Ergot is a fungus in the genus Claviceps that infects cereal grains and grasses, replacing their seeds with dark, hard structures called sclerotia. These sclerotia contain potent chemical compounds that have caused mass poisonings throughout history, inspired modern pharmaceuticals, and played a role in the discovery of LSD. The most common species, Claviceps purpurea, can infect roughly 400 different grass species, but rye is by far its most frequent and economically important target.
How Ergot Infects Grain
Ergot fungi target young, unfertilized ovaries inside the flowering heads of grasses and cereals. Once the fungus takes hold, it slowly consumes the developing seed and replaces it with a dense mass of fungal tissue. This mass, the sclerotium, has a dark purple-black outer layer that protects the fungus from drying out, UV light, and other environmental threats. Inside, the tissue is whitish and packed with storage cells that fuel the next stage of the fungus’s life cycle.
In rye, sclerotia can grow up to 4 to 5 centimeters long, and multiple sclerotia sometimes develop on a single grain head. They’re visible to the naked eye and look like elongated, dark protrusions sticking out where seeds should be. When infected grain is harvested and the sclerotia fall to the ground, they overwinter in the soil and produce new spores the following season, restarting the cycle.
While Claviceps purpurea dominates in temperate regions like Northern Europe and North America, other species cause problems elsewhere. Claviceps africana infects sorghum across the tropics, and Claviceps fusiformis targets pearl millet in Africa and India, where that crop has been grown for thousands of years.
What Ergot Contains
Ergot sclerotia contain between 0.15% and 0.5% alkaloids by weight, and researchers have identified more than 80 individual compounds in this chemical cocktail. All of them share a common structural backbone: lysergic acid, a molecule built on a four-ring system called ergoline. The alkaloids split into several groups based on their complexity. Simpler ones are formed when lysergic acid bonds with small alcohol-like molecules. The larger, more complex alkaloids are chains of three amino acids linked to lysergic acid, creating compounds like ergotamine and ergocristine.
These alkaloids are biologically active in mammals, meaning even small amounts can powerfully affect the body. Their most important effect is constricting blood vessels, which reduces blood flow to the extremities and the brain. This property is what made ergot both a deadly poison and, centuries later, a source of useful medicine.
Ergotism: The Disease Ergot Causes
When people eat bread or grain contaminated with ergot sclerotia, the alkaloids accumulate in the body and cause a condition called ergotism. It takes two main forms, both driven by the same underlying mechanism: the alkaloids trigger intense spasms in blood vessels, cutting off blood supply to tissues.
Gangrenous ergotism, the more visually horrifying form, starts with intense burning pain in the hands and feet. As blood flow is progressively choked off, affected tissues die. In severe cases during historical outbreaks, fingers, toes, and entire limbs turned black, dried out, and eventually fell off without bleeding. This is the form that earned the disease its medieval nickname.
Convulsive ergotism affects the nervous system more directly. Victims experienced seizures, muscle spasms, hallucinations, and a crawling sensation on the skin. Both forms could occur in the same outbreak, though gangrenous symptoms were more commonly reported in European epidemics.
St. Anthony’s Fire and Medieval Outbreaks
Ergotism was one of the great scourges of medieval Europe. The first recorded outbreak of gangrenous ergotism appeared in Germany in 857 AD, and at least 83 epidemics were documented across Europe from 945 AD onward, a list historians consider incomplete. France, Germany, and Scandinavia were hit hardest, largely because rye was a staple grain in those regions.
The disease became known as “St. Anthony’s fire” because people in Catholic countries prayed to St. Anthony for relief from acute skin afflictions. Folk belief held that St. Anthony had cured skin diseases using pork fat, which could soothe inflammation and itching. The “fire” referred to the searing, burning sensation that victims felt in their limbs as blood flow was cut off.
For centuries, no one understood what caused these outbreaks. The German physician Wendelin Thelius was the first to connect ergotism to contaminated grain, after documenting an epidemic in the Kingdom of Hesse in 1596. Nearly two centuries later, a French physician named Tessier observed an enormous outbreak in Sologne, France, in 1778 that killed more than 8,000 people. Tessier pushed for practical reforms: draining fields, cleaning grain thoroughly, and replacing infected rye with potatoes. Sporadic outbreaks continued into the twentieth century, with one striking as late as 1951 in France, affecting nearly 250 people.
The Salem Witch Trials Theory
One of the most debated claims about ergot is that it caused the Salem witch trials of 1692. The hypothesis, popularized by researcher Mary Matossian, argued that weather conditions in Salem could have promoted ergot growth, that the age distribution of those showing symptoms matched known ergot victims, and that the reported symptoms resembled convulsive ergotism.
The theory has been critically examined and largely rejected by historians and scientists. Critics point out that the events at Salem are better explained by the social and political dynamics of seventeenth-century Puritan communities. The symptoms of “demonic affliction” appear to have been learned behaviors, legitimized by a community that believed in witchcraft, rather than signs of poisoning. While the idea makes for a compelling story, the evidence doesn’t hold up under scrutiny.
From Poison to Pharmacy
The same alkaloids that caused mass death also became valuable medicines once they could be isolated and dosed precisely. Ergotamine, one of the larger peptide alkaloids in ergot, is still used to treat migraine headaches. It works by constricting the dilated blood vessels that contribute to migraine pain. The standard dose is a 2-milligram tablet placed under the tongue at the first sign of an attack, with limits of no more than three tablets per day.
Other ergot-derived compounds have been used to control bleeding after childbirth by causing the uterus to contract. The ability of these alkaloids to tighten smooth muscle tissue, the same property that causes gangrene in overdose, becomes therapeutic at controlled doses.
The most famous chemical offspring of ergot is LSD. In 1938, Swiss chemist Albert Hofmann was working with lysergic acid, the core molecule shared by all ergot alkaloids, at the Sandoz pharmaceutical laboratory in Basel. He synthesized a series of lysergic acid derivatives, including the 25th compound in the series: lysergic acid diethylamide, or LSD-25. Hofmann didn’t discover its psychoactive effects until 1943, when he accidentally absorbed a small amount through his skin. The entire history of psychedelic research traces back to this fungal molecule.
How Ergot Is Kept Out of Food Today
Modern grain handling makes large-scale ergotism outbreaks extremely unlikely in developed countries, but the fungus hasn’t disappeared. Ergot still infects rye, wheat, barley, and other cereals every growing season, and food safety standards set strict limits. In the United States, wheat containing more than 0.05% ergot sclerotia by weight is classified as “ergoty wheat” under USDA grading standards.
At harvest and processing facilities, optical-electronic color sorters separate the purple-black sclerotia from grain. This works especially well with lighter-colored wheat and barley, though the bluish-gray color of rye kernels makes sorting slightly more challenging.
On the farm, prevention starts before harvest. Crop rotation breaks the cycle of spores overwintering in soil. Removing wild grasses from field margins eliminates alternate hosts where the fungus can reproduce. Fungicide applications timed around flowering, when the plant is most vulnerable, can suppress infection. Breeding programs are developing wheat and rye varieties with traits that naturally resist ergot, including tighter floret closure and more synchronized flowering, both of which shrink the window during which the fungus can enter the plant. In practice, the best results come from combining resistant varieties with good field management and targeted chemical treatments.