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 AND HOW DO SNAKES KILL?

Safety bite: A snake doesn't kill because it is mean and evil. It kills so that it doesn't get injured by its prey. A snake is quite a fragile creature with a delicate skull and thin teeth and lots and lots of ribs that can break. A struggling prey is not only dangerous when it is being caught, but also when it is being swallowed. A desperate prey with fangs and claws can damage and even kill a snake. There is a record of a boa constrictor that was killed by an anteater that it had partially swallowed!

 

For dangerous prey, a venomous snake will bite and quickly release to minimise contact with the live struggling prey. It will then track the prey in its death throes by smell and eat it only after it is immobile. If the prey is small or harmless, a snake will bite and hang on until the prey is immobilised or it may not even bother to kill it and just swallow it alive!

 

Snakes do not have venom just to bite people. In fact, snakes prefer NOT to bite humans.
For more about snake bites and people.

 

What are the different ways snakes kill prey?

 

By choking: either by biting the neck without venom, or constriction. Constriction kills by suffocation and not by crushing. Once the snake bites the prey, it will instantly throw coils around the prey's midsection. The snake tightens its coils around the prey each time the prey exhales, thus preventing it from inhaling. Sometimes, the coils also prevent the heart from beating. Once the snake has a good grip around a small prey, it may relocate its bite to the neck to kill the prey by severing the spinal cord or by cutting off air supply. It can take a long time for a large reptile prey, e.g., crocodiles, to succumb to constriction, but the snake is usually patient and will wait it out.


The Death Squash: The Australian Woma Python (Aspidites ramsayi) catches rodents in narrow burrows where it cannot coil around them and instead suffocates them by pushing them against the burrow walls. But as this kills the prey more slowly, old Womas are often covered with scars from desperate rodent claws. A rat snake (Pytas) doesn't constrict; instead it squeezes the prey to death in its jaws or by pressing it against a hard object.

 

Biting and injecting venom: Venom not only contains toxins that paralyse or kill, but also powerful digestive enzymes which break down tissue. This is essential as snakes don't have chewing or tearing teeth. Many prey are covered with tough hide and if a snake relied solely on its digestive juices, it would take a long to time to get through to the nutrients. So this is speeded up by snake venom. Venom not only immobilises prey but also starts digesting the prey from the inside. A study showed that when a fer-de-lance (Bothrops asper) is deprived of its venom, it took 12 days to digest a rat instead of the usual 2-3 days.

 

There are different kinds of venom glands. Elapids and vipers have a venom-producing gland between the eye and the rear of the head (right), and a small sac which holds the venom and is connected to the fangs. Muscles around the venom gland squeeze the gland to inject venom through the fang. Accessory glands activate venom just before it is injected. Rear-fanged colubrids produce their venom in Duvernoy's gland and the venom seeps down grooved rear fangs. This is why these snakes have to chew on their half swallowed prey to inject the venom. Snake venom is modified saliva and produced in large glands.

 

Each snake species has it own unique cocktail of chemicals that make up its venom. This is tailored to their main prey or predator. There are two main types of venom, each with its different purpose (as far as the snake is concerned!)

 

Hematoxic which quickly destroys tissue causing massive haemorrhaging, and is very painful.
Neurotoxic which quickly paralyses the victim by shutting down the respiratory system and the heart, causing almost no pain.


Pit vipers found in high mountains or cool climates have venom that is more strongly haemorrhage than those found in the lowlands. This is probably because these pit vipers cannot rely on the sun's heat to speed up digestion like other snakes in the warm and humid lowlands. Their venom helps dissolve the swallowed prey more quickly. On the other hand, seasnakes' venom is highly neurotoxic and quickly paralyses the victim. This is more important to seasnakes as fish are fast and slippery but are easy to digest in the warm oceans.

Toxin titbits...
In the Asian Long-glanded Snake (Maticora, an elapid), the venom gland extends beyond the head up to half the length of the body! Most snakes are resistant to venom of their own species.

 

Ectothermic ("cold blooded") animals seem less affected by snake venom than warm-blooded animals.

Most snakes bite forwards. But the burrowing Stiletto Viper (Atractaspis) strikes backwards. It crawls alongside the prey captured in a tight burrow, shifts its lower jaw away from the prey and stabs backwards and sideways with one of its long hinged fangs. How does a snake bite?


Before biting, most snakes retract their heads forming S-shaped curves with their neck. They straighten out the neck with force to bite the prey. Some snakes can throw almost their whole body forwards to bite the prey, but most use only a short part of their body. Some snakes just reach out and bite without a lunge.

Venomous snakes with long fangs open their mouths very wide when they bite so their mouth obstructs their vision and they actually can't see the prey just before the bite!


Different types of fangs: Fangs are special teeth which have a venom groove or channel.

Aglyphs: Snakes with no specialised fangs, no venom. But some have saliva which is toxic and is introduced into the prey by chewing on it.

 

Fixed back/rear fangs (Opistrogylphs): which are large and grooved. Front teeth are small, cone-shaped. Venom is only injected as the snake swallows the prey. It makes sense to have rear fangs as this is where the tooth can exert the most force. Other non-venomous snakes have enlarged rear teeth to slit eggs.

Fixed front fangs (Proteroglyphs): which are large but short, and grooved, followed by small teeth. In some, the fang is just as short as their ordinary teeth. These snakes tend to hang on after biting, and to chew to get the venom into the prey. In these two types of snakes, their venom is used more to subdue prey that is already captured rather than to kill prey before it is eaten (as elapids and vipers do).

 

Folding front fang (Solenoglyphs): very long, closed venom channel. When not in use, the fangs fold down against the roof of the mouth, sheathed in a membrane. Their longer teeth allow them to inject more accurately and more deeply into the prey.

 

These snakes prefer to bite and release, probably to avoid breaking their longer teeth. They will then track the prey and eat it only when it is immobile. Their mouths can open wide, some almost 180 degrees. More fang facts: Besides fangs, most snakes have ordinary teeth in two parallel rows of on each side of the upper and lower jaws. These teeth usually point backwards, bringing prey into the mouth on first strike and preventing prey from slipping out of the mouth.

 

Ordinary teeth are solid while fangs are hollow with a venom groove or channel. All teeth are replaced regularly. The replacement of an ordinary tooth forms below it, loosening then eventually pushing out the old tooth.

 

For fangs, a series of 5 to 6 fangs in graduated lengths line up in the gums behind and above the functioning fang. A new fang moves into place before the old one is lost or reabsorbed. So for a while, a snake may have two pairs of fangs! Fangs may be replaced more often than ordinary teeth: once a week to once every 6-10 weeks.


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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