10 Juicy Facts About Leeches

Ian Cook
Ian Cook

Leeches get a bad rap, but they’re actually pretty cool once you get to know them—and we're finding out more about them, even today. Recently, a team led by Anna Phillips, curator of parasitic worms at the Smithsonian National Museum of Natural History, discovered a new species of medicinal leech (pictured above) in a Maryland swamp. We asked parasite expert and curator at the American Museum of Natural History Mark E. Siddall to share some surprising facts about the worms we love to hate. 

1. Not all leeches suck blood.

Hematophagous, or blood-feeding, species are only one type of leech. “The vast majority of species are [hematophagous],” Siddall tells Mental Floss, “but it depends on the environment. In North America, there are probably more freshwater leeches that don’t feed on blood than there are blood-feeders.” And even among the hematophagous species, there are not too many who are after you. “Very few of them are interested in feeding on human blood,” Siddall says. “Certainly they’ll do it, if they’re given the opportunity, but they’re not what they’re spending most of their time feeding on.” 

2. Leeches are everywhere.

Japanese leech on a log
Pieria, Wikimedia Commons // Public Domain

“Every continent on the planet has leeches, with the exception of Antarctica,” Siddall says. “And even then there are marine leeches in Antarctic waters.” Humans have co-existed with leeches for so long, according to Siddall, that just about every language has a word for leech. 

3. Leeches have made a comeback in medicine.

Bloodletting for bloodletting’s sake has fallen out of favor with Western physicians, but that doesn’t mean medicinal leeches are enjoying a cushy retirement. Today, surgeons keep them on hand in the operating room and use them as mini-vacuums to clean up blood. “That is a perfectly sensible use of leeches,” Siddall says. Other uses, though, are less sensible: “The more naturopathic application of leeches in order to get rid of bad blood or to cure, I don’t know, whatever happens to ail you, is complete hooey,” he says. How on Earth would leeches take away bad blood and leave good blood? It’s silly.” 

4. Novelist Amy Tan has her own species of leeches.

Land-based leeches made an appearance in Tan’s 2005 book Saving Fish from Drowning, a fact that instantly put the author in leech researchers’ good graces. “There are not a lot of novels out there with terrestrial leeches in them,” Siddall says. So when he and his colleagues identified a new species of tiny terrestrial leeches, they gave the leech Tan’s name. The author loved it. “I am thrilled to be immortalized as Chtonobdella tanae,” Tan said in a press statement. “I am now planning my trip to Queensland, Australia, where I hope to take leisurely walks through the jungle, accompanied by a dozen or so of my namesake feeding on my ankles.”

5. Leeches can get pretty big.

The giant Amazon leech (Haementeria ghilianii) can grow up to 18 inches and live up to 20 years. And yes, this one’s a blood-feeder. Like all hematophagous species, H. ghilianii sticks its proboscis (which can be up to 6 inches long) into a host, drinks its fill, and falls off. Scientists thought the species was extinct until a zoologist found two specimens in the 1970s, one of whom he named Grandma Moses. We are not making this up.

6. Leeches make good bait.

Many walleye anglers swear by leeches. “A leech on any presentation moves more than other types of live bait," pro fisher Jerry Hein told Fishing League Worldwide. "I grew up fishing them, and I think they're the most effective live bait around no matter where you go." There’s an entire leech industry to provide fishers with their bait. One year, weather conditions kept the leeches from showing up in their typical habitats, which prevented their collection and sale. Speaking to CBS news, one tackle shop owner called the absence of leeches “the worst nightmare in the bait industry.”

7. Leech scientists use themselves as bait.

Siddall and his colleagues collect and study wild leeches. That means hours of trekking through leech territory, looking for specimens. “Whether we’re wandering in water or traipsing through a bamboo forest,” Siddall says, “we are relying on the fact that leeches are attracted to us.” Do the leeches feed on them? “Oh my god, yes. We try to get them before they feed on us … but sometimes, obviously, you can’t help it.”

8. Leech sex is mesmerizing.

Like many worms, leeches are all hermaphroditic. The specifics of mating vary by species, but most twine themselves together and trade sperm packets. (The two leeches in the video above are both named Norbert.)

9. Some leech species make surprisingly caring parents. 

“There’s a whole family of leeches that, when they lay their eggs, will cover them with their own bodies,” Siddall says. “They’ll lay the eggs, cover them with their bodies, and fan the eggs to prevent fungus or bacteria from getting on them, and then when the eggs hatch, they will attach to the parent. They’re not feeding on the parent, just hanging on, and then when the parent leech goes to its next blood meal it’s carrying its offspring to its next blood meal. That’s pretty profound parental care, especially for invertebrates.”

10. You might be the next to discover a new leech species. 

Despite living side-by-side with leeches for thousands of years, we’ve still got a lot to learn about them. Scientists are aware of about 700 different species, but they know there are many more out there. “I’ll tell you what I wish for,” Siddall says. “If you ever get fed on by a leech, rather than tearing off and burning it and throwing it in the trash, maybe observe it and see if you can see any color patterns. Understand that there’s a real possibility that it could be a new species. So watch them, let them finish. They’re not gonna take much blood. And who knows? It could be scientifically useful.”

Journey to the Monarch Mosh Pit

iStock/Spondylolithesis
iStock/Spondylolithesis

Each fall, millions of migrating monarchs return to Mexico to wait out winter. The gathering makes Woodstock look like a business conference. Here’s how they get there.

Mosh Pit

In the mountains of central Mexico, the butterflies crowd on the branches of oyamel fir trees. The trees provide a perfect microclimate that prevents the butterflies from getting too hot or cold.

Texas Toast

After winter, the butterflies fly north to Texas in search of milkweed, where they lay their eggs. Many adults will die here; northbound monarchs generally live only three to seven weeks.

Juice Cleanse

One of the reasons monarchs love milkweed? Protection. As caterpillars, they absorb the toxins in the plant, which makes them less tasty to birds.

Connecting Flight

Eventually, a new generation of butterflies will make its way north to Canada. It takes multiple generations of butterflies to reach their final, most northerly destination.

Dine and Dash

On the way, butterflies will eat practically anything. Sure, there’s nectar—but they’ll also slurp the salts in mud.

Catching Air

When fall returns, a new generation of monarchs rides the air currents more than 3000 miles back to Mexico. They navigate by calibrating their body clocks with the position of the sun. (An internal magnetic compass helps them navigate on cloudy days.)

Latitude Adjustment

Monarchs “are one of the few creatures on Earth that can orient themselves both in latitude and longitude,” The New York Times reports—a feat sailors wouldn’t accomplish until the 1700s.

Southern Charm

Miraculously, each generation of southbound monarchs lives up to eight months—six times longer than their northbound descendants. Their longevity might have something to do with a process known as reproductive diapause (which is a fancy way of saying that the insects won’t breed until winter ends).

This Rolling Smart Robot Will Keep Your Cat Company and Help It Exercise, Even When You’re Not Home

Ebo
Ebo

As any true ailurophile knows, cats love to sleep. On average, kitties spend anywhere from 16 to 20 hours of each day napping. But that laziness we often find so charming can sometimes lead to obesity, which can cause some pretty serious health problems for your feline friend. So how do you make sure your cat stays happy and healthy, even when you’re not home? That’s where Ebo comes (or rolls) in.

Ebo is a smart robot designed to keep your cat company and provide them with some much-needed stimulation, especially when you're not around. With more than $90,000 in pledges raised already, Ebo crushed its original $5110 Kickstarter goal, but you can still back the project here, with pledge tiers that start at $159 for a standard EBO and a smart collar that tracks your cat’s activity levels.

The Ebo itself, which is just over two inches tall, connects to Wi-Fi and features an app that allows you to schedule when you want it to start and stop playing with your cat.

When it’s playtime, the tiny robot scans the room to ensure there’s enough space to play safely. Once it makes sure the coast is clear, the robot moves on its own, utilizing an ergonomic design that enables it to wheel in any direction, spin, roll over, or even dance. You also don’t need to worry about keeping your cat’s robot friend charged. If your Ebo happens to be running low on battery, it rolls itself back to its charging station until it’s ready to go again.

According to the designers, Ebo interacts with cats in a way your feline friend understands—through a mix of sound, movement, and light that is always unpredictable. You can even play with your cat through the Ebo with its built-in laser.

The app also allows you to monitor your cat through video. And if they do something cute—as they always do—you can easily snap a photo or shoot a video, edit it, add fun filters, and then share it with others.

The device’s smart collar can be used for up to 30 days on a single charge. Should it get stuck, there’s a safety mode in which it will be released automatically to prevent accidental choking.

If you want an upgrade, there's the Ebo Pro (starting at $199), which features an AI algorithm that analyzes your cat’s mood and motion and adapts for future play.

No matter which Ebo you choose, they all come full of accessories, including decorative soldier, bamboo, onion, or feather caps. And if you order in time, you can snag a model decked out in a Santa hat.

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