10 Things You Didn't Know About Snakes

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6. Spurs and Legs

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Snakes are specialised animals, which are descended from four-limbed ancestors. Some snake families possess vestiges of posterior limbs (pelvic girdles), although in modern snakes the pelvic girdle (representing vestiges of the femur and/or pelvis) is no longer in contact with the vertebral column or is missing altogether.
 
In the Boas and Pythons these vestiges are characterised by external protrusions of keratinised tissue called spurs. Spurs help males to clasp onto the female for breeding. Interestingly, the mechanisms of limb development may not have been completely lost in snakes. It has been observed that hindlimb development halts in Python embryos as a result of mutations in the limb-specific enhancer of a gene known as Sonic Hedgehog (Shh). This gene disrupts the genetic circuit that drives limb growth in snakes. 

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7. Energy Conservation

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Snakes are periodic feeders owing to the fact that they have slow metabolisms, meaning they have low energy requirements. Because they are able to eat such large prey they do not need to eat often. Generally speaking, snakes ingest 6 to 30 meals per year to meet their overall energy needs. If mammals do not eat they will generally perish within a few days or weeks, whereas some species of snakes in captivity can survive for more than a year without a meal. Some rattlesnakes are able to survive without food for up to 2 years! 
 
Digestive efficiencies of snakes vary between 85-95% while some species are able to gain up to 99.8% of the potential chemical energy of their food. The efficiency of their digestive capabilities may be linked with the snakes’ intermittent feeding behaviours. Furthermore, The gut responds rapidly to the presence of food and the intestines will grow more than double in mass to increase the intestines capacity for nutritional uptake. Within a few days, however, the internal organs will begin to atrophy and shrink, this is useful for energy conservation during voluntary fasting periods.
 
Gut passage time can vary from a few hours to days in mammals but snakes are clearly champions when it comes to the maximum passage time for faecal matter. Heavy bodied terrestrial species such as Viperid and Boid species retain faecal material for months at a time.  For example, the maximum defecation interval for the Gaboon Viper is 420 days! The accumulation of faeces may help with anchoring the lower body while the snake strikes. 

  
Gaboon Viper and Long-nosed Tree snake have different morphologies and feeding strategies, resulting in different energy requirements and gut passage times (The ambushing Gaboon Viper requires less feeds and defecates far less frequently while the active arboreal snake species defecates within 24 hours to lighten themselves for locomotion).

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8. Locomotion

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One of the most remarkable features of snakes is how they are able to move so effortlessly through a large variety of landscapes without limbs. Although other animals have evolved elongated, limbless bodies (such as certain amphibians and lizards) non have developed these attributes with such apparent perfection.
 
All snakes can swim by undulating in the water, but sea snakes have specific adaptations to aid in their movements such as vertically flattened, streamline bodies and broad paddle-like tails. Yellow-bellied Sea Snakes are interesting in that they can even swim backwards.
 
Another group of snakes have adapted to flattening their bodies to help them get around; the Paradise Flying Snake. This species of arboreal snake lives up in the canopy and flattens its body horizontally instead of vertically to help capture the air during gliding, effectively turning itself into a parachute. Flying snakes have such remarkable control in the air that they can even change direction mid-glide.
 
Terrestrial snakes are highly accomplished climbers, this is partly owing to the fact that snakes do not just “slither” to get around (also known as lateral undulation), but adopt several strategies to move, including a mode of locomotion called ‘Concertina Locomotion’, which utilises stationary body parts to push or pull the remaining body forward. Snakes can also anchor themselves to a surface using their belly scales like little fingertips to keep a grip. This is extremely useful when climbing challenging surfaces.




([i]a) A corn snake ascending a tree. (b,c) Scales are used to grip tree bark asperities. Snake scales at their (d) minimum and (e) maximum angles of attack (flat). (f,g) A snake climbing an inclined surface. Sliding is prevented by emergency braking associated with lifting of the body (Marzi et al, 2012).[/i]






The gliding Paradise Flying Snake and aquatic Olive Sea Snake flatten their bodies along different planes (flying snakes flatten horizontally to catch the air like a parachute and sea snakes flatten vertically to better streamline themselves while swimming).

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9. Sociality

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Reptiles are often assumed to be a-social with interactions restricted to territorial defence and courtship behaviour, snakes most of all are seen as anti-social solitary animals, but modern biologists are uncovering increasing evidence to the truly complex nature of reptile sociability.
 
 It appears that some squamates (lizards and snakes) are more similar to mammals and birds in their social behaviour then what could have been previously imagined. Several species of Skinks from the genus Egernia will form monogamous pairings and stay in family groups consisting of the two biological parents and their offspring. Some species of skink, such as the Great Desert Skink will also cooperatively build large elaborate burrows for their families. Monogamy is not restricted to this genus but can also be observed in the Shinglebacks (or Sleepy Lizards) and Desert Night Lizards.
 
In regards to snakes, the best-studied snakes for their social behaviour are the rattlesnakes. Rattlesnakes will express many of the same social behaviours as seen in the social lizards, as well as conspecific alarm signals to alert others of the same species to danger and the formation of nurseries where females aggregate and cooperatively care for the young. What’s more fascinating is that these snakes can recognise their family members, even after years of separation and will demonstrate social preferences, habitually avoiding certain individuals they don’t like while seeking out the company of specific individuals. It would seem that rattlesnakes make ‘friends’ with each other. Unfortunately research is severely lacking in regards to social behaviour across a broader range of species, largely because snakes are secretive animals and very difficult to study in the wild. Judging by the current trends of discoveries made about social reptiles it would be more surprising if social behaviour wasn’t more widespread amongst the reptiles.




Rattlesnake mother with her newborn. Photographed by Richard Sanderson.

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10. Intelligence

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It is a common misconception that reptiles lack cognitive abilities. This may be because it is not often studied in reptiles, and even less so in snakes, but there is strong evidence to suggest that reptiles (including snakes) have surprisingly advanced cognitive abilities.
 
Chelonians (turtles and tortoises) tend to take the spotlight for cognitive research, largely because they are thought to have changed little in the last 225 million years, representing animals who lived closest to the time of the reptile-mammal split, and therefore allows us insight into the mental capacities of ancient ancestral reptiles. Cognitive experiments on turtles have demonstrated that reptilian learning and memory capabilities, as well as behavioural flexibility in problem solving and social cognition may closely parallel those observed in mammals and birds.
 
Snakes have been directly studied for their spatial learning and memory capacities, corn snakes directly demonstrated that they are capable of learning spatial and memory based tasks rapidly. Indigo Snakes were conditioned to operate a contact relay and press a key, they have shown that their rate of response to operant conditioning is similar to comparable studies of rats that had been trained to press levers or disc-pecking pigeons.
 
It’s worth bearing in mind that although intelligence is studied more in mammals and birds, they are descendants of the same reptilian ancestors as modern reptiles. Evolution can explain the diversity of species but has no grounds for determining the cognitive capacities of animals.




The Eastern Indigo Snake, considered one of the more intelligent species of snake.

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References

Bull, C.M., (2000). Monogamy in Lizards. Behavioural Processes 51:7-20

Clark, R.W., (2004). Kin Recognition in Rattlesnakes. Proceedings of the Royal Society of London Series B Biology Letters 271, S243-S245

Hellmuth, H., Augustine, L., Watkins, B., and Hope, K., (2012). Using Operant Conditioning and Desensitization to Facilitate Veterinary Care with Captive Reptiles. Vet Clin North Am Exot Anim Pract.15 (3), pp. 425-443

Holtzman, D.A., Harris, T.W., Aranguren, G., and Bostock, E., (1999). Spatial Learning of an Escape Task by Young Corn Snakes, Elaphe guttata guttata. Animal Behaviour 57 (1), pp 51-60

Kardong, K., (1998). Vertebrates: Comparative Anatomy, Function, Evolution (Second Edition). McGraw-Hill

Kleinginna, P.R., Jr. (1970). Operant Conditioning in the Indigo Snake. Psychonomic Science, 18 (1), 53-55

Leal, F. and Cohn, M.J., (2016). Loss and Re-emergence of Legs in Snakes by Modular Evolution of Sonic Hedgehog and HOXD Enhancers. Current Biology, 26 (21), pp. 2966-2973

Lillywhite, H., (2014). How Snakes Work: Structure, Function and Behaviour of the World’s Snakes. Oxford University Press

Marzi, H., and Hu, D.L., (2012). Friction Enhancement in Concertina Locomotion of Snakes. Journal of the Royal Society Interface. 9 (76), pp. 3067-3080

Melissa (2014). Squamate Sociality: Surprisingly Like Birds and Mammals. [Online] Snakes.ngo 

Secor S.M, Stein E.D, Diamond J., (1994). Rapid Upregulation of Snake Intestine in Response to Feeding: A New Model of Intestinal Adaptation. The American Journal of Physiology 266, G695-G705

Vitt, J., and Caldwell P., (2014). Herpetology (Fourth Edition). Elsevier

Wilkinson, A., and Huber, L., (2012). Cold-Blooded Cognition: Reptilian Cognitive Abilities. The Oxford Handbook of Comparative Evolutionary Psychology

Yu-Chung Lin, Ji-Chuu Hwang and Ming-Chung Tu, (2003). Does the Saccular Lung affect the Cantilever Ability of Snakes? Herpetologica 59 (1), pp. 52-57