Sources : Naderos

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Serpents 8.25): Naderos is a serpent that is found in the region of Germany. It is about the thickness of a human arm; the color of the belly is golden, the back is green. Its breath is said to be so noxious, that if you apply a freshly cut stick to its mouth, its breath will cause the bark to erupt into blisters. But if you put a shining sword in its mouth so that its tongue alone touches the sword at the bottom, the serpent infects the sword with its poison, and running up to the top of the sword it infects it with a dark and cerulean color, as if a violent flame had burned it. A man infected with this poison dies, unless he is aided by tyriaca [a medicinal herb]. Now the mode of the poison itself is that, when it has struck a man in the foot, the poison runs in a few moments to the other members, and this by the excessive excess of heat, which is of the same nature as fire, which always rises. Therefore the poison itself always ascends until it touches the heart, and then the man falls and dies. The remedy is that a person who has been struck in the foot is suspended by the feet in a high place with his head lowered, and thus the poison cannot ascend to the heart, but when it reaches the top of the foot it remains in place and cannot descend lower; and then the infected place is cut out and cured by medicines. If any one wishes to walk with impunity, that is safely, in a place where these snakes live, he rubs his feet and hands with rue and wormwood, that is, the limbs which are open to danger, and thus the snake will avoid the man, and with the man protected by herbal remedies it will not dare to touch his limbs. - [Badke translation/paraphrase]

Albertus Magnus [ca. 1200-1280 CE] (De animalibus, Book 25, 41): Naderos is a snake found in Germany and is said to belong to the second category of serpents. It has a length of two or more cubits and a thickness equal to a man’s forearm. Its belly tends to be a golden-yellow color and its back is somewhat greenish; its venom creeps from the location of the bite into the whole body, unless speedy counter-measures are taken. According to reports, it taints staffs and swords if it touches them with its tongue, so much so that the color of the wood or steel is changed. - [Scanlan]