Different species of snakes
When I was on a tea estate in Passara, I had quite a collection of snakes, in large boxes, in the garage. After sometime when I was away for a few days, my wife got the gardeners to take all the snakes and released them in the jungle adjoining the estate.
People find snakes either fascinating or repulsive. Surveys have indicated that snakes are the most disliked animals in the world depending on how you look at them. Since we know very little about them, they are misunderstood and feared.
Many Sri Lankans believe that all snakes are venomous and their bite can kill a human being. They also believe that the best snake is a dead snake. That is not true and I hope that this article will help to change some of those beliefs.
Snakes are reptiles in which category lizards, chameleons, land and water monitors, crocodiles, tortoises and turtles are found. A snake is called Sarapaya in Sinhala and Pambu in Tamil. There are 294 species of snakes in the world and 96 are found in Sri Lanka. Of these, 50 species are endemic to the island.
There are 13 species of sea snakes and 10 species of blind snakes in Sri Lanka. Some snakes are found in all parts of the country from the seas surrounding the island to the highest point - Horton Plains. Some snakes are confined to specific geographic and climatic locations.
Snakes vary in colour patterns from dull to highly ornamented. For example, the ornate flying snake, Malsara in Sinhala, is a very pretty snake. It cannot fly but glides using the membranes it has on its two sides.
Only a few species of snakes are venomous and have venom that can kill humans. In fact only 3 species account for 98% of the human deaths in the country. Most snakes are quite harmless and non aggressive.
When a venomous snake bites its prey, due to the action of the venom the prey gets paralysed. This is the main function of the venom. The venom also helps in the digestion of its food. Different species of snakes have venom of varying strength.
Snakes bite humans purely as a defensive measure. They have no intention whatsoever of consuming humans. The reaction of the human body to the poison depends on the strength of the venom of that particular species of snake. This is called its toxicity.
The strength of the venom depends on the chemical composition and the quantity contained in its venom gland at that time. Generally the bite of a cobra, Russell's viper or krait, is capable of killing a human. This does not happen very often, as generally the snake uses very little venom. The venom that the Green Pit Viper and the Cat snakes carry does not produce a fatal reaction in humans.
Though snakes seem repulsive creatures that look slimy, their skins are not slimy to the touch. Most snakes can swim well. Snakes are limbless and they move along the ground by undulating their bodies. Different snakes have different methods of locomotion. They are aided by the broad ventral scales which they posses. The scales prevent the snake from slipping backwards and also help to propel itself forward. Snakes find it difficult to move on glass or highly polished surfaces.
Snakes do not have eyelids but have a transparent scale covering the eye. Most snakes are predatory in that they catch living species for their food. Most of the snakes feed on animals that have a vertebra, or backbone, but there are some snakes that feed on invertebrates. Some species of snakes catch their prey and swallow them whilst they are alive. There are other species that inject venom into their victims and kill them before swallowing them. The python suffocates its prey by constriction.
Anslem de Silva, the well known herpetologist says that snakes locate their prey by sight, especially the Green Vine Snake - Ahetulla, as well as via chemical cues that are collected with the aid of their bifid (forked) tongues and carried forward to a special sensory organ located on the roof of the mouth, called the Jacobson's organ.
Pit vipers and pythons, in addition to this organ, have thermal receptors, also known as labial pits, which are on or near their lips, that permit them to detect the body-heat of warm blooded prey in darkness.
The tongue is sheathed at the base and is flicked in and out often. It seems a deadly weapon of offence but in fact is quite harmless.
Snakes consume a variety of food depending on their size and their habitats. The large pythons eat spotted deer and the smaller barking and mouse deer, whilst the small worm snakes eat tiny insects and earth worms. Feeding on mosquito larvae has also been observed.
The ground dwelling snakes take in a variety of food from the eggs of chickens and other reptiles, rats, other rodents, lizards, skinks and frogs.
Arboreal or tree-living snakes eat lizards, birds eggs and frogs. Some snakes wait and catch their prey as they come by. Other snakes pursue their prey and capture them. In Sri Lanka the Kukri Snake (Oligodon species) and Cat Snakes (Boiga species) are specialized in feeding on other reptiles and bird's eggs.
Some snakes lay eggs which in turn hatch and bring forth young. These snakes are said to be oviparpous. For example, the cobra, rat snake, python etc. Some other snakes are ovoviviparous in that the eggs develop in the stomach of the mother, who does not provide any nutrition to the developing young one.
The nutrition it gets is only through the yolk of the egg. There are other snakes that are viviparous, for example the vipers, uropeltids, ahetulla etc. They bring forth live young but the embryo obtains nourishment from the mother, in addition to the yolk, snake's eggs are soft shelled and oval or elliptical.
Snakes shed their skins periodically. In most instances, they simply crawl out of their old skin which includes the scale on each eye. Some snakes rub themselves against a rough surface and scrape off their skins. Others go through a narrow gap between two sticks or stones and peel off their skins.
This shedding of the skin is called sloughing or snake moult. The time between each sloughing varies with each species and sometimes between different individuals of the same species. In some cases the skin is shed once a month going up to every six months in other species.
Just before shedding its skin the snake becomes sluggish and dull coloured. It cannot see properly since the transparent scale covering the eye becomes opaque. After sloughing, the snake's new skin is shiny and bright, and the snake becomes active again.
The five most venomous snakes in Sri Lanka are the Cobra (Naja naja) called Naya in Sinhala and Nalla Pambu in Tamil, Russell's Viper (Daboia russelli), Tith Polonga in Sinhala and Kannadi Virian in Tamil, Common Krait (Bungarus caeruleus) Thel Karawalaya in Sinhala and Katu Viriyan in Tamil, Sri Lankan Krait (Bungarus ceylonicus) Dhunu Karawalaya in Sinhala and Yettadi Virian and the Saw-scaled Viper (Echis carinatus).Veli Polonga in Sinhala and Suratti Pambu in Tamil. The venom of these snakes can kill a human being.
The Hump-nosed Viper (Hypnale hypnale) in Sinhala (Polon thelissa) and in Tamil (Kuzhi Viriyan) and the Green Pit Viper (Trimeresurus trigonocephalus) in Sinhala (Pala Polonga) and (Kopi Viriyan) in Tamil are thought by some to be very venomous but they are not.
There are two types of venom that snakes carry. One acts on the nervous system and is called a neurotoxic venom.
These poisons attack the nervous system and also paralyse the muscles of the heart and or the respitory system. The venom of the cobra and the Kraits are neurotoxic. The other type of venom is haematoxic and gets into the circulation system of the blood and clots the blood. It also destroys the capillary walls.
The venom of the krait being four times more potent than that of the cobra. The venom of the Russell's Viper is haemotoxic. Though the deaths of humans in conflict with elephants get much publicity in the media, deaths due to snake bite far outstrip this figure. On an average 60 humans are killed each year by elephants whilst on the other hand around 1200 humans die of snakebite each year.
Some common snakes
Python (Python molorus) -Pimbura in Sinhala and Malai pambu or Periya pambu in Tamil. The python is the biggest snake on the island and grows to about 12-14 feet.
It constricts its prey by wrapping itself round the victim and squeezing the life out of it. It feeds on mammals such as deer, birds and sometimes reptiles like the iguana (Varanus monitor). The female, which is larger than the male, lays a clutch of anything up to 50 eggs and wraps itself round it and incubates it.
It is widely distributed in the island from the plains of the dry zone to the wet zone mountains. It is also widely killed through ignorance. Rat Snake (Ptyas mucosa) Garandiya in Sinhala and Sara Pambu in Tamil. Rat snakes are the most common snakes in Sri Lanka. During hot weather, it comes into dwellings looking for shade and a cool spot.
They move mainly on the ground but some times get on the ceilings of houses looking for rats that form the bulk of their food. They also eat mice, frogs, small birds and lizards. They are not poisonous. I have seen a rat snake eating another snake, which I could not identify.
The male is bigger than the female. It is the second largest snake in the country and could grow up to 12 feet. The female lays eggs.
Coral snakes - These snakes have a strong poison but not lethal to humans. They have brightly coloured underparts. The poison is used to subdue their prey which consists of gekgos, lizards skinks and mice.
Cat snakes - Mapila in Sinhala and Poonai Pambu in Tamil. There are 6 species of cat snakes in Sri Lanka. They are called cat snakes because of the large eyes that these snakes have.
They are snakes that move about at night. Their movement is slow. They feed on frogs, lizards and small birds. Their prey is paralysed by the venom, which they carry. This venom is harmless to humans.
Vine snakes - Ahaetulla Green Whip Snake (Ahaetulla nasuta). Ahaetulla in Sinhala and Kannu Pambu in Tamil. These are thin slender snakes with long pointed snouts.
They wind themselves on trees like a vine or creeper. They are light green in colour, which makes an effective camouflage. They are sometimes at eye level to passing humans and have got a reputation that it pecks at human eyes. This is not at all true. They carry a mild venom which is quite harmless to humans.
There are 13 species of sea snakes found in the coastal waters of the island. Sea snakes, except one species, spend all their life in the sea and do not come ashore. Some times eels in the seas are mistaken for sea snakes.
Sea Snakes are extremely venomous but due to their shy nature they are not encountered easily and even if they are encountered they swim away. However, sea snakes should be treated, when encountered, with extreme caution.
Never handle Sea snake when caught in a fisherman's net. Sea snakes have their fangs in the front of their mouth like the cobra. Sea snakes are fast swimmers. The females are larger than the males.
Sea snakes are ovoviviparous in that they bear live young and therefore do not need to come ashore to lay their eggs. They have about 3-8 young at a time. The exception being the sea kraits (Laticauda sp) that come ashore and lay their eggs. They also rest on shore.
Sea snakes feed mainly on fish and fish eggs. Sea snakes are often caught in the nets of fishermen. The end of their tails is like paddles which facilitate their movement through the water. Though sea snakes are marine dwellers, some swim up river with the tidal movement of the sea.
Blind snakes and Earth snakes
Blind snakes and earth snakes are secretive burrowers with bodies of uniform thickness and blunt heads and tails. In Sinhala, they are known as Kana ulla and Bimmulla and Manallai Pambu in Tamil. They have poor vision, but appear to be extremely light-sensitive and shun any exposure to sunlight.
All are non-venomous and completely harmless, relying on their cryptic habits to escape detection. When handled, many are able to emit a substance that has an offensive smell, from their glands near their cloace, which is at the end of the anal canal.
Blind snakes are insectivorous feeding mainly on earth worms and on termites and the eggs, larvae and pupae of ants. Earth snakes are brightly coloured giving off a shot-effect when sunlight plays on them. They are about a foot and a half long. They are covered with small scales, which are smooth and round.
Their eyes are covered in scales to enable them to move about freely underground. Their tails end up abruptly in a flat shield giving the impression that they have been cut off with a knife. The end of the tail has a number of small spines. Their food consists of worms, small grubs, larvae etc. that are found in the ground. These snakes seem to prefer dark areas probably because it is easy to burrow through the soft earth.
They seem to be nocturnal in that they are found easily at night and also after it has rained.
It is important to conserve snakes since they are an important part of our ecosystems. They play a major role to keep the balance of nature.
Agriculturalists have realized that snakes play an important role in controlling agricultural pests. The after harvest losses in paddy, which is grown all over the country and which is our staple diet, amounts to as much as 15%. This is mainly due to rats consuming the stored grain.
Snakes, especially cobras, Russell's vipers and rat snakes, prey on the rats in the fields, mainly in the harvested paddy, which is stacked up prior to threshing, and in the store houses and thereby greatly reduce their populations.
If there are no snakes in significant numbers, the rat population will increase fast and not only will there be heavy agricultural losses in the rural areas but also problems in urban areas. There are many myths and legends about snakes. Some have an element of truth and some are not at all true. Most of these myths have been handed down the ages from generation to generation.
In the early days, there was very little scientific knowledge and therefore stories and rumours became myths and legends and sometimes were thought of as facts. It is very necessary to carry out awareness programmes, especially for schoolchildren, so that they get a scientific knowledge of the snakes where false myths, beliefs etc. are dispelled.
This would make them more inclined to look at snakes in a different light and not be ready to kill a snake as soon as one is sighted. The book 'Snakes and Other Reptiles of Sri Lanka' by Indraneil Das and Anslem de Silva is a good guide for beginners to identify snakes.
By Jayantha Jayawardene
May 7, 2007