The Predator's Pursuit - Part 4 - Strategy & Execution - Serpents
Perhaps the most infamous of all terrestrial predators remains the snake. These beautiful, yet intimidating creatures are some of the most specialized and successful predators of the wilderness. Snakes may share similar physiology, but there is a great diversity among the families of snakes. Each species is adapted to fill their niche in the environment with their particular physiology and hunting strategies. Snakes use a variety of methods to hunt prey depending on their specialties. Some use their body to constrict, while others envenomate prey. Some wait in ambush for extended periods of time, while others actively seek out their quarry. Whichever physical design or hunting strategy they may possess, it is certain that these amazing creatures have evolved to become some of the most formidable and successful predators in the world. In this article, the various hunting strategies and methods of execution used by snakes will be discussed with a focus on South African snake species.
Snakes incorporate a variety of hunting methods depending on the particular species. Each species of snake differ in one way or another, while overall their physiology is quite diverse. Their prey and hunting strategies differ due to their particular physiological features, such as shape, size, locomotion method, body strength, tooth design, venom prevalence and more. Broadly speaking, snakes either rely on ambush predation or active search and pursuit in the procurement of prey. Due to being ectothermic, their need for warmth limits the amount of energy available for their activity. Therefore, most snakes rely more on ambushing prey than actively hunting, however, a combination of both means are common to different degrees depending on species, environment, prey, and more.
Snakes locate prey using a variety of specialized senses depending on the species, such as scent picked up by the tongue, thermal pits that measure temperature differences, vibrations through the ground detected by the inner ear, and binocular vision for accurate eyesight.
The split tongue of a snake is a well-known feature of these extraordinary creatures. It is believed to have evolved separately between two and four times in the largest order of reptiles known as Squamata. It is used as a sense organ which picks up chemical signals in the environment for navigation. Since the tongue is split, it has the benefit of determining the direction of chemical packages through minute changes in the surrounding environment. Once the chemicals are picked up by the snake's tongue, it is retracted into the mouth where it is placed against the vomeronasal organ which is also known as the Jacobson's organ. This organ analyses the chemical package and sends the appropriate information to the brain providing a detailed analysis of its environment. Though snakes can smell to a limited degree through nostrils, their tongues are the primary means by which they analyze the chemical environment and is far more reliable.
Another remarkable sense adaptation is the ability of some snakes, namely boas, pythons and pit vipers to sense infrared thermal radiation. This is commonly referred to as thermal pits and allow these snakes to perceive temperature variations with outstanding clarity. Any temperature variations of the environment and living animals are easily perceived within a reasonable distance and provide a pinpoint estimation of the prey's location. This sense evolved parallel in both the Boidae (boas & pythons) and Crotanilae (pit vipers), though is believed to have evolved once in the Crotanilae and three separate times in Boidae. Some argue that these pits did not evolve solely for the location of prey items, but also as a means of better thermoregulation. Thus, it provides these snakes not only with an alternative sense but also aids in energy management.
Contrary to popular belief, snakes do possess a form of hearing. This sense, however, does not function well with airborne vibrations as the sound has to be very loud. This is due to having lost the tympanum, or outer ear structure, thus the ability to pick up external airborne sounds are diminished. Instead, they are adept at picking up ground-based vibrations. Snakes still possess an inner ear connected by a single ear bone structure known as the columella auris which is attached to the jaw bone. It is the jawbones then, that pick up on subtle ground vibrations which is then sent to the inner ear for analysis. The snake picks up which jaw and area of the jaw receive ground vibrations first, and is then able to determine the direction of vibration along with its relative distance or strength.
As for sight, the visual ability of snakes is greatly varied depending on particular species. For most snakes, this sense is not at all primary and therefore not nearly as acute as that of many other animals. Snakes that burrow underground or spend most of their time on the ground are known for their weak eyesight, while many arboreal snakes who prefer treelines and shrubs have comparatively decent sight. For the most part, a snake's sight is capable of distinguishing light and dark shades to an adequate degree, while movement can be tracked effectively. Certain species of arboreal snakes, such as the boomslang (Dispholidus typus) and vine snake (Thelotornis capensis) have binocular vision. This allows them to judge distance more effectively by increasing three-dimensional perception which is necessary for their arboreal lifestyle when hunting or navigating branches.
As with all predators in the animal kingdom, a diversity of hunting strategies exist within the suborder of Serpentes which depend on a variety of factors. These are primarily dependent on factors such as physiology, senses, preferred prey items, and coloration, among a few other secondary factors. Hunting may involve actively searching for prey in their respective environments, ambush predation in areas where prey are likely to pass by or even luring prey items through deception. In general, most snakes use a mix of both active search and ambush predation but vary according to the particular species or the environment.
Active pursuit involves moving from place to place and gaining vantage points in order to get close to prey items. Snakes that incorporate this method as their primary hunting style are diverse within themselves. In general, these snakes do not have bold coloration so as to blend more effectively into the environment while on the move. This includes snakes such as cobras, mambas and a myriad of non-venomous constricting snakes. These snakes tend to rely little on ambush predation, but speed and agility instead to close the gap between themselves and their prey even in rough terrain. Locating prey is done in a variety of ways depending on the species of snake. Some cruise along the ground or trees, using their scent to identify common pathways, burrows, nests or animal dens to invade, or simply the ideal opportunity to snatch up prey. This method of hunting is more invasive than ambush predation as burrows and nests are frequently invaded by the predator.
Ambush predation is common in snakes such as adders and to a lesser extent pythons, along with a few other snake species. They are usually strikingly marked and colored, and when out of their respective environments or on the move are easy to spot, however, when in their ideal environments and motionless have exceptional camouflage. This camouflage is related to their environment and niche they inhabit. The beautiful Gabon adder (Bitis gabonica), for example, has complex markings and shapes specifically suited for the forest floor where leaves fall and resemble different colors of decaying foliage. The near-extinct Albany adder (Bitis albanica) has light grey to dark grey colors to suit the rocky pale substrate of its environment. The African rock python is also known for ambush predation by laying in shaded areas out of sight for passing prey, while at times adopting similar hunting strategies to crocodiles by laying motionless and submerged in water for thirsty prey to come and drink. Some of these ambush predation specialists also trick prey by luring them with a tail that mimics the movement of an insect. When a hungry prey item approaches, they are taken by surprise as the snake strikes.
Snakes rely on two primary means of execution. These are constriction and envenomation. Some snakes incorporate a mix of both methods, however, would generally then possess weaker venom. Or, they are back-fanged snakes who need a firm grip for the injection of venom into the prey. Both of these methods are extremely effective in killing prey, as once the prey is bitten most of them are doomed.
This means of execution is horrific for any prey item, though, could lead to a relatively quick death. Constriction implies that the body of the snake coils around the prey item while firmly and surely increasing its powerful bodily grasp. First. the constructor will try to gain a good grip with a quick and powerful bite to hold onto the prey. The snake then coils piece by piece around the animal. Since almost the entire body of the snake is a large set of powerful muscles, especially so in constrictor specialists, the chance of the prey escaping is minute as the total amount of strength imposed in the creature is massive. This method execution is mostly utilized by snakes that do not possess any venom or very little thereof.
Contrary to popular belief, death does not come from crushing the animal to death or prevention of breathing. With every out-breath of the prey, the snake tightens its grip, preventing respiration and also breaking bones as the grip tightens, although these are not the primary causes of death but secondary effects of the constriction. Instead, the constriction prevents blood flow since the heart is not capable of pumping against such pressure, thus oxygen and glucose are cut off from the brain as the blood flow weakens or stops. This is known as ischemia, leading to unconsciousness and cardiac arrest as the true cause of death. It is also known that constriction methods may vary according to the snake species, as the number of coils and their orientations differ. For example some coil only once, others twice and the pattern of the coil may differ from species to species.
On the playground of natural law, unique and powerful chemical weapons evolved as either offensive or defensive measures. Most creatures who bear venom are feared and for good reason. Unlike large predators or trampling beasts, all that is required for envenomation is a single injection through sting or bite from something that may be small enough to hide under a pillow. For this reason, even small creatures such as snakes, spiders, and scorpions are feared as much or even more than large, strong and fierce beasts. This apprehension towards venomous creatures is of evolutionary design, as over vast spans of time, we learned to keep our distance from something so dangerous. Today, venom is used to isolate, study and utilize particular toxic and non-toxic proteins and peptides for medicine. In snakes, the primary use is of course to deal damage.
Venom is a secretion produced by a living organism containing a single or mixture of toxins. It consists of multiple proteins or peptides that act upon a living organism in a variety of ways with the primary purpose of shutting down or deterring prey or predator. In chemically complex venoms, the different chemicals play specific roles in the function of the venom, such as aiding the transport of specific toxins to vital areas or to promote its potency. Thus, not every protein or peptide is harmful on its own but promotes the overall effectiveness of the harmful toxins.
Each of these toxins affects the body in a particular way and may be further specialized depending on the particular species of animal delivering the venom. For example, the toxin mixture of a black mamba (Dendroaspis polylepis) shuts down a living system without targeting specific areas, while some research suggests that green mambas (Dendroaspis angusticeps) have a toxin mixture which is specialized in targeting the heart more specifically.
Venoms are complex in their chemical makeup as a large variety of toxin types exist. Most snakes have a combination of a variety of toxins within their venom which makes classification difficult. Broadly speaking, the primary venom types of snakes are either neurotoxic, cytotoxic or haemotoxic. However, a variety of other toxin types are also to be found mixed in with the primary toxins, such as myotoxins, cardiotoxins, dendrotoxins, k-toxins, sarafotoxins and more. Each of these toxin types has particular biological effects that are detrimental to the function of an organism. Since this subject is vast and complex, only the primary three types of toxins, namely neuro-, haemo-, and cytotoxins of are discussed.
First, neurotoxins are toxic compounds that have an adverse effect on the neurological system in one way or another. A large variety of neurotoxins have been identified that act on the neurological system in a variety of ways. Such as either inhibiting electrical impulse transferred from one synapse to another, or by attacking the synapse itself in a more destructive manner. This is the primary toxin in most elapid snakes, which include mambas, non-spitting cobras and many other less harmful snakes. Once the venom is injected into the prey, it begins to inhibit or destroy the animal's capability of sending electrical impulses throughout the body. Thus it has a paralyzing effect which shuts down the prey's ability to move, breathe, pump blood, and use cognitive ability among other negative effects.
Haemotoxins, as the name suggests affects the blood. Many vipers and cobras possess this venom to a significant extent, while snakes such as the vine snake and boomslang are haemotoxin specialists. This venom may have starkly different effects on the blood. For example, hemolysis which involves the destruction of blood cells would have the cell break apart, causing internal bleeding and thinning of the blood to such an extent that the plasma flows from every part of the animal, such as eyes, ears, mouth, etc. On the other hand, some haemotoxic venoms cause coagulation instead, meaning that the blood is thickened and clumped. When this happens, the ability of blood to flow smoothly through the body is prevented. As the blood turns into a jelly-like clump it eventually causes cardiac arrest as the ability for blood to flow is halted, preventing oxygen and other vital requirements to not reach their vital destination.
Cytotoxic venoms attack cell membranes on a chemical level by utilizing digestive enzymes. The toxin attacks cell walls which break them apart and leads to cell destruction. Instead of targeting a particular type of biological system, such as the neurological network or blood cells in the case of neuro and haemotoxins, the cytotoxin breaks apart whatever cell it can. In this case, the venom is far more localized at the bite in large creatures, and potent enough to easily kill small creatures such as a rodent. Intense pain and swelling immediately set in as the body attempts to combat the venom. In larger creatures capable of surviving such a bite, secondary effects include infection and necrosis if left untreated. Death of a prey item thus ensues as the cells of vital organs are destroyed which leads to organ failure. This venom is characteristic of many adders and spitting snakes, such as the rinkhals (Hemachatus haemachatus) and all spitting cobras. It is this aggressive cell destroying venom that causes damage when it comes into contact with the eyes.
Once prey has been killed via whatever means the particular snake employs, the next step is to ingest it in the signature fashion of the snake. Since snakes cannot rip, tear or chew meat they need to swallow the prey whole in a seemingly uncomfortable display. The exception to this are a few water snakes that hunt crabs and break off limbs piece by piece for ingestion. Though, by far the majority of snakes rely on their highly flexible jaws to ingest prey, which does limit the prey items of a snake to whatever could fit down their throat.
Contrary to belief, a snake is not capable of dislocating its jaw but instead relies on the flexibility and play provided by loosely attached bones. Not all snakes share the same skull anatomy and therefore certain anatomical particulars vary accordingly. For the most part, snakes are capable of opening their jaw to such extents due to loosely connected jaw bones and relatively elastic skin. The loosely connected quadrate bone which connects the bottom jaw to the skull is double hinged, which allows for a wide opening from top to bottom. The relative play that the quadrate and supratemporal bone provides coupled with the fact that the lower jaw is connected in the middle by a stretchable ligament allows for the mouth to widen from side to side.
Even though the jaw may open wide, the size of prey that the snake is able to consume is still limited to the size of the buccal/oral cavity which leads to the oesophagus. If the prey is not too large, it is capable of being moved back into the mouth. When the prey is placed in the mouth it is lubricated via saliva and moved backwards by manipulating the various parts of the loose jaw in what is known as "walk-feeding". This simply implies that one part of the jaw is moved forward while the other parts hold the prey in place at any given moment. For example, the upper left jaw is moved, then upper right, then lower left, then lower right and continues in such a way until the prey is ingested. The elongated anatomy and strong muscles of the snake aid moving the prey further backwards when within the body. Once the prey is ingested, the snake is slow, lethargic and in danger from predators. Thus it would seek shelter and start the long process of digesting a whole animal.
Though snakes may induce fear in the human psyche through evolutionary memory and indoctrination, it does not decrease their value and ability to fascinate. These exceptional predators have evolved to face the world with design and prowess like no other creatures. Their specially adapted physiology, senses, weaponry, and tactics have allowed them to become some of the most successful predators of the natural world and capable of sustaining their place for a long time to come. Whether it is their unique design allowing for agility, speed or strength. Their, ability to remain hidden in plain sight or on the move, their powerful bite or chemical weaponry, they remain amazing natural predators that have more than only their prey fear them.