Venomous snakes have venom glands and specialized teeth for the injection of venom. Members of the families Elapidae, Viperidae, Hydrophiidae, and Atractaspididae (and some from Colubridae, as well) are major venomous snakes.
Venomous snakes use modified saliva, snake venom, usually delivered through highly specialized teeth, such as hollow fangs, for the purpose of prey immobilization and self-defense. In contrast, nonvenomous species either constrict their prey, or simply overpower it with their jaws.
Venomous snakes include several families of snakes and do not form a single taxonomic group. This has been interpreted to mean venom in snakes originated more than once as the result of convergent evolution.
Evidence has recently been presented for the Toxicofera hypothesis; however, venom was present (in small amounts) in the ancestors of all snakes (as well as several lizard families) as ‘toxic saliva’ and evolved to extremes in those snake families normally classified as venomous by parallel evolution.
The Toxicofera hypothesis further implies that ‘nonvenomous’ snake lineages have either lost the ability to produce venom (but may still have lingering venom pseudogenes), or actually do produce venom in small quantities, likely sufficient to assist in small prey capture, but cause no harm to humans if bitten.
Lists or rankings of the world’s “most venomous snakes” are tentative and differ greatly due to numerous factors, including the age and reliability of the data.
Tiger snakes are a type of venomous serpent found in southern regions of Australia, including its coastal islands and Tasmania. These snakes are highly variable in their colour, often banded like those on a tiger, and forms in their regional occurrences. All populations are in the genus Notechis, and their diverse characters have been described in further subdivisions of this group; they are sometimes described as distinct species and/or subspecies.
A genus of large venomous snake in the family Elapidae restricted to subtropical and temperate regions of Australia. Tiger snakes are a large group of distinct populations, which may be isolated or overlapping, with extreme variance in size and color. Individuals also show seasonal variation in color. The total length can be up to 2.1 meters (7 ft). The patterning is darker bands, strongly contrasting or indistinct, which are pale to very dark in color.
Coloration is composed of olive, yellow, orange-brown, or jet-black, the underside of the snake is light yellow or orange. The tiger snake uses venom to dispatch their prey, and may bite an aggressor; they are potentially fatal to humans. Tolerant of low temperatures, the snake may be active on warmer nights. When threatened they will flatten their body and raise their head above the ground in a classic pre-strike stance.
Desert Horned Viper
Cerastes cerastes Or Desert Horned Viper is a venomous viper species native to the deserts of Northern Africa and parts of the Middle East. They often are easily recognised by the presence of a pair of supraocular horns, although hornless individuals do occur. No subspecies are currently recognised.
The average length is 30–60 cm (0.98–2.0 ft), with a maximum of 85 cm (33 in). Females are larger than males.One of the most distinctive characteristics of this species are the supraorbital horns, one over each eye. However, these may be reduced in size or absent (see Cerastes).
The eyes are prominent and set on the side of the head. There is significant se*ual dimorphism, with males having larger heads and larger eyes than females. Compared to C. gasperettii, the relative head size of C. cerastes is larger and there is a greater frequency of horned individuals (13% versus 48% respectively).
The colour pattern consists of a yellowish, pale grey, pinkish, reddish or pale brown ground colour that almost always matches the substrate colour where the animal is found. Dorsally, a series of dark, semi-rectangular blotches run the length of the body. These may or may not be fused into crossbars. The belly is white and the tail may have a black tip, the tail is usually thin.
The common krait (Bungarus caeruleus, also known as Indian krait or Blue krait) is a species of genus Bungarus found in the jungles of the Indian subcontinent. It is a member of the “big four”, species inflicting the most snakebites in India.
The body colour varies from a dark steely blue-black to a pale faded bluish grey. The average length is 0.9 meters (2 ft 11 in) but they can grow to 1.75 meters (5 ft 9 in). Subcaudal scales after the anal plate are not divided. It has large hexagonal scales running down its spine. The narrow white cross bands are more prominent near the tail region. The male is larger than the female and also has a longer tail.
The boomslang (Dispholidus typus) is a large, venomous snake in the family Colubridae. The average adult boomslang is 100-160 cm (3¼-5¼ feet) in total length, but some exceed 183 cm (6 feet). The eyes are exceptionally large, and the head has a characteristic egg-like shape. Coloration is very variable. Males are light green with black or blue scale edges, but adult females may be brown.
In this species, the head is distinct from the neck and the canthus rostralis is distinct. The pupils of the very large eyes are round. The maxillary teeth are small anteriorly, seven or eight in number, followed by three very large, grooved fangs situated below each eye. The mandibular teeth are subequal. The body is slightly compressed.
The dorsal scales are very narrow, oblique, strongly keeled, with apical pits, arranged in 19 or 21 rows. The tail is long, and the subcaudals are paired. Ventrals are 164-201; the anal plate is divided; and the subcaudals are 91-131.
The boomslang is a timid snake, and bites generally occur only when people attempt to handle, catch or kill the animal.
The above data suggest boomslangs are unlikely to be a significant source of human fatalities throughout their distribution range.
There is huge variation among different lists regarding the strength of the venom of the tiger rattlesnake, which is found in the southwestern United States and northwestern Mexico.
One source puts its venom’s LD50 at 0.06 while others have it much higher – and therefore less toxic. What does seem certain, however, is that this species has the highest toxicity of all rattlesnakes, and while the venom it yields is comparatively low, being bitten by one of these snakes should be deemed a critical emergency.
The black mamba (Dendroaspis polylepis), also called the common black mamba or black-mouthed mamba, is the longest venomous snake in Africa, averaging around 2.5 to 3.2 meters (8.2 to 10 ft) in length, and sometimes growing to lengths of 4.45 meters (14.6 ft). It is named for the black colouration inside the mouth rather than the colour of its scales which varies from dull yellowish-green to a gun-metal grey.
It is the fastest snake in the world, capable of moving at 4.32 to 5.4 metres per second (16–20 km/h, 10–12 mph). It has a reputation for being aggressive and highly venomous and is among the world’s most venomous land snakes.
Eastern Brown Snake
The eastern brown snake (Pseudonaja textilis), often referred to as the common brown snake, is a species of genus Pseudonaja. This snake is considered the second most venomous land snake based on its LD50 value (SC) in mice. It is native to Australia, Papua New Guinea and Indonesia.
Adult eastern brown snakes are highly variable in colour. Whilst usually a uniform shade of brown, they can have various patterns including speckles and bands, and range from a very pale fawn colour through to black, including orange, silver, yellow and grey. Juveniles can be banded and have a black head, with a lighter band behind, a black nape, and numerous red-brown spots on the belly.
This species has an average length of 1.5–1.8 m and it is rarely larger than 2 m. Large eastern brown snakes are often confused with “king brown” snakes (Pseudechis australis), whose habitat they share in many areas.
Daboia are commonly known as Russell’s viper and chain viper, among other names.
Daboia is a monotypic genus of venomous Old World viper. The single species, D. russelii, is found in Asia throughout the Indian subcontinent, much of Southeast Asia, southern China and Taiwan.
The species was named in honor of Patrick Russell (1726–1805), a Scottish herpetologist who first described many of India’s snakes; and the genus is after the Hindi name meaning “that lies hid”, or “the lurker.”
Apart from being a member of the big four snakes in India, Daboia is also one of the species responsible for causing the most snakebite incidents and deaths among all venomous snakes on account of many factors, such as their wide distribution and frequent occurrence in highly-populated areas. Two subspecies are currently recognized, including the nominate subspecies described here.
This snake can grow to a maximum length of 166 cm (5.5 ft) and averages about 120 cm (4 ft) on mainland Asian populations, although island populations do not attain this size. It is more slenderly built than most other vipers. Ditmars (1937) reported the following dimensions for a “fair sized adult specimen”:
The head is flattened, triangular and distinct from the neck. The snout is blunt, rounded and raised. The nostrils are large, in the middle of a large, single nasal scale. The lower edge of the nasal touches the nasorostral. The supranasal has a strong crescent shape and separates the nasal from the nasorostral anteriorly. The rostral is as broad as it is high.
The crown of the head is covered with irregular, strongly fragmented scales. The supraocular scales are narrow, single, and separated by 6–9 scales across the head. The eyes are large, flecked with yellow or gold, and each is surrounded by 10–15 circumorbital scales.
There are 10–12 supralabials, the 4th and 5th of which are significantly larger. The eye is separated from the supralabials by 3–4 rows of suboculars. There are two pairs of chin shields, the front pair of which are notably enlarged. The two maxillary bones support at least two and at the most five or six pairs of fangs at a time: the first are active and the rest replacements. The fangs attain a length of 16 mm in the average specimen.
The body is stout, the cross-section of which is rounded to cylindrical. The dorsal scales are strongly keeled; only the lower row is smooth. Mid-body, the dorsal scales number 27–33. The ventral scales number 153–180. The anal plate is not divided. The tail is short — about 14% of the total body length — with the paired subcaudals numbering 41–68.
The color pattern consists of a deep yellow, tan or brown ground color, with three series of dark brown spots that run the length of its body. Each of these spots has a black ring around it, the outer border of which is intensified with a rim of white or yellow.
The dorsal spots, which usually number 23–30, may grow together, while the side spots may break apart. The head has a pair of distinct dark patches, one on each temple, together with a pinkish, salmon or brownish V or X pattern that forms an apex towards the snout. Behind the eye, there is a dark streak, outlined in white, pink or buff. The venter is white, whitish, yellowish or pinkish, often with an irregular scattering of dark spots.
Taipan (Inland Taipan)
The Inland Taipan (Oxyuranus microlepidotus), also known as the Small Scaled Snake and Fierce Snake, is native to Australia and is regarded as the most venomous land snake in the world based on LD50 values in mice. It is a species of taipan belonging to the Elapidae family. Although highly venomous, it is very shy and reclusive, and always prefers to escape from trouble (the word “fierce” from its alternate name describes its venom, not its temperament).
The Inland Taipan is dark tan, ranging from a rich, dark hue to a brownish olive-green, depending on season. Its back, sides and tail may be different shades of brown and grey, with many scales having a wide blackish edge. These dark-marked scales occur in diagonal rows so that the marks align to form broken chevrons of variable length that are inclined backward and downward.
The lowermost lateral scales often have an anterior yellow edge. The dorsal scales are smooth and without keels. The round-snouted head and neck are usually noticeably darker than the body (glossy black in winter, dark brown in summer), the darker colour allowing the snake to heat itself while only exposing a smaller portion of the body at the burrow entrance.
The eye is of average size with a blackish brown iris and without a noticeable coloured rim around the pupil. It has twenty-three rows of mid-body scales, between fifty-five and seventy divided subcaudal scales, and one anal scale. The Inland Taipan averages approximately 1.8 metres (5.9 ft) in length, although larger specimens can reach lengths of 2.5 metres (8.2 ft).
The Inland Taipan’s venom consists of Taipoxin and protease enzymes, the average quantity of venom delivered by this species is 44 mg and the maximum dose recorded is 110 mg. The median lethal dose (LD50) for mice is 2 μg/kg (ppb) for pure Taipoxin and 30 μg/kg (ppb) for the natural venom mixture. Its venom consists mostly of neurotoxins.
Enhydrina schistosa, commonly known as the beaked sea snake, hook-nosed sea snake, common sea snake, or the Valakadyn sea snake, is a highly venomous species of sea snake common throughout the tropical Indo-Pacific. This species is implicated in more than 50% of all bites caused by sea snakes, as well as the majority of envenomings and fatalities.
The rostral scale is longer than broad, and is in contact with four shields; frontal more long than broad, shorter than the parietals; nasals in contact with the two anterior labials; sometimes partially divided; one pre- and one or two postoculars; temporals l–3; seven or eight upper labials, fourth or third and fourth entering the eye, the last sometimes divided; anterior chin-shields rather indistinct, separated.
Scales with a tubercle or keel, in 50–70 rows; ventrals 230–314, slightly enlarged. The snake is usually uniformly dark grey above; sides and lower parts whitish. Young specimens olive or grey with black transverse bands, broadest in the middle. Length of head and body 1110 mm; tail 190 mm.
The venom of this species is made up of highly potent neurotoxins and myotoxins. This widespread species is responsible for the vast majority of deaths from sea snake bites (up to 90% of all sea snake bites). The LD50 value is 0.1125 mg/kg based on toxicology studies. The average venom yield per bite is approximately 7.9–9.0 mg, while the lethal human dose is estimated to be 1.5 mg. All seasnake antivenom is formulated using the Beaked sea snake venom.