A Staff Report from the Straight Dope Science Advisory Board

What's the most poisonous creature on earth?

September 12, 2000

Dear Straight Dope:

On a recent television show about poisonous animals, it was stated that the most poisonous substance known to mankind was the poison of the black widow spider. They went on to state that the only reason each person does not die when bitten is because she does not put that much poison in you. Is this true? I have also seen a program where they stated that the most poisonous animal was the fierce snake of Australia; another program stated that it was the taipan snake of Australia. Which is true?

SDStaff Doug replies:

The problem here is the definition of "poisonous." Realistically, there is one and only one objective criterion to evaluate how deadly any substance is, and that's something called the "LD50." The LD50 is the dose of a substance needed to kill 50% of the subjects within 24 hours.

You can imagine the difficulty of calculating the LD50 of different substances relative to humans. No one goes around doing lab studies that kill people just to figure out how nasty a poisonous substance is. That means that LD50 statistics have to be based on lab studies with other types of animals (usually mice). As one might suppose, (1) there's no guarantee that mice react the same way that humans would to a poison, and (2) there are probably between about 5,000-10,000 different animal toxins in existence, and we aren't even close to testing them all. Furthermore, venom potency varies even within a single species of venomous animal, based on age, health, and other factors.

In the end, it's mostly guesswork. Nonetheless, when you do the research and find out what the LD50s of black widow venom and taipan venom actually are, the black widow loses, at least in mice — it takes 0.9 mg of venom per kg of mouse, whereas the inland taipan species (there are two) has a value of 0.03, making it 30 times more potent. The "fierce snake" is probably just a variant name for one of the taipan species, made up by the folks producing the TV show. There is no such snake name in use anywhere in the world. There is a published estimate for the hooked-nose seasnake as having 0.02 mg/kg potency, but other figures for that same species are less potent, so there isn't even agreement as to which of these two snakes has the most deadly venom. You wanna volunteer to find out?

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