Poisonous or Venomous?

Whenever you write about snakes, someone is sure to step in to correct your terminology, and usually they get it wrong.

First, let's start with a little biology: Almost all snakes are venomous.

The reason for this is not complex: almost all snakes are related to other snakes.

What this means is that the venom gland in "non-venomous" snakes almost always still exists even if they have been moved back in the jaw, the toxin has become weaker or more more specialized, and the delivery system less efficient.

Click to enlarge

Look at the snake skulls above, for example. The snake skull at the very top is that of a black rat snake -- one of the most common harmless and "non-venomous" snakes in North America.

To say a black rat snake is harmless is not to say that it does not have venom: it does. In fact, almost all constrictors (columbridae) have some sort of weak venom.

If you look carefully at the diagram (click to enlarge), you will see that the black rat snake has an ectopterygoid bone about halfway back in its head. This bone presses on the Duvernoy's gland which puts out a small amount of toxin which seems to have an impact only on frogs.

Now venom which is described as "toxic only to frogs" may not sound like a serious threat to humans, and it's not, but consider this: most of the highly venomous" snakes touted in the literature are only "seriously venomous" to mice, which are about the same size as frogs.

To put a point on it, there is more than one kind of venom, and not all venom is equal. Snake venom that can kill frogs may do very little harm to mice, while snake venom that is deadly to mice might have relatively little impact on other mammals.

Snakes, it turns out, are rather specialized predators, and many are highly specialized for either frogs or small rodents -- common food animals low down on the food chain.

A snake has very little reason to arm itself with enough toxin to kill something it cannot eat, and most are not armed for lethally-effective defensive purposes.

Even if a snake has a very toxic venom, it probably emits very little of it -- just enough to knock down a mouse or a rat in a few seconds. If such a highly venomous snake bites a human, it may inject enough venom to result in tissue death at the site of the bite, and to cause pain and perhaps loss of muscle function for days, but fatal snake bites are actually quite rare.

In the U.S., for example, there are about 45,000 snakebites a year, of which 7,000 to 8,000 are caused by venomous snakes. Of these bites by venomous snakes, only 10 to 15 people a year will die -- a survival rate of approximately 499 out of 500. In the U.S., far more people are killed by lightning strikes every year than by rattlesnakes.

To circle back to the topic, then, the term "venomous" does not tell us very much. Almost all snakes have venom, and most of the "dangerous" venomous snakes are actually dangerous only to frogs, mice and small rodents.

OK, so if "venomous" is the wrong word, what is the correct word?

Some may disagree, but it is clearly "poisonous."

What's odd is that some people (including some writers about snakes!) seem to think a poison is defined as something that is eaten or breathed in, but in fact that is not true as any run to the dictionary will tell you.

Websters Dictionary defines a poison as: "1) A substance that causes injury, illness, or death, especially by chemical means; 2) Something destructive or fatal."

The term "poisonous" is defined as "Capable of harming or killing by or as if by poison; toxic or venomous."

Bingo.

A snake that harms people is not a "venomous" snake (almost all snakes have venom); it is a poisonous snake.

Poisonous encompasses venom, but also suggests that the venom is present in large enough doses to harm or kill.

Which, of course, begs the question everyone always asks: What snake is the most dangerous snake to humans?

Well, it's not any snake in Australia (sorry Steve Irwin), nor is it any snake in North America.

The most dangerous snake in the world is not the Cobra, the Gaboon Viper, the Black Mamba, or the Fer de Lance.

The most dangerous snake in the world is the Saw-scaled Viper (Echis carinatus) of Sri Lanka. The Saw-scale Viper is responsible for killing nearly fifty people per million in Sri Lanka every year.

To put this in perspective, in the U.S, where we have a population of over 300 million, we have only 10-15 fatal rattlesnake bites a year (all species), while Sri Lanka (population 20 million) loses about 1,000 people a year from Saw-scale Viper bites alone. Another 200 people a year are lost to other kinds of snakebites (cobra, kraits, and other kinds of vipers) in Sri Lanka.

For the U.S. to have similar snake mortality, we would have to lose 18,000 people a year due to snake bites alone, or about six times the number of people that died in the terrorist attacks of September 11, 2001.

Bottom line: If you decide to live a rural life collecting butterflies in Sri Lanka, invest in a decent pair of boots!

Now when I say that only 10-15 people a year die from rattlesnakes, please realize I am not trying to belittle rattlesnakes.

A rattlesnake bite is a very painful thing and it can kill. In fact, rattlesnakes kill more people in every year that wolves, cougars, black bears, coyotes and alligators combined.

Yes, that's right; that's how few fatal wild animal attacks there are in the U.S.

There is no real reson to fear anything in the woods when the stuff that will really kill you is being openly sold at 7-Eleven by people who do not even speak English!.

You want to know kind of wild animals kills more people in the U.S. than any other?

It's the honey bee (same as in Australia), followed by deer (due to high-speed vehicle-deer impacts).

And, to put that fact in perspective, you are about as likely to die from a lightning strike as you are from a bee sting.
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