Doctors in Missouri were baffled to spot a fly inside a man's intestines during a routine colon screening.

Images taken during the colonoscopy and published in the American Journal of Gastroenterology show the intact fly inside the man's colon.

Matthew Bechtold, the chief of Gastroenterology at the University of Missouri, told The Independent that he had prodded the fly and confirmed it was dead.

fly in intestine
Fly found in a routine colonoscopy (N. Sharma et al., American Journal of Gastroenterology, 2023)

The 63-year-old patient told doctors that he had only consumed clear liquids the day before the procedure and had no idea how the fly had gotten into his colon.

He said he had eaten pizza and lettuce for dinner two days before the procedure but did not remember a fly being in his food.

The finding was described as "a very rare colonoscopy finding and mystery on how the intact fly found its way to the transverse colon."

The transverse colon is the "most mobile" and "longest part" of the large intestine. Bech told told The Independent that the fly could have reached it by entering the patient's body through the mouth or rectum.

He said that if the fly entered through the mouth it would likely have been "degraded" by upper digestive enzymes and stomach acid, meaning that wasn't likely.

However, he said it was also unlikely that it entered through the rectum.

"If from the bottom, an opening must have been created long enough for the fly to fly undetected into the colon and somehow make its way to the middle part of the colon with no light in a very curvy, large intestine," he told the outlet.

Insects can enter the digestive tract if food containing insect eggs or larvae is consumed.

This can lead to "intestinal myiasis," where fly larvae feed on a person's dead or living tissue.

The Centers for Disease Control and Prevention said that while some infested patients display no symptoms, others have reported "abdominal pain, vomiting, and diarrhea."

This article was originally published by Business Insider.

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