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Venomous vs. Poisonous


ISSUE:  Summer 2016

Beware the Jabberwock. Beware the basilisk, too, that terrifying creature of the medieval bestiary that, as Edmund Spenser writes in The Faerie Queene, “From powerful eyes close venim doth convay / Into the lookers hart, and killeth far away.”

The basilisk, the eighteenth-century Jesuit priests-cum-naturalists who first chronicled the Sonoran Desert decided, was none other than the Gila monster, which bears the unflattering binomial Heloderma suspectum, the “suspicion-worthy warty-skinned one.” In A Desert Bestiary, I defend them as being timid creatures that a human has to work to get into trouble with; as a territorial doctor in Arizona remarked, “A man who is foolish enough to get bitten by a Gila monster ought to die.”

The Gila monster and its cousin, the Mexican beaded lizard, are the only two venomous lizards in North America. In the same desert ecosystem, there are plenty of other venomous critters of much more immediate concern, from diamondback rattlesnakes to Africanized bees—and plenty of poisonous ones as well, including the Sonoran Desert toad, Bufo alvarius, whose toxin is often fatal to dogs incautious enough to lick one.

A venomous animal has to deliver a toxin directly, usually by injecting it through a fang or stinger to which a venom-producing organ is attached. The ability to produce and deploy this venom is an evolutionary adaptation that serves both defensive and offensive ends: The venom can be used to fight off a predator, or to prey on other creatures.

By contrast, a poisonous organism does not deliver its toxin directly, but instead carries it through its skin or other organs. A poison, too, can be transmitted throughout the entire body without harming the bearer. This is the case with many kinds of butterflies, moths, and beetles—and many plants as well, adding a soupçon of danger to the whole enterprise of going outside, even if poisons are almost always defensive in nature.

Venom and poison affect human beings in many different ways. A neurotoxin of the sort that a king cobra produces, for example, suppresses breathing unto death. While the allergen produced by poison ivy merely causes a rash, other poisons and venoms can cause tissue destruction and take many months to treat. With the dreaded but elusive marble cone snail, there is no treatment other than time and hope.

Biologists are fond of debating what creature is the most toxic, whether venomous or poisonous. Good money lies on the inland taipan, a snake of Australia a single bite from which could kill a quarter-million mice or more than five dozen humans. The Brazilian wandering spider, the world’s most venomous arachnid, is a contender. Jellyfish, scorpions, rockfish—there’s plenty out there to beware, not least another Brazilian creature only recently described by science, Corythomantis greeningi, a small brown-and-green frog with toxin-bearing spikes as well as poison-filled bumps of skin. That makes it—voilà—both poisonous and venomous.

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