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Ch. 15: The Death-feigning Instinct

Most people are familiar with the phenomenon of "death-feigning,"
commonly seen in coleopterous insects, and in many spiders. This highly
curious instinct is also possessed by some vertebrates. In insects it is
probably due to temporary paralysis occasioned by sudden concussion, for
when beetles alight abruptly, though voluntarily, they assume that
appearance of death, which lasts for a few moments. Some species,
indeed, are so highly sensitive that the slightest touch, or even a
sudden menace, will instantly throw them into this motionless,
death-simulating condition. Curiously enough, the same causes which
produce this trance in slow-moving species, like those of Scarabseus for
example, have a precisely contrary effect on species endowed with great
activity. Rapacious beetles, when disturbed, scuttle quickly out of
sight, and some water-beetles spin about the surface, in circles or
zigzag lines, so rapidly as to confuse the eye. Our common long-legged
spiders (Pholcus) when approached draw their feet together in the middle
of the web, and spin the body round with such velocity as to resemble a
whirligig.

Certain mammals and birds also possess the death-simulating instinct,
though it is hardly possible to believe that the action springs from the
same immediate cause in vertebrates and in insects. In the latter it
appears to be a purely physical instinct, the direct result of an
extraneous cause, and resembling the motions of a plant. In mammals and
birds it is evident that violent emotion, and not the rough handling
experienced, is the final cause of the swoon.

Passing over venomous snakes, skunks, and a few other species in which
the presence of danger excites only anger, fear has a powerful, and in
some cases a disabling, effect on animals; and it is this paralyzing
effect of fear on which the death-feigning instinct, found only in a few
widely-separated species, has probably been built up by the slow
cumulative process of natural selection.

I have met with some curious instances of the paralyzing effect of fear.
I was told by some hunters in an outlying district of the pampas of its
effect on a jaguar they started, and which took refuge in a dense clump
of dry reeds. Though they could see it, it was impossible to throw the
lasso over its head, and, after vainly trying to dislodge it, they at
length set fire to the reeds. Still it refused to stir, but lay with
head erect, fiercely glaring at them through the flames. Finally it
disappeared from sight in the black smoke; and when the fire had burnt
itself out, it was found, dead and charred, in the same spot.

On the pampas the gauchos frequently take the black-necked swan by
frightening it. When the birds are feeding or resting on the grass, two
or three men or boys on horseback go quietly to leeward of the flock,
and when opposite to it suddenly wheel and charge it at full speed,
uttering loud shouts, by which the birds are thrown into such terror
that they are incapable of flying, and are quickly despatched.

I have also seen gaucho boys catch the Silver-bill (Lichenops
perspicillata) by hurling a stick or stone at the bird, then rushing at
it, when it sits perfectly still, disabled by fear, and allows itself to
be taken. I myself once succeeded in taking a small bird of another
species in the same way.

Amongst mammals our common fox (Canis azarae), and one of the opossums
(Didelphys azarae), are strangely subject to the death-simulating swoon.
For it does indeed seem strange that animals so powerful, fierce, and
able to inflict such terrible injury with their teeth should also
possess this safeguard, apparently more suited to weak inactive
creatures that cannot resist or escape from an enemy and to animals very
low down in the scale of being. When a fox is caught in a trap or run
down by dogs he fights savagely at first, but by-and-by relaxes his
efforts, drops on the ground, and apparently yields up the ghost. The
deception is so well carried out, that dogs are constantly taken in by
it, and no one, not previously acquainted with this clever trickery of
nature, but would at once pronounce the creature dead, and worthy of
some praise for having perished in so brave a spirit. Now, when in this
condition of feigning death, I am quite sure that the animal does not
altogether lose consciousness. It is exceedingly difficult to discover
any evidence of life in the opossum; but when one withdraws a little way
from the feigning fox, and watches him very attentively, a slight
opening of the eye may be detected; and, finally, when left to himself,
he does not recover and start up like an animal that has been stunned,
but slowly and cautiously raises his head first, and only gets up when
his foes are at a safe distance. Yet I have seen gauchos, who are very
cruel to animals, practise the most barbarous experiments on a captive
fox without being able to rouse it into exhibiting any sign of life.
This has greatly puzzled me, since, if death-feigning is simply a
cunning habit, the animal could not suffer itself to be mutilated
without wincing. I can only believe that the fox, though not insensible,
as its behaviour on being left to itself appears to prove, yet has its
body thrown by extreme terror into that benumbed condition which
simulates death, and during which it is unable to feel the tortures
practised on it.

The swoon sometimes actually takes place before the animal has been
touched, and even when the exciting cause is at a considerable distance.
I was once riding with a gaucho, when we saw, on the open level ground
before us, a fox, not yet fully grown, standing still and watching our
approach. All at once it dropped, and when we came up to the spot it was
lying stretched out, with eyes closed, and apparently dead. Before
passing on my companion, who said it was not the first time he had seen
such a thing, lashed it vigorously with his whip for some moments, but
without producing the slightest effect.

The death-feigning instinct is possessed in a very marked degree by the
spotted tinamou or common partridge of the pampas (Nothura maculosa).
When captured, after a few violent struggles to escape, it drops its
head, gasps two or three times, and to all appearances dies. If, when
you have seen this, you release your hold, the eyes open instantly, and,
with startling suddenness and a noise of wings, it is up and away, and
beyond your reach for ever. Possibly, while your grasp is on the bird it
does actually become insensible, though its recovery from that condition
is almost instantaneous. Birds when captured do sometimes die in the
hand, purely from terror. The tinamou is excessively timid, and
sometimes when birds of this species are chased--for gaucho boys
frequently run them down on horseback--and when they find no burrows or
thickets to escape into, they actually drop down dead on the plain.
Probably, when they feign death in their captor's hand, they are in
reality very near to death.

W. H. Hudson