Constriction is a method used by various

snake Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more ...

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

to kill or subdue their

prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...

. Although some species of

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 ...

and mildly venomous snakes do use constriction to subdue their prey, most snakes which use constriction lack venom. The snake initially strikes at its prey and holds on, pulling the prey into its coils or, in the case of very large prey, pulling itself onto the prey. The snake will then wrap one or two loops around the prey, forming a constriction coil. The snake will monitor the prey's heartbeat to ascertain when it is dead. This can be a physically demanding and potentially dangerous procedure for the snake, as it accelerates its

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run ...

up to seven times and leaves it vulnerable to attack by another predator. Contrary to myth, the snake does not crush the prey, or break its

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

s. However, several natural observations exist involving wild

Anacondas Anacondas or water boas are a group of large snakes of the genus ''Eunectes''. They are found in tropical South America. Four species are currently recognized. Description Although the name applies to a group of snakes, it is often used to r ...

that show broken bones in large prey. Also, contrary to previous belief, the snake does not cause suffocation by constricting the victim; instead, a study of death caused by boa constrictors showed that constriction "shuts off" blood flow (and therefore oxygen) needed by vital organs such as the

heart The heart is a muscular Organ (biology), organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as ca ...

and

brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...

, leading to

unconsciousness Unconsciousness is a state in which a living individual exhibits a complete, or near-complete, inability to maintain an awareness of self and environment or to respond to any human or environmental stimulus. Unconsciousness may occur as the r ...

within seconds and cardiac arrest shortly thereafter. Further, multiple species of snakes have been shown to constrict with pressures higher than those shown to induce cardiac arrest. In conjunction with observations of oral and nasal hemorrhaging in prey, constriction pressures are also thought to interfere with neural processing by forcing blood towards the brain. In other words, constriction can work by different mechanisms at varying pressures. It likely interferes with breathing at low pressures, can interrupt

blood flow Hemodynamics or haemodynamics are the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms of autoregulation, just as hydraulic circuits are controlled by control systems. The hemodynamic response continuously m ...

and overwhelm the prey's usual

blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure ...

and circulation at moderate pressures, and can interfere with neural processing and damage tissues at high pressures. During constriction events where the prey's heart is impeded, arterial pressure drops while venous pressure increases, and blood vessels begin to close. The heart does not have enough strength to pump against the pressure and blood flow stops. Internal organs with high metabolic rates, including the brain, liver, and heart, begin to stop functioning and die due to

ischemia Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems w ...

, a loss of oxygen and glucose. There is evidence that boa constrictors have more difficulty killing

ectotherm An ectotherm (from the Greek () "outside" and () "heat") is an organism in which internal physiological sources of heat are of relatively small or of quite negligible importance in controlling body temperature.Davenport, John. Animal Life ...

s—animals like lizards and snakes that rely on external heat to regulate their body temperatures. A boa constrictor was observed attacking a spinytail iguana for an hour, and the iguana survived. As this is comparatively recent research (2015), it is possible that other constrictors kill in other ways. It had previously been accepted that constrictors used their body to hold the prey tight and prevent the prey from drawing air into its lungs, resulting in death from

asphyxia Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can ...

, or that the pressure of constriction causes a rise in the pressure in the prey's body cavity greater than the heart can counter, resulting in immediate

cardiac arrest Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possi ...

; data from earlier studies had also indicated that snakes can exert enough pressure for these to be plausible. Certain groups of snakes have characteristic patterns of constriction, including the number of coils they use and the orientation of the coils. Venomous snakes that also use constriction include the mussuranas (ophiophagous South American mildly venomous rear-fanged colubrids which use constriction to subdue snakes including pit vipers), the western terrestrial garter snake (North American colubrid which is an inefficient constrictor and, like most ''Thamnophis'' garter snakes, mildly venomous), some species of ''

Boiga ''Boiga'' is a large genus of rear-fanged, mildly venomous snakes, known commonly as cat-eyed snakes or simply cat snakes, in the family Colubridae. Species of the genus ''Boiga'' are native to southeast Asia, India, and Australia, but due to ...

'' snakes (Asian and Australian rear-fanged colubrids) including the

brown tree snake The brown tree snake (''Boiga irregularis''), also known as the brown catsnake, is an arboreal rear-fanged colubrid snake native to eastern and northern coastal Australia, eastern Indonesia (Sulawesi to Papua), Papua New Guinea, and many islands ...

(''Boiga irregularis''), some species of Australian elapids (including some of the venomous '' Pseudonaja'' brown snakes and one Australian coral snake '' Simoselaps''), and a few Australian colubrids.

References

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External links

"World's Deadliest: Anaconda Devours World's Largest Rodent"
Snakes Predation

See also

References

External links