Snakes of Sri Lanka

By Ifham Nizam

Snake bites are a serious public health issue in Sri Lanka. It has been estimated that nearly 80,000 snake bites occur here every year.Due to fear and poor knowledge, hundreds of thousands of snakes, mostly non-venomous ones, are killed by humans each year.The state spends more than USD 10 million a year on treating snake bite patients.

According to health sector statistics between 30,000 and 40,000 snake bite patients receive treatment in hospitals annually, says Dr. Anjana Silva, who is Professor in Medical Parasitology, Head/ Department of Parasitology, Faculty of Medicine and Allied Sciences, Rajarata University.

To date, 93 land and 15 sea snake species have been recorded from Sri Lanka. While all 15 sea snakes are venomous, only 20% of the land snakes are venomous or potentially venomous.

The term, ‘venomous snakes’ does not mean they cause a threat to human lives every time they cause a bite. The snakes of highest medical importance are the venomous ones which are common or widespread and cause numerous snakebites, resulting in severe envenoming, disability or death,” says Dr. Silva who is also Adjunct Senior Research Fellow – Monash Venom Group,Department of Pharmacology, Faculty of Medicine, Nursing and Health Sciences, Monash University and Research Associate- South Asian Clinical Toxicology Research Collaboration, Faculty of Medicine, University of Peradeniya.

Only five snakes could be considered to be of the highest medical importance in Sri Lanka: Russell’s viper, Indian krait, Sri Lankan cobra, Merrem’s hump-nosed viper and Saw-scaled viper. All but Merrem’s hump-nosed vipers are covered by Indian Polyvalent antivenom, the only treatment available for snake bites in Sri Lanka.

There are another five snake species with secondary medical importance, which are venomous snakes and capable of causing morbidity, disability or death, but the bites are less frequent due to various reasons (Sri Lankan krait, Highland Hump-nosed viper, Lowland hump-nosed pit viper, Green-pit viper and Beaked sea snake)

The snakes of highest medical importance in Sri Lanka are as follows:

1. Russell’s viper (Daboia russelii) (Sinhala: Thith Polanga/ Tamil: Kannadi viriyan)

Medically the most important snake in Sri Lanka. It is found throughout South Asia. It is responsible for about 30% of snake bites in Sri Lanka and also about 70% of deaths due to snake bites in Sri Lanka.

Some 2-5% bites by Russell’s viper are fatal. Widely distributed throughout the country up to the elevations of 1,500m from sea level. Highly abundant in paddy fields and farmlands but also found in dry zone forests and scrub lands. Bites occur more during the beginning and end of the farming seasons in dry zone. It can grow up to 1.3m in length. Most bites are reported during day time.

Over 85% of the bites are at the level of or below the ankle. It is a very aggressive snake when provoked. Spontaneous bleeding due to abnormalities in blood clotting and kidney failure have life-threatening effects.

Dr. Anjana Silva

2. The Sri Lankan Russell’s vipers cause mild paralysis as well, which is not life threatening. Indian Polyvalent antivenom covers Russell’s viper envenoming. Deaths could be due to severe internal bleeding and acute renal failure.
3. Indian Krait (Bungarus caeruleus) (Sinhala: Thel Karawala/ Maga Maruwa; Tamil: Yettadi virian/ Karuwelan Pambu)

It is distributed in India, Sri Lanka, Nepal, Bangladesh, Pakistan and Afghanistan. It is found across the lowland semi-arid, dry and intermediate zones of Sri Lanka. Almost absent in the wet zone. Usually, a non-offensive snake during the daytime; however, it could be aggressive at night.

Common kraits slither into human settlements at night looking for prey. People who sleep on the ground are prone to their bites.

Most common krait bites do occur at night. Bites are more common during the months of September to December when the north-east monsoon is active. Most hospital admissions of krait bites follow rainfall, even following a shower after several days or months without rain.

Since most bites do occur while the victim is asleep, the site of bite could be in any part of the body.

As bite sites have minimal or no effects, it would be difficult to find an exact bite site in some patients. Bite site usually is painless and without any swelling. Causes paralysis in body muscles which can rapidly lead to life threatening respiratory paralysis (breathing difficulty).

3. Sri Lankan Cobra (Naja polyoccelata; Naja naja) Sinhala: Nagaya; Tami: Nalla pambu

Sri Lankan cobra is an endemic species in Sri Lanka. It is common in lowland (<1200m a.s.l), close to human settlements. Cobras are found on plantations and in home gardens, forests, grasslands and paddy fields. It is the only snake with a distinct hood in Sri Lanka.

Hood has a spectacle marking on the dorsal side and has two black spots and the neck usually has three black bands on the ventral side. When alarmed, cobras raise the hood and produce a loud hiss.

Cobra bites could occur below the knee. They are very painful and lead to severe swelling and tissue death around the affected place. Rapidly progressing paralysis could result from bites, sometimes leading to life-threatening respiratory paralysis (breathing difficulty). Deaths could also be due to cardiac arrest due to the venom effects.

4. Merrem’s hump-nosed viper (Hypnale hypnale) Sinhala: Polon Thelissa/ Kunakatuwa; Tamil: Kopi viriyan.

Small pit-vipers grow up to 50cm in length. Head is flat and triangular with a pointed and raised snout. They are usually found coiled, they keep the heads at an angle of 45 degrees. Merrem’s Hump-nosed viper (Hypnale hypnale) is the medically most important Hump-nosed viper as it leads to 35-45% of all snake bites in Sri Lanka.

Merrem’s Hump-nosed vipers are very common in home gardens and on plantations and grasslands. Bites often happen during various activities in home gardens and also during farming activities in farmlands in both dry and wet zones. Hands and feet (below the ankle) are mostly bitten. Bites can often lead to local swelling and pain and at times, severe tissue death around the bite site may need surgical removal of dead tissue or even amputations. Rarely, patients could develop mild blood clotting abnormalities and acute kidney failure. Although rare, deaths are reported due to hypnale bites.

5. Saw-scaled viper (Echis carinatus), Sinhala: Weli Polanga; Tamil: Surutai Viriyan

This species is widely distributed in South Asia. However, in Sri Lanka, it is restricted to dry coastal regions such as Mannar, Puttalam, Jaffna peninsula and Batticaloa. In Sri Lanka, this snake grows upto 40-50cm. It is a nocturnal snake which is fond of sand dunes close to the beach. It could be found under logs and stones during daytime. Bites are common during January and February.

It is a very aggressive snake. A distinct, white colour ‘bird foot shape’ mark or a ‘diamond shape’ mark could be seen over the head. When alarmed, it makes a hissing sound by rubbing the body scales. Although this snake causes frequent severe envenoming and deaths in other countries, its bites are relatively less severe in Sri Lanka. Bites could lead to mild to moderate swelling and pain on the affected place and blood clotting abnormalities and haemorrhage and rarely it could lead to kidney failure.