Open main menu

Page:Popular Science Monthly Volume 72.djvu/185

This page has been proofread, but needs to be validated.
181
THE INSTINCT OF FEIGNING DEATH

Spiders usually feign by folding up their legs, dropping down and remaining motionless. The caterpillars of some of the geometrid moths have the curious habit of attaching themselves to a branch by their posterior legs and holding the body straight and stiff at an angle to the stem, thus forming a remarkably close resemblance to a short twig. Frequently the deceptiveness is increased by a marked similarity in color to that of the branch to which they are attached.

While in most cases a species has a particular attitude which it maintains when simulating death, there are some forms which feign in whatever posture they may be in when disturbed. A good example of this is afforded by the water-scorpion, Ranatra. This insect has the two hinder pairs of legs, which are employed in walking and swimming, very long and slender; the first pair are fitted for grasping the small aquatic animals on which it feeds and are carried straight out in front of the body. It is only necessary to pick one of these insects out of the water to throw it into a stiff, immobile condition which usually lasts several

PSM V72 D185 Ranatra water scorpion feigning death.png

Fig. 2 A Water scorpion, Ranatra, Feigning Death

minutes and sometimes for over an hour. The legs may be closely pressed to the body so that the creature resembles a stick, or they may stand out at right angles to it, or be bent in any position, some in one way and some in another, depending upon how they happen to lie when the feint began. And no matter how awkward the position, it is rigidly maintained until the feint wears off. I have found that young Ranatras, the first day they emerged from the egg and while their appendages were still soft and easily bent, showed the same death-feigning instinct as the adults, although they did not persist in it for so long a time. It is a curious fact that the mature insects can not by any sort of manipulation be caused to feign death while underwater; but as soon as it is in the air it can be caused to feign repeatedly; sometimes a slight touch is all that is necessary to throw it into a rigid state of an hour's duration.

Death feigning does not seem to occur among the lower invertebrate animals such as the Protozoa, Cœlenterates, Molluscs and worms, although some of them may exhibit reactions which are prophetic of this