Lots of people don’t know that there’s a deadly plant known as hemlock in Colorado. In fact, it’s one of the deadliest plants in North America – and it’s everywhere. Western water hemlock (Cicuta douglasii) is a major danger to humans and animals – especially livestock. Read on to learn more about how a pretty little plant, one that looks like a wildflower weed – can and does cause a wide variety of problems.

Hemlock is a dangerous plant. It looks pretty, but it's very poisonous. Western water hemlock (Cicuta douglasii) and poison hemlock (Conium maculatam) are both fairly common in Colorado.
Feifei Cui-Paoluzzo/Moment Collection via Getty Images
Western water hemlock plants are usually about 1.5-6.5 feet tall; poison hemlock plants can grow as tall as 2-8 feet tall. Both have small white flowers on them and can appear rather pretty at first glance.
Robert H. Mohlenbrock @ USDA-NRCS PLANTS Database / USDA NRCS. 1992. Western wetland flora: Field office guide to plant species. West Region, Sacramento, CA.
The leaves look fairly harmless as well.
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Depending on the size of the plant, the leaves can look rather different. You should learn to identify this plant, though, and you should steer clear of it when you see it growing. When in flower, it looks a little bit like the harmless wildflower Queen Anne's Lace.
Steve Dewey, Utah State University, Bugwood.org, CC BY 3.0 , via Wikimedia Commons
You'll usually find it growing in wet areas like marshes, stream banks, ditches, meadows, and wet pastures. It needs water to thrive, so the further from water you are, the less likely you are to encounter it.
Western water hemlock produces a toxin called cicutoxin. It's this toxin that makes western water hemlock the most poisonous plant in North America. Poison hemlock produces coniine, which is similarly dangerous.
James St. John/Flickr
Animals and humans who consume western water hemlock will exhibit the same symptoms including frothing at the mouth, tremors, muscular weakness, seizures, and respiratory failure. Death can occur within 15 minutes of ingestion.
Amounts equivalent to as little as 0.1% of a person's body weight can lead to death.
Anita Gould/Flickr
This plant is very hazardous to animals too, and many farmers and ranches lose livestock to it each year. Consumption of only 0.2%-0.5% of a sheep's body weight, 0.1% of cattle's body weight, or 0.5% of a pig's body weight can be fatal.
Poison hemlock is just as deadly. Both plants should be avoided at all costs. Even contact with one's skin can be very dangerous.
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If someone has consumed hemlock in Colorado, there are treatments for it, but you’ll have to move fast. This plant can kill humans in just minutes, so it’s best to just avoid it entirely and to educate your friends, family, and children about it. If you find some on your property, we suggest you have it removed immediately – and stay safe, Colorado!

Never eat any plants you find in nature unless you absolutely know what you’re doing, and if you’re interested in learning more about safe foraging, perhaps consider taking a tour with a knowledgeable guide, like this Private Rocky Mountain Foraging Experience through Viator.

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