442 MAN BECOMES THE CONQUEROR OF THE WORLD 



Instinctive behavior. In many animals certain important 

 behaviors in life are instinctive, that is, they are performed for 

 the first time without being learned. A wasp lays its eggs in the 

 body of a caterpillar, which it first paralyzes by stinging; the 

 oriole weaves its nest ; the swallow builds its nest of mud ; 

 the trapdoor spider makes its tunnel in the ground and furnishes 

 it with a door — all these and thousands of other examples might 

 be given. The complicated activities of the pronuba moth (see 

 page 94) can be explained only by instinct, for the moth dies 



without ever seeing her 

 offspring. 



Instincts can best be ex- 

 plained, as workers with 

 insects have shown, as a 

 chain of inborn automatic 

 responses or simple re- 

 flexes. For example, an 

 insect's making a nest, 

 stinging the prey, and lay- 

 ing eggs are a series of be- 

 haviors, each one depend- 

 ing upon the one before. 

 If we interrupt the se- 

 quence, as by removing 

 most of the food supply 

 from the nest, or by giving 

 a fly paper soaked in meat 

 juices, instead of decayed 

 flesh, in which to lay its 

 eggs, the life cycle is ended 

 because the insect cannot 

 modify its actions. As Professor Hodge says, a housefly is about 

 as intelligent as a shot rolling down a board. Once the chain of 

 behaviors is set in motion by some outside stimulus, it continues 

 until the life cycle is completed by egg laying. 



Modification of instinctive behavior. Although the French 

 naturalist, Fabre (fa'br'), found that a certain wasp which drags 



C. Clarke 



The squash bug fastens her brown shiny eggs with 

 care beside the midrib of the underside of a large 

 squash leaf which the larvas will feed upon as soon 

 as they hatch. 



