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What is the snake that squeezes its victims?

Rainforest Animals

Animals of the rain forests are provided with a variety of habitats in the different layers of the forest trees. Some live at the top of the tallest trees while others live in the lower zones.

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Snakes, like all reptiles, are cold-blooded animals which cannot adjust their body temperature internally. The constant warmth and humidity of tropical rain forests provide an ideal habitat where snakes can live without having to shelter from heat or cold.

Snakes of the rain forest are well adapted to an arboreal or tree-dwelling existence. Many have long thin bodies with angled scales on their bellies which help the snakes to grip branches. Other species have developed ‘wings’, enabling the snake to escape predators by gliding to another tree or the ground. Ground-dwelling snakes track by scent but in the trees the scent trail is broken whenever the prey crosses to another branch, so many tree-living species hunt by sight. Some have prehensile tails which can grip a branch firmly while the rest of the body moves on. Snakes are well camouflaged; the most common colours are green or brown to match leaves or bark, often with a twig-like or leaf-like pattern.

Emerald Tree Boa © Eric Kilby CC BY-SA 2.0

Like the pythons of Africa and Asia the boas of South America kill by constriction. The largest boa is the anaconda, which averages 35ft in length and hunts along river banks. Other boas include the boa constrictor and the emerald tree boa.

Pythons include many species of non-poisonous snakes which kill their prey, such as birds and small mammals, by constriction. The snake coils its long body round its victim and squeezes it to death. The largest python is the reticulated python of Asia; it can grow to 33 ft long and weigh 300 lb. The 3 ft long burrowing python of Africa is the smallest python.

Venomous Species
Poisonous snakes use their venom mainly for feeding rather than for defence. There are three main groups:

a) Rear-Fanged Snakes
The snakes in this group have the two or three rearmost teeth of the upper jaw enlarged and grooved for injecting venom. Few species are very poisonous and only two, both African tree snakes, are dangerous to humans.

b) Front Fixed-Fang Snakes
The fangs of these snakes are fixed at the front of the upper jaw. This group includes many deadly species, such as the mambas of Africa, the cobras of Africa and Asia, and the coral snakes of the New World.

c) Folding Fang Snakes
These snakes have a large pair of poison fangs at the front of the upper jaw. The fangs lie flat when not needed and are raised when the snake strikes. The group consists of the vipers and pit-vipers, for example the rattlesnakes and the bushmaster snake of Central and South America.


Constriction is a method used by several snake species to kill or subdue their prey. Although some species of venomous and mildly venomous snakes do use constriction to subdue their prey, most snakes which use constriction lack venom. [1] The snake 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 then wraps one or two loops around the prey, forming a constriction coil. The snake monitors the prey’s heartbeat to ascertain it is dead. This can be a physically demanding and potentially dangerous procedure for the snake, because its metabolism is accelerated up to sevenfold and it becomes vulnerable to attack by another predator. [2] [3] [4]

Contrary to myth, the snake does not generally crush the prey, or break its bones. However, wild anacondas have been observed to cause broken bones in large prey. [5] Also contrary to prior belief, the snake does not suffocate the victim. Instead, a study of boa constrictors showed that constriction halts blood flow and prevents oxygen from reaching vital organs such as the heart and brain, leading to unconsciousness within seconds and cardiac arrest shortly thereafter. [6] Further, multiple species of snakes have been shown to constrict with pressures higher than those needed to induce cardiac arrest. [7] [8] [9] 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. [7] [8] In other words, constriction can work by different mechanisms at varying pressures. It likely interferes with breathing at low pressures, [10] can interrupt blood flow and overwhelm the prey’s usual blood pressure and circulation at moderate pressures, [11] and can interfere with neural processing and damage tissues at high pressures. [5] [7] [8]

During constriction when the prey’s heart is impeded, arterial pressure drops while venous pressure increases, and blood vessels begin to close. The heart is not strong enough 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, a loss of oxygen and glucose. There is evidence that boa constrictors have more difficulty killing ectotherms—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. [12] [13]

This relatively recent research (2015) suggests that other constrictors may kill in other ways. It had previously been accepted that constrictors used their body to hold the prey tight enough to prevent it from breathing, resulting in death from asphyxia, [14] or that the pressure of constriction increases the pressure inside the prey’s body higher than the heart can counteract, resulting in cardiac arrest; [15] data from earlier studies had also indicated that snakes can exert enough pressure for these to be plausible. [10]

Certain groups of snakes have characteristic patterns of constriction, including the number of coils they use and the orientation of the coils. [16] [17]

Venomous snakes that also use constriction include the genus Clelia (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), [18] [19] some species of Boiga snakes (Asian and Australian rear-fanged colubrids) including the brown tree snake (Boiga irregularis), [18] [20] [21] some species of Australian elapids (including some of the venomous Pseudonaja brown snakes and one Australian coral snake Simoselaps), and a few Australian colubrids. [1]

See also [ edit ]

References [ edit ]

  1. ^ ab Shine, R.; Schwaner, T. (1985). «Prey Constriction by Venomous Snakes: A Review, and New Data on Australian Species». Copeia. 1985 (4): 1067–1071. doi:10.2307/1445266. JSTOR1445266.
  2. ^
  3. Powell, Devin (25 Feb 2012). «Boas take pulse as they snuff it out». Science News . Retrieved 11 May 2014 .
  4. ^
  5. Yong, Ed. «Snakes know when to stop squeezing because they sense the heartbeats of their prey» . Retrieved 2015-07-23 .
  6. ^
  7. Boback, Scott M.; Hall, Allison E.; McCann, Katelyn J.; Hayes, Amanda W.; Forrester, Jeffrey S.; Zwemer, Charles F. (2012-06-23). «Snake modulates constriction in response to prey’s heartbeat». Biology Letters. 8 (3): 473–476. doi:10.1098/rsbl.2011.1105. ISSN1744-9561. PMC3367750 . PMID22258447.
  8. ^ ab
  9. Rivas, Jesus (January 2004). «Eunectes murinus (green anaconda): Subduing behavior». Herpetological Review. 35: 66–67.
  10. ^
  11. Boback, Scott M.; McCann, Katelyn J.; Wood, Kevin A.; McNeal, Patrick M.; Blankenship, Emmett L.; Zwemer, Charles F. (2015-07-01). «Snake constriction rapidly induces circulatory arrest in rats». The Journal of Experimental Biology. 218 (14): 2279–2288. doi: 10.1242/jeb.121384 . ISSN0022-0949. PMID26202779.
  12. ^ abc
  13. Penning, David; Dartez, Schuyler; Moon, Brad (September 2015). «The big squeeze: scaling of constriction pressure in two of the world’s largest snakes, Python reticulatus and P. molurus bivittatus». Journal of Experimental Biology. 218 (Pt 21): 3364–3367. doi: 10.1242/jeb.127449 . PMID26347553.
  14. ^ abc
  15. Penning, David; Dartez, Schuyler (February 2016). «Size, but not experience, affects the ontogeny of constriction performance in ball pythons (Python regius)». Journal of Experimental Zoology Part A. 325 (3): 194–199. doi:10.1002/jez.2007. PMID26847931.
  16. ^
  17. Penning, David; Moon, Brad (2017). «The king of snakes: performance and morphology of intraguild predators ( Lampropeltis ) and their prey ( Pantherophis )». Journal of Experimental Biology. 220 (Pt 6): 1154–1161. doi: 10.1242/jeb.147082 . PMID28298469.
  18. ^ ab
  19. Moon (2000). «The mechanics and muscular control of constriction in gopher snakes (Pituophis melanoleucus) and a king snake (Lampropeltis getula)» (PDF) . Journal of Zoology. 252: 83–98. doi:10.1017/s0952836900009109. hdl: 2027.42/74530 . Archived from the original (PDF) on 2011-07-20.
  20. ^
  21. Gill, Victoria (2015-07-23). «Boa constrictors’ lethal secret revealed». BBC News . Retrieved 2018-03-30 .
  22. ^
  23. Bittel, Jason (July 22, 2015). «Why We Were Totally Wrong About How Boa Constrictors Kill». National Geographic News . Retrieved 2015-07-23 .
  24. ^
  25. Boback, Scott M.; McCann, Katelyn J.; Wood, Kevin A.; McNeal, Patrick M.; Blankenship, Emmett L.; Zwemer, Charles F. (2015-07-01). «Snake constriction rapidly induces circulatory arrest in rats». The Journal of Experimental Biology. 218 (14): 2279–2288. doi: 10.1242/jeb.121384 . ISSN0022-0949. PMID26202779.
  26. ^
  27. «ADW: Boa constrictor: INFORMATION» . Retrieved 10 May 2014 .
  28. ^
  29. Hardy, David L (1994). «A re-evaluation of suffocation as the cause of death during constriction by snakes». Herpetological Review. 229: 45–47.
  30. ^
  31. Willard, D. E. (1977). «Constricting Methods of Snakes». Copeia. 1977 (2): 379–382. doi:10.2307/1443922. JSTOR1443922.
  32. ^ Bealor, M.T. and Saviola, A.J., 2007. Behavioural complexity and prey-handling ability in snakes: gauging the benefits of constriction. Behaviour, 144(8), pp.907-929.
  33. ^ ab
  34. de Queiroz, Alan; Groen, Rebecca R. (2001). «The inconsistent and inefficient constricting behavior of Colorado Western Terrestrial Garter Snakes, Thamnophis elegans». Journal of Herpetology. 35 (3): 450–460. doi:10.2307/1565963. JSTOR1565963.
  35. ^
  36. Gregory, Patrick T.; Macartney, J. Malcolm; Rivard, Donald H. «Small mammal predation and prey handling behavior by the wandering garter snake Thamnophis elegans». Herpetologica. 36 (1): 87–93.
  37. ^ CHISZAR, D. A. 1990. The behavior of the brown tree snake: a study in applied comparative psychology. In D. A. Dewsbury (ed.), Contemporary Issues in Comparative Psychology, pp. 101-123. Sinauer Assoc, Inc., Sunderland, MA.
  38. ^
  39. «The Brown Treesnake». United States Geological Survey. Archived from the original on 2012-11-13 . Retrieved 2013-04-28 .

External links [ edit ]

  • «World’s Deadliest: Anaconda Devours World’s Largest Rodent»

We Finally Know Why Boa Constrictors Don’t Choke While Crushing Their Prey to Death

(Joe McDonald/The Image Bank/Getty Images)

Powerful ambush hunters, Boa constrictor snakes are notorious for brutally incapacitating their prey – by squeezing them to death before swallowing them whole. Researchers have just discovered how the snakes achieve this without suffocating themselves.

Contrary to popular belief, these nonvenomous reptiles actually kill their victims by choking off the blood flow to their heart and brain, rather than suffocation. This technique – along with super-stretchy jaws – allows them to take down relatively large prey, including wild pigs, monkeys, and ocelots from their forested homes in Central and South America.

But snakes have no diaphragm – the thin layer of muscle mammals like us contract to move air in and out of lungs – so they rely entirely on their rib muscles to breathe. This means when those muscles are busy squashing something externally or squeezing food through their tubular bodies, snakes can’t move air around, too.

Yet these nocturnal nope ropes increase oxygen consumption by almost 7 times while subduing their victims compared to resting rates, and up to 17 times to digest prey a quarter of their own body weight. How boa constrictors manage to squeeze the life out of another animal for up to 45 minutes, yet still are able to breathe, has been a long-standing mystery.

Researchers led by evolutionary biologist John Capano from Brown University used blood pressure cuffs to figure out what happens when different parts of a danger noodle are squished – which sounds like a risky task.

«Either the animals did not mind the cuff or became defensive and hissed to try to get the researcher to leave,» recalls Capano, explaining that the reptiles filled their lungs to hiss, providing the team with the perfect opportunity to measure some big breaths.

By compressing the cuff along different points, the team could assess and reconstruct how the boa’s ribs moved. When the ribs closest to the snake’s head were stifled by the gripping cuff, ribs further towards its tail started to heave in and out.

If the cuff gripped those further back ribs, the front part of the snake would take on the motion.

So, boa constrictors can alter which part of their rib cage is doing their breathing movements – saving themselves from suffocating when their default breathing muscles are otherwise occupied.

Capano and colleagues have dubbed this newfound ability ‘modular lung ventilation’, and suspect it evolved before snakes began constricting their prey.

While long, noodle-shaped bodies have evolved at least 65 times amongst animals with backbones, snakes have the most stunning array of diversity out of all these groups, with nearly 4,000 known species. Some researchers have suggested snakes’ ability to take down a large victim and swallow it whole may have been what gave these animals their edge, by allowing them to consume a greater variety of prey.

Capano and team note modular lung ventilation would have been a key feature in snake evolution: «This remarkable ability to subdue and consume such massive prey may have facilitated entry into novel ecological niches.»

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