Many mammals, insects and reptiles show a kind of adaptive behavior known as playing
dead or tonic immobility.
This behaviour is often seen in animals at the bottom of the food chain, but it can be
exhibited in higher animals as well.
When faced with a threatening situation, an animal may appear lifeless and may even emit
odours that resemble the smell of decaying flesh.
Also known as thanatosis playing dead is often used as a defence mechanism, a trick to catch
prey or a means to sexually reproduce.
Animals use thanatosis to confuse predators and make them lose interest.
When an animal is about to become prey, its body goes into shock and it becomes lifeless.
The animal's muscles relax and it will emit a foul odour that resembles the smell of decaying
flesh, discouraging any predator from eating it.
Sometimes snakes will pretend to be dead in order to fool their predators.
For example, when the Eastern Hognose snake feels threatened, it'll mimic death in an
attempt to avoid being eaten.
Snakes are unique creatures in that they lie on their back with the stomach up when they're
hot.
They also put their tongue out to help cool themselves.
They also emit a foul-smelling liquid from their glands that deters predators.
Certain animals play dead as a defence against predators, entering into emotionless catatonic
state, often dissuades predators as their instinct to kill drives their feeding behaviour.
Since most predators avoid dead or rotting animals, displaying thanatosis in addition
to producing foul odours is enough to keep predators at bay.
Equally, the number of times that an individual can remain static is unpredictable and not
only long.
This means that it will be difficult for a predator to predict when a prospective prey
item will make a movement, thereby attracting its attention and becoming a meal to feed
on.
Charles Darwin documented a beetle that remained static for 23mintues.
Even so the university of Bristol has recorded a single aunt lion larva feigning to be dead
for an outstanding 61 minutes.
Beasts of prey are hungry and cannot wait for long.
Likewise, prey may be missing chances to move on with their lives if they chose to remain
motionless for a long period of time.
So faking death might be best seen as a deadly game of hide and seek in which prey might
win most by faking death, if the predator's alternative victims are available.
The animal most commonly associated with playing dead is the possum.
In fact, the act of playing dead is sometimes referred to as playing possum.
When under a threat, possums can go into shock.
Their heart rate and breathing is reduced as they fall unconscious and become stiff.
By all appearances, they seem dead.
Possums even excrete a liquid from their anal gland that mimics odours associated with death.
Possums can remain in this state for as long as four hours.
A number of different bird species play dead when under threat, they wait until the threatening
animal has lost interest or is not paying attention.
And then they spring to life and make their escape.
This behaviour has been observed in quail, blue, Jays, different species of ducks and
hens.
When under attack, young fire ant workers of the species solenopsis Invicta play dead.
These ants are defenseless, unable to fight or flee.
Ants that are just a few days old, play dead, while ants that are a few weeks old flee.
And those that are a few months old, stay and fight.
Some beetles pretend to be dead when they encounter predators, such as jumping spiders,
the longer the Beatles are able to faint death, the greater their chances for survival.
Some spiders pretend to be dead when facing a predator, house spiders, harvestmen, daddy
long leg spiders, Huntsman spiders, and black widow spiders are known to play dead when
they feel threatened.
Sexual cannibalism is common in the insect world.
This is a phenomenon in which one partner, typically the female eats the other before
or after mating.
Preying mantis males, for example, become motionless after mating to avoid being eaten
by their female partner.
Sexual cannibalism among spiders is also common.
Male nursery web spiders present an insect to their potential mate in the hopes that
she will be amenable to mating.
If the female starts to feed, the male will resume the mating process.
If she does not, the male will pretend to drop dead.
Should the female start to feed on the insect?
The male will revive himself and continue to mate with the female.
This behavior is also seen in the Pisaura Mirabilis spider.
The male offers the female, a gift during a courtship display and copulates with the
female while she is eating.
Should she turn her attention to the male during the process?
The male feigns death.
This adaptive behaviour increases the male's chances of copulating with the female.
Animals also use thanatosis in order to trick prey.
Livingstonii Cichlid Fish are also called sleeper fish for their predatory behaviour
of pretending to be dead in order to catch prey.
These fish will lie down at the bottom of their habitat and wait for a smaller fish
to approach.
When in range, the sleeper fish attacks and consumes the unsuspecting prey.
Some species of Pselahidae Beetle also use thanatosis to get a meal.
These beetles pretend to be dead and are carried away by ants to their ant nest.
Once inside, the beetles Springs to life and feeds on the ant larvae.
The research released today in Science Biology Letters Journal included evaluating the advantages
of faking death.
In terms of when a predator is visiting a small population of notable prey.
Scientists use computer simulations that harness the theorem of marginal value.
A model of classical optimization.
Professor Nigel R Frank's study lead author from the school of biological sciences, university
of Bristol said, Imagine you are in a garden full of identical soft fruit bushes.
You go to the first Bush initially taking and eating fruit is easy and fast, but as
you enter the Bush in search of more fruit, it becomes harder and harder and also consumes
time.
At some point you should make up your mind to go to another Bush and search of fruit.
You are greedy and you want to consume as much fruit as possible.
We use this method to determine a small bird visiting patches of obvious aunt lion pits
and show that aunt lion larvae that waste most of the predator's time by faking death
if they are dropped, change the game outstandingly.
In short, they embolden the predator to look elsewhere.
The suggestion that this model brought is that aunt lion larvae would not win considerably
if they chose to remain motionless for even more time than they actually do.
This advocates that in this race of arms between prey and predators, faking of death has been
lengthened to such an extent that can barely be corrected.
Professor Frank's contention is that playing dead is like a magician distracting the audience,
it diverts their attention from what's actually happening.
It looks like playing dead is a great way to stay alive when you're an ant lion larva,
and it's also a good idea for predators.