Bible (Psalm 58:5-6): "...they are like the deaf adder that stops her ear; which will not hearken to the voice of charmers, charming never so wisely".

Lucan [1st century CE] (Pharsalia, Book 9, verse 780-791; 880-906): [Book 9, verse 780-791] Where first within the dust the venom germ / Took life, an asp was reared of turgid neck / And sleep compelling : thick the poison drop / That was his making, in no fang of snake / More closely pressed. Greedy of warmth it seeks / No frozen world itself, nor haunts the sands / Beyond the Nile ; yet has our thirst of gain / No shame nor limit, and this Libyan death. / This fatal pest we purchase for our own. / Hasmorrhois huge spreads out his scaly coils, / Who suffers not his hapless victims' blood / To stay within their veins. ... Greedy prester swells / His foaming jaws... [Book 9, verse 880-906]: But now befell a death in differing form ; / No melted fate ! A burning prester's fang / Nasidius struck, who erst in Marsian fields / Guided the plough. Upon his face there glows / A redness as of flame : the skin is stretched / On one vast tumor past the growth of men ; / A gory juice puffs out upon the mass / That hides his body, and his corslet plates / Burst with the monstrous bulk. Not to such height / In brazen cauldron boils the steaming wave, / Nor in such bellying curves does canvas bend / To western tempests. Now the pile of flesh / No more contains the limbs ; the shapeless trunk / Burdens the earth : and there, untouched by fowl. / To beasts a fatal meal, they leave the course ; / Nor dare to place, yet swelling, in the tomb. / More dreadful sights the Libyan pests prepared....". On Tullus, great in heart, a noble youth. / Fast bound to Cato with admiring soul, / A fierce haemorrhois fixed. From all his members, / As from a statue pressed in every part / Jets forth a saffron spray, there spouts for blood / A ruddy poison : from the natural pores / Of moisture, gore profuse ; his mouth was filled / And gaping nostrils ; blood were all his tears. / Brimmed full his veins ; his very sweat was red ; / All was one wound. - [Ridley, 1919 translation]

Pliny the Elder [1st century CE] (Natural History, Book 8, 35): ...when asps' necks swell up there is no remedy for their sting except the immediate amputation of the parts stung. Although so pestilential, this animal has one emotion or rather affection: they usually roam in couples, male and female, and only live with their consort. Accordingly when either of the pair has been destroyed the other is incredibly anxious for revenge: it pursues the murderer and by means of some mark of recognition attacks him and him only in however large a throng of people, bursting through all obstacles and traversing all distances, and it is only debarred by rivers or by very rapid flight. It is impossible to declare whether Nature has engendered evils or remedies more bountifully. In the first place she has bestowed on this accursed creature dim eyes, and those not in the forehead for it to look straight in front of it, but in the temples — and consequently it is more quickly excited by hearing than by sight; and in the next place she has given it war to the death with the ichneumon. - [Rackham translation]

Aelianus [170-230 CE] (On the Characteristics of Animals, Book 1, 54; 2, 5; 15, 3; 17, 4): [Book 1, 54]...the bite of the asp alone, I am told, cannot be cured and is beyond help. This creature truly deserves to be hated for being blessed with the power to injure. Yet a monster more abominable and harder to avoid even than the asp is a sorceress, such as (we are told) Medea and Circe were, for the poison from asps is the result of a bite, whereas sorceresses kill by a mere touch, so they say. [Book2, 5] Men have, it is true, recovered after a long while from the bite of an asp, either by summoning excision to their aid or with the utmost fortitude enduring cautery, or they have in their plight prevented the poison from spreading by taking the necessary medicines. [Book 15, 13] The Haemorrhous or "Blood-letter" is a species of snake which lives and has its haunts chiefly among rocky hollows. Its body is one foot long, and its width tapers downwards from its broad head to its, tail. At one time it has a fiery hue, at another pitch-black, and on its head there bristle what look like horns. It crawls softly as it scrapes the scales of its belly along the ground, and its course is crooked. And so it makes a gentle rustling, which; shows how sluggish and how feeble it is. But when it bites it makes a puncture which immediately appears dark blue, and the victim suffers agonizing pains in his stomach, while the belly discharges copious fluid. On the first night after, blood streams from the nose and throat and even from the ears: together, with a bile-like poison, and the bladder emits blood-stained water. [Book 17, 4] The Prester also is a species of snake and if it bites, to begin with it makes men lethargic and quite incapable of bestirring themselves, and in the next place they gradually weaken and are unable to breathe. Further, the bite induces loss of memory, stops the flow from the bladder, and causes the hair to fall; then there ensues a choking which causes convulsions, and life ends in agonies. - [Scholfield translation]

Gaius Julius Solinus [3rd century CE] (De mirabilibus mundi / Polyhistor, Chapter 27.31-32, 34): [Chapter 27.31] The species of asps are many and varied, and indeed, they have disparate manners of harming. ... the hypnale kills with sleep. This last is even -- as Cleopatra may bear witness -- purchased for death. [Chapter 27.32] The haemorrhois brings forth blood with its bites, and, having destroyed the circulation, it lures out whatever is left of life through a stream of blood. Whomever the prester pierces becomes distended, and dies swollen to immense corpulence. [Chapter 27.34] If these monsters hiss, they strike more slowly. They have feelings; they do not rashly stray except in couples. If one is captured or killed, the other, left behind, is maddened. The heads of females are more slender, their bellies more swollen and their venom more harmful. The male is equally smooth, higher, and also meeker. - [Arwen Apps translation, 2011]

Augustine of Hippo [5th century CE] (Sermo 316:2 - In Solemnitate Stephani Martyris; Duri Iudaei in Stephanum): As indeed of asps it is said, that when they are lured by incantations, in order that they may not be drawn from their caves they press one ear to the ground, and use their tail to stop up the other, and yet the enchanter can bring it forth... [This appears to be the first time this method of blocking both ears was described]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 4:12-16): [Book 12, 4:12] The asp (aspis) is named thus because with its bite it introduces and scatters (spargere) venom... Whence the term 'asp', because it kills with a venomous bite. There are different kinds with different appearances, some more harmful than others. And it is said that when an asp begins to give in to an enchanter who has called it with certain special chants so that he may draw it from its cave, and the asp does not want to come out, it presses one ear against the ground and blocks and closes up the other with its tail [so that] by not hearing the magic words it does not go out to the enchanter. [Book 12, 4:14] The hypnalis, a type of asp, is so called because it kills by means of sleep. Cleopatra held this snake to herself and thus was overcome by death as if by sleep. [Book 12, 4:15] The haemorrhois asp is so named because whoever has been bitten by it exudes blood, with the effect that as the veins dissolve it draws out through the blood whatever life there is. [Book 12, 4:16] The prester asp hurries with its mouth always open and steaming.The poet recalled this animal thus (Lucan, Civil War 9.722): The greedy prester, swelling out its steaming mouth. Whoever it strikes swells up and is killed by a tremendous bodily swelling, and this swelling is accompanied by putrefaction. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Serpents 8.2; 8.18; 8.19; 8.26)L [Thomas describes the asp under the names aspide, emorrois and ipnapis.] [Serpents 8.2] The asp [aspide] is a cerulean-colored snake. With its bite it injects poison and scatters it, whence it received its name: for the asp, as Jacobus says, is called poison in Greek: and hence the asp, because it destroys with a poisonous bite. It is enchanted by an incantation, so that it will not kill the enchanter with poison or, as some say, so that the precious stone that naturally grows in its forehead can be taken safely. But it is naturally wary against a charmer; for when it perceives the incantations of the wise magician, it stops one of its ears with its tail, and presses the other to the ground, so that it may not hear the voice of the enchanter. The asp, as Solinus says, lives only with its mate; and hence it happens, that one being slain, the other is incredibly anxious for vengeance: it pursues the slayer, and attacks him in a crowd of any size; it breaks through all difficulties, it penetrates spaces, and, unless it is driven away by rivers or forced to flee, it does not allow the murderer to live. As the Experimentator says, the asp does no harm to the Africans or the Syrians; whence they expose their children to the serpents, and if they bite them, they cast the child out as the product of adultery; if not, they nourish them as if they were their own. When an asp, coming to the table of a certain rich man in Egypt was constantly being fed, she gave birth to offspring, by one of which a guest's son was killed. And when the mother asp had returned to the customary feeding, and having understood her fault, she killed her offspring, and afterwards she did not seek shelter. The teeth of the asp are exceedingly long, so that they appear outside the mouth like a boar.[Serpents 8.17] Emorrois is a snake, as Solinus says, drawing blood with its bite, and drawing out all the blood through the broken channels of the veins. [Serpents 8.19] Ipnapis is a serpent, as Solinus says, a kind of asp, which kills those who it bites in their sleep. For its poison induces sleep, which kills the infected with no impact. Cleopatra placed this serpent on her left arm, placing herself in the tomb next to Antony, so that by its touch she might fall asleep and end her life in a quiet death. Solinus calls this ypnale aspidem because it is a species of asp. [Serpents 8.26] Prester is a serpent, as Jacobus and Solinus say, that always runs with its mouth open and steaming. It is said to descend from the race of asps; whence the poet [Lucan]: And stretching out it mouth, the avid smoking prester. Whoever this serpent strikes, therefore, his body swells enormously as if it were suffering from dropsy [water retention illness], and thus he dies, for reddening is followed by putrefaction, and with sores he is destroyed. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book18.10): Aspis is an Adder worst and most wicked in venime & in biting, & hath that name Aspis, of Aspergendo, springing: for he casteth out e venime, and spitteth and springeth out venime by bitings. For the Gréekes call venim Yos, as Isidore sayth, libro. 12. capit. 4. And it followeth there: Of adders that be called Aspis bée divers manner kind, and have diverse effects and dooings, to noy and to grieve ... Ipalis is a manner adder, that slayeth with sléepe. These manner adders Cleopatra layde by her, and passed out of the lyfe by death, as it were a sléepe. Also Nemorrhois is a manner adder, and hath that name, for hée sucketh the bloud of him that he smiteth, and his veines that is smitten of the adder openeth and breaketh, and he bléedeth to death. For bloud is called Emath in Gréeke. Also Prester is an horrible adder, alwaye with open mouth, & casting and shedding venim, as hée goeth. Lucanus speaketh of him and saith. Oraque distendens avidus spumantia Prester. This adder is a glutton, & sheddeth smoking venim with open mouth. Hée yt is smitten of him, is rented & slaine with horrible infection of the body, as he sayth there. ... and ther be many other adders, & the venim of them is so strong, yt they slay with their venim him yt toucheth them with a speare, as Avicen[na] sayth de venenis. Also Isidor. li. 12. speaketh of this manner adder, yt is called Aspis in generall, & saith, that it is said, that ye adder Aspis, when she is charmed by ye inchaunter, to come out of her denne by charmes & comurations, for she hath no will to come out, laieth her one eare to ye ground, & stoppeth ye other with her taile, & so she heareth not the voice of the charming, nor commeth out to him ye charmeth, nor is obedient to his saieng. Huc vsque Isidorus. Plinius libro. 8. capitulo 24. speaketh of the adder Aspis, & sayth, that the members that bée smit of this Adder do swell, and unneth is any remedie found to heale such biting, without cutting of the partes that bee touched. This flyeng Adder and venimous hath wit to love and affection and loveth his make as it were by love of wedlocke, and liveth not well without companye. Therefore if the one is slaine, the other pursueth him that flewe that other with so busie wreake and vengeaunce, that passeth thinking: and knoweth the slaier, & reefeth on him, be he in never so great company of men and of people; & busieth to slay him, and passeth all difficulties & spaces of wayes, & with wreake of the sayd death of his make. And is not let nor put of, but it be by swift flight, or by waters or rivers: but against his mallice kind giveth remedye and medicine: For kinde giveth him right dimme sight, for his eyen are set in the sides of his head, and be not set in the forehead: and therefore be may not see his adversarye foorth right, but aside. Therefore hee maye not follow his enimy by sight, but he followeth more by hearing and smell: for in this two wits he is strong and mightie, as he sayth. ... Also Marcianus saith, that this Adder Aspis grieveth not men of Affrica and Moores: for they take their childre¯ yt they have suspect, & put them to these Adders: And if the children be of their kind, this adder Aspis grieveth the¯ not: and if they be of other kinde, anone he dyeth by venim of the Adder. And this Plinius sayth expresly, lib. 6. cap. ultimo, and saith, that sometime this beast grieveth no men of the land, and slaieth straungers and men of other lands. And these Serpents spare wonderfully men yt be borne in the same land. So the Serpent Anguis about the river Euphrates, gréeveth not, nor hurteth men of the lande, nor noyeth them that sleepe, if they be of that lande, and paine & slay busily other men, that be of other nations, what nation so every it be. Also there Plinius saith, that Aristotle sayth, that in a certaine mountaine Scorpions grieve no strangers: but they sting & slay men of the countrey. - [Batman]

Slavic Physiologus [15th - 16th century]: The aspide has a wonderful beauty. The male lives in the east and the female in the west. When it is time for breeding, the female comes from the west and the male from the east, and they come to the centre of the earth. [And the female opens her mouth, and the male places his head inside] and the female eats the head of her husband and he dies [and so she conceives]. When she gives birth to her offspring and brings them up, [they] eat their mother's head and she dies. When the offspring grow up, the males go eastward [and the females westward], as their parents did, until their breeding time comes. An area as big as a threshing floor burns from the breath of the female, where she lies. The ground burns three sazhens deep and whatever she looks at, it burns. And how does the enchanter catch her? The enchanter comes to the place, where [the aspide] lies and covers himself with green grass, and pours vinegar on the grass for seven days, until the grass goes mouldy from the vinegar. He takes a stick ten elbows [long] and appears before her eyes from the direction of the wind, so as not to be affected by her [fiery] breath. And shouting from afar, he approaches her. He throws mistletoe at her. [The mistletoe] catches fire and burns. The second throwing drains it. By the fourth throwing, it is burned. And by the seventh throwing, [the aspide] has no more fire. Thus, [the enchanter] approaches her. And she covers herself with [her] tail and, to prevent hearing the enchanter's voice, clogs her ears [because] if she hears, she will die. That is why man has eyes and ears. As the prophet said: "I heard your voice, and I was afraid." Having taken his stick, the enchanter removes the tail [of the aspide] from her eyes and ears, and shouts out loud. And as soon as she has heard, she dies. Then he takes what he needs from her. - [Stoykova, English translation by Mladenova and Stoykov]