The Struggle for Existence 



145 



first found it he was watching in a forest in the Far East when his 

 eye fell on a leaf before him which had been blotched by a bird. 

 He wondered idly why he had not seen for so long another speci- 

 men of the bird-dropping spider (Ornithoscatoides decipiens),' 

 and drew the leaf towards him. Instantaneously he got a charac- 

 teristic sharp nip ; it was the spider after all ! Here the colour- 

 resemblance was enhanced by a form-resemblance. 



But why should it profit a spider to be like a bird-dropping? 

 Perhaps because it thereby escapes attention ; but there is another 

 possibility. It seems that some butterflies, allied to our Blues, 

 are often attracted to excrementitious material, and the spider 

 Dr. Forbes observed had actually caught its victim. This is borne 

 out by a recent observation by Dr. D. G. H. Carpenter, who 

 found a Uganda bug closely resembling a bird-dropping on sand. 

 The bug actually settled down on a bird-dropping on sand, and 

 caught a blue butterfly which came to feed there ! 



Some of the walking-stick insects, belonging to the order of 

 crickets and grasshoppers (Orthoptera), have their body elon- 

 gated and narrow, like a thin dry branch, and they have a way of 

 sticking out their limbs at abrupt and diverse angles, which makes 

 the resemblance to twigs very close indeed. Some of these quaint 

 insects rest through the day and have the remarkable habit of put- 

 ting themselves into a sort of kataleptic state. Many creatures 

 turn stiff when they get a shock, or pass suddenly into new sur- 

 roundings, like some of the sand-hoppers when we lay them on 

 the palm of our hand ; but these twig-insects put themselves into 

 this strange state. The body is rocked from side to side for a 

 short time, and then it stiffens. An advantage may be that even 

 if they were surprised by a bird or a lizard, they will not be able 

 to betray themselves by even a tremor. Disguise is perfected by a 

 remarkable habit, a habit which leads us to think of a whole series 

 of different ways of lying low and saying nothing which are often 

 of life-preserving value. The top end of the series is seen when 

 a fox plays 'possum. 



VOL. I 10 



