The venomous creature fell from an overhead bin and landed on Richard Bell's hair as he was eating lunch last Sunday in his business class seat, according to his wife Linda.
"My husband felt something in his hair. He grabbed it out of his hair and it fell onto his dinner table. As he was grabbing it by the tail it stung him," she told CNN.
She said her husband shooed the scorpion off his tray and it landed in the aisle, catching the attention of a nearby passenger who cried, "Oh my god, that's a scorpion."
The Bells were returning home from a vacation.
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Linda Bell said flight attendants quickly corralled the scorpion and flushed it down an airplane toilet.
"Our flight attendants helped a customer who was stung by what appeared to be a scorpion on a flight last week," United said in a statement.
"Our crew immediately consulted with a MedLink physician on the ground who provided guidance throughout the incident and assured our crew that it was not a life-threatening matter," it said.
Linda said United reached out to her husband Wednesday to apologise and to offer compensation for the incident.
The incident came on the same day, a 69-year-old Vietnamese-American was forcibly removed from a flight of United Airlines in Chicago.
David Dao, the doctor who was videotaped being dragged by police officers, has filed an emergency court request for the airline to preserve evidence, signalling that he would fight the case in court.