One small snake

People love a good snake story, whether true or not. Like the one about Japanese forces using vipers to flush out communist resistance during their occupation of Hong Kong. Although I've heard it recounted as fact several times, I haven't found any records to confirm it. For starters it doesn't make military sense, snakes are far too shy and unpredictable to employ in an army. But that doesn't stop the myth from circulating. It taps into strong feelings of revulsion about both snakes, and the Japanese occupation.

    Local snake catcher David Willot told me another version that sounds more likely. He had heard that the Japanese bred snakes on Stone Cutters’ island in Victoria Harbour. The purpose for breeding wasn't clear. Was it for bio-warfare, or for anti-venom? Knowing now what we know about Japanese chemical weapons labs in northern China, anything is possible. In the final hours of the occupation, as liberation forces were steaming in, the lab-workers abandoned the snakes on the island. Many decades later Willot went to check out the place, hoping to find exotic Southeast Asian rarities, but his faith in the story was weakened when all he found was a mundane crop of local snakes.

    But of course there is nothing mundane about snakes. They are highly evolved reptiles that have shed their limbs in the pursuit of efficiency. So far we have counted 2,800 different species indigenous in pretty much every corner of the globe, except very cold places and New Zealand. Snakes feature in our oldest stories, blamed for millennia in the West for humankind's corrupted nature. They are the subject of crippling phobias and intense fascination. They are worshipped as symbols of power.

    All snakes are predators, though not all of them are poisonous. Some kill by strangulation, others overcome prey with jaws that separate on elastic ligaments. It looks like a tremendous struggle, but this trick, along with their expanding bodies, allows them to eat things that are bigger themselves. Snakes kill a minimum of 40,000 people a year, and a maximum of 150,000 depending on which study you believe.

    Hong Kong is home to 52 species, 14 of them are terrestrial venomous varieties, another eight or so are highly poisonous sea snakes. Four species have been discovered here. A quarter of all snake species found in China are represented in this small territory. The subtropical sun suits them, heating their blood for action. But in the sweltering mid-day heat in summer even snakes seek cooling shelter. 

    Here you are seldom more than a hundred metres from a red-topped minibus, half a kilometre from a Seven-Eleven, or a couple of blocks from an MTR station. But in most places where people live you can make a safe bet that a snake, possibly lethal, will be hidden closer to you than any of these things.

    Snakes have no ears and no eyelids and they use their famous forked tongues for sampling air-borne chemicals in stereo, to detect direction and movement. But perhaps the best-kept secret of snakes is the male's double penises. Herpetologists call them hemi-penes. Casual snake observers are unlikely to see the paired appendage, as they are kept tucked up in a special pocket on the underside. They are used one at a time in an otherwise ordinary act of sexual reproduction.

    The females lay leathery eggs in hidden shelters, unless they are ovoviviparous, meaning egg-layers that keep eggs hidden inside their bodies. Tiny worm-like blind snakes however, have no time for double-penis males, they are parthenogenic – self cloning -- like Garnot’s gecko.

    All snakes are natural wonders but I have to admit that most snake talk fixates on the lethal poisoners, and of course the monster strangler, the Burmese python.

    

Bamboo pit-viper

Hospital records show that the bamboo pit viper is the most prolific biter of Hong Kong snakes, being the likely culprit some 80 or so attacks a year. The aggressive bright green thing can put a person in hospital for days but it doesn’t usually land a fatal dose. It is quite small at around 60 or 70 cm in length, and skinny, but it will hold its position if it thinks it’s under threat, and lunge for a quick strike if the enemy comes within range. Most bites result from people trespassing unaware into a viper’s personal space, often in the dark or at twilight.

National Geographic

    A wound can lead to a lot of bleeding and painful swelling. And though it is rare, there have been cases of necrosis and gangrene. This can lead to amputation of the odd finger tip every now and then.

    Attacks are fast and vicious. The viper’s fangs, kept folded back in the roof of the mouth during rest, swing forward and lock into position in a split second strike. Some bites are dry, the poison held back in reserve or already spent, but others inject a toxic dose. Muscles around the venom glands squeeze the liquid like a plunger, shooting poison through a pair of hypodermic needles. The violence of the strike can leave the attacker with broken teeth, but new fangs quickly move forward from the back of the mouth to replace the old.

Sciencemuseum.org.uk

    Pit-viper venom is a hemotoxin, destroying blood cells, blood vessels, and preventing clots. It is a medical complication for humans, but a slow death to small animals. Once hit the targeted prey will move on with poison running through its body, followed by the silent predator. After a while the victim collapses from internal bleeding and organ failure, as the snake methodically dislocates its jaw and swallows.

    The venomous snakes with their sophisticated poisons are highly evolved. They came about long after their lizard ancestors shed their legs. There is much we don’t understand about their biochemical weaponry, manufactured in modified salivary glands behind their eyes. But there is plenty of interest from biochemists and pharmaceutical companies. The poisons are unique compounds of proteins with evidently powerful effects on living creatures, each major breakthrough in understanding the molecular biology of snake toxin holds a good chance of unlocking future drugs and patents.

    Pit-viper venom, an anticoagulant, has huge potentials in heart and blood pressure medicines. Indeed the poison of similar vipers are already producing registered drugs.

    Snake oil salesmen of the past had a reputation for peddling dubious potions to gullible people, but maybe they were appealing to uncannily knowing instincts.

Today there are several drugs on the market synthesised from snake venom, and there are strong expectations about the future. 

    The first snake-derived drug came about in the 1970s, after researchers noted the speed with which victims collapsed following the bite of a Brazilian pit-viper. They discovered in the venom a protein that caused a sudden drop in blood pressure, and its synthesized version became the first of many ACE (angiotensin-converting enzyme) inhibitors on the market today for the millions of people who suffer from high blood pressure.

    Now Rattle snakes and African saw-scaled vipers also provide two heart disease drugs called eptifibatide and tirofiban. They prevent fatal blood clots in veins and arteries weakened by a build up of plaque. 

    

Malayan pit viper VenomousReptiles.org

Malayan pit-vipers are the hope in research on new drugs for stroke victims. This also focuses on the venom's action against clots, this time in the brain. A protein called Ancrod, found in the venom is known to dissolve stroke forming blood clots up to 6 hours after symptoms start. Trials show promise, and the protein is already used in Europe on patients with deep-vein thrombosis and complications after surgery. 

    Today research continues in cancer treatment, looking in particular at proteins assembled in the venom glands of southern copperhead snakes. Contortrostatin plays a key role as an anticoagulant by preventing blood platelets from attaching to each other. The mechanism it uses to stop the bunching of platelets also has potential use against cancer cells grouping. In addition the protein inhibits the growth of new blood vessels, devastating to tumours, which need to create new capillaries as they spread from organ to organ.

    It isn't just the venom that is interesting to science, the ability to "see" heat is a vital part of the snake's armoury. The name pit-viper suggests a sit-and-wait predator lurking in a pit, a sinister image for a sinister snake. But the "pits" referred to are in fact a pair of small holes below the eyes, housing a heat sensitive organ.

    

University of Georgia

The pit is lined with 7,000 nerve endings able to detect minute differences in temperature, sending signals back to the brain. Key to this action is a gene that humans and snakes hold in common. 

    Biologists call it TRPA1, but I recommend its popular name, the wasabi receptor. In humans the gene helps us to feel pain, in particular the irritation experienced when taking in a dose of mustard, tear gas or wasabi. In vipers the same gene makes a protein that detects heat, triggering signals back to the brain along the nerves. It acts like a switch, activating when a targeted heat spot surpasses a certain temperature. As the snake scans the object in front of it, the data quickly builds up to form a thermal image of the small mammal or bird that forages unsuspectingly within striking range.

    Animal nerds may be interested to note that it is a misnomer to say that snakes can “see” infrared light, at least in the way a specialised camera picks up wavelengths of light in the infrared range. Instead, the snake takes temperature readings at tiny spots, in stereo to help judge distance. The data builds up in the brain, like a jet printer with its tiny dots of ink but each minute dot representing a temperature rather than a colour.