Signs and lesions of water hemlock poisoning:

  • Nervousness
  • Excessive salivation and frothing
  • Muscle twitching
  • Dilation of the pupils
  • Rapid pulse
  • Rapid breathing
  • Tremors
  • Violent convulsions, grand mal seizures
  • Coma
  • Death may occur as early as 15 minutes after a lethal dose is consumed
  • No significant gross lesions

Water hemlock (Cicuta douglasii) is the most violently toxic plant that grows in North America. Only a small amount of the toxic substance in the plant is needed to produce poisoning in livestock or in humans. The toxin, cicutoxin, acts on the central nervous system and is a violent convulsant.

Water hemlock may be confused with poison hemlock because of their similar flowers. However, these two are different plants and cause different types of poisoning. (See poison hemlock chapter in this fact sheet.)

The underground portions of the plant, especially the tuberous roots, are very toxic. People are sometimes poisoned by eating the roots, which they mistake for wild parsnip.

In cases of water hemlock poisoning in humans, take the affected person to the emergency room of the nearest hospital immediately. Call poison control and seek emergency treatment immediately.

Cattle have been known to eat lethal amounts of water hemlock in pastures having adequate forage; therefore, animals should be prevented from grazing over water hemlock-infested areas. Animals have been poisoned by eating roots that have been brought to the surface by plowing or cleaning ditches.

The toxic substance in water hemlock is cicutoxin, a highly poisonous unsaturated alcohol that has a strong carrot-like odor. It is found principally in the tubers but is also present in the leaves, stems, and immature seeds. Leaves and stems lose most of their toxicity as they mature.

Where and when water hemlock grows:

Water hemlock is most commonly found growing in wet meadows and pastures and along stream banks. It starts growing in spring. Water hemlock usually flowers in June or July.

How water hemlock affects livestock:

Livestock usually show signs of poisoning 15 minutes to 6 hours after eating the plant. They develop violent convulsions and may die within 15 minutes to 2 hours after signs appear.

How to reduce loss:

The toxic substances act so rapidly that an affected animal can seldom be saved. Treatment consists of preventing seizures with barbiturates or tranquilizers and supporting respiration. Gastric lavage, activated charcoal, or saline cathartic may be helpful. Seek immediate medical or veterinary treatment.

To reduce losses, keep animals away from places where water hemlock grows. Prevent water hemlock poisoning in livestock by carefully surveying pastures and ranges at a time when the plant can be identified, and eradicate it.

The plants, which usually grow in small patches, are easy to locate. They can be eradicated by spraying or grubbing. Actively growing plants can be controlled with 2,4-D at 2 lbs. ae/acre. Repeat spray treatments until eradication is complete. The stems and leaves of water hemlock increase in palatability immediately after being sprayed with herbicide. Therefore, keep animals away from treated plants for 3 weeks after spraying. Most losses occur early in the spring or after the plants have been sprayed with 2,4-D.

Note: If grubbing the water hemlock, use gloves and be careful to get all of the plant, including roots. Gather and burn every part, don’t leave tubers lying around.