The problem of biodiversity

by Dr Mark Nicholson

I was driving down to our rain-forest patch last week while still on a main road to Kisumu on the eastern shores of Lake Victoria, when I saw a large crowd on both sides of the road. I assumed it to be an accident but I saw no motor vehicle. I slowed, stopped the car, got out and spotted a small snake on the side of the road surrounded by an excitable crowd looking fearful and agitated. I walked straight to the snake which was still wriggling and I saw that its head had been bashed in. I immediately recognized a Rhinoceros Viper, one of the most beautiful snakes in the area.

My fury, of course, was that someone had killed it unnecessarily. I tried to find the culprit but I soon realized that it was me against sixty people who were clearly thrilled to see one less snake in the world. I knelt down to stroke the beautifully patterned rough back. I picked it up gently and carried it to my car, accompanied by gasps from the crowd.

“Itakuua”, someone shouted. “No, it won’t kill me,"  I responded in kiswahili. “Anyway, cars and idiot drivers kill you and you don’t stop using the road.” But I knew I was wasting my breath. Ophidiophobia is written into the human genome for evolutionary reasons: if we did not fear snakes, we would not avoid them, and the chances of a bite would increase. So the vast majority of humans are terrified of snakes, which is a shame as they are fascinating creatures.  Many snake species make great pets and are highly intelligent. 

I am in the biodiversity ‘business’, which means I run projects which protect indigenous biodiversity. It is not my job to play God and determine what biodiversity is good and what is bad. Tourists pay top dollar to see lions these days but to a Maasai, the only good lion is a dead lion. When a lion kills a cow, the traditional response would be to get some mates together, grab their spears and go after the lion.  That has been banned. So the modern method is to poison the bovine carcass with carbofuran (a pesticide banned in Europe and the USA), which then kills lions, hyaenas, wild dog, jackals and vultures.

Very few tourists and few urban residents around Nairobi will ever see a snake. There are at least 200 snake species in East Africa, roughly 50 of which are quite venomous. Fewer than ten percent of all East African species have killed people. The most feared is the Black Mamba but the most dangerous is the irascible Puffadder as it tends to bite first and ask questions later. More people die of Puffadder bites than any other snake. Two of its relatives are the huge Gaboon Viper, which is gentle and super idle, and the Rhinoceros Viper which is known for its extremely loud hiss. I have never heard of a person bitten by a wild Gaboon, which is a good thing as the venom is a complicated mixture of toxins. The largest snake in Africa is the Rock Python, which is not venomous but kills by constriction and has killed and eaten children.  

Snakes in the wild are shy and will do anything to avoid human contact. They benefit us by controlling rodent populations. Angry ones can bite furiously but may be non-venomous. In contrast, some of the most venomous ones are both gentle and lethargic. The purpose of snake venom is twofold: firstly, to incapacitate prey and secondly, to pre-digest. Venom is a mixture of cocktails. Adder bites tend to be haemotoxic and myotoxic, meaning that muscle and blood are broken down. Mamba and cobra bites are mainly neurotoxic, meaning that confusion and paralysis occur, sometimes very quickly. A tourniquet is vital for a neurotoxin, but contraindicated after an adder bite as there is need to dilute the poison to prevent necrosis. When a child is bitten, many more vials of antivenene are needed as the venom will be much more concentrated. The danger of a bite depends on many factors such as when the snake last had a meal, the site of the bite, the aggression of the snake (an angry mamba can bite several times a second) etc.

But venom can also be medicinal: the venom of several species is refined and used for a multitude of illnesses from angina and coronary failure to arthralgia, sciatica and other neuropathies. As research develops, we will find that snake venom has numerous other benefits.

The problem of snakebite largely results from ignorance and lack of caution. Globally, snakebite causes around 80,000-140,000 fatalities annually but this number could be drastically reduced with education, poverty reduction and access to antivenene. People tend to be bitten at night. Torches, electricity in the home and the wearing of good footwear would greatly reduce the likelihood of a bite. Clean houses mean fewer rodents and a lower chance of snakes entering homes and becoming trapped. Temporary evacuation of a house is a more sensible strategy than trying to chase or kill a snake.

Antivenene is expensive and difficult to get, requiring a cold chain and refrigeration. Small rural hospitals do not have the cash to keep antivenene, which does not remain effective in perpetuity. Over the last six months we have had visitations on our forest site from Black Mambas, Forest Cobras, and Gaboon and Rhinoceros Vipers. So my staff are now asking for antivenene but even that has challenges. Polyvalent antivenene covers those species that account for most bites (Black & Green Mambas, Cobras, Puffadders and other adders) but not Gaboon Vipers or Boomslang because of the complexity of the venom and the rarity of envenomation. Administration of antivenene is both complicated and potentially dangerous because quite a lot of people are allergic to horse serum. Access to adrenalin to prevent anaphylactic shock (administered slowly and intravenously) is required concomitantly, along with antihistamine. Medical experience is essential. A few months ago, the mother of a friend was bitten at night and rushed to hospital. She was in shock and was given antivenene. After five days she was released and given a bill of $600. Having reviewed the medical report, I am absolutely certain she was bitten by a non-venomous snake but the hospital could not take a chance. A bite from a neurotoxic snake such as a mamba will show few symptoms before the patient stops breathing. That could take 12 minutes or 12 hours. In contrast, a bad adder bite causes intense pain, huge swelling and, without treatment, necrosis.

Below right: boy with a necrotic leg prior to amputation

Puff Adder bite on the hand

A Great Lakes Bush Viper from the Ruwenzori forest in strike pose. Being both arboreal and nocturnal, it had every right to be grumpy when we flicked it on to the ground. We had spoiled its day and it was quite prepared to spoil ours. 

Below are four Kenyan snakes. Two are completely harmless and two are deadly. Can you guess which are which? Answers at the bottom.

A.   [1]                                                                                                  

B.

C.                                                                                

D.

The sum of all biodiversity makes up the web of life. Whether it is sharks, snakes, scorpions or scolopendrid centipedes, the world would be a poorer place without them even if all can harm or kill us. But then I haven’t experienced their effects first hand or lost a child or friend. My support of these creatures could well come back to bite me.  

Editor's NoteA day after sending me his article, Mark sent me this photo of a Large Rhino Viper "on our plot today with two babies in tow. Staff did not harm them!! Progress!"

[1] A. Jackson’s tree snake (harmless) B. Savannah Vine Snake (gentle, very small but deadly with no antivenene) C. Burrowing Asp (small, deadly and supposedly the snake that killed Cleopatra)   D. Common Egg Eater. (harmless)