Causus resimus

Family : Viperidae

Text © Dr. Gianni Olivo


English translation by Mario Beltramini


With the name of Adders of the night (Causus) is designated a group of venomous serpents ascribed to the viperids and standing among the most primitive in absolute. The venomous fangs are proportionally shorter and the apparatus designated to the erection of the same is much less sophisticated than in the genus Bitis or AtherisWhilst in most of the viperids and the crotalids, the prefrontal bone interacts with the frontal one, causing the tilting of the fangs from set against the palate to erected, in the night adders the erection is allowed only by a partial rotation of the upper maxilla, with, consequently, a less perfect mobility.

Another characteristic differentiating them from the remainder of the viperids is the eye with rounded pupil and the presence of great cephalic scales (most of the vipers have the same rather small). Furthermore, their diet is more limited, as it consists almost exclusively of batrachians, frogs and toads. The liver is much developed and may even overcome the apex of the cardiac muscle and also the kidneys are elongated and of a remarkable size. For what is concerned, finally, the reproduction, it is of oviparous and not ovoviviparous type.

The green night adder (or velvety) (Causus resimus Peters, 1862), is a small serpent, usually long from 30 to 65 cm, with peaks of 75 (the females being bigger), of green colour, varying from the bright green to the yellowish, up to the dark green, at times with tiny and scattered dark dots.

The head is small and little distinct from the body, the eye is of average size and with rounded pupil and is of yellow colour. The summit of the head is covered by 9 big cephalic scales and the apex of the snout is slightly raised like a “Sultan’s slipper” but much less than in the species Causus defilippi. The body is cylindrical, covered by scales with a particular consistency due to which this reptilian looks velvety not only to the sight but also to the touch.

These scales are organized, by mid length, in 19-21 rows, but Ethiopian individuals may have 23 rows, whilst the series of ventral scales varies from 130 to 155. The throat and the ventral parts are paler, yellow or cream and on the head is often standing a dark V. Overall, it’s matter of one of the most beautiful serpents, thanks to its velvety look and of the green colour on which stands, in an almost shameless way, the dark blue of the bifid tongue, when the serpent is darting it through the proper labial opening.

The Causus resimus is a primitive viperid with lot of poorly active venom © Giuseppe Mazza

The Causus resimus is a primitive viperid with lot of poorly active venom © Giuseppe Mazza

When the serpent is upset, it swells the body almost the double of its diameter and emits loud hisses and, when this happens, it becomes evident also the bright blue colour of the hidden part of the scales. Furthermore, it may raise the front part of the body for trying to abash the opponent, at times moving towards it and flattening the neck like a small green cobra. This threatening attitude is common also to other species of Causus.

It is, therefore, a serpent very difficult to be mistaken with others: no other serpent of bright green colour, in Africa, has a body so short and stocky; on the contrary, most of the green coloured species, venomous species, such as green mambas and boomslangs, or harmless ones, like the various grass snakes, tend to be thin and slender.

The green night adder is a terrestrial animal; even there have been reported cases where it was climbing, laboriously, on low shrubs, it moves slowly, but the bite is quick and fast. In spite of the name, it is often active also during the day, especially after heavy rains, when the batrachians, its almost exclusive preys, abound and it is not rare to see it while lying to absorb the heat, especially after a cold night. At ease also in water, it is a very good swimmer and is able to seize frogs and tadpoles and, possibly, also small fishes. It shelters in holes of the ground, dens of rodents, termite mounds, or under debris, leaves or flat stones.

The distribution is vast but irregular. It is present in an ample area in Angola, especially along the coastline; another area is situated in the zone of the Great Lakes and one more in southern Sudan and in south-eastern Ethiopia. The northern part of Congo, the Cameroun and the border Cameroun-Chad host small populations and I saw one of them on the Oubangui River. The preferred habitat is the wet savannah, at low altitude, with high grass and presence of water.

The reproduction is oviparous and the female lays from 4 to 12 eggs which need about four months for hatching, thus allowing the exit of the about 10 cm long young.

The venom is little studied and does not look too toxic for the man, however the venom glands are the longest among the serpents, as they are not limited to the region of the parotid, but spread for a long tract in the neck of the reptilian, on the two sides of the spine and may be even 10 cm long, with long salivary ducts which connect them with the venom fangs. Despite this impressing arsenal, however, the inoculation appears somewhat ineffective, with a dripping more than a real flood of venom getting out from the hollow fangs, furthermore, the poison has a limited toxicity and usually causes pain and swelling but without necrosis.

Some cases, once reported, of alleged lethal poisonings by specimens of the genus Causus, seem to have later revealed as identification errors, possibly due to confusion with other species of reptilians. The polyvalent serum is partially effective on a couple of species but not on all of them and in any case it is not usually necessary as the recommended treatment consists in a careful monitoring of the patient and symptomatic treatment (painkillers, anti-edemics) and, if needed, antibiotics. The immunization or the tetanus vaccination booster is recommended.

Common names: English: Green night adder, Velvety night adder; German: Grüne Nachtotter; French: Vipère nocturne verte, Resimus de Causus; Italian: Vipera della notte verde, Vipera della notte di velluto.


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