Were you to find yourself holding the tail-end of a certain parasite that infects whales, you could be pulling for 40 meters (131 feet) before you got the disgusting thing out. That’s the eye-watering standard set by Tetragonoporus calyptocephalus, previously known as Polygonoporus giganticus, a giant tapeworm that lives deep inside the guts of whales.
Many tapeworm species reach impressive sizes, but the host size of T. calyptocephalus means they likely represent some of the longest parasites on the planet. The most common tapeworms affecting humans are those that end up in the tissues of pigs, cows, and salmon, which is why everyone is so hot on cooking your food properly unless you want to let a giant worm live rent-free in your intestine.
In humans, the longest tapeworms aren’t quite reaching the dizzying lengths of T. calyptocephalus, but there are still some grisly stats that will have you clutching your abdomen.
One shining example hangs in the Meguro Parasitological Museum in Tokyo, where an 8.8-meter (28.9 feet) Dibothriocephalus nihonkaiensis specimen is on display as a rare example of a giant tapeworm that was removed intact from a human intestine. They can get much bigger, however, with a 2009 paper stating that between 2 to 15 meters (6.6 to 49.2 feet) is the typical range, but maximums of around 25 meters (82 feet) have been recorded for this species.
We know that tapeworms have been upsetting stomachs for at least 99 million years, thanks to a rather unique amber fossil that researchers described in March 2024. It marked the first time we’ve found the partial body of one of these parasites in fossil form – previously, all we had was some eggs from Permian shark poop – and it makes sense when you consider their noodly way of life.
“The fossil record of tapeworms is extremely sparse due to their soft tissues and endoparasitic habitats,” said Bo Wang, the lead researcher of a study describing the latest discovery, said in a statement, “which greatly hampers our understanding of their early evolution.”
From whatever prehistoric beast this fossil parasite fell out of, the tapeworm has gone on to be a highly successful parasite with species infecting everything from birds to bears, the latter of which can often be seen marching around with its parasites hanging out for all to see. Impressive, but when it comes to length alone, the whale tapeworm is hard to beat.
T. calyptocephalus doesn’t start out so giant. The head end, known as the scolex, fixes to the whale’s gut and then the worm grows longer and longer as new segments called proglottids emerge. The largest can have as many as 45,000 segments equipped with both testes and ovaries, so they have everything they need to make more eggs even if there aren’t any other worms. That’s right, they’re one a one-worm factory for some of the world’s largest parasites.
Be thankful you live in a time of anthelmintic drugs.
