Docent Informations
What does "docent" mean?
We are a young group. The pioneers started the group in April 1997. Since then, we have grown modestly to 93 docents. The Night Safari Volunteer Rangers were brought under the Docent Programme in March 1999.
The docents are self-run by a committee of docents which co-ordinates inputs from all docents and liaises with the zoo management to put into motion the group's activities.
A docent newsletter is issued every two months so docents can keep up with the latest in zoo happenings and docent activities. Sprinkled with inspiring stories and amusing anecdotes, the Docent Deliberations is always a great read! We also constantly undertake research projects to expand and update our knowledge as well as explore new areas of interest.
Singapore Zoological Gardens Docents
WHY ARE SNAKES LONG?

... the long and short of it ...

 

What are the advantages of being long and narrow?

 

Better temperature control: The large surface area to body volume allows a snake to warm up and cool down faster. This is crucial for a "cold blooded" creature like a snake. By coiling, a snake controls the body surface exposed and thus its body temperature. A snake can also choose to sun only the relevant part of the body (containing food or eggs) without exposing the rest of the body to danger. Warm-blooded animals cannot exploit this body shape because too much heat is lost, e.g., a weasel needs to eat twice as much as a rat of the same weight. For more about why being "cold-blooded" is an advantage.

 

Strength and versatility: Like a piece of string, a snake is strong at looping for killing prey and in movement. With their body shape, as a group, snakes can go virtually anywhere to find prey, hide in ambush or escape predators. Their body shape is ideal for climbing and for creeping into small holes, tangled growths, rocky crevices. They can move on virtually any surface, and also swim and even fly through the air (see below). Being basically just an expandable moving belly, they can contain more food and eggs or young.
What are the special adaptations to being long?

 

Snakes have many vertebrae, always more than 100. A tiny Blindsnake has 600, giant snakes have only about 400. The vertebrae are connected by a ball-and-socket joint with two additional contact points to limit twisting. To maintain strength, only slight movement is possible between two vertebra, so having many vertebra gives flexibility without sacrificing strength. Each vertebrae has a pair of ribs, except the first two pairs so the head can rotate. In most, each rib is attached to a belly scale, which is important for snake movement.

A snake doesn't get more bones as it grows. It gets longer because its bones (and muscles) get bigger. Snakes do grow longer continuously, but more slowly as they mature and imperceptibly as they near adult size.

 

A snake's tail has narrow bones but no ribs. Like some lizards, some tree-dwelling snakes have prehensile tails. Some marine snakes have special tail spines to stiffen their oar-like tails. Unlike lizards, snakes cannot re-grow lost tails.


Elongated internal organs: In other animals, paired organs are found side by side. In snakes, because of their long bodies, these are either stacked one in front of the other; or one of the pair is atrophied. In most snakes only the right lung is functional, and the left lung has disappeared or is reduced to a functionless nub. In the more 'primitive' snakes like pythons and boas, the left lung is much smaller, about one-third the size of the right lung. The single lung is long and narrow, and does the work for two. In seasnakes, this lung may stretch along the entire length of the body to help them float. Many also have a tracheal lung, an enlarged throat which acts as a lung. Similarly, the large intestine is straight (not coiled like ours) and short. The small intestine is coiled and short. Snakes don't have a bladder and excrete uric acid with the faeces.


Snakes have no limbs: All snakes lack a breastbone and shoulder girdle, which support front limbs. Most don't have a pelvic girdle, except some blindsnakes, boas and pythons which have vestigial pelvis and hind limbs as tiny spurs besides the cloaca (right).

 

How do snakes move without limbs? Despite their lack of limbs, snakes move efficiently in trees, underground, water, loose desert sand. They are also strong and can kill large powerful animals many times bigger than themselves. Their flexibility and strength are due to the many powerful muscles that lie in overlapping layers and are connected in complicated ways to the skeleton and the belly scales.


On a limb: Far from being limbless, the snake is actually one very strong, long limb! The Blunt Headed Tree Snake of Latin America specialises in eating sleeping anoles. Anoles nap at the furthest tips of leaves, a built-in predator alert system. A snake creeping up would jiggle the leaf and the anole would simply drop off. The Blunt Headed Tree Snake has a triangular rather than tubular cross-section, and interlocking vertebrae and scales. These allows it to extend up to half its body length into the air without support. In this way, it reaches out and plucks off the sleeping anoles. Other tree-dwelling (arboreal) snakes have prehensile tails. A handy grasping limb to hold on to branches while they lunge out at flying or escaping prey.

Different ways that snakes move:

 

Serpentine, Undulating: The typical zig zag movement, the body moving smoothly in S-shaped curves from head to tail. The fastest way to move and also used for swimming. Thinner snakes move faster this way.

Creeping, Rectilinear, Caterpillar: The skin of the belly is moved by strong muscles in ripples so the edge of the broad belly scales catch onto the surface. Used for creeping up slowly on prey, and to move inside narrow burrows. Climbing snakes have squared belly scales specially suited for creeping. Thicker snakes prefer this, probably because they can't bend much. Not all snakes can creep.

 

Sidewinding: Rolling the body sideways in a looping motion leaving J-shaped tracks (left). Used where the surface is not firm; loose desert sand, or slippery mud flats. Also keeps the snake cool as only a few points of the body is in contact with the hot sand at any one time. Sidewinding has been compared to walking as only a small part of the body is in contact with the ground at one time. Not all snakes can sidewind.

Concertina, Accordion: Alternately stretching and pulling the body from one anchor point to another. Used to cross smooth surfaces, in wide tunnels and for climbing trees which are too big to coil around (right). To climb a smooth small tree, a snake will coil around the trunk with its tail and lower body, reach up to anchor its head on another section of the trunk by coiling around it, then haul up its back end. And so forth.
Jumping: by coiling up the body and then straightening out quickly like a spring, a snake can actually jump some distance.

 

"Flying": The Flying Snake (Chrysopelea) (left) can glide up to 100m. It grips a branch, coils up, then straightens out quickly to launch itself. In the air, it spreads out its ribs, sucks in its guts, the centre-hinged belly scales helping to form a concave surface which acts like a parachute. It undulates as it glides.

But a snake can't move backwards: and can reverse only by pointing its head backwards and pulling its body along with it. So it can't back out of a very tight tunnel. But a snake can strike backwards by moving its head!!


More about snakes


- What are snakes?
- Are snakes cold?
- Why are snakes long?

- What do snakes eat? Do they drink?
- How do snakes swallow?
- How do snakes hunt?
- Why and how do snakes kill?

 

Snake predators and how do snakes protect themselves?
Snake mating, eggs and babies

 

Where are snakes found?
Fascinating snake adaptations to various habitats

Snake bites and first aid

Snakes in danger: role and conservation and snakes in human culture

Snake records: biggest, smallest, deadliest and more

 

- More snakes
- More animals
- General snake links and references



Further informations in german can be found here!

Further Links
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