Vermilion is a mineral red with an insect in its name.
The word goes back to Late Latin vermiculus, "little worm," a diminutive of vermis, "worm." Etymonline says vermiculus was a name for the cochineal insect, a tiny bug crushed to make crimson dye. From it came Old French vermeil, "bright red." From that came vermeillon, a 12th-century word for red lead, cinnabar or cosmetic rouge.
English borrowed the word in the late 1200s as vermiloun. By then it meant cinnabar, natural mercuric sulfide, or the red pigment ground from it. So in English the word has meant the mineral red from its first records. The bug survives only in its etymology. The adjective sense, "of the color of vermilion," appears by the 1580s.
The pigment is ancient. The Metropolitan Museum of Art says cinnabar and vermilion are both mercuric sulfide: cinnabar is the mineral, vermilion the pigment. People have mined cinnabar since at least the 10th millennium BCE. The Met calls natural vermilion the most expensive pigment the Romans used in wall paintings. Their ore came from Almadén in Spain.
Vermilion was also made artificially. In the dry method, mercury and sulfur were heated in a sealed container. The Met says this may have been developed in China as early as the 4th century BCE. Until cadmium red appeared in the early 20th century, vermilion was the most widely used red pigment.
Naming red dyes after small creatures was not unique to Latin. Etymonline traces kermes, another red-dye insect, back through Arabic to Sanskrit krmi-ja, "produced by a worm." Greek speakers went the other way and called it kokkos, "grain." That reflected a mistaken belief that the dye came from part of a plant.
The worm also survives elsewhere in English. Etymonline lists vermin and vermiform among the words built on Latin vermis. Italian verme, from the same Latin word, gave vermicelli, literally "little worms," named for the pasta's shape.