The 7 longest and largest worms in the world

*Overview of the best according to the editors. About selection criteria. This material is subjective, not an advertisement and is not a guide to purchase. You should consult a specialist before buying.

Worms are usually not exactly the “critters” that one admires. There is something repulsive in them, because of what when you meet such a “creeping thing” you want to go home as soon as possible and wash the whole body with a hard washcloth. And if a worm turns out to be very long, slimy and simply unsympathetic, this desire increases many times over.

At the same time, earthworms common in the middle belt of Russia, even the longest and largest are tiny compared to some especially large species. As a rule, these creatures in “our latitudes” grow to 20-30 centimeters – and something always obstructs their normal development. It’s birds, it’s shovels, it’s fishermen. If left unattended and placed in nutrient-rich soils, they can grow to quite impressive sizes.

And how large these invertebrates can be, we will tell you in this material. We’ve rounded up seven of the world’s longest and largest worms! The ranking includes representatives of all three major families, so particularly impressionable readers who are not prepared to get acquainted with the multi-meter-long parasites in the intestines of mammals had better put aside their prepared sandwiches.

An overview of the longest and largest worms in the world

Ranking of the longest and largest worms in the world1The planarian Rimacephalus arecepta1 meter
2Australian giant earthworms30 meter
3Eunice aphroditois6 meters long

lacentonema gigantissima

8.5 meters
5Bovine tapeworm, aka solitaire10 meters
6Broad tapeworm15 meters
  • neus longissimus
  • 60 meters

    7th place: Rimacephalus planaria (Baikal, Russia, up to 1 m)

    Rating: 4.4

    Planarians are one of the simplest flatworms found all over the world. They live in water bodies; they can be found in oceans, seas and even freshwater rivers. Most of them are not very big, about 2-3 centimeters, but the species Rimacephalus arecepta living in Baikal can grow up to 1 meter long!

    Planaria are one of the simplest multicellular. In fact, they are a “crawling stomach”, like sea cucumbers. The mouth opening of these worms is on the belly – and while moving along the lake bed they scrape up even smaller invertebrates. And if the planaria wants to gobble up something bigger – it just extends its throat out of its body and grabs it. The worm’s digestive system is incredibly “advanced” and has its own nerves and muscles. If removed from the animal it will still work for a while and even try to catch its prey.

    Interestingly, the planaria Rimacephalus arecepta, like other members of the species, are hermaphroditic, but require sexual reproduction. So, each worm can be either a male or a female, depending on the situation.

    To move, planarians use special cilia that dot their entire body. Therefore, a worm can both swim freely and crawl on the lake bed. Thanks to its visual organs, the animal is able to determine the top and them, measuring them by the level of light and sense of balance.

    Planaria Rimacephalus arecepta isn’t of interest for the Baikal fish, because this animal is covered by poisonous glands. This is why worms quietly develop to a relatively large size.

    6th place: Australian giant earthworms (Australia, up to 3 meters)

    Rating: 4.5

    Australian giant earthworms

    The Australian giant earthworms are a subspecies of ordinary earthworms, but, as their name implies, they live in Australia. There they calmly grow to an impressive size – on average they are 80 centimeters long, but the maximum recorded size is 3 meters.

    Australian giant earthworms differ from “our” earthworms also in their very noisy behavior. As they move through complex, intricate underground passages, they make noisy noises that resemble clucking or gurgling. It’s from these signals that researchers find these creatures. However, due to the fact that the species is considered vulnerable and is found mainly in Victoria, it is difficult to study it.

    The vulnerability of the species’ position is also stimulated by changes in natural habitat conditions. These giant earthworms prefer to settle on the clay shores of reservoirs in the roots of eucalyptus trees. The soil in these areas contains enough organic and nutrients for the development of invertebrates. Except that in recent years, logging of eucalyptus forests in Victoria has resulted in the species’ natural habitat being destroyed.

    Australia’s giant earthworms simply don’t have time to adapt to changes in habitat. This is because they have one of the slowest ontogenesis (“maturation periods”) of any invertebrate. Sexual maturity in these creatures reaches the 5th year. In general, the worm belongs to the number of long-livers, but even approximate lifespan is not possible to establish because of the endemicity of the species.

    Rank 5: Eunice aphroditois (world ocean, up to 6 meters)

    Rating: 4.6

    Eunice aphroditois

    Eunice aphroditois, one of the largest polychaete worms in the world’s oceans. This predatory and, frankly speaking, rather unsympathetic animal (first of all because of its mouth apparatus) can grow up to 6 meters long! True, the vast majority of specimens seem to be shorter, but that’s not very reassuring.

    Of particular interest is the way this polychaete worm hunts (and lives at the same time). Eunice aphroditois digs deep burrows, where it is placed almost entirely. Only the head of the invertebrate protrudes above the bottom surface. When a fish swims by, the worm suddenly straightens up, grabs it with its hook-like jaws and begins its meal. Eunice aphroditois can wait for a suitable meal for a very long time – studies show that the creature can live without food for a year!

    However, Eunice aphroditois is not fussy about food. If the fish do not swim by – it may well feed on detritus: organic remains of flora and fauna, which “snow” sink to the seabed and are actually a mixture of decomposed corpses of aquatic animals, as well as the remains of the dinners of predators swimming near the surface.

    Like many other polychaete ringworms, Eunice aphroditois has a rather interesting internal structure. Each of its body segments has its own redundant set of organs. Therefore, if for some reason the animal loses a piece of its body – even half of it – it will still survive.

    4th place: Placentonema gigantissima (world ocean, up to 8.5 meters)

    Rating: 4.7

    And here are the parasitic worms. While previous species in this ranking can easily survive in the wild – in clay soils of Australia, on the fresh bottom of the Baikal, or in the salty waters of virtually the entire ocean – Placentonema gigantissima lives only in the internal organs of whales. And these helminthes infect not only the intestines and liver. Studies have shown that Placentonema gigantissima can develop even in the placenta.

    Parasitizing on whales (in particular sperm whales are particularly fond of this species) Placentonema gigantissima can grow to a truly gigantic size, which is reflected in its name. For example, the largest recorded specimen was 8.5 meters long!

    Lacentonema gigantissima belongs to the “roundworm” type, aka “nematodes”. Almost all species of this group are parasitic. They infect mammals, insects and even other invertebrates. In humans nematodes cause trichinellosis, ascariasis and a large number of other diseases. Plant parasites are also found among these ringworms.

    So roundworms are one of the largest groups of parasitic invertebrates on the planet. So it’s no surprise that they’ve reached cetacean mammals.

    Among the roundworms Placentonema gigantissima has an unsegmented body. So they can’t just break up or split apart without mortal danger to existence. Unlike the next parasite in the ranking, which also develops in the human body.

    in third place: Bovine chain, aka solitary (worldwide, up to 10 meters)

    Rating: 4.8

    The bullworm, aka the solitaire

    Bovine tapeworm (solitaire) is one of the most dangerous parasites of humans and cattle. Most common in Africa, South America, and some Eastern European countries. If they are not eliminated, they can grow to up to 10 meters in length, greatly exceeding the linear dimension of the host.

    Like many other parasites, the bullworm goes through three stages of development. The first is an egg. They are excreted from the host organism with the feces and remain on the grass. These plants are then eaten by cattle, primarily cows (which is why the invertebrate got its name). In these mammals, tapeworm passes through the larval stage.

    Larvae remain in the muscle of the animal. This is why eating uncooked steaks from meat of unknown origin is quite dangerous. Together with the muscle, the tapeworm enters the body of the final host – humans. Here it enters the tapeworm stage, beginning to grow and develop.

    In the human body, the bullworm grows to a considerable size. The body of an adult tapeworm consists of 2,000 to 5,000 segments. The solitaire is capable of living for up to 20 years! The adult parasite has an average length of 4 to 10 meters.

    Like many tapeworms, bullflies, though they need to reproduce asexually, are hermaphroditic. Individual segments can fertilize each other. This is why the worm is able to produce up to 600 million eggs annually.

    The disease caused by the solitary worm is called teniarethiasis. It is characterized by cramping-like abdominal pain due to the mobility of the worm, an increase in appetite, as well as a depressing effect on the host’s psyche.

    2nd place: Broad tapeworm (worldwide, up to 15 meters)

    Rating: 4.9

    Broad tapeworm

    The broad tapeworm is another tapeworm that is a human parasite. It enters the body with poorly cooked fish, thus determining the danger of eating poorly cooked seafood (including sushi and other Japanese dishes). After entering humans, the tapeworm attaches itself to the small intestine where it begins to develop, reaching a maximum length of 15 meters. Although, however, most specimens are two to three times shorter. But this is not very reassuring for the hosts.

    The tapeworm has a long and multistage life cycle. The worm eggs, as in the case of the bovine chain, enter the water with the feces from the host organism. In the liquid they turn into a larva coracidium. It swims freely in the water until it meets its first host.

    The first host is the tiny paddlefish. In them, the procercoid larva is based in the body cavities and calmly waits for the arthropod to be eaten by the fish. This is how the worm enters the second host. In fish, it develops into a plerocercoid larva that becomes embedded in muscle tissue.

    The plerocercoid larva enters the human body from badly treated fish. Here it is fixed in the small intestine, where it begins to develop into an adult worm.

    The disease caused by the broad tapeworm is called diphyllobothriosis. It is widespread even within the Russian Federation, but is primarily localized in the basins of various rivers – the Volga, Yenisei, Ob and so on. Also found in Murmansk and Leningrad Regions. The worm can live in humans for up to 20 years.

    Infestation leads to discomfort, abdominal pain, nausea and vomiting, loss of appetite, weakness, drowsiness. The worm also affects the neuro-psychological system. For example, it does not like spicy and salty foods – and therefore, if the host person eats such dishes, he or she will experience unpleasant sensations.

    1st place:
  • neus longissimus (Northern Europe, up to 60 meters)
  • Rating: 5.0

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