Are Hammerhead Worms Harmful to Dogs? (The Truth)

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If you’ve discovered hammerhead worms in your garden or backyard and are concerned about whether they are harmful or can hurt your dog, this article is for you.

This invasive species of flathead worms can be found primarily in many US states, including Pennsylvania, Texas, South Carolina, and a few others.

Our small animal veterinarian will answer all of your queries about the dangers of hammerhead worms to dogs, as well as the symptoms of toxicity and how to get rid of these nasty creatures.

Quick Answer

Hammerhead worms are considered harmful to dogs because they secrete a toxin that if consumed by a dog, can be life-threatening. Though many factors determine how harmful this will be to a dog depending on how much it ate, the size of the hammerhead flatworms consumed, the species, and the size and breed of the dog.

What Happens if A Dog Eats a Hammerhead Worm?

Dogs are naturally very curious creatures who will try to sniff and eat anything that may catch their attention however, occasionally this behaviour can put them in danger.

It’s not uncommon for dogs to eat hammerhead worms because they have striking color patterns and exhibit wiggly movements which peaks the interest of our furry friends.

The outcome of a dog eating a hammerhead worm depends on the species and size of the worm, because research has shown that only two species of these worms contain poisonous toxins.

They are the only land invertebrates known to produce tetrodotoxin, the same toxin secreted by puffer fish.

The good news is that hammerheads produce far less than the puffer and aren’t a danger to humans, but it’s not exactly known what amount would cause major harm to dogs, so be cautious.

Other hammerhead worms are likely not to cause harm.

The size of the hammerhead worm also influences what happens if a dog eats it, because the larger the worm, the more toxin it contains.

Similarly, the size of the dog and species can determine how harmful hammerhead worms will be to your household pets, namely dogs in this case.

Dogs can suffer from neurotoxicity after eating a hammerhead worm and can die due to respiratory collapse.

Is the Hammerhead Worm Toxic to Dogs? (Do They Have Poison?)

Yes, hammerhead worms can be toxic to dogs because they secrete a toxin called tetrodotoxin, a powerful neurotoxin found in puffer fish that may primarily affect the dog’s nervous system and has the ability to disrupt nerve impulses between the brain and the body.

Though it has been found that hammerheads produce less of the toxin than the puffer fish, and it’s impossible to truly know what effect this can have on your furry friend.

If your dog consumes a hammerhead worm, it may experience the following symptoms:

  • Diarrhea and vomiting
  • Lethargy and depression
  • Seizures
  • Dilated pupils
  • Limb paralysis and inability to walk or stand
  • Respiratory collapse (due to the paralysis of intercostal muscles and abdominal muscles which aid in breathing)

If your dogs experience any of these symptoms after eating a hammerhead, get to a vet straight away.

Dogs can be poisoned if they lick the hands of someone who has touched the hammerhead worm and has not washed them; therefore, it is best to always wear gloves so your hands do not come into contact with the worm’s surface.

The effects of tetrodotoxin can be observed within minutes to a few hours, usually for 3 to 6 hours and death could occur within 20 minutes or it might take up to 24 hours.

How To Kill Hammerhead Worms in Your Yard So Dogs Don’t Eat Them

Because Hammerhead worms are flat worms, it is not a good idea to chop them into pieces in order to kill them because each piece can grow back into a complete individual.

Below are a few methods I’ve listed for killing them successfully.

1. Completely Smashing Them

Hammerhead worms should be completely smashed rather than cut into pieces if you want to kill them, because their regenerative cells will be destroyed in this way, making it impossible for them to regenerate.

Do not cut them as fragmentation is one way these invasive worms reproduce, as well as via asexual reproduction.

You’ll be making the problem worse and inviting more of this invasive species into your environment.

2. Vinegar and salt

Vinegar and salt are corrosive to the worm’s skin and are a safe and inexpensive way to kill them.

You can put the hammerheads in a sealable plastic bag and sprinkle salt on them until they’re completely dissolved, at which point you can dispose of the creature inside the bag.

It also means you avoid touching the hammerhead and potentially experiencing skin irritation.

3. Citrus oil

Citrus oil has a strong acidity that can destroy a worm’s skin and internal organs resulting in its death.

Use a similar method as above.

4. Boric acid

You can add boric acid to your garden soil to make it acidic because hammerhead worms cannot survive in acidic soil.

Though this option may also affect beneficial worms like earthworms if the soil gets too acidic.

5. Pesticides

These creatures can be killed with industrial pesticides, but use them with caution as these may also be harmful pets and other animals in the environment.

Can Hammerheads Harm Dogs in Other Ways?

Yes, hammerheads are a broadhead planarian flatworm that can also carry and transmit harmful nematode parasites to your pets, including dogs.

If dogs are lucky enough to avoid the toxins from hammerhead worms, they may not be lucky enough to avoid being infected by parasitic worms.

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Fun Facts About Hammerhead Worms

  • The hammerhead worm is native to SouthEast Asia, but have been discovered in the US from around the 1980’s due to global transport.
  • They prefer a humid, moist environment. Generally, Hammerhead worms live in high-humidity, tropical and coastal regions, as a result.
  • They are light sensitive so prefer dark, damp and cool habitats where they can hide and feed at night.
  • They are carnivorous predators (unlike earthworms who eat dead organic matter) and prey on earth worms, slugs, snails, other insects and insect larvae.
  • They can also track a prey’s slime trail.
  • The way the hammerhead worm feeds on their prey is pretty gruesome. Let’s use earthworms as an example of prey. They will latch on to the earthworm’s body and secrete a glue-like substance so escape isn’t possible.
  • It then opens up its mouth (located in the middle of its body) and releases digestive enzymes which reduces earth worms or other prey to liquefied tissue.
  • Studies show the hammerhead worm uses its toxin for predatory reasons (2) as the toxins are concentrated in their head.
  • But it’s also used as a defense mechancism as shown by the fact that they can lay eggs that are 2-50 times more toxic (3) than the adult worm itself.

Summary and Final Words

Dogs shouldn’t eat hammerhead worms because their bodies secrete a neurotoxin, which is poisonous to them.

How much is harmful isn’t yet fully understood but you want to err on the side of caution.

After ingesting a hammerhead worm, your dog may experience a variety of toxic symptoms.

If you suspect your dog has eaten a worm or is displaying symptoms of toxicity, contact a veterinarian right away.

If you suspect an invasion of hammerhead worms in your garden, then use our tips to get rid of them and protect your animals, plants and pets – including dogs.

Dr. Abdul Basit Javed (DVM, RVMP)


  1. Tetrodotoxin: Biotoxin | NIOSH | CDC. (n.d.). Retrieved September 29, 2022, from
  2. Stokes AN, Ducey PK, Neuman-Lee L, Hanifin CT, French SS, Pfrender ME, Brodie ED 3rd, Brodie ED Jr. Confirmation and distribution of tetrodotoxin for the first time in terrestrial invertebrates: two terrestrial flatworm species (Bipalium adventitium and Bipalium kewense). PLoS One. 2014 Jun 25;9(6):e100718. doi: 10.1371/journal.pone.0100718. PMID: 24963791; PMCID: PMC4070999.
  3. Miyazawa K, Jeon JK, Noguchi T, Ito K, Hashimoto K (1987) Distribution of tetrodotoxin in the tissues of the flatworm Planocera multitentaculata (Platyhelminthys). Toxicon 25: 975–980