Parasites are both kind of disgusting and totally fascinating. Over the last few years, our interest in how they do what they do has grown, especially because parasites are so successful.

Case in point: Did you know that tapeworms, which curl up inside an animal's intestines and survive by skimming nutrients from their digestive tracts, have been around for at least 270 million years? And that there are almost 5,000 different types of tapeworms? (Don't feel bad if you thought "tapeworm" designated one type of creature, not a whole group of them; so did I.)

That number of various kinds of tapeworms is so high because they're well-adapted to the animals they use as hosts. Some are very small, while others are comparatively large — scientists found a 30-foot-long tapeworm inside a sperm whale. Some require different hosts for various parts of their life cycles, while some stay in the same animal throughout their lives. Many tapeworms are specifically adapted to living inside very specific hosts — not just any animal will do. So, we know some things, but there are big gaps in our knowledge about the class of organisms known as cestodes.

Enter the parasite expert

Part of the reason we may have been ignorant about tapeworms is that until recently, they hadn't all been successfully cataloged and described — that's is, until Janine Caira came along. The parasitologist from the University of Connecticut has been fascinated with tapeworms from early in her career. In fact, she discovered a new variety that lives in shark bellies as a Ph.D. student (she named it after a friend), a moment that spurred on her fascination with these brainless parasites.

Caira's enthusiasm for the subject is infectious (see the video above), and it has led to her magnum opus. Over the past eight years, she has cataloged tapeworm species in thousands of animals, eventually discovering 211 species that are new to science. She published the book, "A Survey of the Tapeworms from the Vertebrate Bowels of the Earth," which is based on her work, in 2017.

Detailed tapeworm under the microscope, 3-D rendering This is a 3-D rendering of just one of the many thousands of types of tapeworms that exist on Earth. (Photo: Crevis/Shutterstock)

"...we're talking about a whole group of animals whose habitat is the body of another animal. Just think about that. There has to be really big advantages to being a parasite in order for your life cycle to be so complicated. . . . So how on Earth does that come about?" Caira asked the Washington Post. Her comments point to the fact that there's still lots more to learn about tapeworms.

Caira's work is part of a big push by the National Science Foundation to catalog and understand the 85 percent (or more) of life on Earth that they estimate hasn't been officially discovered and described yet. This is incredibly important work because species — especially those at the margins and those that aren't as well-known — are going extinct every day. (In fact, some scientists think we are in the middle of a sixth mass extinction right now.)

But if you're still wondering why you should care about something as creepy looking as tapeworms, Caira says you have to think bigger-picture than that — at what their presence means to the greater ecosystem, which includes us.

"[Being a parasite] just has to be a whole different way of living," she muses. "I think they have figured out answers to questions we don’t even know are questions yet."

Starre Vartan ( @ecochickie ) covers conscious consumption, health and science as she travels the world exploring new cultures and ideas.

When your passion is tapeworms, you spend a lot of time explaining why they're cool
Tapeworms are gross and fascinating—and there's so much we don't know about them. That's where Parasitologist Janine Caira of U of Connecticut comes in.