Sources : Siren (Serpent)

Isidore of Seville [7th century CE] (Etymologies, Book 12, 4:29): In Arabia there are snakes with wings, called sirens [sirena]; they move faster than horses, but they are also said to fly. Their venom is so powerful that when someone is bitten by them death ensues before the pain is felt. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Serpents 8.35): Sirens are serpents, just as sirens are sea monsters. As the Experimentator says, they live in the region of Arabia and are faster than a running horse. Some of them have wings and can fly. Of these the venom is most effective in bringing death, so that the bite is followed by death rather than pain. But it signifies those who are conscious of sin and full of remorse when they commit sins, and yet are so miserable and weak that they allow themselves to be overcome by wicked temptation. Their sins, according to the apostle, are already judged. The worms of conscience begin to gnaw at them here and will not stop forever. Hence Isaiah: Their worms do not die and the fire is not extinguished. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book18.96): And Isidore lib. 12. saith, that in Arabia be serpents with wings, that be called Sirene & run more swiftly then horses, and doe flye, and also it is sayd, that they flye with wings, and theyr venimme is so strong, that death is self sooner then ach or sore. - [Batman]