A Garden Bad Guy: The Hammerhead Worm

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My youngest daughter was playing outside, rolling over logs and railroad ties trying to find bugs to catch, when she discovered a funny looking worm. She studied it for a minute, and then brought it to me in great excitement.

“Mommy! Look at this funny worm I found!”

I was just as fascinated as she was. As it inched along, it stretched from just a couple inches to nearly six inches long!  What a strange worm, I thought. It’s head resembled that of a hammer-head shark.

Of course I set straight to researching what it was. Not really knowing what to look up, I googled “hammerhead worm”. Sure enough, Wikipedia has a whole article devoted to Bipalium, loosely referred to as the “hammerhead worm”.

What I found out next wasn’t so exciting.

hammerhead in Austin, Texas
By PvilleSteve – Own work, CC BY-SA 4.0, Link

Hammerhead Worms Fun Facts

Latin nameBipalium species
DietCarnivorous (it eats earthworms)
SizeAround 8 inches (20 centimeters)
Sexual Reproductionhermaphroditic

What Are Hammerhead Worms?

The hammerhead worm, the full name of which is Bipalium kewense, is a hammerhead flatworm or land planarian. Its head looks just like a hammerhead shark, as I mentioned. These worms are massive, with some growing to 20 inches long. Most, however, will only grow to about an inch – at least that’s a nightmare to save for another day!

Hammerhead worms secrete thick, dense mucus from their undersides as they move. Some hammerhead worms have stripes, but others do not. They can be found in shades of black, gray, orange, or brown. Sometimes, you might hear hammerhead worms referred to as shovelhead or arrowhead worms. They are frequently found in caves.

Hammerhead worms are often called hammerhead slugs. To be fair, they look a lot like slugs as they move in a slug-like fashion. The cilia on their creeping soles help them glide, and they leave behind a thick string of mucus just like slugs, too.

Although they’re harmless to people, they can be devastating to a garden. Hammerhead worms are considered an invasive species. They prey on earthworms, and can completely decimate a garden if they aren’t taken care of.

Supposedly, if you try to squish them or cut them they’ll multiply and grow into more worms. And other animals don’t like to eat them because they secrete a foul tasting slime.

Great. Another garden pest to worry about.

By Scadgrad – Own work, CC BY-SA 4.0, Link

However, it’s important that you take the time to worry about them. Earthworms are so crucial in any garden because they help fertilize and aerate the soil. Without them, you won’t have much of a garden. Hammerhead worms, particularly a severe infestation of hammerhead worms, can completely ruin you garden’s success.

Hammerhead worms aren’t toxic to people, but they are toxic to other creatures because of their neurotoxins.

That being said, while it’s perfectly safe to touch or interact with a hammerhead worm, we don’t recommend you eat them these planarians contain tetrodotoxin, the same kind of toxin found in pufferfish, rough-skinned newts, and blue-ringed octopus.

It’s not known whether these toxins would produce similar ill effects in humans if ingested – but don’t try it!

What to Do About Hammerhead Worms

As I mentioned, you can’t get rid of hammerhead worms by squishing or cutting them. They will regenerate into new worms when you cut them into pieces, so you will only make your problem worse by reacting with this sort of violence!

They are hermaphrodites, with each worm possessing both types of reproductive organs. The worms reproduce via fragmentation, leaving behind a tail tip stuck to a leaf which then turns into an adult. It only takes a few weeks for the pieces to regenerate, and injured worms can easily repair and produce new tissue.

The best way to kill hammerhead worms is to fill a spray bottle with citrus oil. This is often sold in the cleaning aisle at your local grocery store, although you can also make your own at home.

Here’s the deal – you can’t kill hammerhead worms by simply spraying citrus oil in your general garden area. You have to spray each and every worm until your population is dead.

Designate a certain day of the week – and a time – to spend in “hammerhead hunting.” Go out first thing in the morning, ideally after a heavy rainstorm when the worms will rise to the surface of the soil. Spray the worm until it is completely soaked in citrus oil. If the worm is on a plant or leaf, knock it on the ground so you don’t hurt your plant.

You can spray with citrus oil as often as you’d like, but keep in mind that you will need to do this at least once a week to control the population. If you’re unsure of whether you’ve killed off all the hammerhead worms, check for eggs. These look like tiny black or red cocoons – the cocoons will be filled with eggs. These should be removed and destroyed immediately.

If citrus oil doesn’t seem to be doing the trick, you can also try using vinegar or salt. These, like citrus oil, need to be applied directly to the hammerhead worm in order to be effective. Use a spray bottle or simply pour the ingredients directly on top of the worms to dissolve.

Don’t think you’re immune just because you live in a cold environment, either. These creatures can establish themselves in a greenhouse and disperse quickly into the surrounding area. In a cold climate, they can survive freezing and below freezing temperatures by hiding out in protected locations.

In Closing

We’ve been collecting them in a jar and sprinkling salt over them, which kills them very quickly. I’m afraid to try feeding one to my chickens ’cause if they peck it into two pieces and one gets away it might just turn into a whole new body.

I thought I’d share so you guys can be on the lookout for hammerhead worms around your home and garden. If you find one, sprinkle it with salt or drown it in a jar of water.

This is the first I’ve ever seen or heard of hammerhead worms. Have you ever seen one? Are they a problem in your garden? Be sure to pin this article to your Pinterest so you know where to look should this pesky pest ever pay you a visit.

hammerhead worms Pinterest image

updated 10/29/2019 by Rebekah White


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35 thoughts on “A Garden Bad Guy: The Hammerhead Worm”

  1. I’ve killed at least 20 of them in the last few weeks in my flowerbeds as I moved a retaining wall. I’ve found if I leave the extra retaining wall blocks in the flowerbeds directly on the soil (not on the mulch where the soil dries out) and keep the soil under them and near them moist, that they congregate there and I can turn over the blocks to find them and completely smash them into a slimy streak. It makes me mad because I have a large number of Earthworms and Night Crawlers in my flowerbeds and haven’t been seeing as many as I used to. I’m near Little Rock Arkansas.

    Reply
  2. Found a very small one on my driveway in NC after heavy rains yesterday.
    I thought it was so neat to find something I had never seen before until I identified and read about it.

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  3. Glad I came across this useful information about them and how to permanently remove them from your garden. We found 2 and thought they were baby snakes. Were located in Charlotte, NC

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  4. I just found some under my deck as I was replacing some planks. Now I know part of my problem in the garden adjacent to it. Great info. I’m in North Little Rock, AR.

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  5. Just found one this evening under some wet wood that was stacked up. It looked really creepy so I came in and did some research. Shortly thereafter, I went back outside and immediately poured salt on it. We have a lot of earth worms and I would like to keep it like that. We have a community garden in our subdivision located in Snellville, GA.

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  6. Just saw my first one here in Asheville North Carolina. I put it in a Ziploc and brought it up to find out what it might be. Now that I know, I’ll be on the lookout for them. I’m ready to help out my regular earthworm friends by removing them permanently.
    Thanks for your information!

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    • This year, I have found 7 or 8 of them in my garden here in Weaverville. I first found them last year both in my garden and in the woods behind my house, read about them, and now drown them in soapy water.

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  7. Just saw my very first one ever here in South East Louisiana. I thought it was an earthworm at first. Now I know why I can’t get any earthworms for fishing bait! Ugh!

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  8. I have found vinegar to be highly effective. As long as you are cautious not to spray it directly on the grass on your lawn or plants in the garden, you are good to go. Great tips you got here. Keep it up!

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  9. looking in locations where slugs are found, I started paying attention and killing them. Killed twenty today. Los Angeles, CA. how do I eliminate a
    these things? I found them everywhere on my property.

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  10. Thanks for this important information! Today was the 1st time seeing one of these ugly, slimey worms. I was cleaning loose dirt off a small pot and actually got it on my hand, yuck!! Wasn’t sure if it was a beneficial so I Googled it and found this post. I live just east of Raleigh in Knightdale, NC. Does anyone know where they originate from?

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  11. We just found our first one today. My two and three year olds were walking out our front door and it was inching near our screen door. We jarred it and are passing it on to local science classes. We are in South Louisiana.

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  12. Just found one wrapped around a Dahlia tuber in the Central Valley of northern California. They truly are creepy looking. I’m trying slug/snail killer.

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  13. This is the third year in a row, each year finding a few more than the last. I’m in upstate NY, as such with our cold winters it seems especially disturbing that even our climate isn’t a deterrent to them :/

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  14. In the past two days, I’ve killed 5 of them with salt. Last year, I found 3 all year.

    I wish I knew how to rid my yard of them.

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  15. I found a half dozen on the bark of a tree at its base in my backyard after heavy rains. I didn’t know what they were, but googled them and learned they were hammerhead worms and invasive and prey on earthworms. They were about a foot long! So I sprayed them with a mixture of salt, water, bleach, and vinegar. Killed them quick. No one around here I’ve talked to so far has heard of them before. I’m in Winston-Salem NC. I wonder if they are relatively new to this area, and where did they come from?

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  16. I found one this morning and thought it was a leech. I’ve seen them before but not often. He/she is now in worm heaven using my boot. I have a fairly large garden but actually found on one of my pavers by my pool.

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  17. I’ve been seeing them in increasing numbers for the past year. Now they are all over my yard. I had no clue what they are until now. No wander I can’t find earthworms in my garden, even after planting a ton of them!

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  18. Found one under a brick holding a bag of topsoil closed. I allowed it to go on it’s way not having any idea how invasive they are. Lots of rain after a dry spell must have brought it out. Unless of course it came it the bag of topsoil!
    Greensboro,NC

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  19. I have found two of them in my garden. I threw the first one in the trash, but as I was digging and found the second when I cut it half. So unfortunately I left it in the soil but I didn’t know that they prey on earthworms.Now I know how to eliminate them thanks to your info. I am in Greenville SC

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  20. we found what looks like a few hammerheads wrapped in and around the netting of the skimmer net in our pond. They have a brown& beige stripped body with a hammerhead head. They obviously don’t drown, so what are they? We’re in Charlotte NC.

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  21. Ugh just saw one this morning in San Mateo, CA. Wish I would have researched before acting. I took a little video… then tossed it by the back fence. Wish I could have a do over!!

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  22. Oh Yuck! I’ve not seen one. I live in WV. Not sure if they’ve shown up around our area but I will be looking into more info!

    Reply

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