A fungus known as Claviceps purpurea is known as the plant disease ergot. Ergot does have good uses, as it is used pharmaceutically to produce drugs used to induce labor in pregnant women and to control bleeding after childbirth; ergotamine, an ergot alkaloid, is used to treat migraine headaches.

But it also has a bad side: Eating bread and other grain products contaminated with ergot causes a disease called St. Anthony’s fire. Common during the Middle Ages, this disease caused sensations of intense heat followed by a complete loss of sensation in an infected person’s limbs; if cattle that graze on grains infected with ergot ingest enough, it can cause death or the spontaneous abortion of fetuses. But ergot is now much rarer thanks to improved techniques in grain production and milling.