Sources : Seta

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Worms 9.42): A seta [hair, bristle] is a worm, or rather a snake, as some would have it. It has its name from its nature: for this smallest of animals is like a bristle [seta = saeta, bristle/hair], or like one of the hairs of a horse. Now it is a worm about a cubit long, thin and slender, like a hard and white needle, and each end is the same; since it seems to have no head it can crawl both directions with its tail. It is often found in the streams which come from fountains, being born in uncorrupted waters, yet not from foul. It is so hard that it can barely be crushed by the foot. Even if it is placed in boiling water, it cannot be cooked. Its venom is so strong, that if a man drinks anything containing the poison it causes him to languish and melt away, until it takes away his life in severe torture. This alone brings death, not otherwise. - [Badke translation/paraphrase]