Whale Tapeworm - The World's Longest Parasite

Tetragonoporus calyptocephalus, formerly known as Polygonoporus giganticus, is a giant tapeworm that lives deep in the intestines of whales.

Many tapeworms reach impressive sizes, but the 40-meter length of T. calyptocephalus makes it the longest parasite on the planet , according to IFL Science . The most common tapeworms that affect humans are found in the tissues of pigs, cows, and salmon. In humans, the longest tapeworms don't approach the size of T. calyptocephalus, but some species still reach impressive lengths.

Whale tapeworms can grow up to 40m long. (Photo: Funnyjunk).

A notable example is at the Meguro Parasitological Museum in Tokyo, which has a 28-foot (8.8-meter) specimen of a fish tapeworm ( Dibothriocephalus nihonkaiensis ) . It is a rare specimen of the giant worm to be removed intact from a human intestine. However, they can grow much larger. According to a 2009 paper, fish tapeworms can range from 6 to 50 feet (2 to 15 meters) in length. The maximum recorded size for this species is 80 feet (25 meters).

Researchers say tapeworms have been living in the intestines for at least 99 million years, thanks to a unique amber fossil described in March 2024. It was the first time any part of their body had been found in fossil form. Previously, all that had been collected were tapeworm eggs from Permian shark feces.

'Fossil records of tapeworms are extremely scarce due to their soft tissue and internal habitat,' said lead researcher Bo Wang from the Nanjing Institute of Geology and Paleontology. 'This limits our understanding of their early evolution.'

Tapeworms are incredibly successful parasites, infecting everything from birds to bears. However, tapeworms are hard to beat in terms of length. They don't start out huge. The head of a T. calyptocephalus worm attaches itself to the whale's intestines, and then it grows longer as new segments appear. The largest individual had 45,000 segments, complete with testicles and ovaries.