Flight 1178 from Denver to Des Moines was delayed for nearly six hours on Tuesday after a passenger informed a flight attendant that she found a tick in economy class during a flight from Washington, DC.
The airline decided it couldn't fly the plane until it was cleaned of ticks, so passengers had to wait while another plane was flown from Colorado Springs to Denver. The flight was further delayed because of thunderstorms in the Denver area.
United spokeswoman Robin Urbanski said between one and three ticks were discovered. Urbanski said the airline hasn't figured out how the ticks got on the plane or what type of ticks were found.
The replacement plane shuttled the 107 passengers to Des Moines.
The plane with ticks had begun its day in Chicago. It was cleaned of ticks, checked and put back into service. No ticks were found on passengers.
Ticks are eight-legged parasites that can pass along a number of illnesses to humans, including Lyme disease, which is spread by the deer tick. They are arachnids, a group that also includes spiders and mites.