The seta is found in some medieval encyclopedias. It is a thin worm that is like a bristle or hair (seta = saeta, hair), about a cubit long, looking like a hard white needle. It seems to have no head, since both ends look the same. It is too hard to be crushed and cannot be cooked even in boiling water. Its venom can kill a human.

The Latin word saeta (of which seta is an alternate form) means hair or bristle. In modern biology it refers to any hair-like structure on a living organism, not to a particular species.