THE INSTINCT OF FEIGNING DEATH 



181 



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 



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; some- 

 times 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, Ccelenterates, Molluscs and worms, al- 

 though some of them may exhibit reactions which are prophetic of this 



