Fig. 4.63 Bitis arietans in threatening pose.

Distribution

Africa. B. arietans also on the Arabian Peninsula. See link "Distribution" at the top of the page for detailed information.

  Map 44 Bitis spp.

Biology

B. arietans, B. gabonica, B. nasicornis and B. rhinoceros

These represent the large species in this genus. B. rhinoceros may exeed 2 m in lengh and weigh up to 8,5 kilogramms. Massive, wide head, quite distinct from the body, with a blunt snout and nostrils that are directed upwards. Two horn-like protuberances between the nostrils are present in B. nasicornis and B. rhinoceros. Body very stout and appears small. Besides B. rhinoceros (formerly B. gaboica rhinoceros) Bitis gabonica belongs to the largest viperine snakes, with a length of up to 1.8 m and a circumference of up to 40 cm. B. arietans is on average barely more than 1 m, but up to 1.5 m in East Africa. B. nasicornis reaches a maximum of 1.2 m. B. nasicornis, B. rhinoceros and B. gabonica have very complicated, ornamental markings over the whole body, with long rectangles along the spine and richly decorated rhombi and triangles on their sides. B. nasicornis shows bright shades of yellow, blue, pink, purple, green and brown. B. gabonica and B. rhinoceros in various shades of brown with a characteristic thinner and darker central line on a pale head.

The basic colouring of B. arietans is in shades of grey, yellow or reddish-brown. Along the spine there is a series of lighter, forward-facing chevron-shaped markings that change into cross bands on the tail. Nocturnal, but often found sunning itself during the day.

B. arietans, one of the most common snakes in Africa, is widely distributed in drier zones, such as savannas and grasslands, at altitudes of up to 2,000 m. In the areas in which it is found on the Arabian Peninsula, it occurs in zones with the highest rainfall, generally over 1,500 m above sea level.

B. gabonica, B rhinoceros and B. nasicornis are found in areas with high rainfall. They typically inhabit mesic forests and their fringes, B. nasicornis also in swamps.

Other species: Smaller species, on average between 20 cm (B. schneideri and B. peringueyi) and 40 cm (B. atropos and B. xeropaga). They are all species that inhabit dry, sandy or rocky areas. They possess typical adaptations to a desert-like habitat, such as their side-winding mode of locomotion (see Echis spp.) or burrowing into the sand during their daytime dormant phase. B. xeropaga in mountainous areas, B. atropos from sea level to up to 3,000 m, B. schneideri in vegetated sand dunes.

Head wide and distinct from the body, in B. atropos somewhat elongated. Nostrils directed upwards. In B. peringueyi the eyes are located on the top of the head. B. caudalis and B. schneideri commonly have an enlarged scale over each eye that resembles a horn, B. cornuta cornuta has a tuft of horns consisting of a number of scales.

The basic colouring varies between shades of grey, brown and red, B. peringueyi sometimes also sand-coloured. B. cornuta has several rows of dark blotches, B. xeropaga has distinct dark rectangles with light borders along its spine. B. caudalis has three rows of dark rectangles. B. peringueyi and B. schneideri have indistinct blotchy markings. B. atropos has two rows of dark triangles along the spine with their tips facing each other.

The large species appear sluggish and do not move much. If approached, they rely on their markings for camouflage and rarely flee. As defensive behaviour they puff loudly. B. gabonica, B. rhinoceros and B. nasicornis will only bite if really disturbed. B. arietens and the smaller species are more easily provoked and are quick to bite.

Risk

The larger species are particularly dangerous, with their long fangs (up to 5 cm in B. rhinoceros and B. gabonica!) and large quantities of venom. However, bites by the smaller species, in particular B. atropos, can also be dangerous.

In Africa, B. arietans is considered responsible for many deaths in humans and domestic animals, but there are very few clinical studies. Considering their behaviour and how common they are, puff adders probably cause a large number of bites in many regions of Africa. The incidence of bites due to this species must certainly be much higher than all the other Bitis species together. In Zimbabwe, it has been reported that approximately 75% of serious snakebite incidents are caused by B. arietans (Broadley and Cock 1989). In contrast, a study from neighbouring South Africa showed that many bites that occur at night and cause strong local symptoms, which had previously been attributed to B. arietans, actually turned out to be envenoming due to Naja mossambica (Tilbury 1982).

In the savanna region of Nigeria, where Echis ocellatus is by far the most medically significant species, B. arietans is responsible for only a fraction of the cases of envenoming caused by viperids (Pugh and Theakston 1987a). Of 10 cases reported from this region, 2 were fatal (Warrell et al. 1975).

Literature (biological)

Branch 1999, Broadley 1983, Broadley and Cock 1989, Buys and Buys 1983, Doucet 1963, Gasperetti 1988, Gower et al. 2016, Grasset 1946, Lenk et al. 1999, Joger 1984, Mallow et al. 2003, Marsh and Whaler 1984, Pitman 1974, Roman 1980, Sweeny 1971, Visser and Chapman 1978, Wittenberg et al. 2014