Sources : Asp
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): 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... (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 tumour 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 corse ; / 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, Volume 2, Page 237-245]
Pliny the Elder [1st century CE] (Natural History, Book 8, 35): When the neck of an asp swells up, the only remedy for its sting is to immediately amputate the bitten part.
Aelianus [170-230 CE] (On the Characteristics of Animals, Book 1, chapter 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, Chapter 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, chapter 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 agonising 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, chapter 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): 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.  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. - [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): The asp (aspis) kills with a venomous bite, and from this it gets its name, for the Greek word for poison is ios (as). When an enchanter calls an asp out of its cave by incantations and it does not want to go, it presses one ear to the ground and covers the other with its tail, so it cannot hear the enchantment. There are many kinds of asp, but not all are equally harmful. The dipsas is a kind of asp, called in Latin situla because one bitten dies of thirst. The hypnalis is a kind of asp that kills in sleep, as Cleopatra was freed by death as if by sleep when bitten by one. The haemorrhois is called an asp because anyone bitten by it sweats blood; for the Greek word for blood is haima. The prester (or praester) is a kind of asp that always runs with its steaming mouth open; one bitten becomes distended for rot follows the bite.