Water Hemlock: Dangerous Plants for Dogs

Pet owners watch out this summer for a common, but deadly plant.
By JoAnna Lou, June 2016, Updated September 2021
water hemlock dog toxic

Now that summer is here, and everyone is hanging out by the water, we want to share information about a common but extremely lethal plant called the water hemlock. It's scary because it's found all over North America and can kill so quickly.

I read about a three-year-old Border Collie who died within one hour of ingesting the toxic plant. The dog was playing at Horsetooth Reservoir in Colorado when she chewed on water hemlock, and shortly after, she lost all motor function and succumbed on the way to the veterinarian.

Water hemlock (Cicuta douglasii) is highly toxic to both people and pets. The plant contains the poisonous chemical cicutoxin, which has a carrot-like odor and affects the brain and central nervous system if ingested. Just a few leaves of water hemlock can kill a dog within hours, making it one of the most lethal plants on this continent.

Some animals have even been poisoned from drinking water that has been contaminated with trampled water hemlock roots! The plant grows near bodies of water, like rivers and lakes, and where water collects, like ditches.


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Water hemlock is a tall branching plant that can grow three to six feet. It blooms white flowers in June and July with narrow, serrated leaves. Cow and water parsnip are often confused with water hemlock. All parts of water hemlock are poisonous, with the roots being the most toxic and the most palatable.

If water hemlock is consumed, symptoms begin within a matter of minutes and include drooling, muscle twitching, seizures, and dilated pupils. This quickly turns into respiratory paralysis and then death. If a non-lethal dose is consumed by dogs, there is a chance at recovery, but there may be temporary or permanent damage to the heart or skeletal muscle.

Signs Water Hemlock Poisoning in Dogs

  • Nervousness
  • Excessive salivation and frothing
  • Muscle twitching
  • Dilation of the pupils
  • Rapid pulse
  • Rapid breathing
  • Tremors
  • Violent convulsions, grand mal seizures

If you see your dog eating water hemlock, try to induce vomiting and get to a veterinarian immediately. However, since the toxin acts so quickly, prevention is really the key. Learn to identify water hemlock, and don't let your dog dig and chew wild plants


 Image: iStock