INSTINCT 141 



always hangs its prey in the crotch of a grass plant and then 

 digs a burrow. If an unparalyzed spider is substituted, the 

 wasp will have nothing to do with it, but will fly off in 

 search of another, paralyze it, hang it in a crotch, and start 

 to dig another burrow. Apparently the sequence calls first 

 for the hunt of a spider in natural places, not in the crotch 

 of a grass plant; the placing of the paralyzed victim in the 

 crotch, which then releases the digging reaction; and fi- 

 nally the dragging of the spider into the burrow. There are 

 innumerable cases in the hterature which illustrate the un- 

 reasoning nature of instinct, but probably the most famous 

 is the observation of the grub-feeding instinct of the worker 

 wasp. In this instance, a w^orker wasp was imprisoned with 

 a grub (young wasp) of its own species without any food. 

 Unable to find any food and driven by its instinct to feed 

 the young, the worker bit off the hind end of the grub and 

 offered it to the front end. 



Even in vertebrates, instinct sometimes takes this same 

 rigid turn. The marvelous capacity of the bird for long 

 distance migrations, flights from pole to pole in some cases^ 

 the crossing of trackless oceans with perfect navigation, 

 the great skill of nest-building— all without guidance or 

 teachincT— often obscure in our minds the less desirable facets 

 of their behavior. In their relation to offspring, birds show 

 little reason or memory and still less foresight. If a pair of 

 birds is robbed of all their young, they will be greatly agi- 

 tated, the whole paternal instinct being then frustrated. If 

 one and only one of the young fledglings is left in the nest, 

 the parent birds will show no concern whatever for the 

 missing ones. If one of the young birds dies in the nest, the 

 parents throw it out as though it were a stick. If one is ill, 

 the parents will deliberately neglect it, instead of giving it 

 particular attention. The parental instinct among birds 

 seems to be set off purely by a gaping mouth and squa\\'king 

 cry, as has been easily shown by the experimentalist. The 

 gape and the squawk are the stimuH necessary to the paren- 



