When we think of the largest animal in the world, our mind immediately goes to the majestic blue whalethe giant of the seas. In reality, the real length record holder is a much less glamorous organism: a parasite that lives in the intestines of whales.
It’s about the Tetragonoporus calyptocephalusa tapeworm belonging to the Cestode class, a group of flatworms that infect all vertebrates. This tapeworm can reach the extraordinary length of 40 metersfar exceeding the size of its host.
A giant among giants
The Tetragonoporus calyptocephalus lives mainly in the intestines of whales and sperm whalesincluding the blue whale, the largest animal that ever existed. It prefers arctic waters, where its favorite guest is the sperm whale, the largest toothed animal in the world.
Inside these giants of the sea, the tapeworm reproduces and releases its larvae with the host’s feces, thus continuing its life cycle. But the whale tapeworm is not the only giant of its kind. Many species of tapeworms reach impressive sizes, especially those that infest the tissues of pigs, cows and salmon. For this reason it is essential to cook meat correctly, to prevent these giant worms from finding a home in our intestines.
An evolutionary history spanning 100 million years
The presence of tapeworms on our planet is much older than previously thought. In March 2024, a study published in the journal Geology documented the discovery of a tapeworm tentacle in amber dating back to the Cretaceousabout 100 million years ago.
Since then, tapeworms have continued to thrive and diversify, colonizing all ecosystems. Today they are among the most widespread parasites, infesting a wide variety of animals, including humans.
Human parasites
Humans can also be victims of these intestinal parasites. An impressive example is preserved at Meguro Parasitological Museum in Tokyowhere an example of Dibothriocephalus nihonkaiensis 8.8 meters long, extracted intact from the intestine of a man in the 1980s. There are documented cases of even longer tapeworms, reaching 25 meters!
Contagion in humans occurs mainly through the consumption of raw or undercooked meat contaminated by the adult parasite or its larvae. Among the most common human parasites we find the Taenia soliumknown as “tapeworm”, which is contracted by eating infested pork. Anisakis, a nematode worm that lives in the stomachs of marine mammals and crustaceans, can also infect humans.
A world of parasites
Parasites are a critical component of ocean ecosystems. From jellyfish to coral, from fish to whales, every marine creature has its parasites. They play an important role in the population control and in maintenance of ecological balance.
Some parasites have developed ingenious ways to survive. For example, the tongue-eating isopod attaches itself to the host fish’s tongue and replaces it, feeding on its blood. The barnacle Sacculina, however, infects crabs and manipulates their behavior to its advantage.
