Venomous Snakes

There are about 600 venomous snake species in the world. Of those, about 200 are considered deadly to humans. They produce venom which is injected by their fangs during a bite, in order to kill prey, defend themselves and even aid in digestion of their meal.

It’s important to make a distinction between the terms ‘venomous’ and ‘poisonous’ as they’re used interchangably which is incorrect. Poisonous means it is ingested, inhaled or absorbed into the body. Venom is injected under the skin or into the muscle via fangs. There are a couple of snake species that are both venomous and poisonous if eaten.

How toxic a snake’s venom is is usually assessed by way of a murine LD50 test. This means the dose of venom required to kill 50% of a population of mice or rats, expressed by milligrams of substance per kilogram of test subject body weight. The lower the LD50 is, the more toxic the substance.

Which Snakes Are Venomous?

There’s not one single taxonomic group of venomous snakes, because they evolved the venom separately. Venomous snakes are found anywhere where snakes are found. The Common Adder (Vipera berus) is the only venomous snake in the UK and it is not deadly.

The four main families of venomous snakes are:

Atractaspididae – native to Africa and the Middle East, also known as burrowing asps.

Colubridae – most are harmless but five species, including the boomslang, have caused human fatalities.

Elapidae – this family includes mambas, brown snakes, coral snakes, death adders, cobras and taipans.

Viperidae – true vipers and pit vipers including puff adders, rattlesnakes and cottonmouths.

We’ll cover a few of the individual species later on. The potency of venom varies by species. Other factors in determining how dangerous a snake is includes aggression, so how likely the snake is to bite. The amount of venom delivered by a bite, the locaiton of the bite and access to antivenom and medical treatment.

Effects of Venom on the Body

There are four main types of venom based on the mechanism of action. Snake venom can include a combination of different agents with different effects. For more details check out my coverage of toxins here.

Proteolytic agents break down protein, causing damage to the cells and connective tissue around the site of the bite.

Haemotoxic agents attack the blood cells and damage the heart and cardiovascular system. This leads to clotting disorders, anaemia, tissue and heart damage and will risk death.

Neurotoxic agents attack the nervous system and brain. They cause paralysis, including paralysing the nerves that control breathing and lead to asphyxiation.

Cytotoxic agents attack cells and cause local tissue damage and inflammation at the site of the bite.

Black Mamba

Dendroaspis polylepis. One of the longest venomous snakes in the world and the fastest moving land snake. The black mamba is native to subsaharan Africa. It is the most feared snake in Africa due to it’s speed, size, aggression and how quickly symptoms develop after envenomation.

Their venom acts fast and contains highly potent neurotoxins, cardiotoxins and other dangerous substances. Symptoms develop within 10 minutes of the bite and treatment must be quick, aggressive and thorough. Antivenom is available for treatment of black mamba bites but speed is essential to have a chance of survival.

Common Death Adder

Acanthophis antarcticus. This snake holds the title of ‘fastest strike’ in the world. They go from strike position to biting back to strike position in 0.15 seconds. They don’t flee from people, but may not bite unless actually touched. Mortality rate is 50-60% for untreated bites from these snakes.

They are native to Australia, the home of all kinds of dangerous wildlife. Their speed means that the bite will be over by the time you realise it’s happening. So watch your step.

Caspian Cobra

Naja oxiana. The most venomous snake in Central Asia. Their venom is mainly potent neurotoxins but also includes several cytotoxic and cardiotoxic agents. Symptoms are rapid onset and death can occur within an hour of envenomation. Untreated mortality rate is 75%, the highest of any of the true cobras in the Naja genus.

Eastern Brown Snake

Pseudonaja textilis. The deadliest snake in Australia, it claims the top spot for annual deaths. They are notorious for their temper, aggression and speed. The good news is that Australia reports less than ten deaths per year for snake bites. This is because of awareness, education, medical provision and availability of antivenom.

Non-Venomous Snakes

So if a snake lacks venom, how does it kill its prey? Snakes that don’t use venom are typically constrictors. This group includes pythons, boa constrictors and most other snake species. They hunt by striking and grabbing prey, coiling their body around it and squeezing it to death.

This group includes one of the largest snake species in the world. Eunectes murinus. The green anaconda. They live in tropical South America around the Amazon rainforest. They are dangerous to encounter for sure, but they typically don’t hunt humans.

So, at least you’re safer with these kinds of snakes. People keep many smaller species as exotic pets. Notably the corn snake and the ball python, two species that are fairly docile and tolerate handling well.

Conclusion

That covers the potential dangers of snakes and serpents. If you would like to learn more, start here on Wikipedia. Next week we’ll get into the cultural significance of snakes and some of the mythology surrounding them. I hope you’ll return for that.

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