10 Things You Didn't Know About Snakes

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1. Hearing

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Because snakes are anatomically peculiar in not having an outer ear, it was assumed for a long time that snakes could not hear, it is now known that this is not the case. The outer ear may have regressed due to a fossorial ancestry, but the inner ear still remains intact and functional. Snakes can hear both ground vibrations and airborne sounds, although they are restricted to a limited range of sound frequencies, from approximately 50 to 1000 Hz. By comparison, humans can hear in the range of 20 to 20,000 Hz. Hearing in mammals is assisted by three smalls bones in the middle ear called the ossicles, consisting of the malleus, incus and stapes. The equivalent in reptiles is the articular, quadrate and columella.
 
In mammals, the eardrum is connected to the stapes, and in reptiles it is connected to it’s equivalent, the columella. The two other bones are located in the middle ear in mammals, but in reptiles they are apart of the jaw. Because snakes lack eardrums, the columella leans against the quadrate bone for transmission of vibrations (including airborne sound vibrations) for hearing. What this essentially means is that snakes hear through their jaws.

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2. Vision

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Snakes are peculiar among vertebrates when it comes to the structure of their eyes, even differing from their lizard cousins. In order to focus on a subject, the lens in the eyes of vertebrates changes curvature by means of ciliary muscles, these muscles were lost in ancestral snakes meaning an alternative method of focusing was required. Snakes will instead move the lens forwards and backwards by using muscles within the iris to apply pressure to the vitreous fluid inside the eye, forcing the lens to move forwards, and relax those muscles to allow the lens to passively move back.
 
Snakes generally have good vision, and can even see in colour, although diurnal snakes are dichromatic or trichromatic, meaning that some species who are active during the day possess either 2 or 3 pigmented light receptors responsible for colour perception; the normal condition in humans is Trichromacy, and in mammals is dichromacy, while reptiles and birds normally posses 4 light receptors, and can often see in the Ultra-Violet range. The reason why snakes have poorer colour vision when compared to other reptiles can be once again explained by the regression of the eye during the early evolution of the ancestors of snakes. The light receptor cells of the eye are divided into two groups, rods and cones. Rods are responsible for vision in dim light while cones work best in well-lit conditions and are responsible for colour vision. The photoreceptors that regressed during the fossorial phase of early snakes were in effect rebuilt to accommodate the requirements of the species moving into a day-time lifestyle. This was achieved by repurposing some of the existing rods into cones.

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3. Jacobson's Organ

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Also called the Vomeronasal Organ, this sensory organ is the primary means of how snakes gain information about the world around them. Terrestrial snakes are able to smell in the usual manner, by inhaling through their nostrils (however, aquatic snakes do not possess a sense of smell) but the Jacobson’s organ provides much more detailed information about the odours they are detecting. The tongue (which generally lacks taste buds and does not seem to directly contribute to sensory perception in most cases) is flicked out to sample the air and collect particles, these particles are transferred to the Jacobson’s organ located on the roof of the mouth when the tongue is retracted. The forked nature of the tongue allows the snake to determine the direction of a certain smell. This is further enhanced by the fact that the Jacobson’s Organ is a paired structure and that information collected in each organ is processed separately.

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4. Organs

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Because of the elongated nature of snakes, their internal organs also require elongation, specifically in regards to the lungs, liver, kidneys, and testes. The heart is also elongated and comparatively slender in arboreal species, many of which are exceptionally thin.
 
The lungs of snakes are particularly interesting. The left lung is present in many species but greatly reduced in size and no longer serves any purpose, in some species the left lung has been lost entirely. The right lung, by contrast, is large and elongated and varies in size massively between species, being anywhere between 8-83% the length of the snakes body. The lung is divided into two functionally different regions; the “vascular lung” which is used in respiratory gas exchange (O2 and CO2), and the “saccular lung” which has no respiratory function. The saccular lung functions only as an air sac and may help the snake maintain structural support of its body, especially when the snake stretches to span gaps. Alternatively, the saccular lung may just play a role in maintaining posterior body form. 

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5. Reproduction

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It is often assumed that all snakes lay eggs, there are in fact three modes of reproduction; Oviparity (females give birth to eggs) Ovoviparity (eggs are produced within the female but hatch before giving birth to live young) Viviparity (live birth – no egg is produced). Generally speaking most reptiles are oviparous (egg producers), but certain environmental pressures, such as cool environments or environments which provide very few suitable nesting sites have given rise to live bearing snakes. This allows the snake to keep the young at proper temperatures by constantly adjusting it’s position for optimal thermoregulation, and by extension maintain suitable temperatures for the young she carries, as well as not having to worry about finding a safe and suitable place to lay her eggs. There are, however, disadvantages, such as decreased mobility, leaving her unable to hunt or eat effectively and limitations to how many offspring she can produce.
 
At least one species of snake has an even more bizarre mode of reproduction. The Brahminy Blind Snake (Rhamphotyphlops braminus) (also called the Flowerpot Snake) lays eggs, but all the offspring are female. This species of snake has no males and instead relies on asexual reproduction, effectively cloning itself.