''Causus'' is a genus of

viper The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, and various other isolated islands. They are venomous and have long (relative to non-vipers), hinged fangs tha ...

s found only in

sub-Saharan Africa Sub-Saharan Africa is, geographically, the area and regions of the continent of Africa that lies south of the Sahara. These include West Africa, East Africa, Central Africa, and Southern Africa. Geopolitically, in addition to the List of sov ...

. It is a group considered to be among the most primitive members of the family

Viperidae The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, and various other isolated islands. They are venomous and have long (relative to non-vipers), hinged fangs tha ...

based on head scalation, oviparity, venom apparatus, and because they have round pupils. However, this is contradicted by recent molecular studies.Nagy ZT, Vidal N, Vences M, Branch WR, Pauwels OSG, Wink M, Joger U. 2005. Molecular systematics of African Colubroidea (Squamata: Serpentes) In: Huber BA, Sinclair BJ, Lampe KH (Eds.). African Biodiversity: Molecules, Organisms, Ecosystems. Proc. 5th Intern. Symp. Trop. Biol. Museum Koenig, Bonn, pp. 221-228.Wüster W, Peppin L, Pook CE, Walker DE. 2008. A nesting of vipers: phylogeny and historical biogeography of the Viperidae (Squamata: Serpentes). Molecular Phylogenetics and Evolution 49: 445-459. Seven species are currently recognized. They are commonly known as night adders.Mallow D, Ludwig D, Nilson G. 2003. ''True Vipers: Natural History and Toxinology of Old World Vipers''. Krieger Publishing Company. Malabar, Florida. 359 pp. .Spawls S, Branch B. 1995. ''The Dangerous Snakes of Africa''. Ralph Curtis Books. Dubai: Oriental Press. 192 pp. . Like all other vipers, they are

venomous Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...

Description

These snakes are fairly stout, never growing to more than in total length. As opposed to most

s, where the head is distinct from the neck and covered with small scales, in ''Causus'' the head is only slightly distinct from the neck and covered with 9 large, symmetrical head shields. Also, the eyes have round pupils instead of elliptical ones like other vipers. The

rostral scale The rostral scale, or rostral, in snakes and other scaled reptiles is the median plate on the tip of the snout that borders the mouth opening. Wright AH, Wright AA (1957). ''Handbook of Snakes of the United States and Canada''. Ithaca and London: ...

is broad, sometimes pointed or upturned. The nostril is located between two nasals and an internasal. The frontal and

supraocular scales In scaled reptiles, supraocular scales are (enlarged) scales on the crown immediately above the eye.Mallow D, Ludwig D, Nilson G. 2003. True Vipers: Natural History and Toxinology of Old World Vipers. Malabar, Florida: Krieger Publishing Company. ...

are long. A loreal scale is present, separating the nasal and preoculars. The

suboculars In scaled reptiles, the ocular scales are those forming the margin of the eye.Wright AH, Wright AA. 1957. ''Handbook of Snakes''. Comstock Publishing Associates (7th printing, 1985). 1105 pp. . The name originates from the term ''oculus'' which ...

are separated from the

supralabials In reptiles, the supralabial scales, also called upper-labials, are those scales that border the mouth opening along the upper jaw. They do not include the median scaleWright AH, Wright AA. 1957. Handbook of Snakes. Comstock Publishing Associates ( ...

. The mandible has splenial and angular elements. The fangs are different, too. Unlike other vipers, no hinge action occurs where the prefrontal bone engages the frontal. However, since the maxillary bones rotate almost as far, the fangs can still be erected. The fangs themselves are relatively short. A fine line, or suture, is also present along the length of the fang, representing the vestigial edge where the groove lips meet (from incomplete fang canal closure). The body is cylindrical or slightly depressed and moderately slender. The dorsal scales are smooth or weakly keeled with apical pits. The ventral scales are rounded, and the anal plate is single. The tail is short, and the subcaudals can be either single or paired. Among the viperids, another unique characteristic of this genus is several species have venom glands that are not confined to the temporal area as with most vipers, but are exceptionally long and extend well down the neck. These venom glands, located on either side of the spine, may be up to 10 cm in length, with long ducts connecting them to the fangs.Stidworthy J. 1974. ''Snakes of the World''. Grosset & Dunlap Inc. 160 pp. . Other internal differences also set the Causinae apart: they have unusually long kidneys, a well-developed tracheal lung with two tracheal arteries, and the liver overlaps the tip of the heart.

Geographic range

The Causinae are found in

Behavior

Despite their common name, this genus is active during the day, as well as at night. When disturbed, they will engage in a ferocious hissing and puffing threat display. They may lift the first part of their bodies off the ground in a coil and make a powerful swiping strike; juveniles have been known to come off the ground. Others specimens may raise the first part of their bodies off the ground, flattening their necks and moving forward, tongue extended, like a small cobra. The rather frantic strikes are often combined with attempts to quickly glide away.Mehrtens JM. 1987. ''Living Snakes of the World in Color''. New York: Sterling Publishers. 480 pp. .

Feeding

Their diet consists almost exclusively of

toad Toad is a common name for certain frogs, especially of the family Bufonidae, that are characterized by dry, leathery skin, short legs, and large bumps covering the parotoid glands. A distinction between frogs and toads is not made in scientif ...

s and

frog A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...

s. Gluttony has been reported; when prey is abundant, they may eat until they are literally unable to swallow any more food.

Reproduction

All ''Causus'' species lay eggs (

oviparous Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...

), which among

s is considered to be a more primitive trait, though not unique. The average clutch consists of some two dozen eggs that require an incubation period of about four months. Hatchlings are 10–12.5 cm (4–5 in) in total length (body + tail).

Venom

In spite of their enormously developed venom glands, night adders do not always use them to subdue their prey. The venom would act fast enough, but often they simply seize and swallow their prey, instead. ''Causus'' venom is weaker than that of puff adder. Envenomation normally causes only local pain and swelling. Antivenin treatment should not be necessary. Nevertheless, South African polyvalent serum is known to be effective against the venom of at least two species.Spawls S, Howell K, Drewes R, Ashe J. 2004. ''A Field Guide To The Reptiles Of East Africa''. A & C Black Publishers Ltd. London. 543 pp. . However, envenomation can be very serious and in at least one case a bitten child had to have a

fasciotomy Fasciotomy or fasciectomy is a surgical procedure where the fascia is cut to relieve tension or pressure in order to treat the resulting loss of circulation to an area of tissue or muscle. Fasciotomy is a limb-saving procedure when used to trea ...

. A number of small dogs have had limbs amputated or died due to bites from this snake. The danger from this snake should not be underestimated as a bite from a large individual on a small child could potentially be fatal. No recent deaths have been reported due to this species. Earlier reports of fatalities were based on anecdotal evidence; the species involved likely were not properly identified or the cases were grossly mismanaged.

Species

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Type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

Taxonomy

A long-standing tendency among

herpetologist Herpetology (from Greek ἑρπετόν ''herpetón'', meaning "reptile" or "creeping animal") is the branch of zoology concerned with the study of amphibians (including frogs, toads, salamanders, newts, and caecilians (gymnophiona)) and rept ...

s was to make assumptions regarding the

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

position of this group. McDiarmid ''et al.'' suggested the consensus among the experts in 1999 was that ''Causus'' was basal to all

viperids The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, and various other isolated islands. They are venomous and have long (relative to non-vipers), hinged fangs t ...

, so deserved a separate subfamily. However, two more recent molecular phylogenetic studies have shown ''Causus'' is not only not basal to all

, but in fact appears to be nested within the viperines. Consequently, recognition of the subfamily Causinae is inappropriate.