Introduction

“Urray nyoka!”,  people shout when they see a snake, dangerous or harmless. Most Africans have lost the ancient knowledge of snakes, and nowadays every snake is considered a threat, whilst most of them are harmless and very effective pest controllers. 

Romans, for example, used to keep harmless snakes in their houses to control mice and other pests. Regaining a proper knowledge of snakes should be a priority for everyone who aspires to live and operate in the bush or rural areas, but it might also be useful for those who live in an urban environment too.

Although most of the Southern African snakes are not an issue for humans, about a dozen of them are potentially lethal. It is essential to know them and to treat them with respect and avoid trouble, because – remember it! – snakes bite humans only when they feel threatened.

Taxonomy

Kingdom: Anamalia

Phyllum: Chordata

Sub-phyllum: Vertebrata

Class: Reptilia (reptiles)

Order: Squamata

Sub-order: Serpentes

Families: Boidae, Viperidae, Colubridae, Elapidae

 Snakes are reptiles belonging to the Order Squamata and the Sub-order Serpentes. The earliest snakes fossil has been dated from 135 to 150 million years ago, and it is presumed that snakes evolved from lizards and amphisbaenids (worm lizards). As reptiles, they are vertebrates, with a bony internal structure and a backbone.

There are more than 140 species of snakes in Southern Africa, of which only 37 have fangs and venom that could cause clinical symptoms to humans. Amongst these, only 11 are potentially lethal for humans.

Main Features

Snakes are unique animals with unmistakable features.

Long and slender body

The classic snake shape that everyone recognises is like a piece of rope – many times longer than it is wide.

Ectothermic

Snakes do not have arms and/or legs. A snake uses its trunk or main body for locomotion, thanks to articulated ribs, and catches prey using the fangs and/or the body, depending on the species. The lack of limbs might look like a great limitation from a human point of view, but actually, together with the long and slender body-shape, it allows snakes to colonize a great variety of environments, most of them inimical to humans.

Snakes can climb trees, rocks and walls. They can easily move in narrow crevices or passages, as well as in thick vegetation. They can enter holes and burrows, where many of their prey retreat. They can swim and some species are well adapted to a sea water environment. (Snakes are known for their lack of legs, but certain species, like pythons and boas, possess small, spur-like structures near their tails. These are remnants of hind limbs, a vestige of their lizard-like ancestors who possessed legs.) 

Elongated backbone and articulated ribs

Snakes have an elongated backbone that runs along the entire length of their body with 175 to more than 400 vertebrae, depending on the species. Attached to this backbone are numerous ribs, which are articulated, meaning they are connected in a way that allows for movement of the rib in relation to the spine. This articulation is crucial for the snake’s locomotion, as it enables the ribs to move independently and assist in the snake’s unique modes of movement, such as slithering and climbing.

Scaled skin

The snake’s body is covered by scales, that can be smooth or keeled (have a ridge down the center). The skin does not grow with the body, so when the snake grows, the skin has to be shed or cast off (like a child outgrowing clothes).

Left lung absent or highly reduced

Almost all snakes have a right lung only, with the left lung absent or at least extremely reduced and almost inactive (e.g. pythons). This physical characteristic results in poor blood oxygenation and, as a consequence, snakes get easily tired. This is of a great importance when considering snake handling (see the section below on “Handling snakes”).

No external ears

Snakes do not have any hole connecting their “auditorial system” with the external environment, in other words, they do not have ears. However, they have a very sensitive auditory nerve, capable of picking up vibration from dense mediums, like the ground.

No movable eyelids

A snake cannot blink but the eyes are covered by a fixed membrane of transparent skin that protects them. This membrane is periodically shed with the rest of the skin. As the old skin is about to be shed, this transparent shield becomes opaque, and it is a clear sign that the snake is about to shed the skin.

Retractile forked tongue

Snakes have a forked tongue, rooted in the lower part of the mouth, that can be retracted into a sheath. The tongue can be protruded from the mouth and flicked in the air to pick up olfactory signals. In other words, the tongue is an organ for smelling. (See below, under Senses)

Dislocatable jaws

Snakes are able to dislocate their jaws, which are not jointed, in order to open the mouth very widely and swallow prey that is of a greater diameter than the snake itself. (Snakes do not chew their food.)

Double penis

Male snakes have a “double penis” or, to be more precise, a sexual organ made by two “emipenes”. Only one hemipenes at a time is used during mating.

Teeth modified into fangs

Many species of snakes have modified teeth. Some, like the python, are simply modified to anchor prey during the process of swallowing. In other snakes the teeth have evolved into fangs, that are hollow teeth, connected to the salivary glands. The salivary glands have themselves been modified into venom glands, and the venom can be injected through the fangs, which act like the needle of a syringe.

Neck flattening behaviour

Some snakes, like cobras, can flatten the neck ribs into a hood, giving the neck the well-known flattened shape. This behaviour, usually together with a raised neck posture, is an aggressive or defensive posture, during which the snake displasy a bigger size, to deter the competitor or the aggressor. (Cobras are not the only snakes that can flatten their necks; the rinkhals also does so and, to a certain extent, the black mamba as well.

Oviparous or ovoviviparous

As with every other reptile, snakes reproduce by means of eggs. Some species are oviparous, meaning that they lay eggs, from which offspring hatch. Some others are ovoviviparous, meaning that the eggs hatch inside the body of the female and the living young are ejected apparently like viviparous animals. However, there is no placenta involved, but only eggs that are kept in the body until hatching.

Senses

Generally, snakes have acute senses. Some are well developed, whilst others, like hearing, are less developed. However, we could say that these senses (e.g. hearing) work in a different way compared to mammals or birds, rather than being less developed.

Vision

Generally, snakes have a good vision, though the majority of them tend to ignore stationary objects. Some arboreal species, however,  like the boomslang and twig snakes, have very developed vision, capable of detecting and recognizing stationary prey too.

Hearing

As mentioned above, snakes are unable to hear airborne sounds because they do not have open ears, and their auditory system is not connected with the outside environment. However, they have an auditory nerve that can pick up vibration through dense mediums, like the ground surface.

The auditory bone structure is also different from mammals in that the eardrum is connected to the inner ear by one bone only, the columella, instead three as in mammal ears.

Smell

Scents are picked up by a forked tongue flicking in the air. (Despite popular belief, snake’s tongues cannot sting, only pick up odours.) This tongue is contained in a sheath inside the mouth that can be protruded outside to capture airborne olfactory particles. The forked shape of the tongue can pick up particles from two different directions, obtaining a “stereo” effect that allows the snake to better determine position and distance of detected objects or living beings.

After having picked up olfactory particles, the tongue is pulled back into the mouth to release the particles into the Jacobson’s organ, also called the vomeronasal organ. The Jacobson’s organ is located in the upper side of the mouth, in the palatal area and it detects olfactory signals in the same way the mammalian nasal olfactory organ detects olfactory signals – and sends them through the olfactory nerve, directly to the brain, where they will be analysed and decoded.

Tactile Sense

The tactile sense is highly developed in snakes, since their elongated body is in touch with the ground most of the time.

Their bodies contain many highly sensitive tactile receptors, capable of detecting any minimum changes in the surrounding environment. The high sensitivity of snakes’ body should be taken in count when handling a snake.

Locomotion

Despite lacking limbs, snakes use their bodies to move with agility in many different environments using their body. The powerful muscles and the articulated ribs allow them to perform micro-movements that push the body forward, sideways or upwards, depending on the type of locomotion the snake uses.

Although often exaggerated, the speed of many snakes is quite high, considering that they do not have limbs, and a snake can reach 20 km/h. However, the lack of one lung leads to poor blood oxygenation, and they are not able to keep up this speed for long.

Types of Locomotion

Snakes move using four different types of locomotion depending on the species and the environment they are moving in:

Caterpillar-like movement

This kind of locomotion is so called because it resembles the movement of a caterpillar. The snake moves in a straight line, using its ventral scales only, contracting and extending the body and, undulating along the vertical plane. This locomotion type is mainly used by heavy body snakes, like pythons or puff adders.

Serpentine movement

This is the most common way for snakes to move, allowing them great speed for chasing prey or escaping danger or when disturbed. The body undulates along the horizontal plane, side-to-side, using ground irregularity to push the body forward. The same technique is used when a snake is swimming.

Concertina Movement

This technique is used to climb trees, walls or vertical surfaces. the snake anchors its head on an irregularity of the surface and drags the rest of the body upward. Every irregularity of the surface (branches, crevices, roughness, etc.) can be used by the head or any other part of the body to push and pull the rest up.

This technique is also used, to a certain extent, to move into burrows. Some burrowing snakes have a tail ending with sharp spikes that allow good grip on the burrow’s sidewall, pushing the snake forward.

Sidewinding Movement

This is a typical movement of snakes adapted to a loose surface, like sand dunes. Péringuey’s adder (Bitis peringueyi) uses this type of locomotion to move along the sand of the Namib desert.

Only one or two sections of the body touch the ground at any one time. Then, a section of the body is thrown sideways and followed by the next section.

Another advantage of this type of movement, which is an adaptation to the environment, is that most of the body is not in touch with the very hot sand, while moving.

Skin and skin-shedding

Scales

Snake bodies are covered by scales of different shapes, sizes and colours. Some can be smooth and others can be keeled and a species can be identified according to the scales’ shape, size, colour and distribution along the body. In fact, each species has different pattern of scale.

The pigmentation of a snake is one of the main keys to identifying the species, although colour may change according to age, sex or other factors.

Scales are named according to their position on the snake’s body.

Head Scales

Head scales are the most numerous in shape and vary from species to species. The scales along the mouth (or labials) are called Lower Labial (LL) and Upper Labial (UL), depending by their position. Around the eye, are located the Orbital or Ocular scales. On the rear side of the eye, we can find the Post-orbital (PO), and immediately under the eye we find the Sub-orbital (SBO). Just in front the eye there are the Pre-orbital (PRO) and on top, the Supra-orbital (SUO). Behind the orbital area, we find the Temporal scales (T).

Looking at the head from the top, in the centre we find the Parietal scales, which are usually the bigger head-scales. Moving toward the muzzle, we find the Frontals, the Pre-frontals, the Inter-nasals and the Rostral right on the tip.

Underneath, right on the throat, are located the most advanced Ventral scales, while, proceeding toward the muzzle, we can find the Sub-linguals, the frontal Lower Labials and the Mental scale, just under the Rostral scale.

Dorsal Scales

The dorsal surface of the body is covered by the dorsal scales. These scales can be smooth or keeled, depending by the species.

The keeled dorsal scales are generally common in adders.

The number of dorsal scales can be used to identify the species and can be counted in two different ways, as shown in the following picture.

Ventral Scales

Ventral  scales cover the bottom surface of the body (the ventral area) and they are divided in Sub-caudal (SC), Anal (A) and Ventral scales. The Sub-caudal can be single or paired (see picture below).

Skin Shedding

The skin of a snake does not grow with the body, hence, when the snake grows, the skin has to be shed. This process is called shedding or sloughing.

Walking around in the bush, it is very common to find snake skins.

In juvenile individuals, shedding occurs about 15 times a year, whilst in adults it occurs about 1 to 4 times a year, depending on the snake’s growth rate.

Prior to shedding, the eyes shield becomes opaque, restricting the snake’s vision. This condition usually drives the snake to hide since the limited vision makes it more vulnerable to predation. They also try to warm themselves up as much as possible, basking in the sun longer than usual, to speed up the development of the new skin, so as to shorten this vulnerable period during which they cannot see well.

The snake, then, starts to rub its nose against a hard surface, like rocks or wood, till a piece of skin comes loose. It then moves into thick vegetation rubbing itself against rough surfaces to get the whole old skin (including the eye shields) hooked and pulled off
inside-out (like a sock).

In juvenile snakes, the skin is shed in one whole piece, while in old or large snakes it might be shed in pieces.

Regulation of body temperature

As reptiles, snakes are ectothermic animals that do not internally regulate their body temperature. They do not generate heat internally when metabolizing food, as mammals and birds do. They depend on external sources of heat. They lack the hypothalamus, that part of the brain which in mammals and birds (that are endothermic animals) directly measures the blood temperature and sends instructions to adjust the body temperature. Snakes have to bask in the sun or be in contact with warm objects (e.g. a warm stones) to raise their body temperature, and when they need to cool  down, they simply move from sun to shade.

The advantage of ectothermy is “fuel efficiency”.  In mammals and birds, 90% of the food intake is “burnt” to produce heat and so maintaining the metabolism at a constant level at all time, no matter the weather conditions or the body activity. But if they do not eat, they cannot generate heat and then they die of hypothermia.

Reptiles like snakes, metabolize their food to replace spent energy or to increase the body mass but they do not need to eat to generate heat. This means that the more they eat the bigger they grow, and they can actually spend long periods without food. Many species of snake can survive on only ten meals per year.

Brumation

Because they depend on external sources of heat, snakes (and all reptiles) are sensitive to weather conditions. When the surrounding environment is no longer able to provide the heat they need, like during the coldest winter months, snakes enter in a state of torpor called brumation (often incorrectly called hibernation). Brumation in snakes only occurs where there is a marked difference between summer and winter.

During brumation, snakes find the safest possible place to hide and in which to reduce their metabolism to a minimum, becoming almost entirely inactive and not wasting any energy. When the temperatures rise during springtime and summer they come out from their hiding places, warm up by basking in the sun and become active again. This is why, during Southern Africa’s winter, snakes are very seldom seen, and when spotted they appear to be slow and lazy, whilst during summer they are very active.

Dentition (teeth and fangs)

Teeth and fangs are replaced throughout the snake’s life and venomous snakes (the one equipped with fangs and venom glands) are never without a functional set of fangs, unless severely damaged.

Teeth

The majority of snakes have pleurodont teeth, in other words, teeth that are fused together with the inner surface of the jawbone that holds them. in snakes is to grip prey, Since snakes do not chew their food the main function of their teeth is to grip prey. Hence their teeth are very pointed and sharp.

Fangs

Some snakes had evolved fangs, which are modified teeth. As mentioned above, fangs are hollow teeth with a central channel (that usually ends close to the tip) that is connected to the salivary glands, that have evolved into venom glands. The purpose of this modification is to inject toxic fluid into the prey’s body in order to subdue it, with the fang acting like a syringe. This fluid can also be used for defensive purposes.

Some snakes evolved a different design, and the fang channel suddenly turns outward, approximately mid- way down the fang, allowing them to spit the venom forward for defensive purposes.

Types of Fang

Snakes have different types of fang: fixed, hinged; located in the front area of upper jaw, located in the rear area of the upper jaws.

The following picture shows the three different types of fang present in Southern African snakes.

Each type of fang is peculiar to a certain family of snakes and a certain kind of venom.

• Front fixed fangs are typical of Elapidae family (e.g. mambas and cobras). Usually, these fangs are small to medium size and inject neurotoxic venom.
• Front hinged fangs are generally large and, because of that, have to be folded back against the roof of the mouth for the snake to close its mouth. They generally inject cytotoxic venom and are typical of Viperidae family (vipers and adders).
• Back fangs are generally small in size, inject haemotoxic venom and are typical of Colubridae family (e.g. boomslang and twig snake).

Snake Venom

Difference Between Venom and Poison

• Venom is generally a toxic substance that need to be injected to produce clinical symptoms in the victim.
• Poison produces clinical symptoms if ingested (eaten) or, in some cases, if it comes into contact with skin or other tissues.

Dealing with snakes, we only talk about “venom”. A snake can be a “venomous snake” and it is incorrect to talk about a “poisonous snake”.

The venom in snakes is a toxic liquid which is a modified saliva that is produced and stored in particular glands, called venom glands, which are actually modified salivary glands. The venom glands are situated on either side of the head, roughly behind the orbital area (behind the eyes) and are connected to the fangs through a channel.

Position of venom glands, seen from above

Snakes are able to control the contraction of venom glands, hence they can control whether or not to inject the venom. This often results in “dry bites” when a snake bites a victim for defensive purpose.

Types of Venom

There are four types of venoms produced by snakes: neurotoxic, cytotoxic, haemotoxic and miotoxic. Of these venomsonly the neurotoxic, cytotoxic and haemotoxic are found in Zimbabwe, whilst the miotoxic is present in only in sea snakes.

Each venomous snake species produces, in its venom glands, a mixture containing all these venoms, but generally only one of them is prevalent, whilst the others are present in such small quantity that they don’t have any effect. When we say that a snake has a neurotoxic venom, it means that that particular type of venom is the dominant in the mixture.

Cytotoxic Venom

This venom affects tissue cells, causing severe necrosis (tissue death) and secondary infections. A bite with this type of venom is extremely painful but it rarely causes death in humans. However, this venom can cause severe damage to tissues and limbs, often resulting in the loss of fingers or even limbs. Complications may also arise from secondary infections, leading to kidney failure.

The cytotoxic venom, acting on tissues, can cause damage even if it is not injected. Cytotoxic venom in the eyes, for example, may result in severe damage and may lead to blindness.

Cytotoxic venom is mainly found in vipers and adders (Viperidae family) but also in spitting cobras, that have developed cytotoxic venom since it is the only effective venom if spat in the eyes.

Neurotoxic Venom

Toxins of this venom affect the nerve system, progressively shattering the body functions of the victim. Death is generally caused by cardio-pulmonary failure. To be effective, this venom has to circulate into the fluid vessels of the body (e.g. blood vessels), hence it is effective only if injected. Generally, it does not cause much pain and the swelling is limited.

This venom is typical of mambas, cobras (with some exceptions), rinkhals and generally of the Elapidae family members. However, a few species belonging to other families, like the berg adder (Bitis atropos) have developed neurotoxic venom.

Haemotoxic Venom

Haemotoxic venom affects blood cells by preventing clotting, resulting in internal and external haemorrhages.

A bite with haemotoxic venom results in severe headaches and bleeding from the mucous membranes and from the internal organs.

This venom is typical of Colubridae family members, that usually have back fangs, so that the snake needs to “chew” the bitten part to inoculate the venom. In Southern Africa, only boomslang and twig snake are considered dangerous carriers of this venom.

Miotoxic Venom

Miotoxic venom affects heart functionality, eventually resulting in heart failure. As mentioned, it is only found in sea snakes.

Notable Exceptions

Although the prevalent type of venom is generally associated with a particular taxonomic family, there are some notable exceptions as a consequence of adaptation to a certain environment or survival behaviour.

Most cobras have neurotoxic venom. Spitting cobras, like the Mozambique spitting cobra (Naja mossambica) are an exception, with prevalent cytotoxic venom. These cobras have developed a very particular anti-predation strategy: they are able to spit their venom into the eyes of a potential aggressor, to blind it and so get the chance to escape.

They can spit their venom with an accuracy of about 2 cm at a distance of about the double of their body length: this means that a 1,5 m long M’fezi (Mozambique spitting cobra) can easily hit the eyes of an aggressor, spraying its venom from a distance of 3 m.

For this technique to be effective, two things are absolutely necessary:

1. The venom must be effective on tissue, even if it has not been injected.
2. The snake must be able to spit or spray the venom from a comfortable and safe position.

To achieve these goals, the spitting cobra has evolved adaptations of their venom and their fangs. The venom, from being mainly neurotoxic, which is not active on tissues, has evolved to mainly cytotoxic, capable of causing necrosis and severe damage to tissues, even if not injected. And the venom channel in the fangs has evolved by drastically changing direction halfway down the fang, exiting outward and forward. With this particular shape in venom channel, the snake is still able to inoculate the venom through a bite, but it is also able to spray it forward, simply by raising the head and opening the mouth.

Another snake that has taken an evolutionary path different from its family’s standard is the berg adder (Bitis atropos) The berg adder inhabits rocky and mountainous areas. Its habitat is mainly made up of boulders and vertical walls of rocks and cliffs, where prey that has been bitten by a snake can easily fall a long way when the venom begins to work. If this happens, it would be impossible for the snake to recover its prey and it would have spent energy without getting anything in exchange.

Cytotoxic venom, typical of adders, takes time to subdue a bitten prey, giving them time to move away and eventually fall down. On the other hand, neurotoxic venom is faster and more effective. The berg adder has adapted to maximize the effect of its venom, evolving the typical cytotoxic venom of adders into a neurotoxic venom. When a berg adder bites prey, it will die very fast because of the neurotoxic venom, and the risk of losing its prey is greatly reduced.

In both cases, it would have been impossible to turn a cytotoxic venom into neurotoxic, even during a long evolutionary period; but, as we previously said, every venomous snake produces a mixture containing all types of venoms, hence, in this case, the evolution had simply favoured the more effective venom becoming dominant.

Antivenom

An antivenom is a substance that neutralizes the effect of a venom’s toxins. Two antivenoms are produced in Africa: the polyvalent and the monovalent.

• Polyvalent antivenom is effective on the bites of most of the venomous snakes, but it does not work on the bites of  boomslang, twig snake, sea snakes and small adders.
• Monovalent antivenom is effective on boomslang only.

For some snake venoms there is no antivenom available, for example, for the twig snake. This does not mean that this venom cannot be neutralized, but simply that the extremely limited number of bites does not make the production of a specific antivenom viable.

Antivenom is made with alien proteins, as well as the venoms; hence inoculation of antivenom may cause a worse effect than the venom itself. The risk of an allergic reaction and anaphylactic shock due to the injection of antivenom is always present (in 20% of antivenom administration). That is why, when antivenom is injected, adrenaline has to be readily available.

Adrenaline itself may be very dangerous and result in heart failure if not administrated in the correct dose, which depends on many factors, like weight, age, medical conditions, etc. This means that, to safely provide antivenom to a victim of a snake bite, someone needs to be trained in adrenaline administration as well.

In conclusion, antivenom treatment must be in the hands of medical professionals.

How dangerous is a venom?

The toxicity of a venom is, without any doubt, a good indicator of how dangerous the venom is. But it is not the only factor.

The clinical effects of an envenomation depends not only on the toxicity of the venom, but also on the quantity. Snakes can generally control the amount of injected venom and in some cases they can give just a “dry bite”, in other words, a bite without inoculating any venom.

How fast a venom acts is another important factor to consider. There is a worldwide recognised test to determine the toxicity of a venom: the “LD Test” (“Lethal Dose Test”). This method tests how long a given quantity of venom takes to cause death in a mouse of a given body weight. In Southern Africa, the most toxic venom according to LD Test is the haemotoxic venom of the boomslang.

Venoms and Associated Snake Species

The following table shows the three types of venom and the related species of snakes mainly found in Zimbabwe.

The first column shows the dominant venom, while the second column (“Relevant secondary venom”) shows the non-dominant venom that may also give symptoms.

Dentition & venom classification of snakes

Dentition and, in venomous snakes, the type of venom are particular to each Family of snakes, and so snakes can be grouped according to these two characteristics.

Boidae (e.g. Pythons, Brown house snake) are fangless snakes, since they are constrictors and subdue their preys by constriction. However, they have very sharp teeth, used to catch and hold the prey during constriction.

Elapidae (e.g. mambas, cobras) generally have front fixed fangs, capable to inoculate neurotoxic venom. Exceptions are spitting cobras ((e.g. Mozambique spitting cobra), that produce a mainly cytotoxic venom.

Viperidae (e.g. Puff adder, Gabon adder) have front hinged fangs and generally produce cytotoxic venom. An exception is the Berg adder, that produces neurotoxic venom.

Colubridae (e.g. Boomslang, Twig snake) have rear fixed fangs and inoculate haemotoxic venom.

Diet and Foraging

Hunting

Most snakes are carnivorous (with a few exceptions). They feed on prey (including other snake species) that they hunt using their well-developed senses and either subdue using a venomous bite (venomous snakes) or strangle by constriction using powerful body muscles (constrictor snakes, e.g. pythons).

The snake’s elongated body allows it to pursue prey in every sort of environment, included burrows or tree canopies.

Venomous snakes bite the prey, injecting the venom. If the prey is not too large it is kept i firmly in the mouth until it dies. Larger prey can escape for a while, but they eventually die from envenomation. The snake follows them and eventually consumes them.

Ingestion

Snake dentition does not allow for chewing flesh into smaller pieces, so they have to swallow the prey whole.

Jaws

The jaws of snakes are adapted to swallowing the entire prey.

Lower jaw bones are not fused together in the front, which allows them to operate independently. The upper jaw bones are also loosely articulated and these two features (together with several other adaptations) allow snakes to consume prey of much larger diameter than the snake itself.

A large snake, like an adult Rock python, can swallow a prey as large as an impala or a warthog. During the digestion process, the shape of the swallowed prey is clearly visible inside the snake’s body.

Swallowing large prey is a long process, during which the oral cavity is entirely occupied by the prey’s body. To be able to breathe even when the oral cavity is obstructed by food, snakes have an elongated trachea, which ends in the lower front part of the mouth with a straw-like channel, called the tracheal straw.

Digestion

Strong digestive acids, together with the venom, digest the prey once it has been swallowed. The venom, in fact, it is not only used to kill the prey, but it also contributes to its digestion.

Specialised Diets

Some snakes have developed a very specialised diet while some other snakes’ diet is still unknown, like the Kunene racer(Coluber zebrinus), a small snake found in the Kunene region only (north-west Namibia).

• The Egg-eaters (of which three species are found in Southern Africa: the Common, the Southern Brown and the East African) feed on birds’ eggs and their bodies have been adapted to this particular diet. The mouth is virtually toothless, and the eggs are taken into the mouth and passed on to the neck region. There, a series of bony projections that are part of the vertebrae, together with muscular contractions, crack the eggshell and the contents are swallowed. The crushed pieces of shell are then regurgitated.
• Blind and worm snakes usually feed on termites, ants and their larvae,
• Slug-eaters (two species found in Southern Africa: the Common and the Variegated) feed on slugs and snails only. These snakes locate their prey following the slime trail. They grasp the forepart of a snail and slowly pull out the rest of the body out of the shell.

Reproduction

Snakes reproduce by means of internal fertilization, in other words, they have external sexual organ in male and a sexual receptive cavity in female and that the male’s sexual organ is inserted into the female sexual organ to deposit the sperm. Male snakes in fact have two penises, referred to as hemipenes, and only one is used at a time to copulate.

Mating

Mating occurs in early spring.  Males of some species engage in epic fights during competition to access females, usually performed with the front part of the body, measuring their strength by trying to push the opponent down. They never use their venom in fighting for mating rights.

The male follows a scent trail left behind by the receptive female and when it locates her, the male inspects her with the flicking tongue, to capture olfactory signals of her sexual condition. The male eventually twists the base of its’ tail beneath her to copulate.

Eggs and Incubation

All snakes hatch from eggs but a snake’s eggshell is not hard like in birds. Young snakes are covered in a fine membrane that can be easily ruptured.

Snakes can be grouped in two main groups according to the way their eggs are laid and hatch: Oviparous and Ovoviviparous.

Oviparous Snakes

The majority of snake species lay eggs and leave them for external incubation. These snakes are referred as Oviparous.

Four to eight weeks after mating, the eggs are laid in a hollow tree trunk or in rotting vegetation or hole in the ground or in any other suitable place that can provide them protection.

The number of eggs depends by the species and the female size and can range from 1 or 2 eggs, to more than 60.

Eggs are then abandoned for external incubation. Only a few species show primitive parental care behaviour: the Southern African python (Python natalensis) and the Rhombic skaapsteker (Psammophylax rhombeatus) coil around their eggs throughout incubation, to protect them and raise the temperature in order to assist with incubation.

Humidity and a certain amount of heat are required for the eggs to hatch. Hatching usually occurs after 1 to 3 months after the eggs are laid.

Example of oviparous snakes are mambas, cobras, boomslang, pythons and the brown house snake.

Ovoviparous Snakes

Other snakes retain the eggs inside their body until the eggs hatch, producing fully developed, live young. These snakes are referred as Ovoviparous. Although these snakes appear to give birth to live young, like mammals, this reproduction behaviour must not to be confused with mammalian live birth (viviparous) because no placenta is involved in this process and young snakes are still produced by mean of true eggs.

Most adders, the mole snake and the rinkhals are ovoviviparous.

Hatching and Parental Care

Young are equipped with an “egg tooth” located on the tip of the snout, which is used by hatchlings to break the eggshell. Eventually the egg-tooth is shed.

The young look like a miniature adults and in venomous species they are equipped with fangs and venom glands from birth. In some species, like the Black mamba, newly hatched young already have enough venom to cause serious clinical symptoms in humans.

Once the eggs are laid or the young produced, most snakes show no further interest in their offspring and young are left to their independent life. However, they have a good chance of survival because, in snakes, instinct is predominant over learning and every young snake already know whatever it needs to survive.

Only the Southern African python shows a certain degree of parental care: young may remain with the female for several days after hatching; they leave the burrow during the day to bask, but they return to the protective coil of the female at night.

Female python with her eggs

Predators and Self-Defence

Predators

Snakes have a wide variety of predators, ranging from other snakes, to birds of prey and some carnivorous mammals.

Some birds of prey specialise in predation of snakes: the Secretary bird (Sagittarius serpentarius), for example, patrols bush and vleis looking for snakes. The Brown snake-eagle (Circaetus cinereus) and the Black-chested snake-eagle (Circaetus pectoralis) also feed on snakes.

Amongst mammals, striped mongooses are well known as active snake predators, as well as the dwarf mongoose. Honey badgers also never miss the opportunity to feed on a snake.

The southern file snake (Mehelya capensis), harmless to humans, is an active predator of big snakes like the black mamba or puff adder. This snake appears to have some immunity to snake venoms.

Survival behaviours

• Invisibility is a snake’s primary protection since their potential predators can come from any direction: from land and from the sky. Many species use abandoned termite mounts as a den to rest. Others use tree wood cavities or rock crevices, whilst others simply hide in thick vegetation.
• Camouflage is an efficient tool to remain undetected, both to escape predators and to catch prey. An unmoving snake in its preferred environment is very difficult to detect. A Gaboon viper (Bitis gabonica), for example, has a colour pattern that perfectly matches its habitat of dry and carpets of dead leaves in forests, where it can remain almost invisible.

• Spitting cobras have evolved their unique technique of spitting cytotoxic venom in the eyes of the aggressor, blinding it and so getting the chance to escape.
• Venom in itself is an effective deterrent for some potential predators, although some others (like the honey badger or file snake) appear to have a certain level of immunity to snake venoms.
• Threatening behaviour is one form of protective behaviour. All cobras and also other species to a certain extent, raise the front part of the body and flatten their neckwhen threatened. This aggressive/defensive position makes them ready to strike, but it also makes them appear bigger and more dangerous, so that the aggressor might get alarmed and move away. Some other snakes send clear signals of warning by hissing, like the puff adder or twig snake.
• Thanatosis  (“death feigning”)is a technique used by some snakes, like the rinkhals (Hemachatus haemachatus). When all chances to escape from a predator are over, the snake  becomes immobile, usually with head upside-down, open mouth and tongue out, in a pose that perfectly resembles death. Most predators do not feed on dead animals, so they quickly loose interest in the “victim”. Snakes that practice thanatosis may remain in this state of immobility long enough to deter the predator, often facing contact and a certain level of manipulation. However, they can suddenly “come back to life” and promptly bite, hence it is always advisable not to touch an apparently dead snake.

Snake parasites

Snakes can be victims of ectoparasites like certain species of ticks. Ticks affecting snakes can be soft-body (argasidae) or hard-body (ixodidae). Ectoparasite like ticks can cause serious illness, like anemia, paralysis and eventually death.

Conclusion

The basic knowledge of snakes is extremely important for a hunter or a guide, as well as for anyone who moves, travels or operates in the bush. However, snakes are present in the urban environment as well. Hence, a basic knowledge of these beautiful creatures is very helpful for anyone living in any environment of the Southern African region.