I like to start each day by drinking a nice hot mug of cobra venom.
Did I say cobra venom? I meant coffee. But if I wanted to, I could certainly drink cobra venom, provided I didn’t have any cuts in my mouth or esophagus. I offer this as an example of one of the many ways that “venom” is not synonymous with “poison.” A poison can be anything that harms the body, from complex organic compounds to heavy metals to atomic radiation to bleach under the kitchen sink. But venom is special. Venom is an arrangement of proteins and enzymes that must be injected into a victim’s bloodstream through a mechanical device, such as a fang. Poisons are land mines that anyone can step on; venoms are delivered special to you.
Most of the venomous animals in the world are snakes, but there are a fair number of fish and lizards that deal death as well. The stonefish, the world’s most venomous fish, uses spines to defend itself against attackers, and can certainly kill a human, and gila monsters, one of two North American venomous lizards, produce a neurotoxin which cause an excruciatingly painful paralysis. The world’s most venomous land snake, Australia’s Inland Taipan, has never killed a human due to its reclusiveness, but the venom in one bite is powerful enough to kill 100 people. A few molluscs make the list: the golf ball-sized blue-ringed octopus — again, Australian — has a blinding, paralyzing toxin that will kill a human victim in minutes, and for which there is no antivenin. The venom is nearly identical to that of the marbled cone snail, nicknamed the “cigarette snail” because you’ve got about enough time left on Earth for one cigarette after it stabs you with its neurotoxin-tipped harpoon. But the most venomous animal in the world is the infamous box jelly, the “suckerpunch of the sea,” a nearly-invisible predator responsible for over 5,500 human deaths since 1954. Of course, its fatal deathblow usually comes from the drowning triggered by extreme pain before the venom can stop the victim’s heart.
Clearly, venoms are useful to predators across the animal kingdom: reptiles, fish, insects, cnidarians, molluscs, and even a few amphibians. Why, then, aren’t more animals venomous? And why aren’t there any venomous mammals? And here is where a few of you zoophiles say, What about the duck-billed platypus? Very good; just testing you. The male duckbilled platypus, and only the male, has venomous spurs on its hind legs. The few other venomous mammals are all types of shrew, including one of the rarest and strangest: the solenodon.
There are two living species of solenodon: the Cuban Solenodon, and the Hispaniolan Solenodon, from the island shared by Haiti and the Dominican Republic. They are evolutionary hold-outs from a time when mammals were barely just poking their heads out to survey the bones of the last dinosaurs. They are also incredibly rare; the Cuban Solenodon was declared extinct in 1970, only to have a single individual found again in 2001. It may, in fact, be fully extinct now. Part of their plight has to do with their extremely, unusually low reproductive rate. Another, the introduction of European species to the island. But their primary disadvantage may simply be that they’re funny-looking.
I mean, look at it. Its head is far too large for its body, and its nails too long for its paws. It walks with a clumsy gait, and has been known to trip over itself and fall ass-over-tea kettle when it tries to run. In fact, the only defense this awkward, bumbling creature has seems to be the ability to inject venom into its prey or predators through specially grooved teeth.
The venom and the awkwardness may have more to do with each other than you’d think. After all, the trait for venomous saliva could have evolved in many mammalian species. But most mammals, being endothermic (“warm-blooded”), have enough energy to capture and kill prey without having to subdue it through chemical means. An ectotherm like a cobra may not be able chase down prey and kill it, or defend itself, based on strength and speed alone; it may be cold out, or the predator may be too large or too feisty. So the cobra strikes and withdraws, letting its prey safely escape before it collapses to be eaten at the snake’s leisure. Now, as awesome as venomous wolves would be, a wolf simply doesn’t need venom to take down an elk. The physiological expense of producing venom outweighs its utility.
On a personal note, it’s pretty hard to try to talk Nature out of venomous wolves right now, because I’m stuck on how awesome that would be. But sadly, I must admit they probably don’t exist for a reason, the same reason that there are no venomous birds. Venom exists where vigor does not, or as a way for the small to take down the large, or for the slow to kill the quick. Venom is for the vulnerable. The solenodon, that clumsy troglodyte of a shrew, may actually need its venom due to its huffling slowness. Outmatched by the world, it carries a poisoned dagger.