Common names: Gaboon viper, butterfly adder, forest puff adder, swampjack,[2] (more).
Bitis gabonica is a venomous viper species found in the rainforests and savannas of Sub-Saharan Africa.[1] This is not only the largest member of the genus Bitis,[3] but also the world's heaviest viperid[2] and it has the longest fangs (up to 2 inches),and the highest venom yield of any venomous snake.[2] Two subspecies are currently recognized, including the nominate race described here.[4]
Description
Adults average 122–152 cm (4 to 5 feet) in length with a maximum of 205 cm (81 in) for a specimen collected in Sierra Leone. The sexes may be distinguished by the length of the tail in relation to the total length of the body: approximately 12% for males and 6% for females. Adults, especially females, are very heavy and stout. One female had the following dimensions:[2]
Total length 174 cm (69 in)
Head width 12 cm (4.7 in)
Girth 37 cm (14.65 in)
Weight (empty stomach) 8.5 kg (19 lbs)
In their description of B. gabonica, Spawls et al.. (2004) give an average length of 80–130 cm (32 to 51.5 in), with a maximum size of 175 cm (69.3 in), saying the species may possibly grow larger still. They acknowledge reports of specimens over 6 feet (1.8 m), or even over 2 m (6.5 ft) in length, but claim there is no evidence to support this.[5]
The head is large and triangular, while the neck is greatly narrowed: almost one-third the width of the head.[2] A pair of horns is present between the raised nostrils — tiny in B. g. gabonica, but much larger in B. g. rhinoceros.[5] The eyes are large and moveable,[2] set well forward,[5] and surrounded by 15–21 circumorbital scales.[2] There are 12–16 interocular scales across the top of the head. 4–5 scale rows separate the suboculars and the supralabials. There are 13–18 supralabials and 16–22 sublabials.[2] The fangs may reach a length of 55 millimetres (2.2 in) :[3] the longest of any venomous snake.[2]
Midbody, there are 28–46 dorsal scale rows, all of which are strongly keeled except for the outer rows on each side. The lateral scales are slightly oblique. The ventral scales number 124–140: rarely more than 132 in males, rarely less than 132 in females. There are 17–33 paired subcaudal scales: males have no fewer than 25, females no more than 23. The anal scale is single.[2]
The color pattern consists of a series of pale, sub-rectangular blotches running down the center of the back, interspaced with dark, yellow-edged hourglass markings. The flanks have a series of fawn of brown rhomboidal shapes, with light vertical central bars. The belly is pale with irregular brown or black blotches. The head is white or cream with a fine, dark central line, black spots on the rear corners, and a dark blue-black triangle behind and below each eye.[5] The iris color is cream, yellow-white, orange[5] or silvery.[6]
Habitat
The Gaboon viper is usually found in rainforests and nearby woodlands, mainly at low altitudes,[6] but sometimes as high as 1500 m.[2] Spawls et al. (2004) mention a maximum altitude of 2100 m.[5] According to Broadley and Cook (1975), it is generally found in environments that are parallel to those occupied by its close relative, B. arietans, which is normally found in more open country.[9]
In Tanzania, this species is found in secondary thickets, cashew plantations, and in agricultural land under bushes and in thickets. In Uganda, they are found in forests and nearby grasslands. They also do well in reclaimed forest areas: cacao plantations in West Africa and coffee plantations in East Africa. They have been found in evergreen forests in Zambia. In Zimbabwe, they only occur in areas of high rainfall along the forested escarpment in the east of the country. In general they may also be found in swamps, as well as in still and moving waters. They are commonly found in agricultural areas near forests and on roads at night.[2]
Venom
Bites are relatively rare, due to their docile nature and the fact that their range is mainly limited to rainforest areas.[3] Due to their sluggishness and unwillingness to move even when approached, people are often bitten after they accidentally step on them, but even then in some cases they may not bite.[11] However, when a bite does occur it should always be considered a serious medical emergency. Even an average bite from an average sized specimen is potentially fatal.[3] Antivenom should be administered as soon as possible to save the victim's life if not the affected limb.[9]
The snake's hemotoxic venom itself is not considered particularly toxic based on tests conducted in mice. In mice, the LD50 is 0.8–5.0 mg/kg IV, 2.0 mg/kg IP and 5.0–6.0 mg/kg SC.[12] However, the venom glands are enormous and each bite produces the largest quantities of venom of any venomous snake. Yield is probably related to body weight, as opposed to milking interval.[2] Brown (1973) gives a venom yield range of 200–1000 mg (of dried venom),[12] A range of 200–600 mg for specimens 125–155 cm in length has also been reported.[2] Spawls and Branch (1995) state that from 5 to 7 ml (450–600 mg) of venom may be injected in a single bite.[3]
A study by Marsh and Whaler (1984) reported a maximum yield of 9.7 ml of wet venom, which translated to 2400 mg of dried venom. They attached "alligator" clip electrodes to the angle of the open jaw of anesthetized specimens (length 133–136 cm, girth 23–25 cm, weight 1.3–3.4 kg), yielding 1.3–7.6 ml (mean 4.4 ml) of venom. Two to three electrical bursts within a space of five seconds apart were enough to empty the venom glands. The snakes used for the study were milked 7 to 11 times over a 12-month period, during which they remained in good health and the potency of their venom remained the same.[2]
Based on how sensitive monkeys were to the venom, Whaler (1971) estimated that 14 mg of venom would be enough to kill a human being: equivalent to 0.06 ml of venom, or 1/50–1/1000 of what can be obtained in a single milking. Marsh and Whaler (1984) wrote that 35 mg (1/30 of the average venom yield) would be enough to kill a man of 70 kilograms (150 lb).[2] Branch (1992) suggested that 90–100 mg would be fatal in humans. Further investigation is needed.
In humans, a bite causes rapid and conspicuous swelling, intense pain, severe shock and local blistering. Other symptoms may include uncoordinated movements, defecation, urination, swelling of the tongue and eyelids, convulsions and unconsciousness.[2] Blistering, bruising and necrosis may be extensive. There may be sudden hypotension, heart damage and dyspnoea.[5] The blood may become incoagulable with internal bleeding that may lead to haematuria and haematemesis.[3][5] Local tissue damage may require surgical excision and possibly amputation.[3] Healing may be slow and fatalities during the recovery period are not uncommon.[5]
Bitis gabonica is a venomous viper species found in the rainforests and savannas of Sub-Saharan Africa.[1] This is not only the largest member of the genus Bitis,[3] but also the world's heaviest viperid[2] and it has the longest fangs (up to 2 inches),and the highest venom yield of any venomous snake.[2] Two subspecies are currently recognized, including the nominate race described here.[4]
Description
Adults average 122–152 cm (4 to 5 feet) in length with a maximum of 205 cm (81 in) for a specimen collected in Sierra Leone. The sexes may be distinguished by the length of the tail in relation to the total length of the body: approximately 12% for males and 6% for females. Adults, especially females, are very heavy and stout. One female had the following dimensions:[2]
Total length 174 cm (69 in)
Head width 12 cm (4.7 in)
Girth 37 cm (14.65 in)
Weight (empty stomach) 8.5 kg (19 lbs)
In their description of B. gabonica, Spawls et al.. (2004) give an average length of 80–130 cm (32 to 51.5 in), with a maximum size of 175 cm (69.3 in), saying the species may possibly grow larger still. They acknowledge reports of specimens over 6 feet (1.8 m), or even over 2 m (6.5 ft) in length, but claim there is no evidence to support this.[5]
The head is large and triangular, while the neck is greatly narrowed: almost one-third the width of the head.[2] A pair of horns is present between the raised nostrils — tiny in B. g. gabonica, but much larger in B. g. rhinoceros.[5] The eyes are large and moveable,[2] set well forward,[5] and surrounded by 15–21 circumorbital scales.[2] There are 12–16 interocular scales across the top of the head. 4–5 scale rows separate the suboculars and the supralabials. There are 13–18 supralabials and 16–22 sublabials.[2] The fangs may reach a length of 55 millimetres (2.2 in) :[3] the longest of any venomous snake.[2]
Midbody, there are 28–46 dorsal scale rows, all of which are strongly keeled except for the outer rows on each side. The lateral scales are slightly oblique. The ventral scales number 124–140: rarely more than 132 in males, rarely less than 132 in females. There are 17–33 paired subcaudal scales: males have no fewer than 25, females no more than 23. The anal scale is single.[2]
The color pattern consists of a series of pale, sub-rectangular blotches running down the center of the back, interspaced with dark, yellow-edged hourglass markings. The flanks have a series of fawn of brown rhomboidal shapes, with light vertical central bars. The belly is pale with irregular brown or black blotches. The head is white or cream with a fine, dark central line, black spots on the rear corners, and a dark blue-black triangle behind and below each eye.[5] The iris color is cream, yellow-white, orange[5] or silvery.[6]
Habitat
The Gaboon viper is usually found in rainforests and nearby woodlands, mainly at low altitudes,[6] but sometimes as high as 1500 m.[2] Spawls et al. (2004) mention a maximum altitude of 2100 m.[5] According to Broadley and Cook (1975), it is generally found in environments that are parallel to those occupied by its close relative, B. arietans, which is normally found in more open country.[9]
In Tanzania, this species is found in secondary thickets, cashew plantations, and in agricultural land under bushes and in thickets. In Uganda, they are found in forests and nearby grasslands. They also do well in reclaimed forest areas: cacao plantations in West Africa and coffee plantations in East Africa. They have been found in evergreen forests in Zambia. In Zimbabwe, they only occur in areas of high rainfall along the forested escarpment in the east of the country. In general they may also be found in swamps, as well as in still and moving waters. They are commonly found in agricultural areas near forests and on roads at night.[2]
VenomBites are relatively rare, due to their docile nature and the fact that their range is mainly limited to rainforest areas.[3] Due to their sluggishness and unwillingness to move even when approached, people are often bitten after they accidentally step on them, but even then in some cases they may not bite.[11] However, when a bite does occur it should always be considered a serious medical emergency. Even an average bite from an average sized specimen is potentially fatal.[3] Antivenom should be administered as soon as possible to save the victim's life if not the affected limb.[9]
The snake's hemotoxic venom itself is not considered particularly toxic based on tests conducted in mice. In mice, the LD50 is 0.8–5.0 mg/kg IV, 2.0 mg/kg IP and 5.0–6.0 mg/kg SC.[12] However, the venom glands are enormous and each bite produces the largest quantities of venom of any venomous snake. Yield is probably related to body weight, as opposed to milking interval.[2] Brown (1973) gives a venom yield range of 200–1000 mg (of dried venom),[12] A range of 200–600 mg for specimens 125–155 cm in length has also been reported.[2] Spawls and Branch (1995) state that from 5 to 7 ml (450–600 mg) of venom may be injected in a single bite.[3]
A study by Marsh and Whaler (1984) reported a maximum yield of 9.7 ml of wet venom, which translated to 2400 mg of dried venom. They attached "alligator" clip electrodes to the angle of the open jaw of anesthetized specimens (length 133–136 cm, girth 23–25 cm, weight 1.3–3.4 kg), yielding 1.3–7.6 ml (mean 4.4 ml) of venom. Two to three electrical bursts within a space of five seconds apart were enough to empty the venom glands. The snakes used for the study were milked 7 to 11 times over a 12-month period, during which they remained in good health and the potency of their venom remained the same.[2]
Based on how sensitive monkeys were to the venom, Whaler (1971) estimated that 14 mg of venom would be enough to kill a human being: equivalent to 0.06 ml of venom, or 1/50–1/1000 of what can be obtained in a single milking. Marsh and Whaler (1984) wrote that 35 mg (1/30 of the average venom yield) would be enough to kill a man of 70 kilograms (150 lb).[2] Branch (1992) suggested that 90–100 mg would be fatal in humans. Further investigation is needed.
In humans, a bite causes rapid and conspicuous swelling, intense pain, severe shock and local blistering. Other symptoms may include uncoordinated movements, defecation, urination, swelling of the tongue and eyelids, convulsions and unconsciousness.[2] Blistering, bruising and necrosis may be extensive. There may be sudden hypotension, heart damage and dyspnoea.[5] The blood may become incoagulable with internal bleeding that may lead to haematuria and haematemesis.[3][5] Local tissue damage may require surgical excision and possibly amputation.[3] Healing may be slow and fatalities during the recovery period are not uncommon.[5]
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