Our Better Nature: Animals with Creative (and Disgusting) Methods of Self-Defense

To help explain how evolutionary change occurs over time, Charles Darwin used the phrase “survival of the fittest,” meaning that organisms with traits best-suited to their surroundings are more likely to reproduce and pass on those attributes to their offspring. For most animals, it’s a slow process that takes countless generations, but we see it in real time with microbes.

When an antibiotic is used for a bacterial infection, on occasion there may be a very few individual bacteria that live, perhaps due to a gene variation that lets them break down the drug, or gives them a thicker cell wall. The survivors then multiply to form a new strain of resistant bacteria, eventually giving rise to “superbugs” like Methicillin-resistant Staphylococcus aureus, also called MRSA. The fittest microbes (in this case, those than can withstand a toxin) survived.

But in popular culture, the concept of “survival of the fittest” is often conflated with physical fitness. Extreme sport competitions have adopted the phrase as their motto, and it was even the title of a 2018 reality TV show. In nature, however, the fittest is rarely the strongest or smartest.

Though survival is about finding enough food and water, it’s also about not becoming an entrée on someone’s menu. Other than apex predators, most animals list their occupation as “professional prey” on their résumés. For them, fitness is dodging fangs and claws to live another day.

For a lot of species, fitness is blending in with their background. While I’m enthralled by photos of seamless camouflage, a full-length film on it would be like watching paint dry. On the other hand, I’d buy tickets to watch an animal immobilize attackers with glue-like projectile vomit, spew jets of hot acid at predators, or use its internal organs as projectiles by firing them out its anus toward enemies.

Even faking death to avoid actual death is a theatrical affair. My inclination, if faced with zombies or bears that wanted me for supper, would be to leave quickly. Dropping to the ground inert wouldn’t be top of mind. Yet for a few critters, it seems to work. A well-known example is the Virginia (a.k.a. American) opossum, whose dramatic death reenactments gave rise to the phrase “playing possum,” meaning to play dead, or to be a faker in general.

Young opossum playing dead (Uploaded to YouTube by Amphibiansunrise)

Found throughout the eastern two-thirds of the country and along the West Coast, this native marsupial does not in fact “play” dead. When threatened, an involuntary response called tonic immobility kicks in. Its muscles go rigid and its heart rate and respiration drop sharply. Deeply unconscious in this state, the opossum might be a tempting morsel to a carnivore, except that it also salivates profusely, urinates, defecates, and releases a foul-smelling fluid from its anal glands. Apparently, no self-respecting predator wants to deal with that mess.

Other animals that exhibit this behavior include the eastern hognose snake, as well as a number of rodent and bird species. Tonic immobility can even occur in humans during acute traumatic events.

Chemical defense is an ancient survival tool, used by microbes, fungi, plants, and of course animals. The exemplar of chemical defense may be the striped skunk, abundant in all states except Hawaii and Alaska. They’re very effective, and encounters are memorable and unpleasant.

It’s a good thing the bombardier beetle is not the size of a skunk, or we’d all be in trouble. Distributed throughout North America, this inch-long beetle shoots a boiling-hot (yep, 212 F), corrosive cocktail to nail predators as far as eight inches away. They have two special abdominal chambers, one for hydrogen peroxide, and the other for hydroquinone. When needed, these are combined, along with a catalyst, and a violent reaction ensues, jetting a defensive liquid at about 22 miles an hour.

The bombardier beetle (Uploaded to YouTube by Life | BBC Earth)

The northern fulmar, a gull-like sea bird native to parts of Alaska and other subarctic regions, launches a different sort of cocktail. When confronted by a bird of prey like an Arctic skua, it vomits a stream of putrid, oily goo stored in a stomach compartment. This orange puke often clogs the would-be assassin’s flight feathers so it can’t effectively fly for a time. More importantly, the oil strips the natural waterproofing from the predator’s feathers, which means it can’t float and could easily drown.

A northern fulmar chick vomits a stream of putrid, oily goo (Uploaded to YouTube by Animalogic)

Joining this coterie of spew-happy creatures is the Texas horned lizard. Found in six south-central states, it can squirt up to half its blood supply through its eyes onto an attacker. While you’d think blood would only entice a hungry carnivore, it turns out many animals find the blood of horned lizards noxious. Obviously, a lizard can’t repeat this performance twice in the same day.

The horned lizard squirting blood out of its eyes (Uploaded to YouTube by Nat Geo WILD)

Sea cucumbers, common to all marine environments, have a deeply bizarre defense strategy. The size, shape, and color of a turd, these bottom-dwellers feed on plankton and, well, goop on the sea floor. They look defenseless, but harbor a secret weapon: their innards. When threatened, sea cucumbers self-eviscerate, firing toxic defensive fibers, as well as parts of their digestive tract, and on occasion, internal organs. Luckily, they excel at regeneration.

A sea cucumber self-eviscerates as a means of self-defense (Uploaded to YouTube by Nat Geo WILD)

When your profession is “prey,” you do whatever it takes to be fit and survive.