer to reimburse Sullivan's medical expenses.

"We'll probably never know where the scorpion came from," she said. "People come through Chicago from all over the world."

Such incidents are not unheard of. An American Airlines flight was recently delayed for an hour in Toronto after a passenger was stung by a scorpion that had made its way on board. Paramedics treated the man when the flight from Miami landed. The delay came when officials searched the aircraft to ensure no other critters had stowed away.

Scorpion stings are rarely fatal, except to babies or older people with health problems, said Dr. Stephen Leffler, director of emergency services at Burlington's Fletcher Allen Health Care hospital.

"We don't see many scorpion bites in Vermont," Leffler said.

For a healthy adult, a scorpion sting can mean numbness or shooting pain extending out from the sting, or flu-like symptoms, which Sullivan said he had the next day.

He said he hadn't seen the recent movie, "Snakes on a Plane," starring Samuel L. Jackson.

"I'm pretty selective about what I see," Sullivan said. "Maybe I have to see it now."