Nature in Your Backyard: Mystery “Leech”

My office is located in a fun hallway. And by fun, I mean that my colleagues are always dropping by and sharing stories about the biodiversity in their daily lives, or as was the last week, the physical specimens that they collected while going about the business of their daily lives.

First, a fish biologist dropped off a camel cricket collected from his basement for our Camel Cricket Census. Later in the afternoon, a neurobiologist swung by with a praying mantis perched on his notebook.

Praying mantis perched on lab notebook. Photo credit: Holly Menninger

Praying mantis perched on lab notebook. Photo credit: Holly Menninger

I enjoy these drop-by visits – they are little moments of nature, shared with friends, right in the comforts of my own office.  And I’ll admit, when I’m having a long day, they also give me a much-needed boost. It’s fun to look up from your computer screen and flex your natural history muscles.

Most of the time I become reacquainted with old six-legged friends. But every now and then, I meet a mysterious creature whose identity leaves me scratching my head.

As was the case a few weeks back when another colleague, Jason Flores, came by and told me a curious story about a critter he and his kids encountered on the sidewalk on their morning walk to the bus stop.

It was black and shiny, almost worm-like. He observed it contracting and expanding, occasionally poking its head up in the air. When he visited the bus stop the next morning, the critter was still there, albeit drying out and quickly becoming food for fire ants. He snapped and shared a photo with me.

I pondered this image, trying to recall as much as I could from my days teaching undergrads about animal diversity. I decided, based on the photo and Jason’s description of its behavior that it was most likely a leech. He concurred.

Fire ants devouring a "leech." Photo credit: Jason Flores

Fire ants devouring a “leech.” Photo credit: Jason Flores

A few days later, Jason shared a better photo of another so-called “leech” that he and his kids encountered – again, there it was just hanging out on a suburb sidewalk. I was puzzled by it – What was a leech doing there, just chilling on the concrete?

A "leech" on the sidewalk. Photo credit: Tonya Flores

A “leech” on the sidewalk. Photo credit: Tonya Flores

The only leeches I’ve ever seen in the eastern US were in water (in fact, we recently found some while flipping rocks in a local stream a few weeks ago – check out this video, starting at 3:00). I thought terrestrial leeches were largely confined to the tropics  — I’ve heard some gruesome stories and have seen even gruesomer pictures thanks to friends who did fieldwork in the tropical rainforests of Southeast Asia and Australia.

Yet, something about Jason’s mystery “leeches” didn’t quite sit right with me. I couldn’t make sense of their suburban sidewalk location and their smooth shiny bodies.

So like any good nature nut, I decided to investigate further. With a little Internet sleuthing I learned that there are indeed terrestrial leeches in the eastern US. In fact, two terrestrial leech species can be found living under rotten logs in Great Smokey Mountain National Park; they eat earthworms.

Alas, the article that mentioned terrestrial leeches did not contain photos. So I contacted one of the world’s leading leech experts, Dr. Mark Siddall at the American Museum of Natural History to get his opinion. Who was this creature and why did Jason and his kids find it on the sidewalk?

Mark was kind enough to answer my query, very simply and directly.

It is not a leech, it is a flatworm, probably in the family Geoplanidae.

Doh! We missed that identification by a whole PHYLUM of life – Leeches are in the Phylum Annelida, the phylum of segmented worms, including your friendly neighborhood earthworms. Take a look at the pictures of Jason’s flatworm again – no repeating muscular segments there! Its smooth and shiny surface should have been our first clue to its identity.

Flatworms belong to the Phylum Platyhelminthes. Now that you are thinking about them, I bet you remember flatworms from high school biology – they’re touted as the most primitive example of bilateral symmetry (having distinct left and right sides). Flatworms lack a circulatory system and a body cavity – everything moves through their tissues by diffusion. Flatworms include parasites like tapeworms (see Dr. Eleanor’s recent post about her dog Lucy Bea’s butt worm) but also terrestrial predators, like the one Jason and family encountered on their sidewalk.

Similar to leeches, terrestrial flatworms show hunting behaviors – they use sensory organs near the front end of their body to detect food.  Admittedly, it was Jason’s report of seeking behavior that first led me astray down the leech identification path.

The really cool thing about the terrestrial flatworm is that its mouth is on the underside of its body. When it encounters prey, the flatworm extends a muscular tube called a pharynx through its mouth. It then secretes digestive juices that dissolve prey outside of the flatworm’s body.  With slime and that pharynx, terrestrial flatworms can take down earthworms, snails, slugs and insects.

Now must be the time of year when terrestrial flatworms are out and about. On the same day I heard back from the leech expert, I received an email from Carolyn, a Your Wild Life volunteer in Raleigh, describing flatworms she encountered on a morning walk with a friend:

They were very long – every bit the 10” I have read about.  Dusty brown but no stripes that I remember.  They were out at 7am in the shade last Saturday crossing the 8’ wide greenway on a stream of slime. It was in the low 50’s.  My fellow walker who is terrified of snakes took off but I stayed to look.  Strangest head I have seen, like a breathing fan.  I knew it wasn’t a snake because of the slime and it didn’t take off from the vibration of our steps. 

With my new and improved knowledge of terrestrial flatworms (and leeches), I’m pretty confident that Carolyn encountered a different species of terrestrial flatworm than Jason and his family. I suspect she spotted a “hammerhead worm” in the genus Bipalium, a group that looks quite alien-like with their broad heads.

As you go about the business of your daily lives, keep your eyes peeled for your own backyard mysteries, worm and otherwise. We’d love to hear about them and feature them on the blog!

By |2016-11-22T13:47:18-05:00October 10th, 2013|

About the Author:

Holly Menninger
As Director of Public Science, Holly coordinates our empire of citizen science projects and manages the online science communication here at Your Wild Life. An entomologist by training, she’s a science communicator by passion and practice.


  1. Avatar
    paula March 4, 2015 at 6:01 am - Reply

    Are those worms, the black ones, dangerous to pets such as dogs? Or to people?

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      bel May 18, 2015 at 8:44 pm - Reply

      I wish someone had answered you…can’t find anything about these dudes. I don’t wanna go barefoot or let my kids play in the dirt if we’re gonna get parasites

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    Kara April 1, 2015 at 5:37 am - Reply

    Thank you for this! My boyfriend’s front yard, actually his entire house, has been overrun by many different kinds of bugs. There are definitely an abnormal amount of rollie pollies (pill bugs), black widow spiders, daddy long leg spiders, other weird unknown spiders, ants, earth worms, etc. It’s a freak show over there when the sun goes down. So, tonight I decided to check out my own back yard in order to do a little comparison. I looked in the grass, technically the dirt area between the edge of the sidewalk and the grass, but there weren’t really any of the bugs I recognized from the other house. There were, however, tonssssssss and tons of these small black wet-looking slimy things that I could only deduce as being leeches! Creepy, horrible, little leeches! I mean, loads of them were piled on top of each other. One pile in particular were on top of and covering something. That something turned out to be just half of an earth worm, because they ate the other half. Anyway, all that to simply say thank you, because I too thought those little guys were leaches! It wasn’t until I happened upon this article by way of a Google search for “small garden leeches”, that I learned their true identity! Flatworms, huh? I wasn’t aware of the fact that worms partake in cannibalism. Interesting. Well, there’s my silly story!

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    Jon May 18, 2015 at 5:38 pm - Reply

    Kind of looks like the new terrestrial land leech discovered in nj a few years ago.

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    kris May 23, 2015 at 10:40 am - Reply

    This segment was perfect as I had the exact question and was doing my online research when I found this. Much more assured that my kids aren’t dodging leeches on the back porch.

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    Angela September 7, 2015 at 12:53 pm - Reply

    I live in Louisiana, this spring and early summer, we had an abundance of rain. I started seeing these little worm like creatures swimming in the water in my backyard. My husband said they were leeches, concerned I had leeches I asked my neighbor. He had one attached to his ankle. Once the rains stopped I had a swimming pool put in. I thought once it dried up I would not see them. Wrong! A few are finding there way to my pool. I live in a subdivision with a lake but I don’t live on the lake. They look like the picture in your post. Upon closer inspection they have the round sucker mouth. I would like to get rid of these. If you can help please email me at

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    kimba December 4, 2015 at 1:38 pm - Reply

    Within the past year I’ve seen these things, or something similar ( hard to be sure from the pic- which I thought were leeches) at 2 different locations in Cape Canaveral, Fl. Yesterday morning I saw a different creature on my front walkway and so once again am researching these gross things. Yesterday’s find is a hammerhead worm- another flatworm. Does anyone know if birds eat either of these flatworms ? Be nice if something would eat them !

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    Chelsea December 11, 2015 at 7:04 pm - Reply

    I’m SO glad I saw this, I was sitting outside at 6:30 this evening and found this little worm. I thought it was a leech and when I typed it into Google, this article popped up… I’m so glad he wasn’t a leech, but still sounds creepy. I’d also like to know if they’re safe to touch or if my pets are around them.

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    Chris Caffarel June 8, 2016 at 8:02 pm - Reply

    I have found a leech in my backyard . I live in Charleston , Sc. Please contact me and I’ll send a pic to verify ! Thanks

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    Jessica Crater June 29, 2016 at 10:49 am - Reply

    I am not sure but from what i have read im not supposed to have these where i am. I live on the outskirts of Houston tx.. Humble. I found one right outside my house. Can anyone help me. Should i be cautious and not let my 3 year old and 4 year old outsidein the yard. And are they harmful in any kind of way? I did take a good picture. Just trying to protect my 2 dogs also, qhich are fondland pitbulls. Help?!?!?!

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      Maria Prestigomo March 26, 2017 at 10:41 pm - Reply

      Hi, did you find any information? I stumbled across your comment as I too live in the Houston area and have found three (one shriveled up dead and two live ones) within the past month. I’m concerned since there doesn’t seem to be a lot of information on them….

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      sidney lampman August 20, 2017 at 10:58 am - Reply

      i live in Santa Fe TX. and this morning i found like fifty of em. Sometning has eatin all my plants . What ever is eating them, there not picky. Im wondering if its these things.

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    David Ng March 15, 2017 at 10:00 pm - Reply

    This article is helpful. At least I know it isn’t a leech. Found one moving along the side of the toilet seat I was using! About 4 inches long. Exactly same behavior and looks. The only thing I’m a little worried about is if this creature came from the garden or from me :(

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      JP Jones August 9, 2017 at 2:49 pm - Reply

      JP 8/9/2007 2:41 PM. I found several on my concrete back porch. It’s been raining for days and the ground is saturated. It appears that they are getting away from the ground water in the lawn. I examined one with a “jewelers glass” and discovered a circular mouth that was searching to latch onto something. It had tiny pincers in it’s mouth that resembled a leech. Summerville, S.C.

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    Marie Coar April 16, 2017 at 8:58 am - Reply

    I just found one in my flower bed attached to a segment of earthworm

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    Marie Coar April 16, 2017 at 8:58 am - Reply

    Wish I could attach a pic

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    Rebecca Allen April 16, 2017 at 9:56 am - Reply

    HI, I just found one for the first time ever on my front porch. Amazing. Do wonder if they are not cool to have around cats or dogs, etc.

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    Blair H September 22, 2017 at 9:45 am - Reply

    The first time I encountered some of these(a bunch actually..blech) was in my bosses yard. I found one today on my dog and remembered to look it up. I am glad it’s not a leech, but they still burned when on the skin, and irritated my dogs paw. Im guessing that was the digestion process? Eek I dont like them!

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    Beverly September 26, 2017 at 8:05 pm - Reply

    I have them in my yard. Almost thought it was deer poo but it is black worms. Some longer and some small that look like leechs. Wish we knew what causes them to be here in Marble Falls Tx. Can we put down any pesticide to get rid of them. I think they are killing my lawn grass. Brown patches of dead grass.

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