Recently, I saw this stratagem perpetrated by a creature so low in the scale of animal life, and living amid surroundings so free from ordinary dangers, that, at first, I was loath to credit the evidence of my own perceptive powers; and it was only after long-continued observation that I was finally convinced that it was really an instance of letisimulation.
The animal in question was the itch mite (Sarcoptes hominis), which is frequently met with by physicians in practice, but which is rarely seen, although it is very often felt, by mankind, especially by those unfortunates who are forced by circumstances to dwell amid squalid and filthy surroundings. Sarcoptes hominis is eminently a creature of filth, and is primarily a scavenger living on the dead and cast-off products of the skin. It is only when the desire for perpetuating its race seizes it that it burrows into the skin, thereby producing the intolerable itching which has given to it its very appropriate name. It is only the females that make tunnels in the skin; the males move freely over the surface of the epidermis. The females make tunnels or cuniculi in the cuticle, in which they lay their eggs, and they can readily be removed from these burrows with a needle. While observing one of these minute acarii through a pocket lens, as it crawled slowly on the surface of the skin, I wished to examine the under surface of its body. When I touched it with the point of a needle in attempting to turn it upon its back, it at once ceased to crawl and drew in its short, turtle-like legs toward its sides. It remained absolutely without motion for several seconds, and then slowly resumed its march. Again I touched it, and again it came to a halt, and took up its onward march only after several seconds had elapsed. Again and again I performed this experiment with like results; finally, the little traveller became thoroughly chilled, and, after a fruitless endeavor to again penetrate the skin, ceased all motion and died.
Many of the coleoptera are good letisimulants. The common tumble-bug (Canthon lævis), which may be seen any day in August rolling its ball of manure, in which are its eggs, to some suitable place of interment, is a remarkable death-feigner. Touch it, and at once it falls over, apparently dead. It draws in its legs, which become stiff and rigid; even its antennæ are motionless. You may pick it up and examine it closely; it will not give the slightest sign of life. Place it on the ground and retire a little from it, and, in a few moments, you will see it erect one of its antennæ and then the other. Its ears are in its antennæ, and it is listening for dangerous sounds. Move your foot or stamp upon the ground, and back they go, and the beetle again becomes seemingly moribund.
This you may do several times, but the little animal, soon discovering that the sounds you make are not indicative of peril to it, scrambles to its feet and resumes the rolling of its precious ball. The habit of making use of this subterfuge is undoubtedly instinctive in this creature; but the line of action governing the use of the stratagem is evidently suggested by intelligent, correlated ideation.
Some animals feign death after exhausting all other means of defence. The stink-bug (pentatomid) or bombardier bug (not the "bombardier beetle") has, on the sides of its abdomen near its middle coxæ ("hip bone"), certain bladder-like glands which secrete an acrid, foul-smelling fluid;[112] it has the power of ejecting this fluid at will.
When approached by an enemy, the stink-bug presents one side to the foe, crouching down on the opposite side, thus elevating its battery, and waits until its molester is within range; it then fires its broadside at the enemy. If the foe is not vanquished (as it commonly is), but still continues the attack, the bombardier turns and fires another broadside from the opposite side. If this second discharge does not prove efficacious (and I have rarely known it to fail), the little insect topples over, draws in its legs, and pretends to be dead.
Many a man has acted in like manner. He has fought as long as he could; then, seeing the odds against him, he has feigned death, hoping that his antagonist would abandon him and cease his onslaughts. The stink-bug in this seems to be governed and directed by reason, though the means used for defence must come under the head of instinct. Many a blind, instinctive impulse in the lower animals is, in all probability, aided and abetted by intelligent ratiocination when once it has made its appearance.
I have seen ants execute a like stratagem when overcome either by numbers or by stronger ants. They curl up their legs, draw down their antennæ, and drop to the ground. They will allow themselves to be pulled about by their foes without the slightest resistance, showing no signs of life whatever. The enemy soon leaves them, whereupon the cunning little creatures take to their feet and hurry away.
The most noted and best known letisimulant among mammals is the opossum. I have seen this animal look as if dead for hours at a time. It can be thrown down any way, and its body and limbs will remain in the position assigned to them by gravity. It presents a perfect picture of death. The hare will act in the same way on occasions. The cat has been seen to feign death for the purpose of enticing its prey within grasping distance of its paws. In the mountains of East Tennessee (Chilhowee) I once saw a hound which would "play dead" when attacked by a more powerful dog than itself. It would fall upon its back, close its eyes, open its mouth, and loll out its tongue. Its antagonist would appear nonplussed at such strange conduct, and would soon leave it alone. Its master[113] declared that it had not been taught the trick by man, but that the habit was inherited or learned from its mother, which practised the same deception when hard pushed.[114]
Most animals are slain for food by other animals. There is a continual struggle for existence. The carnivora and insectivora, with certain exceptions, prefer freshly killed food. They will not touch tainted meat when they can procure the recently killed, blood-filled bodies of their prey. The exigencies of their surroundings in their struggle for existence, however, often compel them to eat carrion.