The puff adder Bitis arietans is a large, venomous snake that occurs throughout Africa and in the southwestern Arabian peninsula. This species usually reaches a maximum length of approximately 1 m, but the largest individuals may be nearly twice that long. Its relatively dull coloration, consisting of a pattern of dark chevrons on a lighter tan or brown background, camouflages the snake very effectively. This species is a primarily nocturnal ambush predator, preying on small mammals, birds, lizards, frogs, and toads, and while it spends most of its time on the ground, it can also swim or climb into low vegetation. It is generally slow-moving, but it can strike extremely quickly.
Due to its wide distribution, potent venom, and highly cryptic coloration which makes it prone to being stepped on inadvertently, Bitis arietans is thought to kill more people than any other African snake (Mallow et al. 2003), accounting for nearly 32,000 deaths per year and many more disabilities (Swaroop and Grab 1954). Its venom is highly toxic, capable of causing massive tissue necrosis, hypotension, coagulopathy, thrombocytopenia, and spontaneous bleeding, apparently adapted to immobilize prey and begin the digestive process. However, unlike in some of its close relatives, the venom of B. arietans acts relatively slowly, and with proper treatment, death can be prevented in 90-95% of cases (Spawls and Branch 1995, Lavonas et al. 2002, Mallow et al. 2003).
Bitis arietans is thought to be the most common and widespread snake in Africa, occurring throughout the continent except in some forested regions and extreme deserts such as the Sahara. This species also occurs in Yemen and southwestern Saudi Arabia (Broadley 1983, Spawls and Branch 1995, Mallow et al. 2003).
Distribution: Republic of South Africa, Swaziland, Namibia, Botswana, Zimbabwe, Mozambique, Malawi, Zambia, Angola, Tanzania, Burundi, Rwanda, Uganda, Kenya, Democratic Republic of the Congo (Zaire; except in the Center), Congo (Brazzaville), Gabon, Burkina Faso, Equatorial Guinea, Cameroon, Central African Republic, Niger, Nigeria, Benin, Togo, Ghana, Ivory Coast, Liberia, Sierra Leone, Eritrea, Ethiopia, Somalia, Guinea, Guinea-Bissau, Gambia, Senegal, Mauritania, Western Sahara, Mali, Sudan [abukhalil.mohamed, pers. comm.], Algeria, Morocco, SW Saudi Arabia, Oman somalica: Somalia, N Kenya
Type locality: Cape of Good Hope = South Africa.
Bitis arietans is a relatively large, stout viper, rarely exceeding 1 m in total length but occasionally reaching almost 2 m. Its head is broad, flat, and subtriangular with small, imbricate rostral scales. The nostrils face vertically upwards. There is a circumorbital ring of 10-16 scales, and there are 3-4 scale rows between the suborbital and the 12-17 supralabials (Mallow et al. 2003). The nasal and the rostral are separated by 2-3 scale rows, and there are 13-19 sublabials, the first 3-5 of which border the chin shields. The anal plate is entire (Broadley 1983). There are 29-41 dorsal scale rows at midbody, the inner rows of which are strongly keeled. There are 123-147 ventral scales, and 14-38 subcaudals (no more than 24 in females) (Mallow et al. 2003). Two long, hollow, and recurved fangs are present at the anterior end of the substantially shortened maxillary. These fangs articulate with the shortened maxilla, which in turn articulates with the palatomaxillary arch (Pough et al. 2004). When not in use, the fangs fold up against the roof of the mouth into a protective fleshy sheath. The palatines and pterygoids bear small recurved teeth, which decrease in size posteriorly (Broadley 1983).
This species exhibits some geographic variation in coloration, but in general there is a dark band on the crown of the head and another between the eyes. Two oblique bars extend from the eye to the lip, and the eye itself may be gold to silver gray. Dorsally, the coloration ranges from straw yellow to reddish brown, with a pattern of dark chevrons extending along the back and continuing as 2-6 dark crossbands on the tail, although abundant brown or black speckles may obscure this pattern in some individuals. Coloration on the ventral surfaces is white to yellow, usually with several dark spots (Spawls and Branch 1995, Mallow et al. 2003). Juveniles tend to have golden markings on the head, and their lateral ventral plates are pinkish to reddish. (Mallow et al. 2003). Coloration is somewhat variable within this species, with individuals from the eastern part of its range tending to be more brightly colored than individuals from western habitats, which are paler and more drab. Males in general tend to be more brightly colored than females (Broadley 1983, Branch 1988). Unusual color patterns, including a light vertebral stripe, have also been observed in this species (Branch 1988, Mallow et al. 2003).
Bitis arietans averages approximately 1 m in total length, although the largest specimens recorded exceed 190 cm in length, 6.0 kg in weight, and 40 cm in girth. Males tend to be longer than females, with proportionally longer tails, but females may be more massive, especially when gravid (Mallow et al. 2003).
Bitis arietans is a relatively large, stout viper, rarely exceeding 1 m in total length but occasionally reaching almost 2 m. Its head is large, broad, and flat, and the back bears a pattern of brown, black, and beige chevrons that provide for highly effective camouflage. This coloration is sufficient to distinguish it from all other large adders, which have more “complex, geometric colour patterns” (Spawls and Branch 1995). Additionally, this species can be differentiated from the other members of its genus by the presence of 1-3 scales between the nasal and the first supralabial, 1-2 scales between the nasal and the rostral scales, and molecularly by differences in cytochrome b (Mallow et al. 2003). Bitis arietans is divided into two subspecies, B. a. arietans and B. a. somalica: these can be distinguished by their subcaudal scales, which are keeled in the latter and not in the former (Spawls and Branch 1995).
Bitis arietans may be similar in appearance to its close relatives B. gabonica and B. nasicornis, commonly called the gaboon viper and the rhinoceros viper, respectively. All three species have a thick, stout body with a wide, flat, triangular head. However, B. arietans is smaller than the other two, rarely exceeding 1 m in length. Additionally, its coloration consists of a simple pattern of chevrons in drab shades of brown, black, and beige in contrast to the others’ more complex and colorful patterns (Spawls and Branch 1995).
Bitis arietans occurs in a wide range of habitats, from desert scrub to thick lowland rainforest. This species requires adequate cover, a permanent water source, and a relatively warm climate. It may be most common in semiarid savannas and rocky grasslands, and tends to avoid extreme desert and rainforest habitats. It is found at altitudes between sea level and 3000 m asl. While B. arietans is primarily terrestrial, it can swim with apparent ease and climb into low trees and shrubs. It is nocturnal, and most commonly found hiding in leaf litter or basking during the day (Broadley 1983, Mallow 2003).
Bitis arietans preys primarily on rodents, such as members of the genera Rattus, Mastomys, Rhabdomys, and Arvicanthis, although it has also been documented to eat birds, lizards, frogs, toads, and even button quail, duiker deer, and, in one specimen, a small leopard tortoise. Juveniles tend to consume smaller prey such as orthopteran insects or small toads. This species kills warm-blooded prey animals by envenomation before consuming them, but it has been documented to swallow cold-blooded prey such as toads alive and whole (Broadley 1983, Mallow et al. 2003).
According to Broadley (1983), the primary predators of Bitis arietans are birds of prey, mongooses, and warthogs, although the list of predators provided by Mallow et al. (2003) includes wildcats, genets, honey badgers, foxes, buzzards, eagles, secretary birds, and ground hornbills. This species is also susceptible to parasites such as ticks, mites, worms, linguatilids, and pentastomids, diseases such as canker, and infection by Chlamydia and Salmonella (Broadley 1983, Jacobson et al. 1989, Mallow et al. 2003).
Diseases and Parasites
In addition to parasites such as ticks, mites, worms, linguatilids, and pentastomids, Bitis arietans is susceptible to diseases such as canker, Chlamydia, and Salmonella. Individuals infected by Chlamydia developed pneumonia, hepatitis, splenitis, and enteritis (Broadley 1983, Jacobson et al. 1989).
Life History and Behavior
Like many vipers, Bitis arietans is an ambush predator, tending to lie in wait and attack prey animals that come within striking distance. This species possesses long, hinged fangs presumably adapted to inject its hemotoxic venom deeply into its prey for maximum effect. Rather than holding onto prey animals once it has bitten them, this species lets go shortly after striking, retreats, and re-approaches slowly and carefully, apparently to ensure that its prey has died before swallowing it (Mallow et al. 2003).
Bitis arietans moves primarily by rectilinear locomotion, in which it sequentially raises and moves small sections of its body forward in a subtle wave-like motion to move forward in a straight line. However, this species is also capable of lateral undulation and a crude form of sidewinding (Bogert 1947). While the locomotion of B. arietans is commonly described as sluggish, this species achieves remarkably fast speeds while striking, possibly due to especially powerful axial musculature (Young 2010).
When threatened, this species hisses in “a clear quadraphasic pattern consisting of an initial exhalatory hiss, a brief transitional pause, an inhalatory hiss and a rest or breath-holding phase” (Young et al. 1999), the mechanics of which have been studied in some detail (Young et al. 2001). This loud hiss and simultaneous “puffing” or inflation of the body makes the snake appear larger and more intimidating to a potential predator. This behavior is also at the root of this species’ common name, the “puff adder.” The hissing mechanism in this species does not appear to allow the snake to significantly modify the acoustic qualities of its hiss (Young et al. 1999).
Bitis arietans can do well in captivity if provided with “well ventilated housing, a hiding place, and plenty of water, warmth and sunlight” (Mallow et al. 2003), and the record captive lifespan for this species is 15 years and 10 months (Mallow et al. 2003). The lifespan of wild individuals is thought to be shorter on average, due to predation, habitat loss, and other disturbances.
Lifespan, longevity, and ageing
Bitis arietans is ovoviviparous, with the mating season between October and December and gestation lasting from December to April. Males of this species have been observed to fight over potential mates. In courtship, the male jerkily zig-zags his body over the female while tongue-flicking; successful mating may depend on the female voluntarily opening her cloaca. Females lay clutches of 20-40 eggs which hatch immediately; neonates reach approximately 15-25 cm in total length and 8-16 g in weight. They are active and venomous immediately after birth if not before; it is not uncommon for individuals to hatch inside the mother and exit vigorously, giving rise to the myth that baby puff adders eat their way out of their mother’s body. Juveniles of this species molt before they feed; the skin is usually shed 2-12 hours after birth, but occasionally only 10-12 minutes after birth. While they can kill small prey almost immediately, they can also survive up to three months before their first meal. This species reaches sexual maturity at the age of 45 months, on average (Broadley 1983, Spawls and Branch 1995, Mallow et al. 2003).
In captivity, Bitis arietans achieves its fastest growth rates as a juvenile, growing an average of 18.4 mm in length for every 100 g of food consumed, or approximately 0.49-0.66 mm per day on average during the first 32 months of life (Mallow et al. 2003). Coulson and Riddell (1986) observed a captive individual growing from 8.5 g to 170.5 g and from 160 mm to 550 mm in total length on 391.5 g of food during its first year of life. This individual grew, on average, 0.54 g and 1.3 mm per day on 1.30 g of food per day (Coulson and Riddell 1986). This species reaches sexual maturity at approximately four years old, and while it continues growing after seven years, it grows at a much slower rate (Mallow et al. 2003). In the wild, growth rates may be more variable because of their dependence on food availability, but they are assumed to be similar to the rates observed in captive specimens.
Evolution and Systematics
Bitis arietans was originally described as Cobra lachesis in 1768 by Laurenti, and re-described as Vipera arietans in 1820 by Merrem. However, to avoid confusing this species, a member of the family Viperidae, with the snakes commonly called cobras, which are in the family Elapidae, the International Commission on Zoological Nomenclature (ICZN) suppressed the name Cobra lachesis in 1945. The ICZN adopted instead the current name, Bitis arietans, which was first used by Boulenger in 1896. Bitis arietans currently contains two subspecies, B. a. arietans and B. a. somalica, the latter of which has keeled subcaudal scales and is restricted to Somalia, eastern Ethiopia, and northern Kenya (Broadley 1983, Spawls and Branch 1995, Mallow et al. 2003).
Physiology and Cell Biology
Bitis arietans hibernates during the winter, although it may periodically emerge from hibernation to bask on warm days (Broadley 1983). Broadley (1983) gives a thorough description, with diagrams, of skeletal osteology in this species, and Schaefer (1976) gives a detailed treatment of the physiology of venom movement from the venom gland through the fangs. Young et al. (1999, 2001) have elaborated the physiology of hissing in this species, and Young (2010) discusses the biophysics and muscle physiology of this species’ rapid predatory strikes.
Molecular Biology and Genetics
Statistics of barcoding coverage: Bitis arietans
Public Records: 1
Specimens with Barcodes: 2
Species With Barcodes: 1
Barcode data: Bitis arietans
There is 1 barcode sequence available from BOLD and GenBank. Below is the sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species. See the BOLD taxonomy browser for more complete information about this specimen. Other sequences that do not yet meet barcode criteria may also be available.
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Bitis arietans is a relatively common and wide-ranging snake, and its populations are thought to be healthy and in no immediate risk of decline. As of April 24, 2011, the conservation status of this species has not been evaluated by the IUCN.
Bitis arietans is sufficiently widespread and abundant that its populations are generally thought to be stable. However, habitat loss associated with human agricultural development threatens to reduce populations of this species. Additionally, in some cultures this species is hunted for its body fat, which is thought to cure rheumatism, or tied near hunting trails to kill potential game animals or enemy hunters (Broadley 1983, Mallow et al. 2003).
Relevance to Humans and Ecosystems
Bitis arietans serves as a model for studying the toxicology, morphology, and biomechanics of solenoglyphous snakes (Schaefer 1976). The complexity and effectiveness of this species’ venom has made it the subject of substantial biomedical research, both for the production of anti-venom and for various pharmaceuticals based on its different molecular components.
Bitis arietans is a venomous viper species found in savannah and grasslands from Morocco and western Arabia throughout Africa except for the Sahara and rain forest regions. It is responsible for causing the most snakebite fatalities in Africa owing to various factors, such as its wide distribution and frequent occurrence in highly populated regions. Two subspecies are currently recognized, including the nominate subspecies described here.
The average size is about 1 m (39.3 inches) in total length (body + tail) and very stout. Large specimens of 190 cm (75 in) total length, weighing over 6.0 kg (13.2 lbs) and with a girth of 40 cm (16 in) have been reported. Specimens from Saudi Arabia are not as large, usually no more than 80 cm (31 in) in total length. Males are usually larger than females and have relatively longer tails. The head has a less than triangular shape with a blunt and rounded snout. Still, the head is much wider than the neck. The rostral scale is small. The circumorbital ring consists of 10–16 scales. Across the top of the head, there are 7–11 interocular scales. 3–4 scales separate the suboculars and the supralabials. There are 12–17 supralabials and 13–17 sublabials. The first 3–4 sublabials contact the chin shields, of which there is only one pair. Often, there are two fangs on each maxilla and both can be functional.
Midbody there are 29–41 rows of dorsal scales. These are strongly keeled except for the outermost rows. The ventral scale count is 123–147, the subcaudals 14–38. Females have no more than 24 subcaudals. The anal scale is single.
The color pattern varies geographically. The head has two well-marked dark bands: one on the crown and the other between the eyes. On the sides of the head, there are two oblique dark bands or bars that run from the eye to the supralabials. Below, the head is yellowish white with scattered dark blotches. Iris color ranges from gold to silver-gray. Dorsally, the ground-color varies from straw yellow, to light brown, to orange or reddish brown. This is overlaid with a pattern of 18–22 backwardly-directed, dark brown to black bands that extend down the back and tail. Usually these bands are roughly chevron-shaped, but may be more U-shaped in some areas. They also form 2–6 light and dark cross-bands on the tail. Some populations are heavily flecked with brown and black, often obscuring other coloration, giving the animal a dusty-brown or blackish appearance. The belly is yellow or white, with a few scattered dark spots. Newborn young have golden head markings with pinkish to reddish ventral plates toward the lateral edges.
One unusual specimen, described by Branch and Farrell (1988), from Summer Pride, East London in South Africa, was striped. The pattern consisted of a narrow (1 scale wide) pale yellowish stripe that ran from the crown of the head to the tip of the tail.
Generally, though, these are relatively dull-looking snakes, except for male specimens from highland east Africa and Cape Province, South Africa, that usually have a striking yellow and black color pattern.
This species is probably the most common and widespread snake in Africa. It is found in most of sub-Saharan Africa south to the Cape of Good Hope, including southern Morocco, Mauritania, Senegal, Mali, southern Algeria, Guinea, Sierra Leone, Côte d'Ivoire, Ghana, Togo, Benin, Niger, Nigeria, Chad, Sudan, Cameroon, Central African Republic, northern, eastern and southern Democratic Republic of the Congo, Uganda, Kenya, Somalia, Rwanda, Burundi, Tanzania, Angola, Zambia, Malawi, Mozambique, Zimbabwe, Botswana, Namibia and South Africa. It also occurs on the Arabian peninsula, where it is found in southwestern Saudi Arabia and Yemen.
It is found in all habitats except true deserts, rain forests, and (tropical) alpine habitats. Most often associated with rocky grasslands.
It is not found in rainforest areas, such as along the coast of West Africa and in Central Africa (i.e., central DR Congo); it is also absent from the Mediterranean coastal region of North Africa. On the Arabian peninsula, it is found as far north as Ta'if. It has been reported to be found in the Dhofar region of southern Oman.
Normally a sluggish species, it relies on camouflage for protection. Locomotion is primarily rectilinear, using the broad ventral scales in a caterpillar fashion and aided by its own weight for traction. When agitated, it can resort to a typical serpentine movement and move with surprising speed. Although mainly terrestrial, these snakes are good swimmers and can also climb with ease; often they are found basking in low bushes. One specimen was found 4.6 m above the ground in a densely branched tree.
If disturbed, they will hiss loudly and continuously, adopting a tightly coiled defensive posture with the fore part of their body held in a taut "S" shape. At the same time, they may attempt to back away from the threat towards cover. They may strike suddenly and at a high speed, to the side as easily as forwards, before returning quickly to the defensive position, ready to strike again. During a strike, the force of the impact is so strong, and the long fangs penetrate so deeply, that prey items are often killed by the physical trauma alone. The fangs are apparently able to penetrate soft leather.
They can strike to a distance of about one third of their body length, but juveniles will launch their entire bodies forwards in the process. These snakes rarely grip their victims, instead releasing quickly to return to the striking position.
Mostly nocturnal, they rarely forage actively, preferring instead to ambush prey as it happens by. Their prey includes mammals, birds, amphibians, and lizards.
Females produce a pheromone to attract males, which engage in neck-wrestling combat dances. A female in Malindi was followed by seven males. They give birth to large numbers of offspring: litters of over 80 have been reported, while 50–60 is not unusual. Newborns are 12.5–17.5 cm in length. Very large specimens, particularly those from East Africa, give birth to the highest numbers of offspring. A Kenyan female in a Czech zoo gave birth to 156 young, the largest litter for any species of snake.
These snakes do well in captivity, but there are reports of gluttony. Kauffeld (1969) mentions that specimens can be maintained for years on only one mouse a week, but that when offered all they can eat, the result is often death, or at best wholesale regurgitation. They are bad-tempered snakes and some specimens never settle down in captivity, always hissing and puffing when approached.
This species is responsible for more fatalities than any other African snake. This is due to a combination of factors, including its wide distribution, common occurrence, large size, potent venom that is produced in large amounts, long fangs, their habit of basking by footpaths and sitting quietly when approached.
The venom has cytotoxic effects and is one of the most toxic of any vipers based on LD50. The LD50 values in mice vary: 0.4–2.0 mg/kg IV, 0.9–3.7 mg/kg IP, 4.4–7.7 mg/kg SC. Mallow et al. (2003) give an LD50 range of 1.0–7.75 mg/kg SC. Venom yield is typically between 100–350 mg, with a maximum of 750 mg. Brown (1973) mentions a venom yield of 180–750 mg. About 100 mg is thought to be enough to kill a healthy adult human male, with death occurring after 25 hours.
In humans, bites from this species can produce severe local and systemic symptoms. Based on the degree and type of local effect, bites can be divided into two symptomatic categories: those with little or no surface extravasation, and those with hemorrhages evident as ecchymosis, bleeding and swelling. In both cases there is severe pain and tenderness, but in the latter there is widespread superficial or deep necrosis and compartment syndrome. Serious bites cause limbs to become immovably flexed as a result of significant hemorrhage or coagulation in the affected muscles. Residual induration, however, is rare and usually these areas completely resolve.
Other bite symptoms that may occur in humans include edema, which may become extensive, shock, watery blood oozing from the puncture wounds, nausea and vomiting, subcutaneous bruising, blood blisters that may form rapidly, and a painful swelling of the regional lymph nodes. Swelling usually decreases after a few days, except for the area immediately around the bite site. Hypotension, together with weakness, dizziness and periods of semi- or unconsciousness is also reported.
If not treated carefully, necrosis will spread, causing skin, subcutaneous tissue and muscle to separate from healthy tissue and eventually slough with serous exudate. The slough may be superficial or deep, sometimes down to the bone. Gangrene and secondary infections commonly occurs and can result in loss of digits and limbs.
The fatality rate highly depends on the severity of the bites and some other factors. Deaths can be exceptional and probably occur in less than 10% of all untreated cases (usually in 2–4 days from complications following blood volume deficit and a disseminated intravascular coagulopathy), although some reports show that severe envenomations have a 52% mortality rate. Most fatalities are associated with poor clinical management and neglect.
|Subspecies||Taxon author||Common name||Geographic range|
|B. a arietans||(Merrem, 1820)||Puff adder||Throughout Africa from southern Morocco to Cape Province in South Africa, south-west Arabian Peninsula|
|B. a. somalica||Parker, 1949||Somali puff adder||Somalia, northern Kenya|
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- Viperinae by taxonomic synonyms
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