Joanne Searle was alerted to the unusual lost item while driving in Shipley, near Bradford, at around midday on Saturday.
Barry Cliff, general manager of TLC Travel, told Sky News: “A passenger boarded the bus and shouted from the back, ‘there’s a snake at the back of your bus – stop the bus!’
“The driver – Jo – stopped the bus and the police were called and they came and took it away. It was a 2ft-long corn snake.”
Mr Cliff said he had since heard from the owner of the snake, who said he was taking the reptile to a shop to find out what sex it was.
“When he got to the shop he looked in the box and it was empty,” he continued.
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Mr Cliff added: “We have had false teeth left behind and glasses, phones, wallets and purses, but never a snake.”
West Yorkshire Police described the call-out as “unusual”.