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Like all parasites that can reside within humans, tapeworms likely trigger a sense of revulsion. However, they are also incredibly intriguing. With their specialized adaptations and unique protection, these parasites inhabit a variety of creatures, including us. Here are some key facts about these ancient beings.
1. TAPES WORMS ARE MORE THAN JUST SIMPLE WORMS.
Humans often label any long, slender creature a 'worm.' For instance, there’s a legless lizard known as the slow worm. Similarly, inchworms are actually the caterpillars of moths—they even have legs. Tapeworms earned their name due to their long, flat, tape-like shape.
But if you examine a tapeworm closely (yikes), you’ll discover that they are exceptional parasitic specialists, only remotely related to the common earthworms in your garden. For example …
2. THEIR HEADS FEATURE SUCTION CUPS AND HOOKS.
Head of a Taenia solium, or pork tapeworm. Image credit: Rjgalindo via Wikipedia // CC BY-SA 3.0
Adult tapeworms reside in the intestines of animals—and it's not an easy place to live. For one, it’s constantly subjected to muscular contractions that push digestive material and waste through. Tapeworms have to cling on tightly.
To achieve this, they’ve developed specialized 'heads' equipped with a variety of attachment mechanisms. Some have spines or retractable hooks, while others feature circular suckers or grooves that act like suction cups. Many tapeworms use a combination of these tools. Regardless of the specific mechanisms, the goal is the same: to secure themselves to the intestinal wall, allowing their body to dangle freely and absorb nutrients. Delicious!
3. THEY HAVE THEIR STOMACH ON THE OUTSIDE.
Tapeworms lack their own digestive system. Instead, they rely on their specialized outer surface to absorb nutrients and eliminate waste. And they do this quite effectively.
Your small intestine has finger-like projections called villi, which expand the intestinal surface area, providing more space for food absorption. Similarly, tapeworms are coated in tiny villus-like projections that help them absorb whatever their host consumes.
4. MUCH OF THEIR BODY IS DEDICATED TO PRODUCING BABY TAPEWORMS.
Beyond the 'head' and a sort of 'neck,' a tapeworm’s body consists of a series of segments, each containing both male and female reproductive organs. As the tapeworm forms new segments near the head, older ones move down the body, eventually maturing to produce eggs. The host then excretes either the eggs or segments filled with eggs … and that’s when things get interesting.
5. TAPEWORMS TYPICALLY REQUIRE MORE THAN ONE HOST.
Tapeworm in a human appendix. Wikimedia Commons // Public Domain
These newly born tapeworms are about to embark on a remarkable cross-species journey. Most tapeworms spend their life in two or three different animal hosts. The first host becomes infected by ingesting eggs from the environment, and subsequent hosts become infected by… consuming the earlier hosts. Tapeworms only reach their full adult form—and reproductive capability—in their final animal host.
6. YOUR FAVORITE ANIMAL CAN GET TAPEWORMS.
Humans are not the only creatures that can host tapeworms—not by a long shot. These parasites are found throughout much of the animal kingdom. Dogs and cats can carry them. Birds can too. Fish are susceptible to tapeworms, as are hyenas, antelopes, moose, wolves, insects like beetles and ants… and the list continues.
7. TAPEWORMS CAN GROW TO IMMENSE SIZES.
Adult Taenia saginata tapeworm. Wikimedia Commons // Public Domain
Larger animals have bigger intestines—and consequently, larger tapeworms. Whales get tapeworms, and these massive parasites can grow to lengths of 100 feet or more. That’s more than double the size of the longest giant squid ever found.
8. THEY’RE INCREDIBLY ANCIENT.
Tapeworms are not just widespread—they’ve been around for an astonishingly long time. In 2013, Brazilian scientists revealed the discovery of tapeworm eggs in fossilized excrement from a 270-million-year-old shark. To put it into perspective, that’s many millions of years before the first dinosaurs roamed the Earth.
9. THEY'VE TRAVELED TO UNEXPECTED PLACES.
As Carl Zimmer writes in his book Parasite Rex, there is a rare group of tapeworms that live in marsupials in both Bolivia and… Australia. How did these parasites end up in such distant locations without a plane ride?
The answer lies in continental drift. Ages ago, South America and Australia were once connected, and an ancient marsupial—along with its tapeworm—traveled across the shared land. When the continents drifted apart, the marsupial populations followed suit, and the tapeworms went along for the journey.
10. THEY CAN CONTROL THEIR HOSTS.
A kingfisher holding a stickleback fish. Image credit: Getty Images
Tapeworms depend on their first host being eaten. However, some of them don’t just wait idly for their moment (and for their host’s misfortune).
For instance, one tapeworm species requires three hosts during its life cycle: first a crustacean, then a stickleback fish, and finally a bird. While inside the fish, the tapeworm encourages its host to move towards warmer waters, which are ideal for tapeworm growth. Infected sticklebacks grow larger and become sluggish, making them easy prey for birds.
Another tapeworm species exerts similar influence on ants, making them less inclined to flee when a hungry bird swoops down. It also causes the ants to turn yellow for reasons that remain unclear—but likely not for purely cosmetic purposes.
11. IF YOU HAD A TAPEWORM, YOU MIGHT NOT FEEL ILL.
Humans typically acquire these parasites by consuming raw or undercooked meat, such as beef, pork, or fish. While some people with tapeworm infections may feel weak or nauseous, or suffer from anemia or a vitamin B-12 deficiency, most of the time, those infected feel no different. Often, the only noticeable sign is the presence of those unpleasant yet harmless tapeworm segments in their stool.
As a quick note: while anyone can contract these and other tapeworm infections, they are unfortunately far more common in developing countries and in underserved areas with inadequate sanitation systems.
12. HOWEVER, SOME INFECTIONS CAN CAUSE SIGNIFICANT ISSUES.
Now, here’s where things get seriously unpleasant. Poor sanitation can lead to the ingestion of tapeworm eggs that were expelled by another individual. The larvae hatch and begin to travel through the body, seeking a safe place to reside. They can attach to muscles, brain tissue (where they cause seizures), and other organs, resulting in an infection called Cysticercosis. While this is relatively rare in the U.S., the CDC has classified it as one of five neglected parasitic infections, which are diseases that need more focus.
13. THERE WAS AN INSTANCE WHERE A TAPEWORM CAUSED CANCER.
Adult Hymenolepis nana tapeworms. Georgia Division of Public Health via Wikimedia // Public Domain
In 2013, a 41-year-old man from Colombia went to the doctor, where tests revealed that he had numerous cancerous tumors. However, a closer inspection uncovered something unusual: the cancerous cells were too small to be human. It turned out that this man also had a tapeworm infection—and those cells were from his tapeworm. Yes, a tapeworm caused his cancer.
There’s no reason to be concerned that something like this will happen to you. This was an extraordinary, and extremely rare, event.
14. NO, YOU CAN’T LURE A TAPEWORM OUT WITH MILK.
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A long-standing myth claims that placing a bowl of warm milk near an infected person will cause the tapeworm to crawl out. While this may attract some curious stray kittens, it won’t work on a tapeworm.
Here’s the reality: adult tapeworms live in your intestines. To make it to the mouth, they'd need to navigate a long, winding digestive system, squeeze through a sphincter, crawl up into the stomach, and climb the towering esophagus. And they’d need to sniff out the milk through all that mess of guts. Tapeworms are perfectly content where they are, thank you very much.
If you think you might have a tapeworm infection, see a doctor for the correct prescription and let medical professionals handle your unwanted guest.
This article has been updated from the original version.
