Dia de los Muertos ended yesterday, and you, dear reader, might have detected that issues related to death was the theme of the last two blogs. I had originally thought I might round this up into a trio with a discussion of the Cotard Delusion, a rare neuropsychiatric condition where people believe they are actually dead. Commonly referred to as The Walking Dead Syndrome, patients often starve themselves because they assume a dead body needs no food. Given yesterday’s election outcomes such state might hold its own temptations…

But then I thought we need something more cheerful. Therefore let’s focus on the fact that for some species there is an innate behavior that allows them to escape death, at least temporarily, if they are lucky.

The fancy word for it is thanatosis, or death-feigning, colloquially people call it playing possum. Scientists currently researching this behavior most often refer to it as tonic immobility (TI.) What are we talking about? A large number of species exhibit multiple signs of “being dead” late in the sequence of predation, when they have no other way out, flight obstructed, and contact with their predator already in process. It is a behavior that evolved, not something learned along the way, and it can be found in vertebrates like mammals, birds, reptiles, amphibians and fish, as well as in invertebrates like crustaceans, insects, spiders, butterflies, beetles, ants, bees and wasps.

Prey displays not just a state of stillness (a defense mechanism that is also widespread usually to avoid detection by predators in the first place,) but multiple other signs that are usually associated with death or dying: reduced breathing rates, lowered heart rate, tongue protrusion, urinating and defecating, and setting the eyes wide open. If this state, often held up for hours on end, results in the predator leaving its prey alone, the animal, absent of injuries, can return to its normal existence. In addition, some animals, frogs for example, make themselves extra small so that they are swallowed whole by snakes, and will be regurgitated intact when they secret substances that have the predator throw up. Others, like grasshoppers, make themselves extra large, with their spines exposed, which make them much harder or impossible to be swallowed by frogs who have a limited range for mouth openings.

So how is self-preservation achieved? One possible answer – and there is really not that much knowledge around given that research has only recently started to tackle these questions – is predators’ aversion to long-dead animals, since they might be associated with bacterial pathogens that are best avoided. Recognizing the signs of death might lead to that reaction (suggesting not much else is going on cognitively, since a minute ago that same animal was still very much alive. As an aside: some philosophers are arguing that predators have a concept of death, loosely defined as knowledge of non-functionality and irreversibility. That’s like saying the thermostat on your wall has a concept of temperature, when all it does is recognize a particular state – above or below a certain degree – to kick heat on or off.)

Others suggests that death-feigning interrupts a set sequence in predatory behavior (the usual steps being detection, pursuit, subjugation, kill.) If the subjugation step is interrupted because something is immobile in front of you, the next step might not be executable.

It is also possible that predator animals are highly sensitive to moving targets. If there are salient alternatives all around (a bunch of prey trying to escape) the death-feigning animal might no longer capture the predator’s attention. If there are many fleeing prey to choose from there might also be an opportunity cost to spending time to figure out if the immobilized prey is really dead and ready to be lunch. There is evidence for all of these mechanisms, and they are likely working in a complimentary fashion.

Like all biologically driven behavior, there are costs and benefits attached. For some species, playing dead is the best attempt to survive when they are young and vulnerable. At later stages in development, they might switch to fight and flight mechanisms when they have gained sufficient strength to take the predator on. Death-feigning behavior can be bred into or out of species (for example birds held over centuries in captivity, where they encounter many fewer natural enemies, eventually loose TI behavior, compared to their cousins living in the wild.)

I find all this endlessly fascinating, particularly with an eye on whether humans should imitate that behavior when under attack in nature. Shall we say, it depends. If you are attacked by a bear in the wild, you have to first figure out what kind of bear it is. Playing possum seems to work with Grizzly bears, but with black bears one should fight back.(Ref.)

“To effectively play dead, you should wait until the bear has actually touched you. Bears are smart enough to know that you are faking it if they haven’t touched you and you suddenly collapse.

When trying to play dead, fall onto your stomach and use your arms to cover your head, using the ground to protect your face and stomach. Keep your legs spread wide apart to make yourself more difficult for the bear to move. 

It is likely that the bear will try to flip you over or play with your body. If this happens, you should allow the bear to flip you, but roll all the way over so you end up face-down again.”

Okayyyyyyyy. One slight upside to the sad fact that my canoeing days are over: I don’t have to memorize the rules. Never mind experiencing the attack.

Here’s to escaping all kinds of predation so we can enjoy the good stuff a bit longer. Then again, today’s music reminds us that there is peace on the other side.

Photographs today are the opposite of playing dead – dying maple leaves are playing alive, with one last hurrah of color, pattern, and throwing themselves onto the wind, flying and fluttering in the air around us until they, too, come to rest.