Some species gross out predators to stay alive
by Jeff Beane
For most creatures, the world is a harsh, dangerous place. Aside from starvation, disease and weather, the potential for being eaten is a constant concern for all but a few species.
Predator avoidance strategies are almost as diverse as the species employing them. Some creatures flee. Some hide. Some stand and fight. Some grow intimidatingly large or strong. Some use mechanical weaponry such as teeth, claws, jaws, venomous fangs or stingers; protective armor like bark, scales, shells, thorns or spines; camouflage; or mimicry. And others simply turn their would-be predators’ stomachs.
What’s the grossest thing you can imagine? An open sewer? A tub of vomit? Revulsion to certain things is in fact a beautiful adaptation that could save your life. It’s nature raising a red flag: “Don’t eat this. It’ll make you sick.”
The ugly truth
Some creatures take advantage of such reactions by being revolting. Vultures projectile-vomit. Hedgehogs coat themselves with spit. Slugs and hagfish produce viscous slime. Amphibians exude noxious skin secretions. Some moths mimic bird droppings. Stink bugs, millipedes and many plants boast impressive chemical arsenals. Some add fire power to their delivery — like skunks, bombardier beetles and walking sticks.
And some creatures make like carrion. Opossums perhaps are best known for it, but faking death — also known as thanatosis, or tonic immobility — is widespread. At first glance, it might seem to merely facilitate a predator’s job, but things aren’t that simple. Some predators focus on movement as a primary stimulus for killing. Prey that does something unexpected — like suddenly dropping dead — can confuse a predator so much that it overrides its attack response. Behaviorists call this protean behavior, or proteanism. And if a would-be meal is both bewildering and disgusting, then that’s all the more reason for reconsideration.
The hognose snake
Excelling along these lines are North American hognose snakes, or Heterodon. These remarkable serpents have particularly elaborate defensive repertoires. Frontline strategies include a largely subterranean existence, cryptic coloration and the ability to crawl away rapidly if discovered. When caught or cornered, a hognose goes ballistic — hissing loudly, flattening its body, elevating and spreading its head and neck, tightly coiling its tail, lunging, and bluff-striking with its mouth shut.
Should these scare tactics fail, a convulsive seizure ensues, ending in a death roll finale — the snake motionless, belly up and open-mouthed with tongue dangling. Meanwhile, it releases a nasty-smelling musk, with which it anoints itself during its spastic convulsions. Feces and uric acid also may be expelled, and if the snake happens to have recently consumed a toad or two (its typical prey), then it’ll bring those up as well. Partially digested toad mush is about as appealing to most predators as one might think.
A hognose snake effectively becomes a corpse — not a fresh, delectable corpse, but a nasty, rotten one. On rare occasion, I’ve even seen a seizuring hognose’s body become stiff and rigid, like sun-dried road kill instead of the usual limp.
All North American hognose snake species practice this behavior, but it’s most pronounced in the eastern species, also known as H. platirhinos. The snake doesn’t reason out the deception; rather, it’s a stress-induced reaction that quickly disappears in captive animals. Some believe that the toxins accumulated in the snake’s tissues from its toad diet cause the seizures, particularly because thanatosis also is employed by some other toad-eaters.
Whatever the reason, this behavior is just one of many remarkable strategies in the great survival game.
Jeff Beane is collection manager for herpetology at the North Carolina Museum of Natural Sciences in downtown Raleigh. To learn more, call (919) 733-7450 or visit www.naturalsciences.org.
“Animal Grossology,” a new special exhibit at the North Carolina Museum of Natural Sciences in downtown Raleigh, takes a larger-than-life look at nature’s slime-making, vomit-munching creatures.
Adapted from the bestselling “Grossology” children’s book series by Sylvia Branzei, the exhibit oozes with disgusting science and hilarious hands-on learning games. The exhibit opens Oct. 2 and runs through April 2011.
For more information or to purchase tickets, visit www.naturalsciences.org.