Horsemint is purple plant that grows in Texas. PL identifies it on nature walks, and often tells about how it was used as an insect repellant, which is how it got called horsemint.
PL: “One time a man was there whose dad used it often. His dad had horses, and would bundle up the horsemint, tie to rafters in barn, and shoe horses where the plant would rub on their backs. It worked as an insect repellent to keep flies off horses, that way they wouldn’t more or become too agitated for the farrier.”
Horsemint actually contains citronellol, a natural insect repellent, so it turns out the folk practice in this case is actually very functional. Bug sprays and other commercial products use the same type of ingredients.