Yes, Poison Hemlock is toxic to dogs!
Dogs accidentally consuming the Poison Hemlock plants can show the following clinical symptoms: Vomiting, Prolonged Depression, Incoordination, Hypersalivaton, Sleepiness Or Excitation, Dilated Pupils, Low Body Temperature, Low Blood Pressure, Coma, Seizure And Death (In Rare Cases).
Poison Hemlock consumption is also toxic to Cats and Horses.
Toxic Principles Of Poison Hemlock: Various alkaloids.
More Info About The Poison Hemlock Plant
Scientific Name: Conium maculatum
Family: Umbelliferae.
Also known as: Poison Parsley, Spotted Hemlock, Winter Fern, California Fern, Nebraska Fern, Deadly Hemlock.
The answer is based on information found on The American Society for the Prevention of Cruelty to Animals (ASPCA) website.