Friday, 17 June 2011

Getting intimate with snakes...

Tarangire National Park is known for its snakes and we’ve seen Black Mambas, Puff Adders, Green Tree-snakes, Sand-snakes, Rufous-beaked Snakes, Boomslangs, and encountered Black-spitting Cobras and watched Rock-Pythons climb trees. Considering events in the past few months, and the fear of snakes that was instilled into me as a child, why am I so fascinated by these animals? Well to start with, it might be because I’m fascinated by evolution and how animals (and plants) are related to each other.

For example, snakes belong to a group of animals known as the Tetrapods or 4-legged animals. This might sound a bit confusing but it’s because in their evolutionary ancestry, they evolved from a reptile that was probably very similar to the monitor lizards we know today. In fact, monitor lizards use their forked-tongues the same way that snakes do: to smell or shall we say taste the air. Their forked tongues pick up little particles when they flick them in and out of their mouths, and pass the particles to an organ known as the Jacobson’s organ in the roof of their mouths. The fork in their tongue allows them to tell the direction of their prey. Look at how a monitor lizard swims… you guessed it? It’s called serpentine motion and is actually a very efficient way of moving.

So as I said, I’m as interested in the different groups of animals as in the species themselves. We call these groups by different names and one of the important groupings to have an idea of, are the families. Let’s take this little one that Colin found on his walk.

It’s small, about 30 cm long, and blind. It has a big yellow stripe down its back and can you guess what it’s called? A Yellow-Striped Blind-Snake. Its Latin name is Rhinotyphlops unitaeniatus.
Rhinotyphlops unitaitensis
 Blind-snakes (family: Typhlopidae) belong to a group of snakes that are considered primitive, yet highly specialized and they are closely related to another family called the Worm Snakes (family: Leptotyphlopidae). They first appear in the fossil record 135 million years ago and since then their general body plan hasn’t changed much, it is obviously a highly successful one.
Leptotyphlops scutifrons
Blind-snakes and Worm-snakes are blind because they live under the ground and don’t need to see. Their bodies feel tight, and are cylindrical with a large scale over their foreheads somewhat like a helmet. This acts as a battering ram when they push through the soil. Their tail ends in a spike (caudal spine) that they use as an anchor for pushing through the soil. I think it’s fascinating that these two groups of snakes have special glands in their foreheads whose function no one has yet figured out.

So, enough of the little snakes, what about the big ones? If you’re lucky enough to guide in Tarangire in the dry season, you’ve got to look carefully for Pythons (family: Pythonidae) who like to hang out in trees. The dry season is Tanzania’s equivalent of winter, and so some animals do what animals in colder latitudes do: they hibernate, but here we call it aestivation. They slither up into trees and basically go to sleep for weeks, if not months. They’ve usually had a good meal, and once comfortable, they turn their metabolism down to the region of 1 Calorie per day.
Python sebea
Some people are lucky enough to get to see a python eating something and there are plenty of pictures of pythons swallowing gazelles. How do they do it? Well, snakes have lower jawbones that aren’t fused together like mammals. The python, a constrictor, kills its prey by grabbing it with its sharp hooked teeth and throwing its coils around it. It then squeezes every time the prey breathes out and eventually suffocates it. It then slowly finds the head and opens its mouth as wide as it can. The jawbones dislocate and the skin stretches as it starts to swallow its prey.

Now that is three groups of snakes covered and we haven’t even touched on venomous snakes. Well, that’s because in actual fact, most snakes aren’t venomous and even if they are, you wouldn’t react to most of them. Even the biggest family of snakes, the Colubridae family, which has over 100 species in East Africa, only has 3 species of snake that could harm you. None of these are actually aggressive and they prefer to eat birds and other small animals that they find in trees. Many of the colubrids don’t even have teeth, but the ones that do have enlarged teeth in the back of their mouths and are known to be “back-fanged”.
Philothamnus sp.
The next two families of snakes are actually the ones that give all other snakes a bad rap: the Elapids and Vipers. These two families both have fangs in the front of their mouths, but the Vipers have big fangs that fold back into their mouths, and the Elapids have smaller fixed fangs (not that I’m ever going to look at a snake’s teeth to figure out which family it belongs to). Now, the other thing which I find most fascinating about this very small group of venomous snakes is just that: their venom.

If we’re looking at evolution, how is it that a snake that eats a 30-gram mouse or bird is going to have such potent venom that it could kill me, a 78-kg human being? The most probable answer is that these snakes likely have prey that could actually cause them some harm and so they need fast-acting, powerful venom. Most of the Elapids have neurotoxic venom which acts on the nervous system basically paralyzing the prey. Most of the Vipers have cytotoxic venom which is cell destroying.
Bitis arietans
Naja nigricollis
Of course, the trends always have exceptions and for most of the venomous snakes, their venom is actually unique. Spitting cobras are elapids but they have a cocktail of cytotoxic venom with a little neurotoxic thrown in for effect, kind of like the Tabasco in a Bloody-Mary. Spitting cobras’ fangs also have a cool feature that allows them to spray their venom up to 3 metres. Instead of the venom channel exiting the fang at the very bottom, it makes a 90 degree turn near the bottom allowing the venom to shoot straight forward.  

The last family of snakes (family: Atractaspididae) is an interesting one because scientists have spent a lot of time debating what family they really belong to, or whether they are actually a family on their own. They include centipede eaters and other interesting snakes like that. One of these snakes, probably the most famous, is actually venomous and very deadly in northern African countries, but in eastern and southern Africa it doesn’t usually kill. It is a burrowing snake that kills prey a little larger than termites, like skinks (lizards) for example. You can imagine the adaptations it has to have to be able to catch skinks in the ground. First of all how does it open its mouth to bite its prey when it’s squeezing through a hole in the ground? Instead of even trying to open its mouth, it squeezes past the prey and then basically sticks its fang out of the side of its mouth like a fish hook and pulls back. Pretty ingenious isn’t it? They actually bite a lot of people who try to pick them up and are called a Stilleto-snakes or Burrowing asps.
Don't touch me if you don't know who I am!!!
I could keep going on about snakes, but it might be a better idea to come back to them when we talk about other fascinating things like mimicry or aposematic coloration. But, it wouldn’t be fair not to mention even briefly what to do if you do end up in the unfortunate position of having to deal with a snakebite from a harmful snake.

This website probably has the most comprehensive explanation for what to do, but the basic things to remember and do are:

1.     Stay calm or calm down.
2.     Mark the bite site with a pen.
3.     Immobilize
4.     Evacuate (and if you’re in Tanzania, the best place to get treated is the Meserani Snake Park).

Identifying the snake is important, but most places will treat you symptomatically which means they’ll treat you for the reactions that you’re having.

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