The brown bugs, which passengers described as looking similar to cockroaches, reportedly began to fall from overhead lockers while the plane was getting ready for take-off at London's Gatwick Airport.
Alarmed passengers took to Twitter to share videos and complain to airline Air Transat as the flight was delayed while the plane was sprayed.
Passenger Jenna Sullivan told the Daily Mail the critters were 'disgusting.'
'A bug just fell down between my seat and the man next to me,' she said.
Jenna added that when another fell into someone's lap, a flight attendant told him to kill it.
Travellers were stuck on the tarmac until the airline decided to delay the flight by 24 hours to allow the plane to be fumigated.
In a statement, Air Transat apologised for the delay.
The airline said: 'The safety and comfort of our passengers is of paramount importance, and we are sorry for the delay to our flight to Vancouver which was due to the need to fumigate the aircraft.'
'Passengers were provided with hotel accommodation and meals, and we regret any inconvenience caused by the delay to their journey.'