Sunday, September 17, 2023

Snakeroot's Secret

White snakeroot, Ageratina altissima, flowering in a woodland edge in August.

In the fall of 1818, a 35-year-old pioneer woman fell ill and took to her bed in a crude dwelling near Pigeon Creek in Indiana. She had been caring for her sick relatives and a neighbor before she came down with the same symptoms: lethargy, abdominal pain, fever, nausea, and worse.

She had no medical care, so her health declined quickly. In a matter of days, she slipped into a coma, but before she lost consciousness, she called her two children to her side. When she died, her nine-year-old son, Abraham, is said to have been devastated. He would later write that his mother, Nancy Hanks Lincoln, made him all that he was.

Called sick stomach and later milk sickness, the mysterious illness was a menace on the 1800s wooded frontier. It sickened and killed thousands and terrified thousands more, because its cause was unknown. Faced with the agonizing and unexplained deaths of their family and friends, many pioneers abandoned their settlements for what they hoped would be healthier locations. In some cases, entire towns were deserted, as told by a writer to the Farmers’ Register in 1834:

A Village Depopulated by the Milk Sickness

The following extract is of a letter from a traveler dated at St. Louis:

A few miles below Alton, on the Mississippi, I passed a deserted village, the whole population of which had been destroyed by the “milk sickness.” The hamlet consisted of a couple of mills and a number of frame houses, not one of which was now tenanted; but the dried weeds of last year choaked [sic] the threshold of the latter, and the raceways of the mills were lumbered up with floating timber, while the green slime of two summers hung heavy on the motionless wheels. Not an object but ourselves moved through the town; and the very crows themselves seemed to make a recruit around the fatal place when they came in view of the thickly sown burial ground on the skirts of the deserted village. (1)

Although the settlers often found the illness again in their new homes, their knowledge was building. They recognized that cattle stricken with “the trembles,” a shaking weakness that progressed to more severe illness, could cause a similar condition in people who drank the cows’ milk or ate their beef, butter, or cheese. The illness tended to appear later in the season, from mid-summer through fall, and it was worse in dry years. Newcomers to areas stricken with the illness were advised to avoid eating beef or dairy products from July to the first frost.

That good advice likely prevented many cases of illness, but the ultimate cause of milk sickness remained unknown, or at least debated, for decades. In hindsight, it didn’t have to be. Unfortunately for many who would later become ill, an early and accurate warning was largely missed, in part because it came from a woman. Actually, from two women.

In Illinois around 1830, Anna Pierce Hobbs Bixby, a nurse and midwife called Doctor Anna, was grieved about the cause of milk sickness. It had killed her mother and sister-in-law and it had disabled her father, who developed a chronic, disabling form of the illness called “the slows.” She suspected the cause was something cattle were eating, so she followed them into their wooded pasture to record what they ate.

While she was there, she is said to have met an elderly Shawnee woman hiding from forced relocation to a reservation in Kansas. After the elderly woman learned what Doctor Anna was looking for, she identified white snakeroot as the plant that was making animals and people sick. The women parted, and the fate of the Shawnee elder is lost in history.

Now known by the scientific name Ageratina altissima (formerly Eupatorium rugosum, E. ageratoides, and E. urticaefolium), snakeroot’s phenology matched the seasonality of the sickness. It flowers in mid-summer into early fall, coinciding with the time milk sickness tended to occur. Its habitat was another good match. Snakeroot grew in woodlands, including the forested pastures where cattle then commonly grazed, and it persisted in drought. When they had no choice, cattle ate snakeroot.

White snakeroot range in North America (left) and the upper Midwest (right). USDA NRCS 2023.

With this new-found knowledge, Doctor Anna began experimenting. She fed the plant to animals, including calves, and found that they developed the trembles. Convinced that she had found the cause of milk sickness, she spread the word. She grew a garden of white snakeroot to teach others what it looked like, and she urged farmers to pull it out of their pastures. They did, and her advice is thought to have saved many lives, at least in southeastern Illinois.

But that’s as far as it went. Whether her work was dismissed or not widely published or both, it didn’t get much traction. Instead, physicians and settlers alike continued to speculate about the cause of milk sickness. They blamed all kinds of things: arsenic or other metals, bacteria, bad water, poison oak, poison ivy, and other agents. Some blamed miasmas, imaginary, poisonous exhalations from the earth that misted the vegetation and sickened the cattle.

As the debate continued through the 1800s, milk sickness nearly vanished. That was another mystery, although a welcome one. Two hundred years on, we know why it disappeared: Cattle came to be pastured not in the woods but in cultivated pastures where snakeroot was excluded, and commercial operations combined and diluted milk from many sources. If the contaminant was present in the milk, it was at lower concentrations, too low to produce the severe illness caused by chronic consumption of tainted meat and dairy products.

Even as milk sickness waned, research continued into its cause. The poisonous-plant hypothesis eventually held after other possibilities were eliminated, and snakeroot was finally confirmed as the cause of the illness in the early 1900s, almost 100 years after the Shawnee woman and Doctor Anna warned of its dangers.

In 1928 or 1929, James F. Couch, a chemist with the USDA, identified the toxin in snakeroot that had caused so much suffering. He described it as “a viscous . . . oil with a pleasant aromatic odor” and named it tremetol after the tremors it caused (2). The compound is present in all parts of the plant and is also found in rayless goldenrod, aka jimmyweed (Isocoma pluriflora), a plant native to the Southwest.

Milk sickness, or chronic tremetol poisoning, is rare now, but the University of Minnesota includes snakeroot among the plants known to be poisonous to livestock. While there is some concern that a return to small-scale, “natural milk” could result in cases of (now treatable) milk sickness, today white snakeroot is more often appreciated as a late-season source of nectar or pollen for bees, wasps, and flies and as a likely host plant for moth larvae (3). It’s available from many native plant nurseries – with some history attached.

To learn how to identify white snakeroot, see this page from the Friends of Eloise Butler Wildflower Garden.

Cited References

(1) A Village Depopulated by the milk sickness. Farmers' Register. Oct1834, Vol. 2 Issue 5, p308-309. 2p. [Obtained through the Hennepin County Library’s database of  American Antiquarian Society (AAS) Historical Periodicals Collection: Series 2.]

(2) Trembles (or milk sickness). James F. Couch. Circular No. 306, United States Department of Agriculture. 1933.

(3) White snakeroot. Illinois Wildflowers, website accessed 9-17-23. 

Additional References

Milk Sickness. Curtis Wood, NCPedia, 2006.

The “Slows”: The Torment of Milksickness on the Midwest Frontier. Walter J. Daly, Indiana Magazine of History 102 (1): 29-40, March 2006.

The Death of Nancy Hanks Lincoln. Philip D. Jordan, Indiana Magazine of History 40 (2): 103-110, June 1944.

Religion and Removal among the Shawnee from Ohio into Kansas. Brady DeSanti, International Journal of Humanities and Social Science 3 (4): 46-56.

How an 1800s Midwife Solved a Poisonous Mystery. Will McCarthy, Smithsonian Magazine, July/August 2023. [Note: A photograph in the article incorrectly labels white snakeroot flowering in spring. It flowers in mid-summer to fall.]

USDA, NRCS. 2023. The PLANTS Database (, 09/17/2023). National Plant Data Team, Greensboro, NC USA.

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